Chapter 9. Properties of Sound Waves
Learning Objectives
Describe the physical properties of sound waves.
Explain how the physical properties of sound waves influence our perception of sound.
Review
Review
Select the NEXT button to continue with the Review.
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.
Review
Review
Select the NEXT button to continue with the Review.
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).
Review
Review
Select the NEXT button to continue with the Review.
3. Frequency determines the pitch of the sound, while amplitude determines the loudness.
Review
Review
Select the NEXT button to continue with the Review.
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.
Practice 1: Properties of Sound Waves
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.
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.
Practice 2: Frequency and Pitch
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.
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.
Practice 3: Amplitude and Loudness
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).
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.
Practice 4: Complexity and Timbre
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. |
asset/activities/sound_waves/img/48UN07a.svg |
|
asset/activities/sound_waves/img/48UN07b.svg
|
|
|
asset/activities/sound_waves/img/48UN07c.svg
|
Quiz 1
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.
Quiz 2
Quiz 2
Look carefully at these two waves and answer the question. Then, select the CHECK ANSWER button.
Conclusion