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The Stimulus Input: Sound Waves

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AP Exam Tip 1.6-9 What ar e the characteristics of air pr essur e waves that we hear as sound?
1.6-9 What are the characteristics of air pressure waves that we hear as sound?

Both light and sound travel in Like light waves, sound waves vary in shape ( Figure 1.6-17 ). The height, or amplitude, of
waves. In each case, under- sound waves determines their perceived loudness. Their frequency (measured in hertz )

standing the meaning of varying determines the pitch we experience. Long waves have low frequency — and low pitch.

amplitude and length of the waves
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is important for the AP exam. Short waves have high frequency — and high pitch. The sound waves produced by a violin
are much shorter and faster than those produced by a cello or a bass guitar.
We measure sound intensity in decibels, with zero decibels representing the absolute
frequency the number of threshold for hearing. Every 10 decibels correspond to a tenfold increase in sound intensity.
Distributed by Bedford, Freeman & Worth Publishers. Not for redistribution.
complete wavelengths that Thus, normal conversation (60 decibels) is 10,000 times more intense than a 20-decibel whis-
pass a point in a given time (for per. And a temporarily tolerable 100-decibel passing subway train is 10 billion times more
example, per second).
intense than the faintest detectable sound. If prolonged, exposure to sounds above 85 decibels
pitch a tone’s experienced can produce hearing loss. Tell that to basketball fans at the University of Kentucky who,
highness or lowness; depends on
frequency. in 2017, broke the Guinness World Record for the noisiest indoor stadium at 126 decibels
( WKYT, 2017 ). Hear today, gone tomorrow.
Figure 1.6-17 Short wavelength = high frequency Great amplitude
The physical properties of (high-pitched sounds) (loud sounds)
waves
(a) Waves vary in wavelength (the
distance between successive
peaks). Frequency, the number
of complete wavelengths that
Long wavelength = low frequency
can pass a point in a given time, Copyright © Bedford, Freeman & Worth Publishers. Small amplitude
depends on the wavelength. (low-pitched sounds) (soft sounds)
The shorter the wavelength, the
higher the frequency. Wavelength
determines the pitch of sound.
(b) Waves also vary in amplitude
(the height from peak to trough).
Wave amplitude influences sound (a) (b)
intensity.

The sounds of music A violin’s

short, fast waves create a high pitch.
The longer, slower waves of Chi-chi
Nwanoku Obe ’ s double bass create a

lower pitch. Differences in the waves’
height, or amplitude, also create
Vereshchagin Dmitry/Shutterstock Courtesy of Eric Richmond/The Chineke! Foundation
differing degrees of loudness.

136 Unit 1 Biological Bases of Behavior

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