Chapter 9. Properties of Sound Waves

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.

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).

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

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.

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.

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.

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.

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.