**Sound pressure** or **acoustic pressure** is the local pressure deviation from the ambient (average or equilibrium) atmospheric pressure, caused by a sound wave. In air, sound pressure can be measured using a microphone, and in water with a hydrophone. The SI unit of sound pressure is the pascal (Pa).^{[1]}

A sound wave in a transmission medium causes a deviation (sound pressure, a *dynamic* pressure) in the local ambient pressure, a *static* pressure.

Sound pressure, denoted *p*, is defined by

where

*p*_{total}is the total pressure,*p*_{stat}is the static pressure.

In a sound wave, the complementary variable to sound pressure is the particle velocity. Together, they determine the sound intensity of the wave.

*Sound intensity*, denoted **I** and measured in W·m^{−2} in SI units, is defined by

where

*p*is the sound pressure,**v**is the particle velocity.

*Acoustic impedance*, denoted *Z* and measured in Pa·m^{−3}·s in SI units, is defined by^{[2]}

where

- transmission medium causes a deviation (sound pressure, a
*dynamic*pressure) in the local ambient pressure, a*static*pressure.Sound pressure, denoted

*p*, is defined bywhere

*p*_{total}is the total pressure,*p*_{stat}is the static pressure.

## Sound measurements

### Sound intensity

In a sound wave, the complementary variable to sound pressure is the particle velocity. Together, they determine the sound intensity of the wave.

*Sound intensity*, denoted**I**and measured in W·m^{−2}in SI units, is defined bywhere

*p*is the sound pressure,**v**is the particle velocity.

### Acoustic impedance