 Use the review sheet online.
 Work out the online quiz.
 Read the chapters and review the homework.

 Beats - the periodic variation in loudness of two sounds played together
 The beat frequency is equal to the difference in the frequency of the two sounds.
 What is the beat frequency when a 262 Hz and a
266 Hz tuning fork are sounded together?

 Modulation - an impression of the sound wave on a higher frequency radio wave
 AM
•
Amplitude Modulation
• 535 kHz to 1605 kHz
 FM
•
Frequency Modulation
• 88 MHz to 108 MHz

 What is the difference between noise and music?
•
Answer: The appearance of the waveform.
Mac Mic


… is the "highness" or "lowness" of a tone.
 Pitch corresponds to frequency.
 Concert A on the Musical Scale has a frequency of 440 Hertz.

Major Scale
Letter Frequency Frequency
Note Name (Hz) ratio Interval do C 264 re D 297 mi E 330 fa F 352 sol G 396 la A 440 ti B 495 do C 528
9/8 Whole
10/9 Whole
16/15 Half
9/8 Whole
10/9 Whole
9/8 Whole
16/15 Half


…is the characteristic sound that allows us to distinguish between two musical instruments.

Same Note - Different Instrument

 Harmonic
• a partial tone that is an integer multiple of the fundamental frequency
 Fundamental Frequency
• the lowest frequency of vibration
• a.k.a. the first harmonic

Harmonics
 Harmonics on a Guitar String
 Harmonics in an Organ Pipe
•
Open on one end, close on the other
•
Open on both ends

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
…is a mathematical method that will resolve any periodic wave form into a series of simple sine waves.
 See Figure 20.9.

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Sound Intensity and Loudness
 Intensity of Sound
• refers to the amplitude of the pressure variations in the sound wave

 Loudness
• the physiological sensation directly related to the sound intensity
• measured in bels
•
1bels = 10 decibels

 Loudness
•
A sound of 1 0 decibels is or 10 1 or 10 times as intense as 0 decibels.
•
2 0 decibels is 10 2 or 100 times the intensity 0 decibels.
•
How much more intense is sound at
100 dB than sound at 50 dB?
–
Answer: 100000 times

Source of Sound
Threshold of Hearing
Conversation
Ear Damage Begins
Amplified Music
Jet Airplane at 30 meters
Loudness (db)
0
60
85
110
140

Review Questions

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COMPACT DISCS
 Phonograph players give analog signals.
 Digital signal is in binary code.
 CD has flats and pits and is sampled 44,100 times per second.

1. The quality of a musical note can be changed by simply playing the note on a different instrument.
(a) True
(b) False

2. The three characteristics of a musical tone are loudness, quality, and timbre.
(a) True
(b) False

3. Frequencies of sound that are too high for the human ear to hear are called...
(a) faster than the speed of sound
(b) supersonic
(c) infrasonic
(e) subsonic

4. For the same temperature for air, does sound travel faster in humid Galveston or in dry El
Paso?
(b) El Paso
(c) same speed in either city

5. The bending of sound through air of uneven temperature is called
(a) reflection
(c) interference
(d) reverberation
(e) resonance

6. Lightning is seen, then ten seconds later thunder is heard.
Approximately , how far away in meters is the thunder cloud?
(a) 10,500 m
(b) 5280 m
(c) 1050 m
(e) 680 m

7. A 250 Hz tuning fork and a
260 Hz tuning fork are vibrating near each other. How many beats per second are heard?
(a) 255
(b) 510
(d) 250
(e) 260

 URL - Animated Vibrating String
 Demo - Harmonics on a Guitar
 Demo - Organ Pipe
 URL - Animated Organ Pipe

Common Sound Intensities
Source of Sound
Jet 30 m away
Intensity (W/m
2
)
10
2
Sound Level (db)
140
Air-raid siren, nearby
Disco music, amplified
Riveter
Busy street traffic
Conversation in home
Quiet radio in home
Whisper
Rustle of leaves
Threshold of hearing
1
10
-1
10
-3
10
-5
10
-6
10
-8
10
-10
10
-11
10
-12
60
40
20
10
0
120
110
90
70