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:
“He’s made a harp of her breast-bane,
Whose sound wad melt a heart of stane.
He’s ta’en three locks o’ her yellow hair,
And wi’ them strung his harp sae rare.”
—Unknown. Binnorie; or, The Two Sisters (l. 41–44)
“Under the pressure of the cares and sorrows of our mortal condition, men have at all times, and in all countries, called in some physical aid to their moral consolations—wine, beer, opium, brandy, or tobacco.”
—Edmund Burke (1729–1797)