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:
“Midnight has come and the great Christ Church bell
And many a lesser bell sound through the room;
And it is All Souls’ Night.
And two long glasses brimmed with muscatel
Bubble upon the table. A ghost may come;
For it is a ghost’s right....”
—William Butler Yeats (1865–1939)
“I am convinced that our American society will become more and more vulgarized and that it will be fragmentized into contending economic, racial and religious pressure groups lacking in unity and common will, unless we can arrest the disintegration of the family and of community solidarity.”
—Agnes E. Meyer (1887–1970)