Chapter 49. Making and Locating Sounds

Learning Objectives

amplitude

the height of a sound wave, measured as the distance between the peak and the midpoint; related to the loudness of a sound

frequency

the speed with which a sound wave moves up and down, measured as the number of peaks per second; related to the pitch of a sound

localization

in auditory perception, identification of the direction of the sound source

loudness

whether a sound seems soft (weak) or loud (intense)

pitch

whether a sound seems low (deep) or high (squeaky)

sound wave

the bands of high and low pressure that travel outward from the sound source

Making and Locating Sounds

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Illustration: a sound wave or waves striking a human ear

Learning Objectives:

Describe how sound waves are produced.

Explain how the differences in sound waves striking each ear allow the brain to determine the direction of the sound.

Review

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1. A vibrating object creates sound waves, and those waves move away from the object in all directions.

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2. Because we have two ears, separated by about 6 inches, we can localize the sound—that is, identify the direction of the sound source.

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Illustration: show top view of human head; front of head facing upward in illustration; show sound source at right, with sound waves radiating from source and traveling through air to strike the right side of head; do not show or label the sound shadow

3. If a sound is coming from our right, the sound waves strike the right ear slightly earlier than they strike the left ear. The intensity (loudness) of the sound is also slightly greater in the right ear.

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4. Our brains measure the difference in timing and loudness of a sound, and use that information to calculate the sound's location.

Practice 1: Making Sounds

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Practice 1: Making Sounds

Play the animation to view a sound wave being created and traveling through the air.

The image displays a series of sound waves. When the sound waves are tall and frequent, the sound is louder and higher pitch. When the sound waves become shorter and less frequent, the sound is softer and lower pitch.

Vibrating objects influence the air molecules surrounding them. This produces sound waves of alternating high and low pressure. The waves radiate out in all directions.

If an object vibrates with greater force (more movement), the size, or amplitude, of the wave increases, resulting in a louder sound.

If an object vibrates faster, the wave cycles between high and low pressure at a faster rate. This increase in frequency produces a sound with a higher pitch.

Practice 2: Locating Sounds

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Practice 2: Locating Sounds

Play the animation to watch how we determine the direction of a sound source.

Because we have two ears, our brain compares the timing and intensity of the sound waves arriving at each ear, and uses any differences to localize the sound (that is, identify the direction of the sound source).

If a sound is coming from our left, the waves reach the left ear slightly earlier than the right ear.

If a sound is coming from our left, the waves reaching the left ear have a slightly greater intensity (loudness) than those entering the right ear.

If there is no difference in timing or intensity of the waves, the brain knows that the sound must be located directly in front, behind, above, or below us.

Quiz 1

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1,0, 0,1, 1,0, 1,0, 0,1

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Try to respond to the statements again.

Quiz 1

For each statement, select one of the buttons to indicate whether the statement is True or False. When a response has been placed for all statements, select the CHECK ANSWER button.

True	False
		Vibrating objects compress the air molecules around them, creating sound waves.
		If a vibrating object begins to move more rapidly back and forth, the sound wave it produces will increase in amplitude.
		Changes in the frequency of a sound wave are associated with changes in the perceived pitch of the sound.
		As a sound begins to fade away, the sound wave gradually decreases in amplitude.
		It is very difficult to locate sounds that are directly to the left or directly to the right of our head.

Quiz 2

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Quiz 2

View the animation and answer the question. Then, select the CHECK ANSWER button.

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Try to answer the question again.

Select the NEXT button and move to the Conclusion.

This person knows that the sound is coming from the right because the sound waves strike the right ear __________ and with __________ intensity.

later; more

later; less

earlier; more

earlier; less

Conclusion

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