Sound pressure or acoustic pressure is the local pressure deviation from the ambient (average, or equilibrium) atmospheric pressure, caused by a soundwave. In the air, sound pressure can be measured using a microphone, and in the water with a hydrophone. The unit for the sound pressure is the pascals (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 standard reference for the sound pressure in an air or other gases is 20 µPa, which is usually considered the threshold of human hearing (at 1 kHz). Learn more.