Woofer Tester Pro
Speaker Tester
User Guide
 Smith & Larson Audio
PO Box 229
Savage, MD 20763
USA
Phone +1 781.259.1804 • Email: tech@woofertester.com
Table of Contents
1.
INSTALLATION & SETUP............................................................................................................. 5
1.1.
1.2.
1.3.
1.4.
1.5.
1.6.
2.
GETTING TO KNOW YOUR WOOFER TESTER PRO ................................ ................................ ................... 5
INSTALLING THE SOFTWARE ................................ ................................ ................................ ...........6
WTPRO.LIC LICENSE FILE ................................ ................................ ................................ ...........7
SETTING UP THE HARDWARE ................................ ................................ ................................ ...........7
SOFTWARE AND HARDWARE INSTALLATION NOTES ................................ ................................ ................9
HARDWARE CONNECTIONS ................................ ................................ ................................ ........... 12
NAVIGATION .............................................................................................................................13
2.1.
2.2.
2.3.
2.4.
2.5.
2.6.
2.7.
2.8.
2.9.
2.10.
2.11.
2.12.
2.13.
2.14.
2.15.
2.16.
2.17.
2.18.
3.
3.1.
3.2.
3.3.
4.
4.1.
4.2.
4.3.
4.4.
4.5.
4.6.
4.7.
4.8.
MENU BAR ................................ ................................ ................................ .............................. 14
TESTS, SIGNAL CONTROL AND REAL-TIME METER WINDOW ................................ ................................ ... 14
WT CONTROL WINDOW ................................ ................................ ................................ .............. 16
SETUP CONTROL WINDOW ................................ ................................ ................................ ........... 18
OVERLAY WINDOW ................................ ................................ ................................ .................... 25
T/S ENTRY WINDOW ................................ ................................ ................................ ................. 26
FFT AND OSCILLOSCOPE WINDOW ................................ ................................ ................................ . 27
IMPULSE AND WATERFALL CONTROL WINDOWS ................................ ................................ .................. 28
TIME ALIGN - AVERAGING MICROPHONES ................................ ................................ ......................... 31
X-Y PLOT WINDOW ................................ ................................ ................................ ................... 32
VIEW MENU OPTIONS ................................ ................................ ................................ ................ 35
WOO FILES & SCREEN CONFIGURATION ................................ ................................ .......................... 40
VIEWING, FORMATTING & CONVERTING RESULTS ................................ ................................ ............... 41
OPTIONS MENU ................................ ................................ ................................ ........................ 43
TOOLS MENU ................................ ................................ ................................ ........................... 46
PRINTING FILES/GRAPHS ................................ ................................ ................................ ............. 49
EXPORTING RESULTS ................................ ................................ ................................ .................. 49
HELP MENU ................................ ................................ ................................ ............................. 49
CALIBRATION ...........................................................................................................................50
CALIBRATION, COMPONENT & LINEAR TESTING ................................ ................................ .................. 50
LOW POWER PORT CALIBRATION ................................ ................................ ................................ ... 50
HIGH POWER PORT CALIBRATION ................................ ................................ ................................ .. 55
THIELE SMALL DRIVER MEASUREMENT................................................................................... 59
REVEALING THE THIELE-SMALL MODEL USING ELECTRICAL TESTS ................................ ............................ 59
FINDING MASS AND SPRING CONSTANTS THAT SET FREE AIR RESONANCE FS ................................ .............. 59
DRIVER Q................................ ................................ ................................ ............................... 60
DRIVER FREQUENCY DEPENDENT INDUCTANCE (LE IS NOT SIMPLE INDUCTANCE)................................ ........... 61
NON LINEAR SUSPENSION AND MOTOR CHARACTERISTICS ................................ ................................ ..... 61
THE TS TESTS (WHAT IS MEASURED)................................ ................................ ............................. 62
Q AND FS TEST (LAUNCH FROM ‘Q,FS TEST’ BUTTON) ................................ ................................ ......... 62
VAS TEST (LAUNCH FROM ‘VAS TEST’ BUTTON)................................ ................................ .................. 64
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4.9.
4.10.
4.11.
4.12.
5.
DRIVER SIMULATION AND BOX DESIGN ................................................................................. 68
5.1.
5.2.
6.
SIMULATION AND PHYSICAL BOX DESIGN ................................ ................................ .......................... 68
FIRST PASS SIMULATION ................................ ................................ ................................ ............. 69
IN-BOX ELECTRICAL TESTING ................................................................................................. 70
6.1.
6.2.
6.3.
7.
BOX ELECTRICAL TEST ................................ ................................ ................................ ................ 70
AUTO-ALIGN VBOX (ALIGN SIMULATED AND IN-BOX IMPEDANCE) ................................ ............................ 70
SIMULATED VERSUS MEASURED IN-AIR RESPONSE ................................ ................................ ............... 71
ADVANCED THIELE SMALL TESTING: AC & DC COMPRESSION............................................... 72
7.1.
7.2.
8.
AC COMPRESSION TESTING ................................ ................................ ................................ .......... 72
DC COMPRESSION TESTING ................................ ................................ ................................ ......... 73
INTERACTIVE CROSSOVER DESIGN™ (ICD) ............................................................................ 76
8.1.
8.2.
8.3.
8.4.
8.5.
8.6.
8.7.
9.
A PHYSICAL VERSUS SIMULATED CROSSOVER DESIGN EXAMPLE ................................ ............................... 76
CREATING AN ELECTRONIC CIRCUIT FILE ................................ ................................ .......................... 78
CIRCUIT FILE SYNTAX................................ ................................ ................................ ................. 81
ICD COMPONENTS AND DEVICES ................................ ................................ ................................ ... 82
ICD AND XVR EDITOR AND SIMULATION CONTROL ................................ ................................ ............. 83
ICD DRIVER PROTECTION CIRCUIT ................................ ................................ ................................ 84
ARBITRARY CROSSOVER DESIGN (XVR FILES)................................ ................................ .................... 84
HARMONIC & SINAD DISTORTION MEASUREMENT................................................................87
10.
10.1.
10.2.
11.
11.1.
11.2.
11.3.
12.
12.1.
12.2.
12.3.
4
BOX TEST (LAUNCH FROM BOX TEST BUTTON) ................................ ................................ .................. 65
MAKING A SUITABLE TEST BENCH ................................ ................................ ................................ .. 65
DRIVER BREAK-IN ................................ ................................ ................................ ..................... 66
ARBITRARY IMPEDANCE PLOTS (ARB1 AND ARB2 BUTTON) ................................ ................................ . 67
TEST TOOLS AND CALCULATORS .........................................................................................88
ALIGNING THE TESTER FOR MEASURING CAPACITORS ................................ ................................ ........... 88
ZOBEL CALCULATOR ................................ ................................ ................................ ................... 90
DEMONSTRATION FILES ...................................................................................................... 91
CONDUCTING A SIMPLE ELECTRICAL TEST ................................ ................................ ......................... 91
THIELE-SMALL SIMULATOR & BOX DESIGN DEMONSTRATION ................................ ................................ .. 92
DEMONSTRATION OF AN IN-AIR TEST ................................ ................................ .............................. 95
DIGITAL SIGNAL PROCESSING TERMINOLOGY AND CONCEPTS ....................................... 96
NYQUIST SAMPLING THEOREM ................................ ................................ ................................ ...... 96
RECONSTRUCTION FILTERS ................................ ................................ ................................ .......... 96
UP-SAMPLING FILTERS ................................ ................................ ................................ ............... 96
© Smith & Larson Audio
Woofer Tester Pro User Guide v1.1
INSTALLATION & SETUP
1. INSTALLATION & SETUP
1.1. Getting to know your Tester
Tester Front Panel
The front of the test measurement box contains the line-in and line-out ports as well as the phantom powered
microphone inputs as shown below:
Line-in
port
Line-out
port
Power
LED
Phantom powered microphone inputs
Tester Back Panel
The back of the measurement box contains an auxiliary 5V power port (for when there is only one low power port), USB
port, a high-power test port and a low-power test port:
USB port
Auxiliary 5V port
for low power
USB hosts
(not required in most
cases)
Low-power
test port
High-power test port
Note: The WT Pro uses about 160 mA @5V from the USB port. Most USB ports will supply this directly.
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INSTALLATION & SETUP
1.2. Installing the Software
6
1.
Insert the CD-ROM into your computer. If the installation process does not start automatically, run setup.exe from
the CD-ROM. This will start the software install wizard:
2.
Click Next. The next dialog box shows the license agreement. Please read it and select “I agree” if you concur and
then click Continue to proceed with the installation.
3.
Next, select an existing directory using Browse or create a new one by typing a name in the text box. By default,
a WTPRO directory gets created on your C: Drive and you’ll be asked if you want to create a new directory. Click
OK to continue.
© Smith & Larson Audio
Woofer Tester Pro User Guide v1.1
INSTALLATION & SETUP
4.
The last step in the software installation shows you the latest readme.txt file and asks if you want to add a desktop
icon and an entry in the Windows Start  Program. Select the appropriate options and click Finish. The software
installation is now complete.
1.3. WTPRO.LIC License File
WTPRO.LIC (a software license and hardware key-file) must be copied to the installation directory to enable the
WT-Pro hardware and software. This file will be important if you download software updates from the web.
.
1.4. Setting up the Hardware
1.
To setup the hardware, connect the USB cable between the Tester and computer’s USB port.
indicate new hardware has been detected and the following dialog box pops open:
2.
Select the “Install from a list of specific location (Advanced)” option and click Next
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Windows will
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INSTALLATION & SETUP
The following dialog box appears:
3.
Click the Browse button
In the file dialog box that opens, select the WTPRO directory that you created earlier and click OK
4.
Click Next
If you are using Window XP, a warning may appear about Windows Logo testing. This driver is compatible with all
versions of Windows. Click Continue Anyway to continue the installation
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INSTALLATION & SETUP
5.
When file copying is complete, click Finish to complete the installation
In Win XP You will see a system tray message that your new hardware is installed and the hardware setup is now
complete.
If you manually installed the drivers and did not already plug the Tester into your computers USB port, do so now.
Windows will now detect the Tester.
1.5. Software and Hardware Installation Notes
Software Installation
The software can be installed by directly copying files from the CD, or by using the SETUP.EXE installation program. There
are no Windows registry entries made and the only drivers required should already be available if you meet the following
requirements.
Windows Generic USB Driver Installation
When the tester into your system you may find that the drivers are already installed and there is nothing to do. If not,
Windows will identify that a 'USB Audio Codec' has been installed and the new hardware wizard will start. Following the
wizard's instructions will eventually configure the Windows default driver for USB Audio Devices. This may require you to
install drivers from the Windows installation CD.
Note: Windows always assumes that any newly installed device will become the new default device. This will redirect your
PC's default sound output to the tester. You will want to disable this by going into the control panel and changing the
default sound device.
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INSTALLATION & SETUP
Additional Steps for Windows Vista Users
When Windows Vista installs the ‘USB Audio Device’ driver, the initial default will be set for 1 channel 22 kHz. This must be
changed for the Tester to operate properly. The changes made here may revert back if the operating system is updated, or
a new audio device is installed.
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1.
From the Start menu, open the Control Panel and select ‘Hardware and Sound’. The Tester will be identified as
using an ‘USB Audio Codec’.
2.
Click on the ‘Recording’ tab and look for the Microphone that uses the ‘USB Audio Codec’.
3.
Click on the microphone properties, and then select the ‘Levels’ tab.
4.
Next, click on the ‘Advanced’ tab and change the settings to 2 channels, 44100 Hz sampling rate. Check the two
‘Exclusive Mode’ check boxes giving the tester application control of the device. Click OK.
© Smith & Larson Audio
Woofer Tester Pro User Guide v1.1
INSTALLATION & SETUP
5.
Repeat Step 4 for the ‘Playback’ tab (2 channel 44100 Hz sampling).
6.
Go to the ‘Enhancements’ Tab and make sure that the ‘Disable all enhancements checkbox’ is selected.
7.
Make sure that the Playback, Record and Tester sampling rates all match. 44100 Hz is the recommended sampling
rate for Vista and is the default setting on the Tester. Sampling rates are changed in the Options pull-down menu
or from the ‘Comp & Size’ tab in the Setup Control window.
Software Installation Notes
The software can be installed by directly copying files from the CD, or by using the SETUP.EXE installation program. There
are no Windows registry entries made and the only drivers required should already be available.
Windows Generic USB Driver Installation Notes
When the tester is plugged into your system you may find that the drivers are already installed and there is nothing to do. If
not, Windows will identify that a 'USB Audio Codec' has been installed and the new hardware wizard will start. Following the
wizard's instructions will configure the Windows default driver for USB Audio Devices. This may require you to install drivers
from the Windows installation CD.
Windows always assumes that any newly installed device will become the new default device. This will redirect your PC's
default sound output to the tester. You will want to disable this by going into the Windows control panel and changing the
default sound device.
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INSTALLATION & SETUP
1.6. Hardware Connections
! WARNING !
DO NOT CONNECT ANYTHING EXCEPT FOR A DRIVER TO THE LOW POWER TEST PORT
Basic Thiele Small testing and parameter extraction does not require more than a few milli-amps of current, which is easily
powered by the USB port. The high power port is a ‘pass through’ port that senses the voltage and current at the load. The
high power port is amplifier safe (ground referenced, non-bridged), but do not let the amplifier touch the low power port!
Connecting a Driver
The provided test leads with a banana jack at one end and alligator clips at the other will be used to connect drivers to the
Woofer Tester. Calibration resistors (and shorts) are also used during the calibration routine. These will be connected
directly to the Woofer Tester, or to the end of the test leads depending on the parameter being measured.
Connecting lineout to an amplifier for breaking in a driver
Before testing a driver, it is often desirable to break the driver in for an hour or two. Basically 'fresh' driver parameters are
not the same as when the driver has been exercised for some time. This is accomplished, and with far less voice coil
heating, by using a test tone frequency equal to the driver’s free air resonance Fs. The line level RCA jack outputs can be
connected to an amplifier to provide this signal. Frequency is controlled from the WT Control Window.
Note: In normal operation, the Y-jacks are used to provide the line out-in signal loop back. Removing the Y-jack opens the
signal chain allowing line-level devices like preamps to be tested.
Note: Since the Woofer Tester must share PC resources, dropouts may occur if the operating system becomes overloaded.
Using only software to control signal levels is therefore not advised. A pre-amplifier or an integrated amplifier with a volume
control allows you to set the software level to maximum and then cut back the level manually.
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Woofer Tester Pro User Guide v1.1
NAVIGATION
2. NAVIGATION
This section of the user guide gives an overview of the software features, explains how to view, print and export results and
configure system settings. Now that you have connected up your Woofer Tester Pro and started the software, you will see
the main window shown below. The program consists of an outer Frame window that then contains multiple child windows.
Figure 2-I - Main Window
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NAVIGATION
2.1.
Menu Bar
On the top of the screen is the menu bar with eight pull-down menus from which you can perform the following functions:
2.2.
Menu
Functions
File
Open and create WOO Files (described in the next section), export results to various file formats
and capture graphics
View
Open test windows, set graphing options and customize screen
Options
Configure sweep parameters, measurement frequency, drive level, signal mode, sample rate,
buffer size, set microphone gains, button modes and select operational modes
Tests
Calibrate and conduct measurements
Tools
Set atmospheric conditions for tests, calculate effective size of non-circular speaker, design an air
core inductor
Results
Export test results to the editor, format output, convert electrical results into effective box
parameters, design a tank circuit
Window
Arrange windows on screen
Help
Help on using the Woofer Tester Pro
Tests, Signal Control and Real-time Meter Window
Figure 2-II – Tests, Signal Control and Real-time Meter Window
Test and Data
Selection
Test Frequency and
Signal Level
The left hand side of the screen contains the Thiele Small Test buttons, the signal
frequency and level controls and the real-time meter window as shown in the picture
on the left. This window contains buttons for various tests and shows the current
real-time frequency, measurements, levels and other parameters.
Real-Time Meter
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Woofer Tester Pro User Guide v1.1
NAVIGATION
Buttons with Multiple Click Regions
Buttons can consist of multiple click regions. The first five buttons, Q/FS Test, Vas Test, Measure Box, Arb1 sweep and
Arb2 sweep have two regions. Clicking the button on the left changes the data view in the main window. Clicking the
button in the middle or on the right conducts the test:
Click on the left side of the button to
switch the data view
‘X’ indicates current data view
Click the button on the right or middle
to conduct this test
Clicking the Frequency Hz and Drive Level buttons on the left decreases the frequency and drive level while clicking on
the right increases them. Clicking the buttons in the middle brings up a dialog box to enter a specific value.
Decrease levels by clicking on
the left
Increase levels by clicking on
the right
Click button in the middle to
bring up a dialog box
Enter desired value and click OK
STOP-RUN-RUNn/Stop Sweep/Start Sweep button
The text of this button changes depending on whether the signal mode is SINE wave sweep, or real-time processing. If the
mode is real-time, the button is split into three active STOP, RUN and RUNn regions. The stop mode action (what halts) is set
in the Options pull down menu or ‘Size&Comp’ tab in the Setup Control Window.
When not testing impedance and phase, the last two buttons in the window allow you to quickly set the line sources. The
first button is reference A and the second button is reference B. Each has the following options:

LL = Line-in Left Channel

LR = Line-in Right Channel

ML = Microphone Left

MR = Microphone Right
Click on the appropriate label to select the line source.
Real-time Meter Output
The measurement window below the buttons shows the main real-time outputs of the ongoing test. It also indicates the
current sweep point and sweep ratio, which are variable settings that can be changed in the Options menu.
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NAVIGATION
2.3.
WT Control Window
The WT control window consists of a results area on top and a graphing area on the bottom. The results area shows the
output of the latest Q/FS, Vas and Box tests. The results area can be minimized or maximized using the [-] and [+] buttons.
Minimize
Maximize
Text
Changing the Title in the Output Window
Clicking on the first row of the output area pops up a dialog in which the graph title can be changed. This title will also be
entered into the Setup Control Window ‘Overlay’ tab that controls overlay and active data destination buffers.
Buttons in the Graphing Area
The graphing area displays sweep and real-time signals that are generated. There are two groups of buttons at the top of
the graph; two in the left corner and three in the right corner labeled Setup, Auto and Data.
Buttons
16

Auto – Single clicking this button turns autoscaling on and off. With autoscaling turned on, the range of the phase
degree or response axis automatically adjusts to fit the data. This is useful in the initial stages of a new driver test,
where you do not yet know what levels of response you will get from the driver. Turning autoscaling off fixes the
range of the x or y axis at the current level.

Data – The Data button on the left turns the phase response line off while the button on the right turns the
response line off. Clicking the button again, turns the lines on again.

Setup – This button opens the Setup Control window, which is described in section 2.4.
© Smith & Larson Audio
Woofer Tester Pro User Guide v1.1
NAVIGATION
Setting the Measurement Frequency
The two Xs in the graph mark the current data measurements at the selected test frequency. This data is also displayed in
the real-time meter window. When enabled, clicking on the graph will change the current measurement frequency. As the
mouse hovers over a data line, an additional value is interpolated from the known data points (the drawn line) and displayed.
The data label disappears as the mouse moves away:
Interpolated
Data
Hover
Current
measurement
frequency
X’s show current measurement
frequency and values
Adding/Removing Datapoints from the Graph
After you have measured a driver, depending on the number of data points used in the measurement, you might find pieces
of a curve that are not smooth. The missing curve segments can then be smoothed out by adding additional measurement
points:
1. Go to the Options menu  Left Mouse Button Action  Set Frequency Control in WT Control Window and make
sure this option is checked
2. Left-click on the segment of the curve that you want to smooth out. The frequency will change and the
measurement Xs will move to that location.
3. Wait for data processing to complete. Processing is complete when the impedance reading in the real-time
measurement window displays an Ω sign.
New measurement is processing
(spinning ‘/’ on Z reading)
New measurement is complete
(indicated by ‘Ω’ on Z reading)
4. Now click the right mouse button to add the new data point to the curve.
It is also possible to remove a bad data point from the graph:
1. Go to the Options menu  Left Mouse Button Action  Set Frequency Control in WT Control Window and make
sure that it is checked
2. Hold down the Shift key and move the mouse to the data point you want to remove. Notice how the Xs change
color.
3. While holding down the Shift key, right click the mouse button to delete the data point.
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NAVIGATION
2.4.
Setup Control Window
Calculation of Response and Impedance - Frequency Domain Division
Tester response and impedance are mathematically defined as the ratios of 'measured' and 'reference' signals. Frequency domain
division yields direct measurements of amplitude and phase and eliminates a post-processing step where pre-measured reference
signals are subtracted from the measured signal.
Setting the Measurement and Reference Signals
The 'Setup & Control' window is opened from the View menu or by clicking the Setup button in the WT Control window.
The ‘Setup’ tab then shows the measured 'A' and 'B' reference sources as well as the test and signal types. Other controls
include microphone gain, compensation and response smoothing.
The left and right ADC channels each select one of four signals. The left side includes Line Left, Mike Left, LoZP volts, HiZP volts and
the right includes Line Right, Mike Right, LoZP amps and HiZP amps. Some combinations like using the LoZP channel as a microphone
response reference will not make sense.
A
B
Signal
Anal Mode Comment
---------------------------------------------------MikeL LineR
Sine
db(A/B)
Mike(L) sine response (ARBx sweep)
MikeL LineR
Impulse
db(A/B)
Mike(L) Real-time response ->Buffer
MikeL LineR
MLS
db(A/B)
Mike(L) Real -time response ->Buffer
MikeR LineL
Impulse
db(A/B)
Mike(R) Real-time response ->Buffer
MikeR HiZP V
Impulse
db(A/B)
Mike R response - AFTER amplifier
MikeR MikeL
Impulse
db(A/B)
Measure room gain
LineR LineL
Any
db(A/B)
Response of a line level device
LoZP V LoZP A
Sine
LoZP
Low Power Swept impedance and phase
LoZP V LoZP A
Impulse
LoZP
Low Power Fast impedance and phase
HiZP V HiZP A
Sine
HiZP
High Power impedance and phase
HiZP V HiZP A
Impulse
HiZP
High Power Fast impedance and phase
Drive Signals
Each signal type has a different frequency distribution characteristic. Pure tone sine waves are single tone and therefore have the
highest possible signal density.
Broad band or ‘real-time’ signals contain all frequencies at the same time. The speed this provides is convenient, but this
also spreads out the energy and it opens the possbility that non-linear effects will cause computation errors. In theory, all
real-time signals will give the same result, but this is not always the case, especially at higher power levels.
The Impulse mode for example has more low frequency content than the MLS or NOISE modes making it more suitable for measuring
a woofer. Conversely, MLS and Noise are good for measuring tweeters. Care should be taken with the MLS and Chirp sine modes as
these modes have zero crest factor meaning the low and high frequency energy can be quite high.
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NAVIGATION
Line and Microphone Compensation
Both microphone and line input sources can be compensated using FRD files, or two-stage user defined filters. Additionally,
compensation can be applied to either the measurement or reference channels, and it can be enabled or disabled by signal
source type (line or mike). When an option is not valid, it will be grayed out.
The filter method provides up to third order high pass compensation by cascading a first (upper adjuster) and second order
(lower adjuster) high pass filter. When properly adjusted, this will often yield reasonably flat response for the supplied
Behringer ECM8000 test microphones down to ~10 Hz. The two corner frequencies can be adjusted by comparing the
measured response to a system with a known roll off. For example, a sealed box system exhibits a predictable 20db/decade
roll-off rate below cut off. Just be sure to close-mike the driver (the microphone is less than a few cm away) and do not
forget that many amplifiers limit low frequency output to prevent speaker damage. The low power test port’s constant
current source can also be used to measure the pressure inside a sealed box. In this case, flat response occurs since the
constant current will produce a constant force and therefore a constant pressure, all the way down to 0 Hz. Like the sealed
box, be sure to measure well below the resonance point and make sure that the box is totally free of leakage and loss. This
also happens to be the same pressurization effect seen in automotive and small room installs.
FRD file compensation loads an FRD formatted microphone compensation file in either a 2 or 3 column format of “Frequency
dB Phase” or “Frequency dB” with no commas. Laboratory grade ‘calibrated’ microphones can be quite expensive, but this
method does provide the best possible high frequency compensation.
Show Impedance at Tester Terminals or End of Cable
If a full low-level calibration is performed, the resistance and inductance of the test leads will be known. This allows the
tester to recalculate the measured impedance for either end of the cable. Measuring at the tester terminals is often desired
when measuring resistors, capacitors and inductors. It is also sometimes helpful to measure driver Thiele-Small and in-box
parameters at the tester leads ,as this is what the amplifier sees as its load. See the section on Calibration for more
information.
Size & Comp: Buffer Size and Creating a ‘Zero’ Reference
The current buffer size is set using the radio buttons on the left hand side. As
the current buffer size (used for FFT and continuous sine) size is increased, the
computation window becomes longer in time, and frequencies are defined with
greater resolution. You can trade buffer size for speed.
The buttons along the right hand side are then enabled or disabled depending on
the availability of a ‘zero reference’ compensation file. Zero referencing is the
subtraction of the compensation value from the current measurement. This can,
for example, be used to measure the change in room response for different
microphone locations (room modes). You would do this by measuring the
response in front of your speaker (the reference) and then zero reference that
response. The next step would be to move the microphone around the room.
Options include creating, deleting, loading or enabling a compensation file.
The number of Windows buffers used and the number of frames used to create averaged results is set at the bottom of this
window.

Sampling Rate - Set the tester’s sampling rate here. This rate should match the default device settings for Windows
Vista.

Number Audio Buffers - Audio buffering requires at least two buffers, one for computing and one to be passed to the
operating system for input or output. This is known as double buffering. The idea is that if the OS becomes busy the
buffer will be large enough not to have a data interruption. Since the Tester is averaging data and the frame sizes can
vary, adding an additional audio buffer can sometimes help.

Buffers Averaged - Box-car averaging computes a return value from the average of the last N frames. This reduces
noise, but it also slows down response. Larger FFT sizes, more Windows audio buffers and longer box car averaging all
slow down response time.
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NAVIGATION

RUN/STOP all IO and Processing - When a real-time processing signal mode is stopped using the
STOP-RUN-RUNn button, analog input is halted, output is zeroed and data processing halted. This freezes the display.

RUN/STOP IO only (allow re-process) - When a real-time processing signal mode is stopped using the
STOP-RUN-RUNn button, analog input is halted and the output is zeroed. However, data processing continues
allowing adjustment of the impulse time gate, octave binning and similar data processing.

RUN for N - Clicking the right hand side of the STOP-RUN-RUNn button will cause the analog IO to operate for N
frames and then halt. To operate properly, N must be set higher than the number of audio buffers+2. This count is
needed to flush old or incomplete frames through the hardware and software.
Axis Control
The Axis control tab is identical to the Axis dialog that opens when the left hand side of graph window is clicked except this is
a child window. A child window allows you to select and work in other windows. The controls in this window include
X- display Extents: Low and high frequency limits
Y- Extents: Y axis min and max limits (one for each half-buffer).
Line Smoothing: Drawn line positions are effected (not data averaging).
Real-Time Octave Binning: Complex real-imaginary data is averaged before becoming display data.
Line width and color schemes: Set black or white background
Sweep Points and Sweep Ratio: SweepRatio^N = SweepHi/SweepLo
Test Bailout Ratio: This is the final frequency step that will be taken as the Q,Fs and Vas tests zero in on their final values.
Smaller values will take longer time to complete, but will result in more accurate frequency readings.
Sine mode test points
sweep ratio^N = SweepHi/Lo
Real-Time Octave Binning
Test Bailout Ratio
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Overlay Control
The ‘Overlay’ tab is used to enable one data buffer for data entry in the WT Control Window and up to 32 data overlays in the Overlay
Window. The first column is used to enable multiple overlays, and the second to enable the current destination buffer.
Buffers Displayed in Overlay Window
Box, ARB1, SimZP and SimRx
ARB1 is Data Destination
Displayed in WT Control Window
Title Column
Each buffer can be given a unique name by clicking in the list box. Some buffers will have pre-assigned names that go with a
particular usage. For example, the first buffer is assigned to the Q/Fs test procedure and is therefore traditionally assigned that name,
as are the first seven buffers.
Info Column
The info column contains information about how a buffer was configured when it was activated. This process is automatic. If you type
something in this column it may be overwritten.
+dB, +Ph, Dly and Pol Columns
The data entered in these columns is used to shift response curves (impedance is not affected) up and down. Additional phase
polarity (enter + or -) and wrapping control is provided, whereby a time shift (in data samples) can be applied to the raw data before
it is processed.
Left-Button Sets
If the Frequency option is selected, the current test frequency can be set using a left mouse click in the graph area of the WT Control
window (or Overlay window, if the same buffer is enabled). If the Phase Wrap option is selected, a time delay (in data samples) will
be calculated that will cause the phase to unwrap until it equals the selected mouse point. This is an easy way to set values in the
Delay column.
Buf->File and File->Buf Buttons
These buttons are used to save and restore the currently selected file to an external file. This option allows you to virtually extend the
number of buffers beyond 32.
STOP-RUN-RUNn button
The button text changes depending on whether the signal mode is SINE wave sweep, or real-time processing. If the mode is realtime, the button is split into three active STOP, RUN and RUNn regions. The stop mode action (what halts) is set in the Options pull
down menu or ‘Size&Comp’ tab. This button is also found in the WT Control window.
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Calc +dB Offset, Calc +Ph Offset
These buttons open the following dialog box. A frequency entered into the ‘Measure at’ field will fill the Measurement field
with the value at frequency, in this case –13.2295. If the desired value at frequency is then 10.0, the required offset
difference would be –13.2295-10 or –23.2295. Clicking on the Copy Calculated Offset from Above button enters the
offset into the Overlay Control.
Mike Position and Gating Control
Microphone and reflector distances entered in this window are converted to a ‘time gate’ that is applied to the burst sine
signal. This time gate is not the same as the impulse time gate window for real-time response measurements. In this case,
the gate width is automatically adjusted to the timing and width of the burst. Timing is derived using a secondary MLS signal
that is added to the burst. This improves frequency response, but also creates a variable time delay that corrupts phase.
Disable MLS to measure phase.
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THD/IMD (Distortion) Setup & Control
Harmonic content, Inter-modulation and Noise and Distortion tests are controlled from this window. Harmonic (i.e. THD) is relative to
a single test frequency, while inter-modulation results from the non-linear combination of two frequencies. Signal-versus-Noise and
Distortion is what is left over from a THD test after the fundamental is removed. THD and IMD levels and frequencies can also be
viewed and measured from the FFT child window. A SINAD view similar to an oscilloscope is available in the XY plot window.
H1&H2 goto Buffer 13
H3&H4 goto Buffer 14
H5&H6 goto Buffer 15
Set Test Point
with Mouse click
1 kHz Fundamental
3 kHz, 3rd harmonic
5.5 kHz Primary signal
200 Hz secondary signal
5.1, 5.3 5.7, 5.9 kHz, IMD
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SnapTS™ Fast Testing
Real-Time Thiele-Small Testing can be useful for rapidly testing a driver or when tracking parameters during a test. The constant
current sine test method should be used when accuracy is important. This includes the Q,FS and Vas tests. Sine testing is capable of
far wider dynamic ranges, much improved frequency accuracy, a true constant current mode, and is able to reject noise. It therefore
offers much higher precision. Portions of this test are embedded into the DC offset test.
1. To use Snap TS™, first select a real-time impedance mode and then connect the driver.
2. Next enable the Acquire QFs Data radio button. If the data is clean and stable, and the sweep lo and sweep high
points are sufficiently far apart to measure Re and Le, the upper data values will be filled in.
3. Click on the Freeze button to freeze the Q,Fs information
4. The next step requires entering the effective piston diameter and selecting either the Delta Mass or Test Box method for
calculating Vas. Enter the appropriate values.
5. Click on the Aquire Vas Data button. If the Vas results are valid the remaining TS parameters will fill in.
6. Freeze the data and optionally copy the test results to the TS Control window’s test data or simulator.
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2.5.
Overlay Window
The Overlay window compares multiple data sets including response and impedance data from the Thiele-Small Simulator. The graph
display is similar to the WT Control window, except that it includes a row of data buffer selection buttons along the top. These buttons
correspond to the first seven buffers that are assigned to particular tests and functions. The remaining 32 buffers are multiple use
‘arbitrary’ buffers and are selected in the Setup & Control window’s Overlay tab.
The image on the left compares the measured Fs/Q data from a 4” mid-bass driver to the simulated impedance and phase using a
large box to simulate ‘open air’. The extremely close fit is a good indication that the model is accurate.
Another useful overlay window feature is that real-time response data can be overlaid with a second buffer. The right hand image
shows the real-time response overlay of a physical ‘soldered together’ crossover and the ICD simulated equivalent circuit. The
extremely close fit shows that the real world and modeled world are in agreement.
Advanced Tip: Viewing Driver Compression
The tester configuration dB (Mike R/HiZP V) is interesting since this calculates the right channel
microphone response relative to the amplifier’s terminal signal. Response will be unaffected by
amplifier gain but not by driver compression.
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2.6.
T/S Entry Window
The Thiele-Small Entry window is used to both design and verify box designs. Vented, sealed, passive radiator and band pass box
models are supported. Other advanced features include the automatic alignment of the simulator to measured box values, simulation
of frequency dependent inductance (Le, Rem, Xem), pipe resonance effects, various Q loss factors, small room and car boost effects,
selection of TS models from compression tables and cable loss. This example shows how well the measured and then simulated
vented box model has been matched to the actual in air response.
Simulated and
measured Response
and Phase are an
accurate match
Buttons select an
Overlay of simulated and
measured response and phase
Select Box Type
Copy Test
Data Into
SImulator
Auto align simulator to
measured box impedance
The overlay window is used to view simulated response or impedance curves. As shown in the example above, this can be very useful
when comparing simulated and measured impedance or response. T/S data is normally copied from the test environment, but T/S
parameters from a manufacturer’s data sheet can also be entered manually. Once in the simulator, parameters become adjustable.
Parameter adjustments in the simulator only affect the simulator. If necessary, simply recopy from the test environment.
Tip:
An overlay of the simulated and measured impedance will show how well the auto-align feature has
guessed the effective box size, tuning and Q. Manually adjusting the simulation parameters will sometimes
achieve an even tighter fit.
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2.7.
FFT and Oscilloscope Window
The FFT and Oscilloscope window displays the measurement and reference signals in either the frequency or time domain.
Pull down and check menu options control the display and measurement options.
FFT (OSC off)
When the FFT response mode is chosen, the left mouse button can be used to select a measurement point. There are four
measurement modes that find the largest magnitude over a particular range. The frequency response can also be displayed
on a linear or logarithmic scale.
FMAX
- DC to F-nyquist (1/2 sampling rate) range is searched
MOUSE - A left mouse click sets the measurement point
FOUT
- The measurement point is set to the tester’s frequency output
LOCK
- The measurement point is locked and does not change
OSC (FFT off)
An oscilloscope view is displayed, where the time base is set to the largest magnitude signal. The displayed units are in raw
ADC values, voltage or amperage, depending on the display mode and signal. The signal names appear below the buttons.
Example
A 16384 point FFT was selected and an input frequency of 1234.567 Hertz was applied. The –80 dB 3703.701 hertz third
harmonic was then measured at 3703.686 Hz showing a 0.025 Hz accuracy.
Note: Fourier theory defines the frequency domain resolution of an FFT (bin resolution) to be:
Hz/bin = SampleRate / PointsTaken
FFT resolution is often on the order of several hertz or tens of hertz and may not be sufficient for some measurements. An
additional algorithm significantly improves this resolution at the selected frequency. Resolution is still dependent on frame
size (bigger is better) and sampling rate, but resolution is improved to <0.01 Hz when the peak is sufficiently large and is
uninvolved with nearby signals (and the crystal time base is corrected).
Keep in mind that mathematical accuracy is not the same as absolute accuracy and that the testers frequency accuracy is determined
by its time base. The tester’s time base tolerance is +/-30 PPM or 0.03 Hz per 1 kHz of measured signal. If you require higher
absolute resolution, please contact us.
Similarly accurate 'math' routines are used when generating the sine wave outputs. In this example the output frequency was set to
1234.567 Hz, and the loop back confirms this. If however two tester’s are used with the output of one feeding the input of the other,
the potential measurement error will be +/-60 PPM or 0.06 Hz per 1 kHz of measured signal.
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2.8.
Impulse and Waterfall Control Windows
Real-time response is calculated by dividing the measurement and reference. A second algorithm then finds the signal time
displacement that is used to unwrap phase. This response is passed back through an inverse FFT revealing the system time
domain impulse response.
When applied to the in-air frequency response of a speaker, multiple impulses are seen. If a time gating window is applied,
the primary speaker impulse can be separated from the secondary floor, ceiling and wall reflections. The forward FFT process
is called again, revealing the speaker response, minus the secondary room reflections.
Tip:
Shorter time gates decrease low frequency content and reduce resolution. Impulse time gating is most useful
when measuring mid-range and tweeter responses. If the Impulse window is not open, the time gate
parameters are unknown and time gating is disabled. The Impulse Control window controls both the
response and 3-D Waterfall views.
Longer CSD Time
Span shows more
low frequency
content
Time Span=37 mS
Extended low frequency
resolution shows
Rippling’ from reflections
Time Span=2.25 mS
Less rippling, but
low frequency is less defined
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Impulse View Modes and Edge Control (Windowing)
Unwanted frequency domain energy can be introduced if a sharp transition occurs at either the start or stop tick. The
process of multiplying the signal by a function that softens these edges is known as windowing. In this case, a leading and
lagging modified raised cosine function (Blackman window) is applied. If the edge transition is minimal, the window is more
‘rectangular’. An adjustable edge allows the window to be modified from rectangular to Blackman.
Impulse, Step and Log(Impulse) View Modes
Theoretically, the mathematical integration of the impulse response reveals the step or square wave response of the system.
This is, however, highly dependent on a number of factors like the low frequency performance of the microphone, preamp
and A-to-D converter. It is nevertheless often useful, since it shows low frequency decay as a time signal.
STEP response the integral of
the impulse response
Another useful time domain view is the logarithm of the impulse magnitude. This view shows the impulse and room
reflections, where the magnitude is shown on a logarithmic scale revealing reflections that would otherwise not be visible.
This is known as room decay and is similar to RT60. RT60 is the time that it takes acoustic energy in a room to decay by 60
db after being passed through a band pass filter.
Here, absolute magnitude is shown on a logarithmic scale
versus time. The room energy has decayed by nearly 60 db
before becoming limited by the noise floor
Looking at the same data in the frequency domain shows that
the noise floor is mostly low frequency energy.
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Cumulative Spectral Decay, Growing and Sliding Fourier Transform Views
Different frequency domain viewing methods reveal different types of information. The setup for each depends on what you
want to see.
Cumulative Spectral Decay (CSD Button)
CSD (left) shows FFT slices as the time window shrinks from the left hand side. The display shows the total spectral energy
within the time window as energy is removed, hence the name, Cumulative Spectral Decay. Since the initial higher energy
pulse is removed first, this method shows the decay characteristics of a driver or speaker.
Growing Waterfall 'Forward Time' FFT (Growing Button)
The growing 'Forward Time' waterfall (middle) shows response slices as a function of time, as the time window grows from
the right (the left is stationary). This method shows energy building with time. Again, tick marks '1' and '2' can be moved to
change the gating window trading off low frequency resolution for rejecting room reflections.
Sliding Fourier Transform (SFT Button)
The SFT plot (right) maintains a constant width time window by simultaneously sliding the left and right markers. A constant
width is analogous to perceived loudness making this display useful for analyzing room decay and echo. This is similar to
RT60 where the filter Q is set by the SFT gate width. The ‘SFT decay’ mode uses the first slice as a zero reference with each
successive slice showing the energy difference with respect to time.
Waterfall Controls
Zoom (Zoom button)
Clicking on the left zooms out, clicking on the right zooms in.
Controlling the Modified Raised Cosine Transition Region (RCOS)
The lead-in and lead-out transition region can be 'smoothed' using a modified raised cosine window function. However, since
the impulse response has been located in time using a frequency domain technique, windowing in a traditional sense is not
required. This adjustment may help in some cases.
Flip front To Back (FLIP button)
The 3-D display is drawn either front to back or back to front.
Slice, Sheet, Color and Wire Frame View (SLICE and SHEET buttons)
Clicking the left side creates a wire frame display, and the right side fills in with color.
Frequency Domain Smoothing (Binning)
FFT response is combined into ‘bins’ on a per-octave resolution basis.
Refresh Data (Refresh button)
The 3-D data set is refreshed.
Auto-Scale Data (AUTO button)
The current 3-D data is auto-scaled and displayed.
Export (Export button)
This button exports the impulse view data in ASCII format.
Sizing and Rotating the Display
The 3-D plot can be rotated and sized from the impulse control window using the arrow, page up, page down, insert, delete,
home and end keys.
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2.9.
Time Align - Averaging Microphones
The tester’s ability to accurately measure acoustic distance allows it to sum and add the left and right microphone time signals. The
effect is that the incident impulse is preserved and secondary impulses are averaged. This real-time method requires the simultaneous
measurement of both microphones when measured against the internal ‘MATH’ reference for the B-side divisor.
Note: Time of arrival is relative to the internal reference. Absolute distance is no longer meaningful. No time gating or line smoothing
was used.
Figure 2-III - Left Microphone
Figure 2-IV - Right Microphone
Figure 2-V - Left + Right Microphones (Averaged)
Reduced frequency
domain reflections
Reduced time
domain reflections
Setup: Open Setup Control Window, select A side ‘measure’ MikeR (or MikeL), ‘B’ side reference MATH, Analysis db(A/B),
signal type impulse, MLS, noise or chirp
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2.10.
X-Y Plot Window
The X-Y plot window is used to view and compare similar data sets. In particular, this window is used to view changes in TS
parameters and distortion as AC or DC levels are changed, or it can be used to view any two time-domain inputs in either a
Lissajoux or oscilloscope display.
The AC compression test creates a tabular list of driver TS parameters with increasing drive level (you can get this report
from the Results pull down menu). A simple examination reveals parameter variation with drive level that can be called up in
the Simulator to show the AC response at a particular level. On the other hand, the X-Y plot window allows you to visually
graph each parameter versus drive level, or any other parameter.
Compliance and BL versus AC drive level
The small discontinuity between the low and high power port data is the result of suspension settling (see the section on TS
testing regarding Cms variation with drive level). A discontinuity will also occur if the two ports are not exactly calibrated
identical. Use the high power calibration resistor to align both ports.
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DC bias testing also produces a table of TS parameters, but these parameters are derived from a small signal analysis at a
particular DC bias point. AC simulation of the TS model does not make sense in this case, but these parameters do reveal
useful information about driver construction such as mechanical offsets, suspension and motor linearity with excursion.
These views show an offset in the suspension as well as the voice coil.
Note on Suspension Compliance:
A careful examination of the AC and DC results will often show a wide range of input levels, usually up to the point
where suspension limiting begins, where the suspension mechanical spring constant (inverse of compliance) significantly
decreases as the AC test signal level is increased. This effect is much larger than the static changes seen in the DC
offset test. Cms (suspension compliance) is significantly dependent on break-in, drive-level and temperature. The
underlying mechanism(s) are a function of how the molecular bonds respond to these conditions:

The suspension mechanically loosens with usage. This is commonly referred to as "break-in" and is
dependent on the excursion incurred (itself a function of frequency and drive level) and duration.

The suspension compliance is affected by changes in ambient temperature.

The suspension will self-heat due to mechanical energy loss. This is mostly a function of Rms and drive level,
though at high drive levels, misbehavior of the suspension can come into play.
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As the DC bias test is run, a sine wave signal can be specified that either tracks Fs or remains fixed at the frequency when
the test begins. A harmonic analysis can then be used that reveals additional mechanical problems. However, keep in mind
the raw data provided in this case is a cumulative effect of all DC and small signal AC parameters. In the absence of an
infinite baffle this test can be performed in an open-air test jig using a closely spaced microphone. The absolute level of Fs
and its harmonics are therefore typically low due to back-side cancellation. A trend at a particular frequency will however
still be valid.
The XY window can also be configured to view SINAD, or Signal versus Noise and Distortion. Normally SINAD measurements
are given in decibels as the amplitude ratio of the fundamental signal to all remaining noise and distortion. The XY plot
version of this algorithm uses the measured amplitude to create a sine wave at the fundamental frequency that is then
subtracted. If the remaining signal is then plotted against the fundamental, data views of NAD vs Magnitude, Lissajoux and
oscilloscope are possible.
Note: The Xn / int(Xn) button numerically integrates the data. Microphones produce signals that are equivalent to pressure,
that in turn is proportional to mass-air velocity. Integration shows mass-air displacement.
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2.11.
View Menu Options
There are various ways to view the data and test results in the Woofer Tester Pro. Selecting View 
from the menu bar gives the following list of viewing options, each of which is its own separate
window:
View
View Name
Function
WT Control
Graphs impedance and response of the current test signal, shows realtime Thiele Small parameters and current test frequency
Overlay
T/S Entry
Enter Thiele-Small and measured box electrical parameters for use in
simulator
Results Editor
Measurement results are copied into this editor to save in a text file and
for further processing
ICD Editor
FFT
Woofer Tester Pro User Guide v1.1
Overlays multiple real-time or static data series
Enter the circuit for the crossover design you want to simulate
The upper FFT window shows the left channel and the lower window
shows the right channel of the digitized signal.
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View
View Name
Waterfall
Function
Displays a waterfall graph of the response in multiple time windows
Impulse & Waterfall Controls the time window of the response data sample. Zoom in on the
Control
data.
Setup Control
XY Plot
Graph Axis Control
Set test parameters here: input/output channel, drive signal, analysis
mode, microphone controls, compensation and offsets. Graphing
parameters can also be adjusted here.
XY plot the following data:
- AC compression Thiele Small parameters
- DC compression Thiele Small parameters
- Harmonic content versus DC bias.
- Noise and Distortion versus fundamental drive signal
Modifies the graphing options by changing the X and Y axis range, turns
autoscaling on and off, sets frequency ranges and number of sweep
points.
In addition to selecting data and test windows, the View menu contains a number of options to change attributes in these
windows, such as applying Bezier Line Smoothing, setting the FFT Resolution, changing the line width in graphs, adjusting
the color schemes and changing the legend. These options are described next.
View  Bezier Line Smoothing
This option applies to the WT Control and Overlay View only and is turned off by default. When
turned on, Bezier line smoothing applies a polynomial algorithm to interpolate between points in
the graph resulting in a smoother looking response curve. However, as the curve may not even
pass through the original data points caution has to be taken when using this feature so as not to
misrepresent the measurement.
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View  FFT Resolution (Octave Granularity)
This WT Control and Overlay graphs show data points that are converted from linear spaced FFT data using a ratio metric or
octave scale. The display granularity is set here. By default, the resolution is set to 256 points providing reasonable
resolution.
High Resolution, 47 points/octave
Low resolution, 3 points/octave
View  Line Width
This option adjusts the width of the lines in the graphs. Adjust to value upward to increase the thickness of the line.
View  White Color Scheme
By default, the background color in graphs is set to black. For publishing, however, a white background might be preferred.
The View  White Color Scheme menu option changes the background color.
View  Pick Colors
The Pick Colors option is used to change the color scheme of graphed data. The 16 Custom colors are arranged in 8
vertical pairs, with each pair corresponding to a pair of colors that can be used in the tester’s graphing windows.
The first pair corresponds to the first of 32 data buffer pairs. That buffer is commonly
called the ‘Q,Fs’ buffer since it is associated with that test. The second vertical pair
corresponds to the ‘Vas’ buffer (the second of 32), the third is ‘Box’, followed ‘ARB1’,
‘ARB2’, ‘SimRX’ and ‘SimZP’. Since there are only 8 custom colors, the colors then
repeat. As an example, the default curve color settings for the ‘Q,Fs’ test buffer is
Turquoise for Phase, and Red for Impedance, the 1st and left-most Custom color pair.
To change the color of the ‘Q,Fs’ phase plot, first left-click on the bottom box
(Turquoise) of the left-most vertical pair. The box highlights, and the curve color
appears above Color/Solid. Next, select a new color from the basic color palette, the
color spectrum, or enter values for Red, Green and Blue. Picking Bright Green from Basic colors causes the new color to be
shown in Color/Solid. The highlight will move away from the Custom color Turquoise box, but this is remembered.
Now, left-click the Add to Custom Colors button: The bottom left-most Custom colors box changes to Bright Green.
Finally click OK. The Phase Curve and the left margin scale, etc., are now displayed in Bright Green.
View  Reset Colors
This option resets any changes to the color scheme back to the default settings.
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View  Change Legend
If you want to use the frequency response graph in a test report, for example, you can add a custom legend to the graph
with the View  Change Legend option. The following example shows how to add a legend for a driver called “TEST
DRIVER 1” to the frequency response graph along with the current date and time.
Add Legend and
pointers to
Frequency and
Impedance
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
Select View  Change Legend from the menu bar to open the dialog box below. You will see some lines of text
consisting of codes shown in [ ] and their assigned values. The codes determine the size and position of the legend
text and whether pointers are drawn or not.
To add a legend, change the first line in the dialog box from [OFF] to [ON] to show the legend.
The TEXTPOS(column,row) code sets the location of the legend.
In the third line, set the font size by changing the size code from
[SIZE(20)] to [SIZE(16)].
Replace “Verdana” with “Arial” next to the FONT tag to change
the font.
The WIDTH attribute sets the line width of the arrow pointers.
Let’s change it to 2.
To change the color of the font or a line, use the
[COLOR(RGB())] statement. On line 6, we are using it to set the
color of a border we are going to draw around the text in line 7.
Change the RGB values to RGB(0,0,0) for black.
Line 7 draws a border around our legend text. The values (6,0,28,5) specify the columns and rows of the upper
left and lower right corners.
On line 9 is the first line of text in the legend
To automatically include a current date and time, use the %DATE% code as in line 10.
The COLOR(ZBUFx) codes on lines 11 and 13 set the colors for the frequency and impedance values. The value
(ZBUF3) sets the color to match the color scheme in the existing graph.
%FREQ%, %PVAL%, and %ZVAL% represent the current frequency, phase and impedance values.
To draw an arrow pointer to the current impedance and phase values in the graph (represented by the two Xs) ,
use the [ARROWTO(x,y)] statement. In our case, the x value is derived with the GETX(FRQ) statement, which
reads the location of the current frequency value on the screen. PVAL(FRQ) reads the phase value associated with
the current frequency. The number 15 after the PVAL(FRQ) code represents the size of the arrowhead. Change it
to 12.
Lastly, add an [OFF] statement to signify the end of the legend definitions. Any text after an [OFF] statement is
considered a comment. The text in your window should now look like this (line numbers not included):
Line #
1
2
3
4
5
6
7
8
9
10
11
12
13
14
Code
[ON()]
[TEXTPOS(8,2)]
[TEXTWT(700)][SIZE(14)]
[FONT("Arial")]
[WIDTH(2)]
[COLOR(RGB(0,0,0))]
[BORDERTXT(6,0,28,5)]
[COLOR(RGB(100,255,150))]
TEST DRIVER 1, WT-Pro
%DATE%
[COLOR(ZBUF3)]Frequency=%FREQ%
[COLOR(PBUF4)]Phase=%PVAL% [ARROWTO(GETX(FRQ),PVAL(FRQ),12)]
[COLOR(ZBUF3)]Impedance=%ZVAL% [ARROWTO(GETX(FRQ),ZVAL(FRQ),12)]
[OFF()]
15. Click OK to add the legend.
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The following table lists all the codes available to create a legend:
Function
Syntax
ARROWTO
[ARROWTO(x,y,size)]
BORDERPIX
[BORDERPIX(50,10,200,50)]
BORDERTXT
[BORDERTXT(6,0,28,5)]
COL
[COL(c)]
COLOR
[COLOR(RGB(r,g,b))]
DRAWX
FONT
GETX
DRAWX[(100,50)]
[FONT("Arial")]
[GETX(f)]
LINETO
[LINETO(200,50)]
MOVETO
OFF
ON
PVAL
RGB
ROW
SIZE
STARTCOL
STARTROW
TEXTPOS
TEXTWT
WIDTH
[MOVETO(200,50)]
[OFF()]
[ON()]
PVAL(f)
[RGB(r,g,b)]
[ROW(r)]
[SIZE(s)]
[STARTCOL(c)]
[STARTCOL(r)]
[TEXTPOS(c,r)]
[TEXTWT(w)]
[WIDTH(w)]
ZVAL
[ZVAL(f)]
FRQ
ZBUF
PBUF
%DATE%
%FREQ%
FRQ
ZBUF
PBUF
%DATE%
%FREQ%
%NAME%
%NAME%
%PVAL%
%ZVAL%
%PVAL%
%ZVAL%
Description
Draws an arrow from current position of the legend
text to a specified [x,y] position. The x,y position can
be determined by a function, ie GETX or PVAL. Size
is arrow point size
Draws a box. The location/size of the box is specified
in pixel pairs [x1,y1]&[x2,y2] for the upper left and
lower right hand corner respectively.
Draws a box. The location/size of the box is specified
in columns/rows pairs [x1,y1]&[x2,y2] for the upper
left and lower right hand corner respectively.
Sets text to start at column c.
Sets font/line color using an rgb() value where
r=red, g=green and b=blue. R,g,b values range from
0 to 255.
Draws an 'X' at pixel position [x,y].
Sets the font.
Gets horizontal pixel position x at freqeuncy f.
Draws line from current legend position to [x,y]
specified in pixels.
Moves current line position to [x,y].
Turns legend off, adds a comment.
Turns legend on.
Gets P value (Phase) for frequency specified in f.
Returns rgb() color.
Sets text row to r.
Sets text size to s.
Starts all text at column c.
Starts all text at row r.
Sets upper left corner of text to column, row c,r.
Sets the thickness of the font.
Sets the line width of the arrows to w.
Gets Z value (Impedance) for frequency specified in
f.
Gets current frequency.
Sets color of Z value (Impedance).
Sets color of P value (Phase).
Displays current date in mm/dd/yyyy form.
Displays current frequency as a string.
Displays the driver name from the real-time meter
window.
Displays current P value (Phase) as a string.
Displays current Z value (Impedance) as a string.
Note: If the ‘X’ value in the ARROWTO function is replaced with GETX(FRQ), the arrow will dynamically move as you select a
new test frequency. The following example draws a line and arrow from point(20,30) to the current frequency and phase
value.
[moveto(20,30)][arrowto(GETX(FRQ),PVAL(FRQ),15)]
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NAVIGATION
Arranging the Test Windows
When you have multiple windows open, a quick way to arrange them is via the Window menu option.
The windows can be arranged vertically, horizontally or in cascading order. For example, with the Tile Vertical
option, four open windows will arrange like this:
2.12.
WOO Files & Screen Configuration
A .woo file is a configuration file for Woofer Tester desktop and measurement settings. It allows you to save a specific
window arrangement of your desktop along with the parameters of your current test setup. The software also loads and
saves a .CFG file (actually a WOO file) each time it starts and stops.
File  Woo File  Save Woo File
To save your current desktop configuration, chose File  Woo File  Save Woo File from the menu bar, select a filename
and click Save.
File  Woo File  Load Woo File
The next time you start up the Woofer Tester application, you can simply load a saved .woo file to bring you back to where you left
off. Go to File  Woo File  Load Woo File, select the desired configuration file and click Open. This will restore you desktop view
and measurement options.
Note: Some parameters that make no sense are not saved. For example, the SINAD oscilloscope view
and the Bezier line smoothing options are not kept.
File  eXport  [Export Options]
The tester exports data to a number of different file formats:
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
ASCII – Exports data from all buffers and result windows to a text file.

BassBox – Exports Thiele Small parameter measurements to a .log file for import into BassBox

LMS –
Exports frequency, impedance and phase data points for import into LMS software.

ZMA -

FRD –
Exports frequency, impedance and phase data points for import into WTPro crossover designer
(refer to chapter 8 on Crossover Design) or third party software.
Exports frequency, db amplitude and phase for third party crossover design software.
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NAVIGATION
File  Capture Graphics  [Graphics and Print Options]
The current graphical image can be saved to a BMP file or directed to your printer. Depending on the selected options, this
can be the entire desktop or just the child window you are working with. Keep in mind that print conversion drivers, such as
those that convert to PDF, can be used for the target printer. If the window is not graphical or contains text fields these are
sent to the printer as text. LPI is the acronym for Lines Per Inch. More lines per inch (bigger numbers) produce smaller
printed text.
2.13.
Viewing, Formatting & Converting Results
Results from the latest Thiele-Small parameter measurements, box tests, calibrations and Arb sweeps are automatically
saved and can be viewed via the Results menu option. For a shortcut to opening these windows, use the function keys F4 –
F9.
All result windows have a similar format, which is a text editor that lets you copy, save and edit the results, as shown below:
On the left-hand side of the results windows are buttons for the editing functions:

Load – loads a previously saved results file

Save – saves the current results to a text file

Copy – copies selected text to the clipboard

Paste – inserts text from the clipboard

Cut – deletes selected text

SelAll – selects all text
Results  New Speaker Title
With the Results  New Speaker Title menu option, you can modify the title in the WT Control window output. Selecting this
option, opens a text dialog box. Enter the new title here and click OK. This will change the title as shown below:
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NAVIGATION
Results  Results Data Formatting
The second formatting option in the Results menu, Results Data Formatting, determines in what format the results are
written to the results window. By default, results are saved in scientific number format and columns are separated with a
pipe character [|]. The pipe-delimiter is useful when results are later imported into Excel, for example.
Results formatted in scientific number format and pipe
delimited
Results formatted in decimal
delimiter
format without pipe
To change the number format, select Results Data Formatting from the Results menu and uncheck the Scientific number
format option:
Similarly, to remove the pipe-delimiter, uncheck the first option and click OK.
Results  Create Driver Label
This option takes the real-time measurement results from the WT
Control window and saves them in a format useful for creating a
label that can then be affixed to the driver being tested.
Results  Copy between buffers
For a simulation, it can be useful to be able to temporarily save a
data set that is later to be used in a data overlay. Selecting the
Copy between buffers option opens the dialog box shown below.
Choose the result set to be temporarily saved from the left-hand
column. From the right-hand column, select the target buffer to
hold the data and click OK. You can also save and load buffers
to files. This is a good way to move data between woo files
without copying the entire woo file.
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NAVIGATION
Results  Clear Data Buffer(s)
The Clear Data Buffer(s) function will reset results to zero based on one of the tree options selected.

Clear all data on start – resets all result sets each time the application starts up

Clear all data now – instantly resets all result areas

Clear current data buffer – resets the buffer currently selected as indicated by an X
Current buffer selection
2.14.
Options Menu
In the Options menu, various system and test configurations can be set.
Options  Frequency Dependent Le Test Method
This option allows you to choose between three different Thiele Small measurement models: 1)
the classic “Bare Tank” test, 2) a two point frequency dependent test method and 3) a three
point frequency dependent model.
The effects of frequency dependent inductance (Le is not constant) can be 'backed out' during
the Q, Vas and Box tests resulting in models that lead to higher accuracy box simulations.
The two point curve fit method uses the impedance and phase at SweepHi and Revc (Z at DC)
to calculate Rem/Xem coefficients. This simpler method always produces results but may be
slightly less accurate.
The three point method finds two high frequency points near SweepHi that have a positive
phase slope. This usually produces a better upper frequency fit but it may not converge. High
frequency negative phase slopes are created when the test lead inductance is significant
compared to driver Le and the test leads are not calibrated or moved.
Options  Sweep
The Sweep start and Sweep end menu options allow you to set a test frequency range. This feature is useful for
zooming in on a particular range. These options automatically adjust the x-axis scale in the graphs of the WT Control
and Overlay windows.


The number of Sweep Points is configurable. A higher number of sweep
points yields more accurate results, but also increases the measurement
time. Enter the desired number of sweep points in the dialog box and type
OK.
The
maximum
number
of
points
allowed
is
512.
The SweepLo, SweepHI, Sweep Points and Sweep Ratio are related to each other by the following equation. Basically
this says that as a test progresses from the lowest frequency (SweepLo) the test frequency increases by SweepRatio
until SweepHi is met:
Sweep_High = Sweep_Low * Sweep_Ratio^Sweep_Points
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NAVIGATION
Search Ratio Min determines the minimum sweep ratio, which is the stopping point for the search algorithm as it zeroes in on the final
frequency value. A minimum search ratio of 1.001 means that the final value will be determined by a sweep ratio of 0.001%.
Options  Measurement Frequency
This submenu option is used to set the measurement frequency. It can be set either to a predetermined frequency ranging
from 20.0 kHz to 1Hz or a user defined frequency, which is entered via a dialog box.
Options  Drive Level
Drive levels can be set to predetermined value, user-defined values or full scale (100%) with this menu option. User defined
values are input into a dialog box. The range of predetermined drive levels is from 0.1% to 50 %. Small drive levels like
0.1% are used for high resistance values or T/S testing during an AC compression test.
Tip: The measurement frequency and drive level can also be set in the
WT Control window using the signal control buttons.
Options  Mute button includes AGC
AGC stands for Automatic Gain Control and applies to drive level control. With AGC turned on, drivel level will increase to just
below the clipping point. This feature is helpful for setting levels in high impedance circuits.
When AGC is turned on, the mute button has three modes: MUTE, UNMUTED and
UNMUTED – AGC.
Options  Show drive level in Amps
Changes the drivel level on the WT Control window signal button from % to amperes.
Options  Left Mouse Button Action
This option controls the behavior of the left mouse button when used in the WT Control window graph.

Set Frequency Control in WT Control Window - when checked, enables the left mouse button to select the current
measurement frequency in the WT Control window. This feature is used to add or remove data points from a curve
as described in section 2.3 WT Control Window.

Adjust Phase in WT Control Window - when turned on, enables the left mouse button to adjust phase in the graph
of the WT control window.
Options  Signal Mode
Select the type of signal mode to use in a test with this option. There are 14 modes to choose from:
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
Real-time modes include Impulse, MLS, Noise, Chirp and are used for fast impedance testing

Sine mode is used for producing high precision results
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NAVIGATION
Note:
Each signal type will have a different drive level and frequency content characteristic. The Impulse mode for example
has more low frequency content than the MLS or NOISE modes making it more suitable for measuring a woofer.
Conversely, MLS and Noise are good for measuring tweeters. Care should be taken with the MLS and Chirp sine modes,
as these modes have zero crest factor meaning the low and high frequency energy can be quite high. In all cases,
excessive drive levels can damage delicate drivers. Please see the ICD tweeter protection circuit, described in Chapter
8, for a possible solution.
Options  Smoothing (all real-time modes)
Select this option to turn FFT averaging on and off. When enabled, it smoothes response curves from noisy signals.
Smoothing applies to Impulse, MLS, Noise, Chirp signals.
Tip: Signal mode and Smoothing can also be set in the Setup Control Window
Options  Buffer size, frames and averaging
This menu option allows you to the change buffer size, the number of buffers and the number of frames averaged in signal
processing.
! Changing these settings can impact your system performance.

Buffer size - determines the size of the data sample processed at one time. A larger buffer size will require more
memory from your system. Depending on the performance of your CPU, you might see a delay in signal updates at
larger buffer sizes.

Number of buffers – is the amount of data chunks processed at one time. The recommended setting is 2, but
the system handles up to 8 buffers. Increasing the number of buffers can enhance performance of lower CPU
systems. To change the number of buffers, type a number from 1 to 8 into the dialog box and click OK.

Frames averaged – sets the number of frames averaged per data point. For higher precision, enter a higher
value for this setting. However, keep in mind that a higher value will increase processing time. Therefore, for fast
testing, this value would be set to a lower number. The system will average up to a maximum of 8 frames.
Options  Sample Rate
The system has four sampling rates to choose from: 48kHz, 44kHz, 22kHz and 11kHz. The default is set to 44kHz, which is
the sample rate used in CDs. A low sample rate is used to measure low signals and a high sample rate will increase the
quality of the data.
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NAVIGATION
Options  Measurement Channel & Reference Channel
The measurement channel option sets the signal source, while the reference channel sets the base signal for the test. These
settings can also be selected in the Setup Control window and are covered in the following chapters.

Line L – left channel

Line R – right channel

Mike L – left microphone

Mike R – right microphone

LoZp V – low power voltage channel

LoZp A – low power amperage channel

HiZp V - high power voltage channel

HiZp A – high power amperage channel

Ref – reference channel
Options  Mike Gain
The tester has a Mike Gain option that controls the input level of both
microphones. In room response measurements, for example, the gain on the
left microphone can be set to a different level than the right microphone to
compensate for the distance between the two.
Options  Analysis Mode
This option selects the analysis mode for a particular test and will be covered in later chapters
under various topics. Analysis mode can also be set in the Setup Control window.
2.15.
Tools Menu
Tools  Set Atmospheric conditions
Atmospheric conditions that affect the calculation of Thiele Small parameters and the simulator response are set here.
Inputs include temperature, humidity and atmospheric pressure. Outputs are density, speed of sound and acoustic
impedance.
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NAVIGATION
Tools  Ellipse/Oval Calculator
This calculator finds the effective diameter and area of elliptical/oval drivers, or drivers that have a phase plug or exposed
pole piece. Vas is defined as the volume of enclosed air that creates an air spring of equal stiffness to that of the driver.
Therefore, stationary mechanical components like phase plugs and pole pieces with unsealed dust caps do not contribute.
Furthermore, the outer suspension is measured at its 50% points since the outer edge does not move while the inner edge
moves with the cone.
To calculate diameter and area, enter the following data in the dialog box:



Major dimension (mm or inches) – enter the length of the long side from center of suspension to center of
suspension
Minor dimension (mm or inches) – enter the length of the short side from center of suspension to center of
suspension
Phase Plug Diameter – Enter the diameter of the central phase plug or exposed pole piece. Enter zero if the dustcap is sealed.
The calculator then calculates area in m2/inches2 and effective diameter in mm and inches.
entry for phase plugs, but does not include an oval calculator.
The Vas test includes a similar
Tools  Design Air Core Inductor
The air core inductor tool will help you design air core inductors for your crossover designs.
1. Enter the desired inductance value in the first field and click enter.
2. Input the inner diameter (D) - larger diameters produce lower inductance.
Hit enter.
3. Next, enter the height in inches (H). Click enter.
4. In the fourth field, enter the wire gage in AWG and hit enter.
5. Next, input the wire insulation in inches and click enter.
6. Lastly, (if important) set the temperature in degrees Celsius and click
enter.
7. The results at the bottom tell you how much wire you will need to wind on
to the form.
Tools  Master Level Mixer (Windows Vista Users only)
The input and output session levels can be temporarily changed with this menu option. Note that the default settings, defined in the
“MIXERLVL.CFG” configuration file, are not changed by the mixer. You must manually change “MIXERLVL.CFG” to make a permanent
change to the input and output levels.

Mute – turns the input/output off.
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NAVIGATION

Lock 100%/25% - sets the master output level to 100% and the microphone-in level to 25% (Tester default
settings).

Manual Entry – select this option to manually enter a level setting between 0 and 1.

Enable All – enables all audio devices in the list.
Adjust the volume with the UP and DN buttons
Adjust the volume by selecting the ‘Manual Entry’
checkbox and entering a value
Tools  Auto-Set (Windows Vista Users only)
This menu option resets the current mixer levels to the values specified in the
“MIXERLVL.CFG” configuration file. The message on the right appears on startup if the
mixer settings do not match the specified levels. The message asks you to confirm
changes in mixer settings.
Windows Vista allows users to set different master volume levels for the various audio devices
connected to the computer. By default, Vista requires the (microphone) input level to be set to
25% and the output to 100%.
“MIXERLVL.CFG” is located in your Tester’s installation directory and can be configured by editing
the file (you should not need to change this).
Contents of MIXERLVL.CFG:
Edit volume settings in MIXERLVL.CFG file.
Values are in % and range from 0 to 1.
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NAVIGATION
2.16.
Printing Files/Graphs
Depending on the type of window open, you have the option to print or save to a file, either as a BMP graphics image, or as an ASCII
text file.
Note: Some print drivers that perform format conversions are compatible. For example, printing a graphics image to a PDF converter
will produce a PDF.
2.17.
Exporting Results
Test data can be exported in a number of formats. The export
type will depend on what you want to do with the data. A
common export is a ZMA files that is used in the Interactive
Crossover Designer.
2.18.
Help Menu
Online help, as well as calling up your web browser and connecting to the Smith & Larson Audio Website can be done here. The
Enable Button Help option turns popup help messages on and off.
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CALIBRATION
3. CALIBRATION
CAUTION:
You may not want to connect an amplifier to the tester until you are familiar with the tester and
using/calibrating the low power test port.
3.1.
Calibration, Component & Linear Testing
The low power port must be calibrated to use the tester. For best results, calibrate both the High and Low Test ports. Two calibration
routines are run for each port. The first routine calibrates impedance and phase, and the second calibrates the voltage and current
readings. Cable effects will also be mathematically removed.
3.2.
Low Power Port Calibration
Low power test port calibration begins by configuring the tester for a Sine test signal and LoZP operation. This can be done from the
Options pull down menu, or from the Setup Control Window. Selecting the LoZP mode automatically sets the Measurement and
Reference sources.
Sine Wave Signal Mode
Low Power
Impedance &
Phase
Analysis
Low Power Calibration Steps
Start the calibration routine using the ZP Calibrate button, or using the Tests pull down menu:
Begin ZP
Calibration
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CALIBRATION
The first dialog box that opens will ask whether you want to perform a full or simple calibration. Both methods are similar in that they
will use the calibration resistor and or short to set the tester’s internal gains and offsets. The difference is that, in full calibration mode,
the test leads’ inductance and resistance are measured. If a full calibration is made, test lead impedance compensation can be turned
on or off. In simple calibration mode, the tester and lead parameters are combined making measurements at either end of the test
cable the same.
Note to Windows Vista Users:
The following dialog box opens reminding users to check and/or adjust the master level settings. The master level
settings are: 100% for playback and 25% for recording. The dialog flashes red if an improper configuration is
detected.
The Continue button brings up step 1 of 5, which asks that the calibration resistor be attached to the tester (full), or at the
end of the test leads (simple). This measurement is made at 200 Hz and sets the low frequency gain.
If you are using a high resistance cable, the ‘Pass’ message may not appear. You can override this by clicking OK. If the
resistance is stable, calibration will be valid, but a little less accurate.
Full Calibration
Simple Calibration
Measuring at the tester terminals isolates
the cable
The internal tester and external test lead
resistance are combined
The WT2 is identical in operation to the low power port
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CALIBRATION
Note: Measurements are not instantaneous. High-level noises around the test area are rejected using tuned narrow band
filters. This slows down the calibration. The 1-10 Hz band is particularly slow and takes several seconds to complete. Wait
until the ‘Check Connections’ message changes to ‘Pass‘ before hitting NEXT.
Process Step
Setup Info
Measurement
Wait for
‘Check Connections’ to change to
‘Pass’
The calibration resistor is re-measured in step 2 at the test lead terminals (Full) or end of the test leads (simple) using a
higher test frequency.
Full Calibration
Simple Calibration
The calibration resistor is then replaced with a short. The measurement is again either made directly at the tester terminals
(full) or at the end of the test leads (simple). A shorting bar made from a banana jack and section of buswire may be helpful
here. For the simple calibration method simply connect the alligator clips.
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Full Calibration
Simple Calibration
Using a shorting bar
Short the test lead ends
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CALIBRATION
Step 4/5 is another shorting test. In full calibration mode, the cable is inserted into the circuit and measured using a short at
the far end. This physical configuration is already setup for the simple calibration mode. Wait for ‘Pass’ and press NEXT.
Full Calibration
Simple Calibration
Step 5/5 is the final high frequency test that measures cable inductance.
Full Calibration
Simple Calibration
Calibration is complete and the test results are sent to the results window.
Using an ARB Sweep To Verify Calibration
An arbitrary sweep will show calibration quality. Use the Axis Control to set the SweepLo and SweepHi points and click ARB1. As the
test runs, you will notice the impedance is very flat. To see just how flat, use the Axis Control window to narrow the impedance range
to 9.995 and 10.005 ohms. The next image shows the change in test lead inductance. The testers calibration process will take this
into account as long as the cables do not change. To get the best possible results use a ‘zero length’ test cable by plugging directly
into the tester or use a section of speaker cable. Zero length calibration is very useful when measuring components and cables.
Arbitrary sweep showing calibration flatness
Scale: 0.001 ohm/division
0.004 degrees/division
Comparison of shorted test lead inductance loop
when tightly wrapped or wide-open.
900 nH tight, 2200 nH open
Tip: The inductance of pair of simple test leads varies considerably. A test cable can be made from a
section of speaker wire, banana jack and alligator clips.
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CALIBRATION
Low Power Port Voltage and Amperage Calibration
Impedance and phase calibration tunes the voltage and current ratio on an absolute scale.
This test must be run from the Test pull down menu. Leaving the 10-ohm calibration resistor connected to the low power
port, choose Tests  Calibrate  Calibrate Volt/Amp.
Using an accurate DVM, measure the test load voltage and enter the value as shown. A 60 Hz frequency is used since many
AC voltage tester’s are intentionally band limited. Enter the value from the DVM into the Volts from DVM window in the dialog
box and click OK.
Enter AC RMS voltage from DVM here
The low power test port is now fully calibrated.
Alternate Configurations
A shorting bar made from a spare banana jack can be quite helpful. The second image shows the ‘zero length’ test cable
configuration that is used when extreme accuracy is required.
Using a Banana Jack for the Short
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Zero Length Calibration with Cal-R and Short
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CALIBRATION
3.3.
High Power Port Calibration
High power test port calibration begins by connecting the line outputs to your test amplifier and returning one of the amplifiers outputs
to the LOAD side of the high power test port. Be sure to connect the ground-side of the amplifier to the black 5-way binding post.
CAUTION:
A ground-referenced amplifier, with the ground connected to the black terminals, must be used for
proper operation. Voltage at either black terminal (ends of the sensing resistor) should not exceed 4
Vrms.
If the leads are swapped, or if the amplifier ground lead is resistive, a large common mode signal will be
created at the differential sensing inputs (between the black terminals). Placing the sensing resistor in
the ground side of the amplifier improves the high gain sense amplifier’s Common Mode Rejection Ratio
(CMRR). This increases the tester’s usable dynamic range.
The 0.5 ohm sense resistor is connected between the
black terminals.
High Power Port with amplifier leads connected to the
AMP terminals (left) and 10 ohm calibration resistor
on the LOAD side (right)
The amplifier’s ground-side terminal is connected to
the left ‘AMP’ side black terminal.
The next step configures the tester for sine test signal mode HiZP operation. This can be done from the options pull down
menu, or from the Setup Control Window. In both cases selecting the HiZP mode also automatically sets the Measurement
and Reference sources.
Sine Wave Signal Mode
High Power
Impedance & Phase
Analysis
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CALIBRATION
Start the calibration routine using the Calibrate button, or using the ‘Tests’ pull down menu:
Begin ZP
Calibration
High Power Calibration Steps
The initial dialog that opens will ask for you to OPEN the load side terminals. This establishes a baseline measurement of the open
circuit voltage and amplifier gain. Open circuit voltage is first measured at 60 Hz.
Open circuit voltage is then measured at 15 kHz
The third step measures internal signal isolation. In this step you disconnect or disable the amplifier output, but DO NOT ADJUST THE
VOLUME.
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The amplifier is reconnected allowing the tester to measure the terminal voltage with the test load applied. Terminal voltage should
be a little lower than in steps 1 or 2.
Step five is the last calibration step. It finalizes measurement of the total amplifier side resistance and inductance.
Calibration is now complete. You are then asked if you want to include any LOAD side cable effects in your measurements. Select NO
(you can enable this later in Setup control)
High Power Calibration Results
The high power calibration results include a measurement of the total amplifier side resistance and inductance.
This is the sum of the amplifier and AMP side cable. If the CABLE characteristics are known, they can be
subtracted leaving a measurement of the amplifier output resistance and inductance. This can then be used to
compute a damping factor.
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CALIBRATION
High Power Voltage and Current Calibration
High power voltage and current calibration is similar to that of the low power port, except that an optional additional calibration is
included for DC offset testing. Select Tests  Calibrate  Calibrate Volt/Amp from the menu. The tester automatically performs the
calibration. If you do not have a DC coupled amplifier, or do not need to do those types of tests, ignore the Cal DC option.
The high power test port is now fully calibrated.
Capacitor Measurement
The menu option Tests  Capacitor Measurement Setup is used to fine-tune the low power port for measuring small value capacitors.
Crossover capacitors are typically quite large compared to the internal capacitance of the test port that is typically 350-550 pF. When
capacitance is large, simply placing a 10 kohm resistor across the port will create a DC path for the port’s constant current source. If
these values are fined tuned, sub 100 pF measurements are possible. The process is simple. Click on the Auto Complete button
and wait for the alignment to complete. Then click ACCEPT. You can also step through manually to see how each alignment step
works.
Measuring Revc
The Tests  Measure Revc menu option simply calls the Re test from the Q/Fs test (and stops).
Linearity Tests
The Woofer Tester Pro also includes two linearity tests: The first test measures Thiele Small parameters versus changes in
the AC drive level (compression). The second test measures Thiele Small parameters versus DC bias revealing voice coil and
suspension alignment and linearity. Select the Tests  Linearity Tests menu option to conduct these tests.
More information on linearity tests can be found in the XY plotting window, and in the section on TS parameter testing.
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4. THIELE SMALL DRIVER MEASUREMENT
! WARNING !
The LOW POWER TEST PORT differential current source output (banana jack) is not ground
referenced and cannot be safely connected to grounded or externally powered equipment without
risking damage to the device. This applies to Amplifiers and Oscilloscopes.
Simple ‘two terminal’ devices like Loudspeakers, Crossovers, RLC devices, or hand
held meters (that are free floating relative to ground) are the only acceptable loads.
The actual process of measuring a woofer can be fairly complex but the basic concept is that drivers are mechanically
resonant transducers that are coupled to an amplifier on one side and air on the other. The physical electrical, mechanical
and acoustic characteristics are then broken down and modeled. The tester’s job is therefore to reveal this information with
minimal effort and with maximum accuracy. Extensive literature on T/S modeling already exists on this topic, so only basic
theory is covered. An overview of how the tester performs these tests and why this is important is provided at the end of
the section.
Baseline measurements are typically made using a modest 1-3mA drive, so you may not hear the tester working. This
modest level provides a large enough signal to make accurate measurements while at the same time not driving the
mechanical mechanism to the point that a suspension or motor non-linearity has appreciably changed the at rest
characteristics. This is known as a small signal model. Using smaller or much larger (WTPro high power port) test signals
later reveals these characteristics in detail over a wide range of drive levels.
Baseline Thiele Small models are found using a search algorithm and sine wave test signals. Sine wave testing is used since
this provides the best possible signal to noise ratio, is highly repeatable, provides constant current at all frequencies, does
not excite other resonance points, and ensures the mechanical components of the driver are biased equally positive and
negative. The real time impedance modes will show similar graphs, but these are not sufficiently accurate to extract
information suitable for further analysis.
4.1.
Revealing the Thiele-Small Model using Electrical Tests
The electrical load of a speaker is a very important parameter for an amplifier, but more importantly, these characteristics
reveal the Thiele Small (T/S) model. This is achieved by measuring the driver in an un-modified ‘open-air’ state followed by a
modified state where either the mass or the compliance is physically altered.
Analyzing the height and sharpness of the electrical resonance peak also reveals the electrical and mechanical ‘Q’ or ring
down characteristics. Later, when the driver is placed into a sealed or vented box, these same principles are applied to
reveal the system level characteristics of the completed system.
4.2.
Finding Mass and Spring Constants that Set Free Air Resonance Fs
The free air condition is achieved when a driver is attached to a solid un-moving frame of reference with no enclosed air
volume behind it. In this configuration the cone, voice coil and suspension each have a contributing mass. Likewise, the
suspension components are mechanical springs attaching the mass components to the driver frame. The resonant frequency
of a spring and mass system is given by:
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 Kms 
Fs  2 * 

 Mms 
(1)
where
Fs = Mechanical system resonance in Hertz (also known as Fms)
Kms = Mechanical system spring stiffness in Newtons/Meter
Mms = Mechanical system moving mass in kg
Electrically, the tester sees a mechanical resonance as a parallel circuit consisting of a capacitor and inductor with an
additional resistor (the voice coil) in series. This equivalent circuit then rings at the same frequency as the mechanical
resonance. The tester measures this frequency by applying a series of test signals that are designed to search for the zero
phase crossing that coincides with the impedance maxima.
Note: In the T/S model mechanical suspension stiffness (Kms) is electrically equivalent to a capacitor whose value is
Cms=1/Kms. Therefore Cms ‘compliance’ is often used when describing a T/S model. Compliance is simply the inverse of
stiffness.
The next step is to modify either Mms or Kms. Modifying Mms is known as the delta mass method and modifying Kms is
known as the delta compliance or test box method. The new resonance equations are shown in equation 2.


Kms

Fsmod  2 * 


Mms

Madd


(2)
 ( Kms  Kbox) 

Fsmod  2 * 
Mms  

where
Madd = Additional mass added to the cone
Kbox = Stiffness of air spring from a test box
By knowing the before and after resonance, plus the added mass or box air stiffness, a little bit of algebra reveals the
following two equations. The first is used when the delta mass method is selected and the second for delta compliance.
Mms 
Madd

Fs
Fsmod
(3)
Kms 
2
1
Kbox
 
Fsmod
Wfree
4.3.

2
1
Driver Q
Driver ring down characteristics are determined by various mechanical and electrical losses that dissipate energy. Mechanical
losses include friction losses, mainly in the suspension, and acoustic radiation. Electrical losses include the voice coil
resistance, but can also include cable loss and eddy current loss in the magnet structure.
Electrical and mechanical system Q’s (Qes and Qms) are found in the free air test by measuring three frequency points Fs, F1
and F2. Fs is the point where Zmax occurs (also the zero phase crossing), and F1 and F2 where Z=sqrt(Zmax*Revc). Here
are some equations for Q:
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Zmax
Re
Qms  Fs*
( F 2  F1)
4.4.
Qes 
Qms * Re
( Zmax  Re)
Qts 
Qms * Qes
(Qms  Qes)
Driver Frequency Dependent Inductance (Le is not simple inductance)
The next evolution in T/S modeling includes voice coil inductance ‘Le’. When Le is added to the standard T/S model, it not
only affects response but it also causes Fs to shift upward in frequency. That is, if not taken into consideration during a
driver measurement, the true value of Mms, Kms and Rms will be hidden.
On yet even closer examination, Le is found to be a combination of frequency dependent resistance and inductive reactance.
The tester measures these values first and then ‘backs them out’ during each test to reveal the true values of Mms, Kms and
Rms. The simulator model then uses these parameters to achieve a very high degree of simulation accuracy.





Xem  Kxm * 2 F
Lem  Kxm * 2 F
4.5.
Erm

Rem  Krm * 2 F
Resistive component of Le reactance
Kxm
Inductive component of Le reactance
Exm 1
Xem Expressed as an Inductor
Non Linear Suspension and Motor Characteristics
Conventional Thiele Small measurements are performed at low signal levels to avoid non-linearity and distortion. Therefore
simulation and modeling would only be valid at low levels, conveniently avoiding suspension and motor non-linearity issues.
The tester includes an AC analysis of the electrical versus drive level (see Advanced Topics).
Note on Suspension Compliance:
A careful examination of the AC and DC results will often show a wide range of input levels, usually up to the point where
suspension limiting begins, where the suspension mechanical spring constant (inverse of compliance) significantly
decreases as the AC test signal level is increased. This effect is much larger than the static changes seen in the DC
offset test. Cms (suspension compliance) is significantly dependent on break-in, drive-level and temperature. The
underlying mechanism(s) are a function of how the molecular bonds respond to these conditions:

The suspension mechanically loosens with usage. This is commonly referred to as
"break-in" and is dependent on the excursion incurred (itself a function of frequency and drive level) and
duration.

The suspension compliance is affected by changes in ambient temperature.

The suspension will self-heat due to mechanical energy loss. This is mostly a function of Rms and drive level,
though at high drive levels, misbehavior of the suspension can come into play.
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The AC drive level test relies on the testers ability to measure a very accurate baseline driver model. For example, if the
tester can accurately measure Fs variation with drive level, and Mms is assumed to be constant, any variation in Fs must be
attributable to variations of the driver suspension compliance Cms. A simple calculation, but the value of Fs must be very
accurate. Similarly, Qes variation is an indicator of motor characteristics.
Monotonic sinusoid test signals are used to focus energy at a single frequency while tuned narrow band filters are used to
reject out of band signals. An additional advantage is that the drive current can then be held constant at all frequencies (the
high power port simulates constant current). Using this type of signal, the Low and High power test ports each cover a
100:1 range in drive level or 10,000:1 in power. When combined (e.g. WT2 and WT-Pro), the drive level variation is
10,000:1 and power is 10,000,000:1.
Broadband excitation signals like MLS, noise, impulse and chirp are excellent for fast impedance testing, but should be
avoided when precision T/S modeling is required. Simply put, these signal types do not provide the same degree of precision
or noise immunity. An additional problem is that the drive level density with respect to frequency is not constant. True
constant current (or constant voltage) methods will produce better and more reproducible results.
Note: The test port directs the load voltage and current to the measurement and reference channels. Matched filters on
each channel then provide a complex vector value on a sample-by-sample basis allowing a precise calculation of phase and
amplitude. A vector divide then reveals a precise measurement of impedance Z and phase P.
4.6.
The TS Tests (What Is Measured)
The industry accepted standard drive level for Thiele Small testing is that a low level constant current source should be used
to avoid various non-linear effects, but not so low that readings become erratic. The precision of the low power test port
exceeds almost all previous hardware methodologies allowing the user to select a wide range of drive levels. The Woofer
Tester compression tests have been written to automatically extract T/S models over a continuum of drive levels.
As the Woofer Tester sweeps from low to high frequency, it will automatically find and measure woofer resonance and other
test points and then automatically calculate the Thiele Small model parameters. As it does this, you will see the test
frequency go up and down in ever decreasing step sizes as it zeros in on the point of interest. Tester settings that define
accuracy, runtime and the final ‘good enough’ ratio are all defined in the options pull down menu. The zeroing-in
methodology is similar to measuring Fs, Qms, Qes and Vas using a frequency generator, voltmeter (and phase meter if you
have one). It is also known as the constant-current method of measuring TS parameters.
4.7.
Q and Fs Test (Launch from ‘Q,Fs Test’ Button)
The ‘Q and Fs Test’ is launched from the control window using the Q, FS Test button on the left. Voice coil DC resistance is
measured first, followed by frequency dependent inductance (Rem and Xem coefficients), then Fs and finally the F1 and F2 Q
measurement points. When complete, results will be posted to the text area at the top of the window, as well as the Results
window.
Click[-] to shrink text
area
Click Button Middle
to start Test
Click left of the Button
Edge to select and view a
buffer
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Q,Fs ‘Free Air’ Test
DC resistance is found by measuring the complex impedance at two low frequency points, calculating the real component at
each frequency and then interpolating to zero hertz. The low power port uses 1 and 2 Hertz as the test frequencies while
the high power port uses 5 and 10 Hertz. The 5 and 10 Hz frequencies were chosen since it is unlikely most users will be
using DC capable power amplifiers. There is also the option of manually entering a value for Re.
Coefficients for Rem and Xem (frequency dependent Le) are found next by making one or more high frequency
measurements. Rem and Xem are then calculated for each test frequency and subtracted from the measured terminal
impedance leaving only the effects ofMms, Cms, Rms and Re.
The test then moves on to finding Fs by starting a sweep at the SweepLo frequency. If the tester is properly calibrated, and
the test environment good, phase should be positive. The sweep then continues upward looking for the first zero phase
crossing. The frequency step ratio is then decreased and the direction reversed. The tester uses this methodology to zero in
on a value for Fs. Phase is used because the tester can directly measure phase at any test frequency and the phase slope at
Fs is steep. Depending on setup, precision can be quite high. The step ratio, bailout and other parameters can be adjusted
to trade test time for precision.
F1 and F2 are found next by zeroing in on frequency points above and below Fs where:
 Z max 
Z0  

 Re 
The test finishes by filling out the rest of the impedance curve.
Note:
You should periodically check calibration.
The low power test port output is a constant current source. Therefore, voltage is proportional to
impedance and high impedances will produce proportionally higher voltages.
If the required voltage exceeds the available internal voltage the clipping indicator will let you know the
tester is producing erroneous results. If this occurs during a test, simply decrease the test drive level and
start over. Sometimes it is helpful to run an arbitrary sweep first to roughly determine driver
characteristics.
Do NOT block or restrict vented pole piece airflow. This will create a tiny sealed box air spring that will
shift your measurements.
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4.8.
Vas Test (Launch from ‘Vas Test’ Button)
VAS testing requires that you modify the free air set up using one of three options. As before, the test begins by clicking in
the middle of the Vas Test button. The delta mass or delta compliance methods are most popular, while the third,
calculating Vas from a known efficiency, is most useful when creating electrical models for mid ranges and tweeters.
Click Button Middle to
start Test
Delta Mass ‘Easy Nickel’
Measuring Piston Diameter
After entering the piston diameter, added mass or box volume, each of the ‘delta’ tests is quite simple. The only
measurement made finds the modified Fs frequency allowing the remaining TS parameters to be calculated. Similar to the Q
and Fs test, the effect of frequency dependent inductance is backed out of the impedance measurement.
The known efficiency method is a mathematical reversal of the efficiency equation. Knowing efficiency, piston diameter, Fs
and Qes is enough to reveal a full model. Simulated response accuracy will however be compromised if there is any error.
This method is most useful when tracking parameter variation of a known driver, or when creating an electrically equivalent
TS tank circuit for a crossover design tool. In that case, response is a don’t care.
Delta Mass
The delta mass test is arguably the easiest to perform given that suitable test masses are easy to acquire and almost any
solid surface can be used as a test bench. In this test, a mass is added to the driver cone causing the free air resonance to
go down. Accuracy is a function of the weight measurement, suspension linearity and the tester’s ability to resolve the
resulting frequency change. Given that traditionally Thiele Small tests were performed with analog sine sources and
voltmeters whose accuracy and repeatability might be questionable, the accepted practice has been that a 25% change in
resonance should be targeted. The Woofer Tester is easily more accurate so this can be cut back considerably. The
software ‘suggested’ mass however still honors the traditional 25% guideline.
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The ‘Easy Nickel Test Mass’ method is particularly helpful for acquiring suitable test masses. Newly minted US Nickels have
weighed 5.0 grams since 1938! If a lighter mass is needed, the copper coated zinc pennies (after 1983) are 2.5 grams. The
following link contains information for US, European Euro, Australian and other coins.
http://www.woofertester.com/coinweight.htm
Delta Compliance
The delta compliance method uses a known test box volume to increase the total stiffness, which then also increases Fs. The
quality of the test results, in this case, depend on the accuracy of the box volume calculation (excludes driver displacement,
bracing, etc.) and new resonance frequency. The test box should not be stuffed with damping material.
Tips:
The tester has enough excess precision that a 25% decrease in resonance is no longer necessary. A
10% change is usually sufficient. This is particularly useful when drivers are simply set on a firm
surface with gravity acting on the cone and test mass. This deflects the suspension from its zero
point. That is, a less than ‘traditionally optimal’ test mass can be used.
Decrease the drive level if the coins begin to jiggle or bounce.
Use caution when applying sticky substances to a cone. Stains are possible so you may want to
consider using the back side of the cone. Excessive force can also weaken or damage a cone.
4.9.
Box Test (Launch from Box Test Button)
In-box testing reveals information about the actual alignment of the driver after it has been mounted into a suitable
enclosure. When this data is used in conjunction with Thiele Small Simulator the effective box size, tuning and losses are
revealed. The simulator will also auto-align itself using this data revealing the actual in-box acoustic response.
The file “demo2_simulator.woo” contains previously acquired data for a 165 mm (6.5 inch) computer sub-woofer. In-air data
was also taken showing how the simulated and actual response will eventually align. See the demo section for additional
information on this demo.
This test finds the impedance peaks and minima where the zero phase crossings occur. The simulator then uses this
information when an auto-align is requested. If the alignment is successful, the resulting simulated response will closely
match the actual response. See the simulator section for information on using the auto-align feature.
4.10.
Making A Suitable Test Bench
Electromechanical devices such as loudspeakers exhibit impedance and phase variation whenever a resonance occurs. Driver
resonance is created when the kinetic energy (moving mass) and potential energy (suspension spring) are in balance.
Electrical and mechanical loss (resistance) then limits the magnitude of the peak by bleeding off some of the stored energy.
The position, height and width of the resonance peak are then converted to parameters suitable for box simulation.
To accurately measure these parameters you will need to create a suitable test bench where outside influences do not
disturb each test. There are two basic setup configurations that you can use, each with pro's and cons.
Vertical Orientation (Cone is facing upward)
Simply laying a driver on the floor and performing tests is definitely easy to do, but other suitable stiff and heavy surfaces
may be preferred. The tester can help you identify suitable test surfaces by examining the phase of an arbitrary sweep. An
unsuitable surface will show a in the phase plot, and if very bad, a kink in the impedance plot.
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Some floors (even concrete) will resonate strongly. This has to do with the mass to stiffness ratio and loss factors for the
particular test point. The center and corners of a table would be an example where the leg at the corner substantially
increases stiffness. The corner of a large and heavy speaker cabinet will often work quite well.
An alternative method is to suspend the driver using a bungee cord. In this case the resonance is set by bungee cords
spring stiffness and the mass of the driver resulting in a resonance of about 1 Hz. Driver Fs is ultimately affected because
this forms a two mass resonant system. That is, since the driver is no longer firmly attached to a solid reference, Fs will shift
slightly upward. If you want to be more precise, increase the overall hanging mass by adding weights to the driver.
Suitable test masses are also easy to find. In the United States, Nickels have been manufactured with the same composition
since 1938 and weigh 5.0 grams.
Note: A Blocked Vented Pole Piece will form a small sealed enclosure
An 18” Driver suspended from a Telescope Tripod
Additional information can be found at this link
http://www.woofertester.com/bunjiggy.htm
Horizontal Orientation (Cone is facing sideways)
In practice the suspension rest position depends on all of the forces acting on it, and this comes down to orientation and
gravitational forces. Suspension non-linearity and mechanical offsets also affect the measured suspension stiffness.
Mounting a driver sideways solves this problem (no suspension sag), but a different kind of test jig and some kind of sticky
test mass will be required.
Mounting the driver between two old (massive) speaker boxes is one solution, or a sling can be improvised that mounts the
driver in free air, similar to the example shown above.
You will also need to use an accurately measured mass of clay or soft caulking. Keep in mind that placing clay on the front
side of a paper or composite cone can stain or damage the cone.
4.11.
Driver Break-In
Driver break-in is often necessary to mechanically loosen newly manufactured suspension components. For example, the
chemical and mechanical bonds that are formed in a resin impregnated cloth spider can change dramatically as they become
stretched. It therefore makes sense that to design a box you will want to get measurements that are based on how the
driver will be ultimately used. Break-In can be a fast or slow process depending on the driver.
Break-in is most easily accomplished, and with far less voice coil heating, when the test frequency is set to the driver free air
resonance, Fs.
At Fs mechanical energy is alternately stored as inertial moving mass or as potential energy in the
suspension spring. High excursions are also possible at lower frequencies but with higher power requirements.
As the driver breaks in, Fs will decrease and or excursion will increase. Frequency and amplitude can be controlled using the
control window but it is strongly advised that you control volume at the amplifier instead to avoid accidental overdrive.
Tip:
You may experience dropouts if the operating system becomes overloaded. Adding a pre-amplifier or
integrated amplifier with a volume control may be desired since this will allow you to set the tester output
level to maximum. You can then set the maximum level manually.
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! WARNING !
MECHANICAL OVERDRIVE IS PARTICULARLY EASY TO DO WHEN FREQUENCY IS SET
BELOW FS. FS ALSO TENDS TO DROP WITH BREAK-IN.
Begin with a moderately low level for the first 15 minutes and then slowly increase level. Mechanical
resonance should be visible to the naked eye. If not, occasionally go back and retest the driver.
UNDER NO CIRCUMSTANCES SHOULD THE LOW POWER TEST LEADS BE ALLOWED
TO TOUCH OR CONNECT TO THE AMPLIFIER.
4.12.
Arbitrary Impedance Plots (ARB1 and ARB2 Button)
Arbitrary sweeps do not perform any kind of test. These simple impedance plots over a frequency range are useful when
comparing drivers, crossovers inductors and more. The real time impedance modes and data buffer copy options are
particularly useful when working with these buffers.
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DRIVER SIMULATION AND BOX DESIGN
5. DRIVER SIMULATION AND BOX DESIGN
5.1.
Simulation and Physical Box Design
A simulation is initially performed using the driver’s measured Q/Fs and Vas test data to find a suitable box alignment. In theory, the
effective box volume and tuning will align with the physical but this is rarely exact. In the final box alignment step, the in-box electrical
impedance curve will be used to auto-align the simulator revealing the true response.
The simulator is controlled from the TS Entry Window and its output is viewed from the Overlay window allowing the simulated output
to ‘overlay’ measured impedance and response data either passively or in real time. The ‘copy buffers’ option can also be used to save
and compare a number of response runs.
View Simulated Response
(SimRX)
View Simulated Impedance
(SimZP)
Overlay
Window
TS Entry
Window
Tip:
If you do not see an output, the drive level may be set to zero.
Check 1W reference level to bring the display back.
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5.2.
First Pass Simulation
Box design begins by copying the test environment driver parameters (Q/Fs and Vas test data) into the simulator using the Copy>Simulator button. A dialog box will then open asking you if you want to copy the Q/Fs, Vas and Box data. Check the ‘Q/Fs’ and
‘Vas’ options leaving the ‘Box data’ option unchecked. Box data is valid only after testing and converting electrical box data. There is
no box to test yet, so this is irrelevant (used later).
An initial good starting point is to start with a sealed box by clicking on the ‘Sealed’ radio button and setting or adjusting the box
volume equal to Vas. Next, set or adjust all of the Q loss parameters to a value higher than 1000. At this point, the box type,
volume and tuning are iterated until a satisfactory alignment is found. An initial port tuning for a vented box will be the driver Fs.
Note, that in a vented box a low port tuning frequency is essentially the same as a sealed box. At this point, you can evaluate acoustic
response and phase, cone displacement, port air velocity and expected electrical characteristics. You can also enable and simulate
pipe resonance effects and room/car pressurization effects.
Want to View
Simulated
Impedance
What to copy
Box Adjustments
What to
view
Copy Test Data to
the Simulator
Auto-Align (use
later!)
Tip:
A very large box volume is essentially ‘free air’ and can be used to compare the simulated and measured
impedance plot from the Q/Fs test. Using the frequency dependent inductance ‘RemXem model’ will yield
the best possible results.
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IN-BOX ELECTRICAL TESTING
6. IN-BOX ELECTRICAL TESTING
6.1.
Box Electrical Test
A very useful simulator feature is the ability to compare simulated and measured in-box impedance curves. When the two are aligned,
the simulators box volume and tuning are said to be the effective box volume and tuning, but more importantly the simulated
response will accurately reflect the measured response. In-box electrical impedance is measured by connecting the speaker box
(without the crossover) to the low power port and clicking on the Measure Box button.
The Box test finds three points of interest, Flo, Fmin and Fhi and from these computes Fm, Fsb, Ha and Alpha. Fm is the port tuning
frequency. Fsb, Ha and Alpha are parameters that are used with charts that are found in various other simulators and publications.
Points of Interest
Flo, Fmin, Fhi
Begin Box
Test
6.2.
Auto-Align Vbox (Align Simulated and In-Box Impedance)
The Auto-Align Vbox button will align the simulator to the measured data. By aligning the simulator, not only will the electrical data
be similar, but also the response. Initially you will be asked to choose between two alignment methods that constrain the estimated
box volume, or the original TS model.
Auto-Align
method
Constrain Cms
This method finds a best fit by finding a box volume and tuning while holding the TS model constant. This method is
generally quite accurate when the original TS model is accurate and the box volume is comparable or smaller than Vas.
Under these conditions the position of the upper resonance peak is dominated by the box air compliance.
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Constrain Vbox
When box volume is large compared to Vas, the driver compliance dominates the box air spring compliance. In this case
small variations in Cms would cause significant errors in the estimated box volume method. This method is similar to the
‘Vas from a vented box’ method, except that by pre-measuring the TS parameters the motor constants and driver mass are
well known.
This method is also preferred when the drive level is substantially higher than when the TS model was originally made, or if a
new un-broken in driver is used. This is because driver suspension Cms is highly dependent on break-in, drive level, aging or
heating.
Auto Alignment Complete
A status message is then shown letting you know the parameters found before committing them to the simulator. If necessary, adjust
the box volume and tuning, followed by the Q loss parameters.
Auto-Align
status
Peaks and Zero
crossings line up
6.3.
Simulated versus Measured In-Air Response
If the simulator electrical alignment is successful, the final step is to view the response. This example compares the actual in air
response using a Woofer Tester Pro. The woofer and port in this case are on opposite sides of the enclosure allowing the driver
response to be shown in isolation.
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ADVANCED THIELE SMALL TESTING: AC & DC COMPRESSION
7. ADVANCED THIELE SMALL TESTING: AC & DC COMPRESSION
7.1.
AC Compression Testing
To measure suspension non linearity versus AC level select the following menu option:
Tests  Linearity Tests  Measure TS versus AC Level
This test requires a precision low power TS baseline before the test begins (this is not automated and must be done first). This
baseline establishes the driver’s moving mass, Re and motor constants. The driver is then configured for open air Q/Fs testing.
As the test progresses, drive levels are ratio-metrically decreased from 100% to 1% resulting in changes in Fs, Qms, Qes and Zmax.
By then using the established Mms as a constant, the only parameter that can effect Fs is compliance Cms. Similarly, variations in Qms
can only be attributed to changes in Rms and Qes by changes in BL. The process is continued resulting in a graph like the one shown
below. The X-Y plot window is then used to view and compare the Thiele Small Parameters .
Example
Fs for this driver dropped from a high of 84 Hz at 29 A to 58hz at 100 mA (usable Xmax). Fs then climbed steeply with increasing
drive level as the suspension bottomed out. This example clearly shows why different test levels produce different results for the
same driver. The WT2 and WTPro test discontinuity was caused by the suspension 'settling' as the initial test level was quite high and
was sufficient to begin bottoming the suspension causing considerable mechanical noise.
Note On Suspension Compliance:
Suspension non-linearity is sometimes intentional. An example would be controlling displacement at maximum excursion.
This test shows a continuum of TS parameters dependent on drive level. This is known as ‘stiction’. What is not shown is how the
suspension changes with time, break-in and temperature.
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A careful examination of the AC and DC results will often show a wide range of input levels, usually up to the point where
suspension limiting begins, where the suspension mechanical spring constant (inverse of compliance) significantly decreases
as the AC test signal level is increased. This effect is much larger than the static changes seen in the DC offset test. Cms
(suspension compliance) is significantly dependent on break-in, drive-level and temperature. The underlying mechanism(s)
are a function of how the molecular bonds respond to these conditions:

The suspension mechanically loosens with usage. This is commonly referred to as
"break-in" and is dependent on the excursion incurred (itself a function of frequency and drive level) and duration.

The suspension compliance is affected by changes in ambient temperature.

The suspension will self-heat due to mechanical energy loss. This is mostly a function of Rms and drive level,
though at high drive levels, misbehavior of the suspension can come into play.
7.2.
DC Compression Testing
To measure suspension non linearity versus DC level select the following menu option:
Tests  Linearity Tests  Measure TS/THD versus DC Bias
DC offset testing also requires a precision low power TS baseline to establish the driver’s moving mass, Re and motor constants (this is
not automated and must be done first). The driver is then configured for high power open air Q/Fs testing. This dialog box is used to
set the test options.
Pick Real-Time Impedance Signal Type
A real-time impedance mode is preferred in this test. However, different signal types may produce differing results. The options here
provide both low and high frequency energy. It should be noted here that real time signal types are actually not symmetric.
Choose if Le and THD are to be measured
Le and THD can optionally be measured with higher precision using a sine wave. Le is measured at 4x the Fmin zero phase crossing.
Choose AC and DC drive levels
AC and DC levels are entered as a percentage of amplifier drive when the test reaches 100%. The indicated levels are found by
measuring the amplifier gain using an AC signal.
As the test progresses, DC levels are increased from 0% to 100% of the selected maximum level in increasing positive and negative
steps. This allows the test to be stopped or the amplifier shut down. As the levels increase, changes in Fs, Qms, Qes and Zmax are
detected using a technique similar to that in the AC compression test. The X-Y plot window is then used to view and compare the
THD and Thiele Small Parameters.
DC bias testing also produces a table of TS parameters, but these parameters are derived from a small signal analysis at a particular
DC bias point. These parameter variations reveal useful information about driver construction such as mechanical offsets, suspension
and motor linearity with excursion. This example shows an offset in the suspension as well as the voice coil.
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ADVANCED THIELE SMALL TESTING: AC & DC COMPRESSION
As the DC bias test is run, a sine wave signal can be specified that either tracks Fs or remains fixed at the frequency when the test
begins. In this case, harmonic analysis also reveals mechanical offsets. However, keep in mind that the raw data provided in this case
is a cumulative effect of all DC and small signal AC parameters. In the absence of an infinite baffle, this test can be performed in an
open-air test jig using a closely spaced microphone. The absolute level of Fs and its harmonics are therefore typically low due to backside cancellation. A trend at a particular frequency will however still be valid.
The XY window can also be configured to view SINAD, or Signal versus Noise and Distortion. Normally, SINAD measurements are
given in decibels as the amplitude ratio of the fundamental signal to all remaining noise and distortion. The XY plot version of this
algorithm uses the measured amplitude to create a sine wave at the fundamental frequency that is then subtracted. If the remaining
signal is then plotted against the fundamental, data views of NAD vs Magnitude, Lissajoux and oscilloscope are possible.
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ADVANCED THIELE SMALL TESTING: AC & DC COMPRESSION
Note: the Xn / int(Xn) button numerically integrates the data. Microphones produce signals that are equivalent to pressure, that in
turn is proportional to mass-air velocity. Integration shows mass-air displacement.
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INTERACTIVE CROSSOVER DESIGN™ (ICD)
8. INTERACTIVE CROSSOVER DESIGN™ (ICD)
CAUTION:
Failure to use the ICD Tool Properly can result in damaged drivers or amplifiers. Refer to Section 8.6
Tweeter Protection Circuit for more information.
With the Interactive Crossover Designer (ICD), you can design both, physical and arbitrary crossovers.
ICD simulates soldered together physical crossovers using a SPICE circuit file (*.CIR extension) that defines the connections,
RLC (resistor, capacitor, inductor) values and driver impedances (as ZMA files). The circuit file itself can be input by hand, or
captured using a number of third party schematic capture programs. Additional features include a driver protection circuit
that is virtually ‘removed’ in software as well as a time delay option that simulates changing the driver to driver front to back
spacing.
Arbitrary filters are defined solely on a mathematical basis using *.XVR extension files. These files have uses ranging from
simulating DSP and other electronic crossovers to defining hypothetical conventional crossovers that are based on driver
measurements. The format itself is similar to the FRD export format except that two channels are defined and in this case
the data is an input that defines the tester’s output signals. In this case the simulated outputs represent a direct connection
from the amplifier to the driver.
The ICD simulator allows you to test crossover designs on your desktop before having to physically build them. Simulated
and actual crossovers can then be tested in real-time by moving around the room with the microphones and seeing the
responses on the screen.
Notes:

Signal I/O is only active when the WT Control window is open.

The ‘Math Reference’ is always used when calculating ICD response
8.1.
A Physical Versus Simulated Crossover Design Example
We will use an example to show the process of designing a physical crossover. The process consists of the following steps:
1.
Create an electronic circuit file. There are free, third party applications available for designing electronic circuits.
Linear Technologies’ LT SPICE (or SWITCHER CAD) is used in this example but other schematic capture tools will
also work. This step is described in detail in the next section.
2.
Convert the electronic circuit schema into a Berkeley Spice net-list file. Conversion as well as language syntax are
described in section 8.3 Circuit File Syntax.
3.
Add the speaker’s characteristics via a ZMA file. This is described in section 8.4.
4.
Simulate the crossover.
The sample crossover we build in this section was constructed from a 6.5” woofer and 20 mm polycarbonate tweeter.
Terminal block connections for each driver were then positioned on the back of the enclosure coinciding with connectors in
the removable physical crossover. Each component was carefully measured and then input into an ICD circuit file.
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Figure 8-I - Front, Back and Back with Crossover Installed views of the Test System
Note:
This tester will measure resistors, capacitors and inductors very accurately. There is also an air core inductor design
wizard in the Tools pull down menu
The following ICD circuit file was created to model the physical circuit.
Figure 8-II – File Contents of 'DEMO.CIR'
*******************************************************
* 2nd order high pass, 1st order low pass
*
* (1) 615uH
(2)
*
o----L1----+----------+
*
|
|
*
| C1
| |
*
=== 6uF
+-+/ Z1
*
(3)|
| |) DEMO_WO.ZMA
*
|
+-+\
*
R1 4
| |
* (0)
|
|
*
o----------+----------+
*
* (1)
3uF
(4)
5ohm
(5)
*
o----||----+-------R2--+--------+
*
C2
|
|
| |
*
|
|
+-+/ Z2
*
L2
R3
| |) DEMO_TW.ZMA
*
| 274uH
| 4ohm +-+\
* (0)
|
|
| |
*
o----------+-----------+--------+
*******************************************************
Vsig
1 0
AC
10
**************************
L1
1 22 615uH
RL1
22 2
0.1
C1
2 3
6uF
R1
3 0
4
Z1
2 0
"demo_wo.zma"
**************************
C2
1
4
3uF
L2
4
44
274uH
RL2
44
0
0.3
R2
4
5
5
R3
5
0
4
Z2
5
0
"demo_tw.zma" 5
***************************
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INTERACTIVE CROSSOVER DESIGN™ (ICD)
Notes:
To ensure accuracy, each component was individually measured using the low power test port. This also provided additional
information like the DC resistance of the inductors.
Channel balance should be adjusted for maximum accuracy.
Driver compression effects will cause the impedance ZMA file data to be drive level dependent. For maximum accuracy use a
test level and test method that is similar to the ICD simulation. Additional modeling elements might include cable effects
Tip:
You can use the balance control of your amplifier to simulate level padding
Figure 8-III shows the final result; a near perfect amplitude and phase match between the physical and simulated crossover
was achieved.
Figure 8-III - Comparison of Simulated & Physical Crossover Response (2.5 dB/Division scale)
No frequency or time domain smoothing has been used.
8.2.
Creating an Electronic Circuit File
This section describes how to use third party schematic entry tools to generate an electronic circuit file and compatible Spice net-list.
Examples are given for a professional tool, OrCad by Cadence, as well as a free tool, Linear Technologies’ LT-Spice/Switcher-Cad that
can be downloaded from http://www.linear.com/designtools/software/switchercad.jsp.
To be compatible with as many schematic capture tools as possible the ICD compiler follows a the original Berkeley Spice component
format. That is, components are considered simple and do not support loss, parasitic or other additional parameters. Enter these as
extra circuit components.
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Linear Technology: LT-Spice/Switcher-Cad (A PSpice Derivative)
LT-Spice/Switcher-Cad is primarily intended for simulating circuits made from devices made by Linear Technology Corporation. In
normal operation, net-lists are internally generated and compiled using the PSpice compiler. An ICD compatible net-list can, however,
be exported using a copy and paste after viewing the SPICE netlist. A driver schematic symbol does not exist, so you will need to
create one, or download the .ASY from www.woofertester.com.
Notes:
The LT-Spice net-list view box is not an editor, but you can select and copy the text using ctrl-A to select all text and ctrl-C to copy it to
the windows copy buffer. Use the paste command or ctrl-V to copy the net-list into the ICD editor.
Zn Driver variables are passed in by right clicking and modifying the model parameters. They can be entered on one line, or multiple
lines. Use the ‘Visible’ check mark to make them visible.
Spice Net-List (copied from view window)
* D:\wtpro\ltspice_demo_xo.asc
L1 N005 0 275µH
C1 N005 N001 2.98µF
R3 N002 N003 .1
V1 N001 0
Z1 N003 0 demo_wo.ZMA 0.1
Z2 N006 0 demo_tw.zma 5.1
L2 N001 N002 616µH
C2 N003 N004 6.43µF
R1 N004 0 4.0
R2 N006 0 4.0
R4 N006 N005 5.0
.backanno
.end
Woofer Tester Pro User Guide v1.1
Listing for SPEAKER.ASY file
Version 4
SymbolType CELL
LINE Normal -20 -48 -12 -48
LINE Normal -16 -52 -16 -44
LINE Normal 16 60 -7 32
LINE Normal 16 -44 -7 -16
LINE Normal 0 -24 0 -48
LINE Normal 0 41 0 64
RECTANGLE Normal -28 32 -32 -16
RECTANGLE Normal -11 37 -28 -21
RECTANGLE Normal -7 32 -11 -16
RECTANGLE Normal 20 64 16 -48
WINDOW 0 29 -7 Left 0
WINDOW 3 29 16 Left 0
SYMATTR Value 8.ZMA
SYMATTR Value2 0
SYMATTR SpiceLine 0
SYMATTR Prefix Z
SYMATTR Description Driver (Left=0 Right=1)
PIN 0 -48 NONE 0
PINATTR PinName +
PINATTR SpiceOrder 1
PIN 0 64 NONE 0
PINATTR PinName PINATTR SpiceOrder 2
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INTERACTIVE CROSSOVER DESIGN™ (ICD)
OrCad Capture For Windows: Schematic Entry Tool
OrCad Capture is widely used in the EDA industry for generating schematics and circuit boards. A SPICE simulation option is also
available. The spice net list is generated using the generate Net-List option. OrCad allows a great deal of latitude when specifying
component designators, allowing a wide range of symbols. Check the netlist output for compatibility.
Note: To facilitate mixed digital, analog and RF designs, OrCad uses multiple ground symbols. These symbols need to be ‘connected’
to the SPICE ground by the user. Click on the ground symbol and rename the name to GND to create a compatible netlist. Use the
first circuit you build this was as a template.
* Revised: Sunday, October 21, 2007
* Revision: NA
*
R1 702 703 .1
R2 705 704 .2
L1 704 0 500uH
C1 703 705 6uF
V1 702 0 1
Z1 703 705 demo_wo.zma 0
Z2 705 0 demo_tw.zma 5
.END
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INTERACTIVE CROSSOVER DESIGN™ (ICD)
8.3.
Circuit File Syntax
ICD Virtual crossovers are defined using Berkeley Spice formatted ASCII files containing a net-list. Each line in the net-list
contains a device statement followed by node connections and a component value. Each node represents a wire soldered
together in the physical crossover. The ICD compiler converts this list into left and right test signals that then simulate the
effect of a physical crossover. With care, the resulting crossover will often be close enough that little or no additional
tweaking of the physical circuit will be needed. ICD eliminates the need to physically build a crossover greatly reducing time,
effort and money spent.
Example
The following example shows an input signal connected between node 1 and ground (node 0). A capacitor C1 then connects
the input signal to the tweeter that is connected between nodes 2 and 0. Likewise, inductor L1 passes a signal to the woofer
connected between nodes 3 and 0.
Since tweeter and woofer loads are not simple resistors, highly accurate simulations are only possible when these loads are
defined using ZMA impedance files. ZMA files are created from either the low or high power port using the FileExport
option. If you do not have a ZMA file, you can replace the FILE.ZMA argument with a numeric value.
A driver protection circuit consisting of a series resistor and diode clamps can also be included with each load (this is highly
recommended). Simply add the resistance value after the ZMA statement and the signal will be modified resulting in an
accurate simulation, but with a well protected driver.
******************************************************************
*
(1)
C1 4uF
(2)
*
+----------------||-----------+
protection circuit
*
|
L1 2mH
|
+ --+
*
+------/\/\-----+ (3)
+----| |----+
*
|
|
| |
Z=tweeter.zma
* Vsig +
Z=woofer.zma + ----| |----+
*
|
|
+ --+
*
|
|
|
*
///
///
///
******************************************************************
Vsig
1 0 AC
1
* Input signal
C1
1 2 4uF
* High pass capacitor
L1
1 3 2mH
* Low p ass inductor
Z1
2 0 "tweeter.zma" 5.0 * Five_ohm+diode clamp protection
Z2
3 0 "woofer.zma"
* No protection (direct connect)
******************************************************************
!
Note:
A ground point must always be defined and it must always have the value zero ‘0’
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INTERACTIVE CROSSOVER DESIGN™ (ICD)
8.4.
ICD Components and Devices
ZMA Impedance Files
The left ‘woofer’ and right ‘tweeter’ loads interact with the ICD defined circuit using ZMA files to define the load impedance
and phase. ZMA files can be captured and saved using any of the available test signal types and impedance test modes.
Capturing ZMA data using a test signal type and drive level similar to the one used during the ICD simulation produces the
best results. This is because driver and box parameters often shift with drive level.
ZMA files are exported from the File pull down menu:
File  Export  Export buffer to ZMA (impedance)
Z1 and Z2: DRIVER LOADS
The left and right ‘Zn’ driver load statement connects the ZMA or constant value load to the simulated crossover. On the
physical side, a driver protection circuit in the form of a series resistor and diode-clamping network can be specified.
Usage:
Z1|Z2|ZL|ZR
N0
N1
value|impedance.zma [Rseries]
Examples: Z1 0 3 6 5
* Right channel, constant 6 ohm load, Rs=5
Z2 5 6 "tweeter.zma" 4 * Left channel, ZMA defined load, Rs=4
Notes:
Zn: ZL and ZR connect to the left and right respectively. However, some schematic entry tools will insist on a numeric value
here. In that case, even values of n (a number) will connect to the left channel and odd values to the right
A front to back time adjustment can be set in the ICD control window
Amplifier Signal Source
A single signal source must be defined representing the crossover input from the amplifier. The signal source is then
mathematically swept from DC to F=SampleRate/2, and the network evaluated filling in the Fourier spectrum. One of the
node numbers for the signal source must be '0' (ground).
Usage:
Vn
N0 N1 [value]
Example: Vsig 0 1 * signal is connected to nodes 0 (ground) and 1
Resistors, Capacitors and Inductors:
RLC components are specified as simple devices. Parasitic and loss effects such as inductor DC resistance are entered as
separate components.
Usage:
Rn
Cn
Ln
Examples: R1
C1
L1
82
N0
N0
N0
0
3
4
N1
N1
N1
3
4
0
value
value
value
6.1
4.2uF
820E-6
* 6.1 ohm resistor connected nodes 0 (ground) and 3
* 4.2uF capacitor connected nodes 3 and 4
* 820uH inductor connected to nodes 4 and 0 (ground)
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INTERACTIVE CROSSOVER DESIGN™ (ICD)
8.5.
ICD and XVR Editor and Simulation Control
The ICD and XVR Editor and Simulation control window is similar to the results editor except for the addition of simulation controls.
Simulations are allowed for *.CIR and *.XVR extensions only. ICD circuit files can be created manually, or using third part schematic
entry tools. Use the View  Interactive Crossover Designer menu option to open the ICD edit window.
Standard Edit Controls
Start/Stop
Simulation
View Real-Time or simulated
Negate or Delay Left
Channel
XVR file loaded
(ungrayed text)

Offset (m or ms) – Adjusts the effective acoustic distance from the left to right channel either by meter distance
or millisecond value.

Negate - Negates the left channel output and simulates swapping of the driver connection

ShowZP – Calculates and displays system level impedance using the SimZP buffer. The SimZP buffer is used,
since this buffer is updated with TS simulated data. If you want to keep this data, copy it to another buffer or file.

View Measured - Shows dB response of line or microphone signal

View Modeled - Shows dB response of mathematical model (no noise)

5 and 3 Column XVR Format – Sets the format of your XVR file
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INTERACTIVE CROSSOVER DESIGN™ (ICD)
8.6.
ICD Driver Protection Circuit
Circuit Analysis
Diodes D1 through D8 clip excessive voltage and limit the power that can be applied to the load. In this example a high
wattage 2.5-ohm resistor (and F1, which is a light bulb) becomes the amplifier load should diode clamping be required. Fuse
F1 is chosen to match the amplifier or resistor’s maximum safe current and power. A similar circuit appears on the left side
of the clamp resulting in a nominal 5.0 ohms series resistance.
Light bulbs also make suitable fuses. In this case the positive temperature coefficient of the filament resistance keeps
resistance low until a substantial current begins to flow. Tweeter test signals usually have a low average energy so the bulb
has little time to heat. A 12W (12V, 1Amp) automotive bulb usually works nicely. Simply account for the filaments cold
resistance by measuring the total resistance. Diode clamping will not occur under normal test conditions and the current in
F1 and F2 is low. Many variations of this circuit are possible. You could for example easily add LED clipping indicators.
8.7.
Arbitrary Crossover Design (XVR files)
XVR response files can be used to pick the initial crossover frequency point, help find an initial filter topology, or to create a
totally arbitrary response. In particular, XVR files set the amplitude and phase at a particular frequency. The response of a
DSP or line-level electronic crossover can therefore be simulated using an XVR file.
The Interactive Crossover Designer uses an XVR file format, which is similar to the FRD format, except that both, left and
right channels, are defined. In addition, the data defines both outputs and not the measured response of an input. That is,
XVR files are the reverse of FRD files.
As an example, consider that when a crossover topology is initially chosen it is often desirable to know the front to back
acoustic distances between driver pairs. This is found using an arbitrary response filter by setting up a sharp transition and
looking at the phase difference. Furthermore, an amplitude step would also indicate the need for some kind of padding
circuit.
XVR File Formats
The ICD handles two XVR file formats shown in Figure 8-IV below. The first format, shown on the left, contains 5-columns
with left and right channel data on the same line with a common frequency. This format is suitable for automatic export
and read-in to a spreadsheet for example.
The second format contains only 3-columns of data and is similar to two concatenated FRD files with LEFT and RIGHT
directing the response definition to each output. In this case, the left and right frequencies do not need to match. Response
for undefined frequencies points are interpolated from the data points that are known.
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INTERACTIVE CROSSOVER DESIGN™ (ICD)
The two examples below are identical with both abruptly transitioning the woofer and tweeter test signals at 5 kHz.
Figure 8-IV - '5KSHARP.XVR' 5 column and 3 column formats
************************************
* High + low pass filters
* Freq
db(L) ph(L)
db(R) ph(R)
************************************
1.0 -100.0 +90.0
0.0
+0.0
4990.0 -100.0 +90.0
0.0
+0.0
4995.0 -100.0 +90.0 -100.0 -90.0
5000.0
0.0
+0.0 -100.0 -90.0
9600.0
0.0
+0.0 -100.0 -90.0
***************************
* High + low pass filters
* Freq
db
phase
***************************
RIGHT
1.0 -100.0 +90.0
4990.0 -100.0 +90.0
4995.0 -100.0 +90.0
5000.0
0.0
+0.0
9600.0
0.0
+0.0
END
***************************
LEFT
1.0
0.0
+0.0
4990.0
0.0
+0.0
4995.0 -100.0 -90.0
5000.0 -100.0 -90.0
-100.0 -90.0
END
Notes:
Frequencies must be >= 1Hz and < SweepHi
Frequencies must increase
The outputs are rescaled (same scale both sides)
XVR Overlay of Woofer & Tweeter Response
The first picture below overlays the ARB1 and ARB2 buffers by using the amplifier balance control to collect and capture data
for each channel. The second image then shows the acoustic summed response captured to the BOX buffer by setting the
balance at center. The abrupt phase change of about 100 indicates an acoustic distance of D=(Angle/360)*(C/Frq) =
32mm between the drivers. Note: The delta effective distance between drivers is a function of the phase angle at a
particular frequency. In this sense, both drivers are variables also making the effective delta distance a function of
frequency. However this information is still useful input for crossover design.
Figure 8-V - Frequency Defined Response filter (XVR) Overlay of Woofer and Tweeter Response
Tweeter
Balance-RIGHT
Woofer
Balance-LEFT
Abrupt 3 kHz transition with two
responses within this sharp edge
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INTERACTIVE CROSSOVER DESIGN™ (ICD)
Acustic sum
woofer+tweeter
Balance-CENTER
Phase step
(acoustic distance)
The last image shows the final overlay of the woofer, tweeter and acoustic summation using an ICD designed crossover. The
crossover point was shifted up to 5 kHz to get a smoother transition.
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HARMONIC & SINAD DISTORTION MEASUREMENT
9. HARMONIC & SINAD DISTORTION MEASUREMENT
Harmonic Distortion (HD) is a measure of the harmonic content produced when a single frequency is applied. Therefore, this test is
performed using a sine wave sweep. HD analysis is enabled in the Setup Control window ‘Distortion’ tab. Six harmonics are measured
with results being plotted to any three user selectable buffers (picking buffers >7 is suggested since the lower 7 are for primary tests).
You can either view HD directly from this window, or if a sweep is used, from the Overlay window.
Primary and secondary (IMD) frequencies
Select Distortion Test
And data destination buffers
Select Buffers for display
2nd through 6th Harmonics
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TEST TOOLS AND CALCULATORS
10.
TEST TOOLS AND CALCULATORS
The tools and calculators mentioned in other chapters are described in greater detail in this chapter.
10.1.
Aligning the Tester For Measuring Capacitors
The low power tester measures a very wide range of resistors, inductors and capacitors when properly configured. Since the tester’s
constant current output produces an output voltage proportional to load impedance, some care must be taken to prevent impedance
from going to infinity, or the drive level must be decreased. Decreasing the drive level is a suitable solution for resistors and inductors,
but capacitors require an extra shunting resistor.
Start by switching to the LoZP mode using a sine test signal. Then add a 10k shunt resistor using a spare banana jack, which can be
easily plugged into or removed from the tester. Next, click on Tools  Capacitor Measurement Setup to open the alignment dialog
box. Finally, click on the Auto Complete button. The alignment algorithm then automatically measures the shunt resistor, followed
by the internal tester capacitance.
Larger capacitors can be also be measured but they must be non-polarized. In these cases, a smaller shunt resistor (like 100-1
kohms) will work. The goal is to have a shunt capacitor that is sufficiently large in value that the full dynamic range of the tester is
used for the capacitor being measured. Large capacitors have lower reactance and therefore can be measured with lower shunt
resistance values.
Since capacitive reactance is inversely proportional to frequency, capacitors are typically not tested at low frequency. Testing large
capacitors at high frequency can also lead to a problem where the capacitors reactance begins to be small compared to the test lead
reactance that is inductive. These effects are easily seen when a swept test over a suitable frequency range is used.
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TEST TOOLS AND CALCULATORS
This table shows the results of measuring a 100pF+/-2%, 1200pF+/-2%, and 2.0uF+/-2% capacitors. The 2uF capacitor was
measured plugged directly into the tester as well using the supplied test leads.
Note: Wiring can have a measurable effect.
Frequency
1200pF+/-2%
2uF+/-1%
2uF+/-1%
short leads Long leads
-----------------------------------------------------------100.0 110.515E-12
1.177E-09
1.993E-06
1.993E-06
130.0 104.768E-12
1.172E-09
1.993E-06
1.993E-06
169.0 103.938E-12
1.168E-09
1.993E-06
1.993E-06
219.7 101.989E-12
1.167E-09
1.992E-06
1.992E-06
285.6 101.640E-12
1.166E-09
1.992E-06
1.992E-06
371.3 100.841E-12
1.166E-09
1.991E-06
1.991E-06
482.7
99.981E-12
1.165E-09
1.991E-06
1.991E-06
627.5 100.001E-12
1.165E-09
1.990E-06
1.990E-06
815.7
99.772E-12
1.165E-09
1.989E-06
1.990E-06
1060.4
99.355E-12
1.164E-09
1.989E-06
1.989E-06
1378.6
99.519E-12
1.164E-09
1.988E-06
1.988E-06
1792.2
99.369E-12
1.164E-09
1.987E-06
1.988E-06
2329.8
99.087E-12
1.164E-09
1.987E-06
1.988E-06
3028.7
99.178E-12
1.164E-09
1.986E-06
1.989E-06
3937.4
99.094E-12
1.164E-09
1.987E-06
1.992E-06
5118.6
99.018E-12
1.164E-09
1.988E-06
1.997E-06
6654.2
98.919E-12
1.164E-09
1.992E-06
2.008E-06
8650.4
98.892E-12
1.164E-09
2.000E-06
2.026E-06
11245.5
98.824E-12
1.164E-09
2.015E-06
2.061E-06
14619.2
98.754E-12
1.163E-09
2.041E-06
2.122E-06
19004.9
98.680E-12
1.163E-09
2.090E-06
2.238E-06
20000.0 101.437E-12
1.165E-09
2.096E-06
2.263E-06
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100pF+/-2%
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TEST TOOLS AND CALCULATORS
10.2.
Zobel Calculator
Zobel compensation networks negate the rising driver impedance caused by series inductance Le. Le is, however, a function of
frequency and even includes frequency dependent resistance. In addition, the target impedance might not be Re, but an arbitrary
value. The Zobel calculator will do this and is launched from a Simulator Entry window button.
Begin by selecting the frequency you want to compute a solution at. The simulator is then called to compute the uncompensated
impedance and phase. If you then enter a desired impedance and phase, the tool will compute the required RC ‘Zobel’. You can also
optionally have the simulator calculate the resulting impedance plot.
Note: SimZP is recomputed each time the simulator is called, so the data will not persist. If you want the resulting impedance plot to
persist, use the ARB1 buffer destination.
Overlay Original and Zobel
compensated
Impedance plots
Select Frequency and Target Impedance
Start Zobel
Calculator
Note: Zobel compensation affects impedance, not driver terminal voltage. Changes in response are a function of the crossover.
Refer to the section on Interactive Crossover Design for designing and building crossovers.
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DEMONSTRATION FILES
11.
DEMONSTRATION FILES
The demonstration files in this section are found on the installation disk or from the web. Demo files showing the WT2 are
compatible with the Speaker Tester and Woofer Tester Pro.
11.1.
Conducting a Simple Electrical Test
1. Connect the test leads to the Woofer Tester 2 and to the driver as shown below.
2. Double-click the SL icon on your desktop to launch the Tester application
3. Next, open the demo file by selecting File  Woofile  Load Woofile from the menu bar. In the file open
dialog box that pops up, select the file called “demo1_simple_zp.woo” and click Open
Your screen now displays the WT Control window and you can hear the Chirp-Sine signal the tester is using to conduct the
electrical test:
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DEMONSTRATION FILES
11.2.
Thiele-Small Simulator & Box Design Demonstration
To use the Thiele-Small Simulator, leave the tester connected. The WOO file used in this demo contains previously acquired
data for a 165 mm (6.5 inch) computer sub-woofer. Additional in-air data was also taken to show how the simulated and
actual response will eventually align.
1. Open the demo file by selecting File  Woofile  Load Woofile from the menu bar. In the file open dialog box
that pops up, select the file called “demo2_simulator.woo” and click Open
2. Your screen now displays the T/S Entry window on top and the Overlay window on the bottom. (You
might have to re-tile them to fit your screen via the Window  Tile Horizontal menu option). The left
half of the T/S Entry window displays the Thiele Small parameters of a speaker – in this case a 6” name
brand computer speaker. The right half of the window contains the box values.
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DEMONSTRATION FILES
Box values
Driver T/S
parameters
Box types
Buffer
select
Simulation models
Acoustic
Simulation Output
What-if Simulated
Response
What-if
Simulated Acoustic
Phase
3. At this point, the TS parameters are preloaded into the simulator environment and you can begin modifying
the box volume, tuning and port dimensions to achieve the desired response. This is the initial ‘what-if’ stage
of designing a box. As you make these adjustments and turn on and off various display options, you will see
the response and other parameters change. For example, you can change the blue line to display various
acoustic simulation outputs such as simulated acoustic phase, Xmm or velocity of the driver, port or combined
‘speaker’ response.
4. Next, disable the SimRX curve and enable SimZP by clicking on those buttons above the graph in the
Overlay window. The display changes to show the expected impedance curve of your ‘what-if’ design.
5. The next steps are to physically build the box based on the values from your simulated box design and
measure the in-box electrical data. To measure the in-box electrical data, reconnect the speaker (box with
driver installed) to the Woofer Tester and click on the Measure Box button in the WT Control window (see
also Chapter 6). The tester then generates data that will be used in the Simulator ‘Auto-Align’ feature
described next.
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DEMONSTRATION FILES
6. After building the box and measuring the in-box electrical characteristics, you don’t actually know if your
physical box design has measured up to your ‘what-if’ design. Reasons for this include potential box
dimension or port size errors, forgetting to include the volume displacement of the driver/bracing, or an
interaction of the port or driver to the cabinet walls.
To find out how closely your new box matches your previously simulated box design, click the Auto-Align
button in the T/S Entry window. This finds the effective box volume, tuning and loss. A dialog box then
tells you what the effective volume and tuning need to be in order to make the curves match.
By clicking OK, the effective box volume and tuning are loaded into the
simulator and the new simulation reflects the actual response of the
speaker. If this is not what you had originally intended in your ‘what-if’
design, you would now need to make modifications to the physical box.
Results
This first image shows the ‘What if’ (yellow) and ‘Effective’ (pink) response from aligning electrical measurements. The next
picture shows the simulated and actual driver response (using a microphone) with a deep notch at the port tuning frequency.
In this case, the port was acoustically isolated by being physically located on the back side of the cabinet.
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DEMONSTRATION FILES
11.3.
Demonstration of an In-Air Test
To conduct an In-Air test, leave the current driver connected. The low power port acts as a low power amplifier and this
setup is sufficient to see the response.
1. Open the demo file by selecting File  Woofile  Load Woofile from the menu bar. In the file open dialog
box that pops up, select the file called “demo2_simple_in_air_response.woo” and click Open
2. Your screen displays the WT Control window in the front and the Setup Control window in the back. The
graph displays the response of the speaker.
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DIGITAL SIGNAL PROCESSING TERMINOLOGY AND CONCEPTS
12.
DIGITAL SIGNAL PROCESSING TERMINOLOGY AND CONCEPTS
A number of signal processing algorithms are used with the tester. The terminology and signal processing concepts are not difficult to
understand and may lead to a better understanding of digital audio.
12.1.
Nyquist Sampling Theorem
One of the most important and yet widely misunderstood concepts in signal processing is that a sinusoidal signal must be sampled
with at least two samples per wave to perfectly reproduce the original signal magnitude and phase. The part that is not stated is that
it might take many more samples to capture the original magnitude and that reconstruction can produce a sine wave with the correct
magnitude but that the duration of that sine wave will be lengthy in time.
Consider the following diagram where the signal frequency has been chosen to be close to half of the sampling rate. Simple
observation shows that at some times the instantaneous amplitude is zero, and yet at others it is maximum. If the view is backed out,
an amplitude modulation is revealed that would probably not reproduce good sound. This would seem to be at odds with the Nyquist
criteria. Next, observe that as the frequency is decreased, amplitude modulation becomes less and less noticeable. It would therefore
seem that if the sampling rate were sufficiently higher than the predicted Nyquist rate, the result would be good reproduction, and
without too much modulation distortion (and indeed this is true).
12.2.
Reconstruction Filters
If the sampled sinusoidal signal is then input to a high-Q filter, amplitude modulation is decreased and the output approaches a steady
state. The filter topology will greatly influence ring down characteristics, but the original steady state sine wave can be reproduced.
12.3.
Up-Sampling Filters
Though it is possible to build high-Q reconstruction filters using analog components, this is rarely used because of the number of
components required. It is much easier to build these filters using a digital filter. High-Q filters, and especially those that will exhibit
transient performance suitable for audio reproduction, fall into a sub category known as an up-sampling filter. The up-sampling name
is derived from the fact that rather than processing the data directly, additional samples are introduced between the original samples
increasing the effective sample rate.
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Index
Compression, 72
Crossover, Physical, 76, 81
Cumulative Spectral Decay, 29, 30
A
AC Compression Test, 32, 44, 73
AC Level, 72, 73
AC Response, 32
Acoustic distance, 31, 83, 84, 85
Air Core Inductor, 47, 48
Amplifier, 82
Amplifier Signal, 82
Amplitude Modulation, 96
Analysis Mode, 18, 46
arbitrary crossover, 76
ARROWTO, 38, 39
Atmospheric conditions, 46
Auto Complete, 58, 88
Automatic Gain Control (AGC), 44
Axis Control, 20, 36, 53
D
DC Bias, 33, 34, 36, 58, 73, 74
DC Compression Test, 73
Delta Mass Test, 64, 65
Diode clamping, 84
Displacement, 28, 34, 65, 69, 72, 75, 94
Distortion
Setup & Control, 23
Distortion Measurement, 87
DRAWX, 39
Drive Level, 15, 44
Compression, 78
Drive Signal
Impulse, 18, 28, 31, 36, 44, 45
MLS, 18, 21, 22, 31, 44, 45, 62
Sine, 18, 40, 44
Drive Signals
Chirp, 18, 44, 45, 91
Impulse, 18, 28, 29, 36, 44, 45
MLS, 18, 22, 31, 44, 45, 62
Signal Mode, 44
Sine, 18, 24, 44, 50, 59, 91
SnapTS Fast Testing, 24
Driver compression effects, 78
Driver Label, 42
Driver Q, 60
B
Bezier Line Smoothing, 36
BORDERPIX, 39
BORDERTXT, 38, 39
Box Alignment, 70, 93, 94
Box Design, 68, 92
Buffer
Clear all data now, 43
Clear all data on start, 43
Clear current data buffer, 43
Copy between, 42
Number of, 45
Size, 45
E
C
Calibration, 12, 19, 50, 51, 52, 53, 54, 55, 56,
57, 58
Capacitor, 58, 88
Capacitor Measurement, 58, 88
Circuit Analysis, 84
circuit file, 76
Circuit File, 76, 78, 81
Cms, 32, 60, 62, 63, 70, 71, 72, 73
COL, 39
COLOR, 38, 39
Color Scheme
Setting, 37
Woofer Tester Pro User Guide v1.1
Ellipse/Oval Calculator, 47
Excitation Signals, 62
Export
Results, 49
F
FFT, 19, 23, 27, 28, 29, 30, 35, 36, 37, 45
FFT Resolution, 36, 37
FONT, 38, 39
Frame averaging, 45
FRD File, 19, 40, 76, 84
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Free Air Resonance, 59
Frequency Defined Filter (FDR), 84
Frequency Dependent Le Test Method, 43
Frequency Domain, 18, 30
Frequency Domain XE "Frequency Domain"
Smoothing, 30
FRQ, 38, 39
Fs, 12, 20, 21, 24, 25, 34, 37, 58, 59, 60, 61, 62,
63, 64, 65, 66, 68, 69, 72, 73, 74
G
Gating Control, 15, 21, 22
GETX, 38, 39
Graph Axis Control, 36
H
Harmonic Distortion (HD), 87
High Power Test, 62
High-Q Filter, 96
HiZP A, 18
HiZP V, 18
File, 14
Help, 14
Options, 14
Results, 14
Tests, 14
Tools, 14
View, 14
Window, 14
Microphones
Compensation, 19
Time-Align Averaging, 31
Mike Position, 15, 21, 22
MikeL, 18, 31
MikeR, 18, 31
Mms, 60, 61, 62, 72
Monotonic sinusoid, 62
Motor Characteristics, 61
MOVETO, 39
N
NAD, 34, 74
Non-Linear Suspension, 61
Nyquist Sampling Theorem, 96
I
ICD
Editor, 35
Impedance, 18, 19, 37, 38, 39, 54, 67, 70, 73, 82
Inductance, 61
Inductor, 47, 61
Installation & Setup
Hardware Setup, 7, 9, 12
Low-power test port, 5, 7, 9, 12
Software Installation, 6
Interactive Crossover Design (ICD), 49, 76, 83,
84, 88, 90, 91, 96
Interactive Crossover Designer (ICD), 25, 35, 49,
76, 77, 78, 79, 81, 82, 83, 84, 86, 90
K
Kbox, 60
Kms, 60, 61
L
Legend, 38
LINETO, 39
Lissajoux Display, 32, 34, 74
LoZP A, 18
LoZP V, 18
M
Madd, 60
Mass, 24, 59, 64, 65
Measurement Frequency, 17, 44
Menu
98
O
Octave Binning, 20
OFF, 38, 39
Offset, 22, 24, 83
ON, 38, 39
Options Menu
Adjust Phase in WT Control Window, 44
Left Mouse Button Action, 17, 44
Set Frequency Control in WT Control Window,
17, 44
Oscilloscope, 27
Overlay Window, 21, 25
P
PBUF, 39
Phase
Difference, 84
Slope, 43, 63
Wrapping, 24
Print
Files, 49
PVAL, 38, 39
Q
Qes, 60, 62, 64, 72, 73
Qms, 60, 62, 72, 73
R
Real-time Meter Window, 14
Real-time mode, 44
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Woofer Tester Pro User Guide v1.1
Reconstruction Filter, 96
Reconstruction Filters, 96
Reference Signal, 18
Rem, 26, 43, 62, 63, 64
Response filter, 84
Results
Scientific Number Format, 42
Results Editor, 35
Results Menu
Copy between buffers, 42
New Speaker Title, 41
Results Data Formatting, 42
Results Window
Copy, 41
Cut, 41
Load, 41
Paste, 41
Save, 41
SelAll, 41
Revc, 43, 58, 60
RGB, 38, 39
RLC, 76, 82
ROW, 39
RT60, 29, 30
S
Sample Rate, 45
Sampling Rate, 19
Setup Control Window, 16, 46, 87, 95
Mike Pos Tab, 22
Overlay Tab, 25
Size&Comp Tab, 15, 21
SnapTS Tab, 24
THD/IMD Tab, 23
Signal Mode, 44
Simulation, 25, 32, 65, 69, 90, 92, 93
SINAD, 23, 34, 40, 72, 73, 74, 87
SIZE, 38, 39
Smoothing, 20, 30, 36, 45
Software License, 7
SPICE, 76, 79, 80
Spring Constant, 59
STARTCOL, 39
STARTROW, 39
STOP-RUN Operation, 15, 20, 21
STOP-RUNn Operation, 20
Sweep
End, 43
High, 43
Low, 43
Start, 43
Sweep Points, 43
Sweep Ratio, 43
Woofer Tester Pro User Guide v1.1
T
T/S Entry Window, 26
TEXTPOS, 38, 39
TEXTWT, 38, 39
Thiele Small
Driver Measurement, 50, 59, 68, 70, 72
Parameters, 35, 36, 46, 58, 92
Tweeter, 84, 85
U
Up-Sampling Filter, 96
Up-Sampling Filters, 96
US Nickel, 64, 65
V
View Menu
Pick Colors, 37
Reset Colors, 37
W
Waterfall Graph, 28, 30, 31, 36
Waterfall Plot
Cumulative Spectral Decay, 30
Growing Waterfall, 30
Sliding Fourier Transform, 30
WIDTH, 38, 39
Windows Vista, 10, 19
WOO File
Load, 40, 91, 92, 95
Save, 40
WT Control Window, 12, 16, 17, 21, 44
Adding/removing datapoints in graph, 17
Autoscaling, 16, 36
Changing the Title, 16
X
Xem, 26, 43, 62, 63, 64
XVR Editor, 83
XVR File, 76, 83, 84, 85
X-Y Plot Window, 32
Z
ZBUF, 39
ZMA, 76
ZMA File, 40, 49, 76, 77, 78, 81, 82
Zobel Calculator, 90
ZVAL, 38, 39
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