THTR 357-Intro to Audio
Technology
Tech Lecture 7: Block Diagrams
Introduction
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This section discusses block diagrams and speaker
plots, with specific application to theatre
productions.
Remember that although there is still a great deal
of variety used in graphically notating sound
systems (even thought sub-committees exist in
AES USITT and NSCA to standardize these
symbols)
7.1 General Discussion
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A block diagram is a graphic description of the
signal path through a device, or series of devices.
The block diagram consists of individual
functional entities connected in a specific way.
The purpose of a block diagram is to present the
logical structure of equipment in simple, readily
accessible form.
7.1 General Discussion
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Example:
The sound designer, or system engineer sends a block
diagram to the shop, and the shop builds and installs the
system according to the block diagram.
This happens frequently on touring shows, or shows
designed by out of town designers, etc.
The system engineer or designer may never see the system
until after it has been fully installed. Mistakes can be
extremely costly, both in terms of time and money.
Because of the high cost of mistakes, great care must be
exercised when preparing block diagrams.
7.1 General Discussion
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Examples of Block Diagrams:
– Signal processing equipment (mixers, delays, eq., etc,
found in product data sheet
– Instruction manual
– System Block Diagram (e.g. theatre productions,
touring shows, etc. NOTE: see Section 17, pp. 213-224
of Yamaha Manual)
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Be carefull not to confuse block diagrams with
schematic (component level) diagrams.
7.1 General Discussion
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Two Fundatmental Caveats:
Always organize the block diagram to show
how the signal flows through the system.
Remember that the block diagram presents
the logical organization of a device or a
system.
7.1 General Discussion
We will concentrate on symbols commonly
used in System Block Diagrams, such as
those used to prepare sound systems for the
Performing Arts, sound system consulting
and contracting, etc.
 For variations that relate to reading or
creating component block diagrams, consult
the text.
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7.2 Symbolic Conventions
7.2.1 Amplifiers
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Preamp or Single
Channel Power
Amplifier
Two Channel
Power
Amplifier
Amplifiers are always denoted by a triangle.
System Block Diagrams typically show power
amplifiers (although outboard preamplifiers
appear as triangles also).
We use two types: single channel (often used with
amps bridged for mono output), and dual (most
common type, used with amps powering two full
range loudspeakers, or the low frequency and high
frequency drivers in bi-amped systems).
7.2 Symbolic Conventions
7.2.2 Other Devices
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Unity Gain or
Attenuating
Device
Yamaha Rev 5
All other devices that exhibit unity gain, or loss are
denoted with a rectangle, except loudspeakers.
The name of the device is centered in the box, or
placed nearby if it is not practical to include it in
the box.
All devices on the block diagram (including
amplifiers and loudspeakers) must show make and
model number.
7.2 Symbolic Conventions
7.2.2 Other Devices
Straight lines of medium thickness are used to
show equipment interconnection.
 Where there is potential ambiguity regarding
inputs and outputs, the name of the input or output
(as it appears on the rear of the device) is shown in
the box.
This is almost always the case with mixing consoles.
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7.2 Symbolic Conventions
7.2.3 Loudspeakers
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Loudspeaker
Biamplifierd
Loudspeaker
Loudspeakers are shown as a single driver, even if
they employ passive crossovers
Biamplified loudspeakers are shown as separate
elements to make connection to amplifier channels
clear.
7.2 Symbolic Conventions
7.2.4 Other Commonly Used Symbols
M ike
Oscillator
Signal
Ground
Transformer
Pad
Fader
Switch
Autoformer
Intercom
Headset
Earth
Ground
Stereo
Headset
Chasis
Ground
7.2 Symbolic Conventions
7.2.4 Other Commonly Used Symbols
7.2 Symbolic Conventions
7.2.4 Other Commonly Used Symbols
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A Title Block should include the following
information:
Title or Venue
by
System Block Diagram
Venue Name, Address
Directed by:
Sound Designer:
Date:
Plate:
Sy st em Designer:
of
Revised:
Scale: None
7.3 Notational Conventions
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Block diagrams usually are created so that signal
flows from left to right--inputs on the left, and
outputs on the right.
Feedback loops such as signal processors will
typically be routed in the opposite direction.
7.2 Symbolic Conventions
7.3 Notational Conventions
Crown
Macrot ech1200
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Truss Center
Meyer UPA 1B
It is usually not necessary to provide individual labels for
separate channels of two channel devices such as
processors, amps and speakers. Convention dictates that
the top or left component is the left channel or channel 1,
and the bottom or right component is the right channel or
channel 2.
7.5 Analysis of Simple Block Diagrams
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Pin 1 of XLR is ground
Pin 2 (hot) is transformer isolated
Differential input amplifier (e.g. balanced) vs. single-ended
Rotary gain controls gain of amplifier, not level going into
amplifier 6-40 dB
7.5 Analysis of Simple Block Diagrams
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Pin 2 (hot) goes to + of amp (e.g. normal polarity)
Pin 3 (neutral) follows - sign through to pin 3 of line output
Note that most single ended amplifiers invert the polarity of
the signal. This may or may not be restored to normal
polarity internally
7.5 Analysis of Simple Block Diagrams
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11 stages of EQ in series:
High Pass Filter (variable frequency)
Low pass filter (variable frequency)
9 Bands of graphic EQ with variable boost/cut
Transformer isolated balanced output
7.5 Analysis of Simple Block Diagrams
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Non-inverting circuit in which pin 2 is hot. ALWAYS
make sure by consulting owners manual or checking.
Fixed gain
EQ/Bypass switch
EQ feeds single ended non-inverting amplifier
7.5 Analysis of Simple Block Diagrams
Feedback
Polarity
+
-
Feedback
Level
Delay Time Select
Mix
Output
Input
A/D
Anti-Aliasing
Filter
Input
Level
Memory
D/A
Reconstruction
Filter
Feedback
In/Out
VCO
(CLock)
LFO
Modulation
Depth
Modulation
Rate
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Delay
Time
Block diagram shows only logic structure of device.
Input control level in a buffering amplifier
Low pass anti-aliasing filter to prevent digital distortion.
Dry signal picked off after this point.
7.5 Analysis of Simple Block Diagrams
Feedback
Polarity
+
-
Feedback
Level
Delay Time Select
Mix
Output
Input
A/D
Anti-Aliasing
Filter
Input
Level
Memory
D/A
Reconstruction
Filter
Feedback
In/Out
VCO
(CLock)
LFO
Modulation
Depth
Modulation
Rate
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Delay
Time
Feedback combined with original signal next. Note that
feedback loop is analogue. Note polarity reversal switch
and level control in feedback loop. Feedback allows
creation of multiple echoes, reverberation, flanging, etc.
depending on time delays chosen.
7.5 Analysis of Simple Block Diagrams
Feedback
Polarity
+
-
Feedback
Level
Delay Time Select
Mix
Output
Input
A/D
Anti-Aliasing
Filter
Input
Level
Memory
D/A
Reconstruction
Filter
Feedback
In/Out
VCO
(CLock)
LFO
Modulation
Depth
Modulation
Rate
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Delay
Time
A/D converts analogue to digital.
Memory delays signal (note user controls).
D/A follows and converts signal back to analogue.
Dry/wet mix control followed by low pass filter to remove memory's
clock frequency.
7.5 Analysis of Simple Block Diagrams
Feedback
Polarity
+
-
Feedback
Level
Delay Time Select
Mix
Output
Input
A/D
Anti-Aliasing
Filter
Input
Level
Memory
D/A
Reconstruction
Filter
Feedback
In/Out
VCO
(CLock)
LFO
Modulation
Depth
Modulation
Rate
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Delay
Time
Voltage controlled oscillator (VCO) controls clock rate
which controls delay time. Low frequency oscillator
(LFO-typically .01-20 or 100 Hz) allows delay time to be
modulated by, in this case, a triangle wave. LFO
frequency controls rate of modulation.
7.6 The Speaker Plot
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The Speaker Plot is a separate but crucial diagram
used in sound system design.
The Speaker Plot is not intended to show how
equipment is connected, or to give an
understanding of signal flow, but to depict the
location of sound system components that have an
important physical relationship to the theatre
space.
7.6 The Speaker Plot
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The speaker plot includes all loudspeakers,
practicals (i.e. sound effects devices such as
doorbells, wind machines, telephones, etc.), racks,
consoles, microphones and cables shown in their
exact location in the space.
Where possible, and necessary to the proper
installation, objects are shown scaled to proper
size.
7.6 The Speaker Plot
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Where possible, and necessary to the proper installation,
objects are shown scaled to proper size. In situations where
an object is physically smaller than can be accurately
depicted, or size is not of concern in the implementation, a
symbol may be used, accompanied by an explanatory key.
Key:
microphone
headset
headset cable
speaker cable
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If the Sound System Designer is responsible for
intercommunications systems, these locations must
also be included on the Speaker Plot.
7.6 The Speaker Plot
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The Speaker Plot is typically constructed using the
Ground Plan and Section of the set and
auditorium, as furnished by the scene designer.
Hopefully, the Ground Plan and Section will be
submitted in software form, to make it easy for the
Sound System Designer to modify into a useful
form.
7.6 The Speaker Plot
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These modifications include:
1. Remove all non-essential details from the plot such as set
dimensions, labels, construction notes, etc. If an item has no
bearing on the sound installation it probably is not needed on the
plot;
2. Keep the basic outline of the set, or sets, but use a very light guage
pen thickness to ensure that the scenic elements always appear in the
background;
3. Use a slightly thicker pen to draft cables, including snake, speaker
cables, etc.
4. Use an even thicker guage to draft objects such as speakers, console
location, rack locations, etc.
7.6 The Speaker Plot
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5. Make sure that speaker dimensions are accurate, and
shown on both the Ground Plan and the Section. This is
necessary to make sure that:
They fit in the scenery the way they are intended to fit;
They aren't in the way of other scenery;
They have clear, unobstructed sightlines to the audience, if desired;
The location of the horns is clearly specified.
6. The Speaker Plot is typically given to the Tech Director, who
is responsible for any working drawings that need to be
accomplished to get the speakers rigged, located in scenery,
etc.
7.7 The Shop Order
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The final component of the technical drawings is the shop
order.
The shop order is used to collate every piece of equipment
required by the production.
Rental Shops typically prepare their bids based on the shop
order, and producers base their budgets on the shop order.
Therefore, every single piece of equipment, cable,
interconnect, direct box, transformer, snake, etc., must be
accurately specified in the shop order.
7.7 The Shop Order
If this doesn’t happen, there will typically be
no money in the budget to rent additional
equipment, and the sound designer will have
to figure out how to do without.
 Shop orders that are consistently erroneous or
incomplete will cause sound designers or
systems engineers to get very good at job
hunting!
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