Day 6Exam I is on Thursday.

Be sure to attend lab this week.

ReviewReview 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?

BeatsBeats

Radio Broadcasts 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

Chapter 21

Musical Sounds

Noise Versus Music

What is the difference between noise and music?

• Answer: The appearance of the waveform.

Mac Mic

NOISE VERSUS MUSIC

Pitch... … 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 FrequencyNote Name (Hz) ratio Interval

do C 264 9/8 Wholere D 297 10/9 Wholemi E 330 16/15 Halffa F 352 9/8 Wholesol G 396 10/9 Wholela A 440 9/8 Wholeti B 495 16/15 Halfdo C 528

Quality...

…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

BackBack

Fourier Analysis... …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 10 decibels is or 101 or 10 times as intense as 0 decibels.

• 20 decibels is 102 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 Loudness (db)

Threshold of Hearing 0

Conversation 60

Ear Damage Begins 85

Amplified Music 110

Jet Airplane at 30 meters 140

Review Questions

Day 7

Exam I is on Tuesday.

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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

(d) ultrasonic

(e) subsonic(d) ultrasonic

4. For the same temperature for air, does sound travel faster in humid Galveston or in dry El Paso?

(a) Galveston

(b) El Paso

(c) same speed in either city

(a) Galveston

5. The bending of sound through air of uneven temperature is called

(a) reflection

(b) refraction

(c) interference

(d) reverberation

(e) resonance

(b) refraction

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

(d) 3400 m

(e) 680 m

(d) 3400 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(c) 10(d) 250(e) 260

(c) 10

End of Section...

URL - Animated Vibrating String

Demo - Harmonics on a Guitar

Demo - Organ Pipe

URL - Animated Organ Pipe

Common Sound IntensitiesSource of Sound Intensity (W/m2) Sound Level (db)

Jet 30 m away 102 140

Air-raid siren, nearby 1 120

Disco music, amplified 10-1 110

Riveter 10-3 90

Busy street traffic 10-5 70

Conversation in home 10-6 60

Quiet radio in home 10-8 40

Whisper 10-10 20

Rustle of leaves 10-11 10

Threshold of hearing 10-12 0