Teacher’s Guide
012-06101C
Physics Labs with Computers, Vol. 2
P42: Sound Waves
Teacher’s Guide - Activity P42: Sound Waves
(Power Output, Sound Sensor)
Concept
Waves
DataStudio
P42 Sound.DS
Equipment Needed
Sound Sensor (CI-6506B)
Musical instrument
ScienceWorkshop (Mac)
P32 Sound Waves
Qty
1
1
ScienceWorkshop (Win)
P32_SOUN.SWS
Equipment Needed
Speaker (WA-9303)
Tuning Forks (SF-9326)
Qty
1
1 set
What Do You Think?
If you could see a sound, what would it look like? Would a pure musical tone look different from
a scream? What about a sneeze?
Take time to answer the ‘What Do You Think?’ question(s) in the Lab Report section.
Background
Most of the sounds we hear are noises. The impact of a falling object, the
clapping of hands, the sound of traffic, and most of human speech are noises.
Noise corresponds to an irregular vibration of the eardrum produced by some
irregular vibration source.
The sound of music has a different characteristic, having more or less
periodic tones produced by some regular vibration source. (Of course,
musical instruments can make noise as well!) A graph representing musical
sounds has a shape that repeats itself over and over again. Such graphs can be
displayed on the screen of an oscilloscope when the electrical signal from a Sound Sensor is
measured.
Pythagoras found that notes played together on musical instruments were pleasing to the ear
when the ratios of the string lengths were the ratios of whole numbers. Galileo introduced the
concept of frequency. A sequence of notes of increasing frequency makes up a musical scale.
Many different scales exist. The simplest musical scale in many Western cultures is the “just
major scale” (for example, “do-re-mi-fa-so-la-ti-do”). In this scale, the ratio between frequencies
of two successive notes is 9:8, 10:9, or 16:15. For example, the ratio of “re” (297 Hz) to “do”
(264 Hz) is 9:8 (or 1.125). Most music written in the Western world uses the “even-tempered
scale”, which has thirteen notes and twelve intervals. The ratio between all successive notes is
exactly the same (1.05946).
SAFETY REMINDER
•
Follow all safety instructions.
For You To Do
This activity has two parts. In the first part, use the DataStudio or ScienceWorkshop program to
generate output signals to a speaker. Use the Sound Sensor to measure sounds from the speaker.
In the second part, use the Sound Sensor to measure sounds from an instrument such as a
harmonica or recorder and from a human voice.
Use the program to monitor and display input signals measured by the Sound Sensor.
TP42
©1999 PASCO scientific
p. 63
Physics Labs with Computers, Vol. 2
P42: Sound Waves
Teacher’s Guide
012-06101C
Part A: Generate Musical Tones
PART IA: Computer Setup
1.
2.
3.
4.
Connect the ScienceWorkshop interface to the
computer, turn on the interface, and turn on the
computer.
Connect the Sound Sensor’s DIN plug to Analog
Channel A.
Connect the speaker into the ‘OUTPUT’ ports on the interface.
Open the document titled as shown:
DataStudio
P42 Sound.DS
ScienceWorkshop (Mac)
P32 Sound Waves
TPUT )
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(±5
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300
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Sc ie
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2
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(±1
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1
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LS
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DIG
ScienceWorkshop (Win)
P32_SOUN.SWS
•
The document opens with a Scope display and a Fast Fourier Transform (FFT) display.
The Signal Generator output is set to automatically start and stop with data recording.
•
•
The DataStudio file also has a Workbook display. Read the instructions in the Workbook.
The ScienceWorkshop file also has a Signal Generator window.
PART IIA: Sensor Calibration and Equipment Setup
•
1.
p. 64
You do not need to calibrate the Sound Sensor.
Arrange the Sound Sensor in front of the speaker so the Sound Sensor can detect the
signal.
©1999 PASCO scientific
TP42
Teacher’s Guide
012-06101C
Physics Labs with Computers, Vol. 2
P42: Sound Waves
PART IIIA: Data Recording – Generate Musical Tones
1.
2
•
3.
•
4.
Start recording data. (In DataStudio, click ‘Start’. In ScienceWorkshop, click ‘MON’.)
Hold the Sound Sensor near the speaker. Set the first Signal Generator frequency at 264 Hz
(‘do’ on the ‘just major scale’).
Click the ‘Frequency’ to highlight the value and type in the new value. Press <enter> or
<return> to activate the new frequency.
Examine the FFT display. Compare the value of the fundamental frequency in the FFT to
the output frequency in the Signal Generator.
Use the ‘Smart Tool’ (in DataStudio) or the ‘Smart Cursor’ (in ScienceWorkshop) to
measure the fundamental frequency in the FFT.
Repeat the process for the rest of the frequencies in the first musical scale (the diatonic
scale).
Note
do
re
me
fa
so
la
ti
do
Letter name
C
D
E
F
G
A
B
C(octave higher)
Frequency (Hz)
264
297
330
352
396
440
495
528
Diatonic C Major scale (just major scale)
TP42
©1999 PASCO scientific
p. 65
Physics Labs with Computers, Vol. 2
P42: Sound Waves
5.
Teacher’s Guide
012-06101C
Repeat the process for the frequencies in the second musical scale (even-tempered
chromatic scale).
Note
do
re
me
fa
so
la
ti
do
Letter name
C
C Sharp
D
D Sharp
E
F
F Sharp
G
G Sharp
A
A Sharp
B
C(octave higher
Frequency (Hz)
262
277
294
311
330
349
370
392
415
440
466
494
524
Equal-tempered Chromatic scale
6.
p. 66
Click ‘Stop’ to end.
©1999 PASCO scientific
TP42
Teacher’s Guide
012-06101C
Physics Labs with Computers, Vol. 2
P42: Sound Waves
Part B: Musical Instrument
PART IB: Computer Setup
1.
2.
Use the same computer setup as in Part A. However, you will not need to use the ‘Output’
feature. Click the ‘AUTO’ button in the Signal Generator window to turn off the automatic
signal output.
Disconnect the speaker from the interface.
PART IIB: Sensor Calibration and Equipment Setup
•
1.
You do not need to calibrate the Sound Sensor.
Arrange the musical instrument so you can play musical tones into the Sound Sensor.
•
This part is easier to do with a partner who can run the computer and hold the Sound
Sensor while you play the musical instrument.
PART IIIB: Data Recording – Musical Instrument
1.
2.
3.
4.
Start recording data. (Remember: Click ‘MON’ in ScienceWorkshop.) The data should
appear in the Scope and FFT displays.
Play a single note (for example, middle C) into the Sound Sensor.
Examine the waveform of the musical sound in the Scope display.
Measure the fundamental frequency in the FFT display. If the waveform has harmonic
frequencies, use the ‘Smart Tool’ or ‘Smart Cursor’ to measure and record them as well.
How can you distinguish the harmonics from the fundamental frequency in the FFT
display?
5.
6.
TP42
Repeat the process for a different note.
Click ‘Stop’ to end.
©1999 PASCO scientific
p. 67
Physics Labs with Computers, Vol. 2
P42: Sound Waves
Teacher’s Guide
012-06101C
Part C: Voice
PART IC: Computer Setup
•
Use the same computer setup as in Part B.
PART IIC: Sensor Calibration and Equipment Setup
•
1.
You do not need to calibrate the Sound Sensor
Arrange the Sound Sensor so it will be able to record your voice.
PART IIIC: Data Recording – Voice
1.
2.
3.
4.
5.
6.
7.
p. 68
Start recording data. (Remember: Click ‘MON’ in ScienceWorkshop.) The data should
appear in the Scope and FFT displays.
“Sing” a single tone into the Sound Sensor.
Examine the waveform of your singing in the Scope display. Experiment by trying
different vowel sounds at approximately the same pitch. For example, switch from “OO”
to “EE” to “AH” to “UU” to “AY”. Try other mouth shapes.
Measure the fundamental and harmonic frequencies in the FFT display.
“Whistle” a single note into the sensor. Examine the waveform in the Scope and measure
the fundamental and harmonic frequencies in the FFT display.
Change the pitch of your whistle. Examine the waveform and measure the frequencies.
Stop monitoring data.
©1999 PASCO scientific
TP42
Teacher’s Guide
012-06101C
Physics Labs with Computers, Vol. 2
P42: Sound Waves
Lab Report – Activity P42: Sound Waves
What Do You Think?
If you could see a sound, what would it look like? Would a pure musical tone look different from
a scream? What about a sneeze?
Sounds are made up of waves, so one way of seeing sound is to make a plot of its waveform. A
pure musical tone would have nice rounded symmetrical waves, while a scream would have
large amplitude and be very uneven and a sneeze would take very little time, and be very jagged,
like a bunch of mountain peaks pushed close together.
Questions
Analyzing the Data: Generate Musical Tones
1.
How do the notes in the diatonic scale sound compared to the notes in the chromatic scale?
Answers will vary. The notes in the diatonic scale tend to sound less evenly spaced than the notes
in the chromatic scale.
2.
Do any of the notes in either scale have harmonic frequencies?
Answers will vary. In the examples shown, the notes do not have harmonic frequencies.
Analyzing the Data: Musical Instrument
1.
Describe the waveform of a single note on the musical instrument. Does it have harmonic
frequencies?
The waveform of a single note on the musical instrument in this example is less uniform than the
tone produced by the speaker. It does have harmonic frequencies.
2.
If the note has harmonic frequencies, how does the value of each harmonic compare to the
value of the fundamental frequency?
Answers will vary, but harmonics are always integer multiples of the fundamental frequency (e.g.
2f, 3f, 4f, etc.). In this example, the harmonic frequency is two times the fundamental frequency.
Analyzing the Data: Voice
1.
Describe the waveform of one of your singing tones. Does it have harmonic frequencies?
Answers will vary. In this example, the waveform is less uniform that the waveforms produced by
the speaker or the musical instrument. The waveform is periodic, but appears to be the result of
a combination of simpler waves. The waveform in our example does have harmonic frequencies.
TP42
©1999 PASCO scientific
p. 69
Physics Labs with Computers, Vol. 2
P42: Sound Waves
2.
Teacher’s Guide
012-06101C
How does the waveform of one of your singing tones compare to the waveform of a single
note from the musical instrument?
Answers will vary. In this example, the voice waveform is more complex than the musical
instrument waveform.
3.
If the tone has harmonic frequencies, how does the value of each harmonic compare to the
value of the fundamental frequency?
Answers will vary.
4.
Which vowel sounds have the least complex waveform? The most complex?
Answers will vary. In general, the waveforms of “AH” and “OO” are less complex than “EE”
and “AY”.
p. 70
©1999 PASCO scientific
TP42
Teacher’s Guide
012-06101C
Time Estimates
Physics Labs with Computers, Vol. 2
P42: Sound Waves
Preparation: 15 min
Activity: 30 min
Objectives
Students will be able to…
•
use a Sound Sensor to measure sounds generated by an interface, by a musical instrument, etc.
•
use the ‘Output’ feature of the software to generate musical tones
•
analyze the signal input from the Sound Sensor using the ‘Scope’ and ‘FFT’ displays of the software
•
determine the fundamental and harmonic frequencies (if any) of the sounds
•
compare the sound signals
Notes
For Part A, the volume of the sound from the speaker will seem to increase as the frequency of
sound increases for either the diatonic or chromatic scale. Challenge your students to keep the
sound sensor at the same position relative to the speaker during all of Part A, and to monitor the
amplitude of the signal that is displayed on the Scope.
The fundamental is a high peak; the harmonics are low peaks at higher frequency than the
fundamental.
Part A – Generate Musical Tones
These examples are the DataStudio FFT and Scope for a 264 Hz tone on the diatonic scale. The
sweep speed on the Scope is set to 10000 samples per second. The sensitivity is set to 0.05 volts
per division.
TP42
©1999 PASCO scientific
p. 71
Physics Labs with Computers, Vol. 2
P42: Sound Waves
Teacher’s Guide
012-06101C
Part B – Musical Instrument
These examples are the ScienceWorkshop FFT and Scope for a note played on a recorder.
Part C – Voice
These examples are the DataStudio FFT and Scope for a note produced by “whistling”.
p. 72
©1999 PASCO scientific
TP42