Sound Pressure

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:

    Strike on your drummes, spread out your ancyents!
    Sound out your trumpetts, sound out amaine!
    —Unknown. Sir Andrew Barton. . .

    English and Scottish Ballads (The Poetry Bookshelf)

    The area [of toilet training] is one where a child really does possess the power to defy. Strong pressure leads to a powerful struggle. The issue then is not toilet training but who holds the reins—mother or child? And the child has most of the ammunition!
    Dorothy Corkville Briggs (20th century)