Concept Practice
Properties of Sound Waves

Chapter 9. Properties of Sound Waves

amplitude
the height of a sound wave, measured as the distance between the peak and the midpoint; related to the loudness of a sound
perception
organizing and interpreting information from the senses to understand its meaning
complexity
the shape of a sound wave; related to the specific object that produced the wave
pitch
whether a sound seems low (deep) or high (squeaky)
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
timbre
the distinctive quality of a sound; related to the complexity of the wave
loudness
the apparent intensity of a sound; whether a sound seems soft (weak) or loud (intense)
Properties of Light Waves
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Learning Objectives:

Describe the physical properties of sound waves.

Explain how the physical properties of sound waves influence our perception of sound.

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Review

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1. We hear sounds when sound waves cause our eardrums to vibrate. These sound waves have two main properties, or characteristics: frequency and amplitude, plus a minor property called complexity.

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2. Frequency is the number of wave peaks in a set period of time (typically one second), and amplitude is the height of the wave peaks (distance from midpoint).

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The first image has four sound waves representing low-pitched sound. The second image has eight waves representing high-pitched sound. The waves in the second image are the same height as the first image but are skinnier.
The first image has short sound waves representing soft sound. The second image has medium height waves representing moderate sound. The third image has tall waves representing loud sound.

3. Frequency determines the pitch of the sound, while amplitude determines the loudness.

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The image has sound waves that vary in height and width but form a repetitive pattern.

4. A third property of waves called complexity, or waveform (note shape of wave), determines the timbre, or characteristic quality, of the tone. Timbre allows us to perceive the difference among different instruments playing the same note.

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Practice 1: Properties of Sound Waves

Use the sliders to vary the amplitude and frequency of the sound wave. Then, select the PLAY button to listen to the sound you have specified.

The figure is a line graph that displays the sound waves created by altering frequency and amplitude.
Amplitude
The figure is a line graph that displays the sound waves created by altering frequency and amplitude.
The figure is a line graph that displays the sound waves created by altering frequency and amplitude.
Frequency

We hear sounds when sound waves cause our eardrums to vibrate. These sound waves have two main properties, or characteristics: frequency and amplitude, plus a minor property called complexity. Let’s explore the two main properties with this interactive graph.


When you’ve finished exploring this graph, let’s take a closer look at each sound wave property.

NOTE: With some types of speakers or headphones, you may not be able to hear the sounds produced by the highest and lowest values of the Frequency and Amplitude sliders.
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Practice 2: Frequency and Pitch

Select each wave to hear the pitch that corresponds to that wave.

The frequency of a sound wave refers to the number of times the wave repeats its cycle (that is, the number of peaks) in a given unit of time. The frequency of a sound wave influences our sensation of pitch—whether a tone sounds "high" or "low." The higher the frequency of the sound wave, the faster the vibration of the eardrum, and the higher the pitch we hear.

The first image has one sound wave representing 250 Hertz.
The second image has two waves representing five hundred Hertz.
The third image has four waves representing one thousand Hertz.
The fourth image has eight waves representing two thousand Hertz.

These four waves have different frequencies, measured in Hertz (cycles per second), abbreviated as Hz. Human ears can detect frequencies from about 20 Hz to 20,000 Hz.

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Practice 3: Amplitude and Loudness

Select each wave to hear the relative loudness of that wave.

The amplitude of a sound wave refers to the height of a wave (which indicates the amount of sound energy the wave is carrying). Amplitude is related to the loudness of the sound. Higher amplitude means more physical intensity (producing a louder sound).

The first image has two short sound waves representing twenty decibels.
The second image has two medium waves representing thirty decibels.
The third image has two tall waves representing forty decibels.

These three waves have different amplitudes, measured in decibels (units of sound pressure, abbreviated as dB). The waves are not drawn to scale, because each increase of 10 decibels would make the wave 10 times higher.

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Practice 4: Complexity and Timbre

Select each wave to hear the sound of the instrument that produced that wave.

The third characteristic of a sound wave is its complexity, or waveform. Waves can be simple or complex—complex waves are composed of several simple waves mixed together. Waveform is related to timbre—the "signature" quality of the sound that enables us to tell the difference in the same note played on a flute, a piano, or a violin.

These three waves have different waveforms because they were produced by different musical instruments.
The first image is for a flute. It has sound waves that start short but get taller and then stay the same height.
The second image is for a piano. It has sound waves that vary in height and width but have sharp peaks regularly occurring.
The third image is for a violin. It has sound waves that stay about the same height but have sharp dips scattered throughout.
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Quiz 1

Match the terms to the descriptions by dragging each colored circle to the appropriate gray circle. When all the circles have been placed, select the CHECK ANSWER button.

Perhaps you should go back to review the properties of sound waves.
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timbre
pitch
loudness
determined by frequency of sound waves
determined by amplitude (intensity) of sound waves
determined by complexity (waveform) of sound waves
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Quiz 2

Look carefully at these two waves and answer the question. Then, select the CHECK ANSWER button.

There are two images. The first image is labeled A. It has two tall sound waves. There are two images. The second image is labeled B. It has four medium sound waves.
Select the NEXT button and move to the Conclusion.
Try to answer the question again.
Which of the following statements is true?
Wave A has higher frequency and lower amplitude than Wave B.
Wave A has lower frequency and lower amplitude than Wave B.
Wave A has lower frequency and higher amplitude than Wave B.
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Congratulations!
You have completed the activity Properties of Sound Waves.