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AMPLITUDE

المؤلف:  Parviz Birjandi

المصدر:  AN INTRODUCTION TO PHONETICS

الجزء والصفحة:  C7-P157

2026-07-30

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AMPLITUDE

The amplitude of a sound wave is the degree of motion of air molecules within the wave, which corresponds to the changes in air pressure that accompany the wave. The greater the amplitude of the wave, the harder the molecules strike the eardrum and the louder the sound that is perceived. The amplitude of a sound wave can be expressed in terms of absolute units by measuring the actual distance of displacement of the air molecules, the changes in pressure as the wave passes, or the energy contained in the wave.

Ordinary speech, for example, produces sound energy at the rate of about one hundred-thousandth of a watt. All of these measurements are extremely difficult to make, however, and the intensity of sounds is generally expressed by comparing them to a standard sound, measured in decibels. Amplitude is the characteristic of sound waves that we perceive as volume. The maximum distance a wave travels from the normal, or zero, position is the amplitude; this distance corresponds to the degree of motion in the air molecules of a wave. As the degree of motion in the molecules is increased, they strike the ear drum with progressively greater force. This causes the ear to perceive a louder sound. A comparison of samples at low, medium, and high amplitudes demonstrates the change in sound caused by altering amplitude. The three waves in figure 7.5 have the same frequency, and so should sound the same except for a perceptible volume difference.