Sound pressure or acoustic pressure is the local pressure deviation from the ambient (average, or equilibrium) atmospheric pressure caused by a sound wave. Sound pressure in air can be measured using a microphone, and in water using a hydrophone. The SI unit for sound pressure p is the pascal (symbol: Pa).
Sound pressure level (SPL) or sound level is a logarithmic measure of the effective sound pressure of a sound relative to a reference value. It is measured in decibels (dB) above a standard reference level. The commonly used "zero" reference sound pressure in air or other gases is 20 µPa RMS, which is usually considered the threshold of human hearing (at 1 kHz).
Read more about Sound Pressure: Instantaneous Sound Pressure, Sound Pressure Level
Famous quotes containing the words sound and/or pressure:
“There is a silence where hath been no sound,
There is a silence where no sound may be,
In the cold grave—under the deep, deep sea,
Or in wide desert where no life is found,”
—Thomas Hood (1799–1845)
“This is a catastrophic universe, always; and subject to sudden reversals, upheavals, changes, cataclysms, with joy never anything but the song of substance under pressure forced into new forms and shapes.”
—Doris Lessing (b. 1919)