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]

Mathematical definition

Sound pressure diagram:

1. silence;
2. audible sound;
3. atmospheric pressure;
4. sound pressure

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

${\displaystyle p_{\text{total}}=p_{\text{stat}}+p,}$

where

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 by

${\displaystyle \mathbf {I} =p\mathbf {v} ,}$

where

p is the sound pressure,

v is the particle velocity.

Acoustic impedance

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

${\displaystyle Z(s)={\frac {{\hat {p}}(s)}{{\hat {Q}}(s)}},}$

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 by

${\displaystyle p_{\text{total}}=p_{\text{stat}}+p,}$

where

p_total is the total pressure,

p_stat is the static pressure.

Sound measurements

Sound intensity

Main article: 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 by

${\displaystyle \mathbf {I} =p\mathbf {v} ,}$

where

p is the sound pressure,

v is the particle velocity.

Acoustic impedance

Mai

Sound pressure, denoted p, is defined by

where

p_total is the total pressure,

p_stat is the static pressure.

Sound measurements

Sound intensity

Main article: 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 IIn 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

${\displaystyle \mathbf {I} =p\mathbf {v} ,}$W·m⁻² in SI units, is defined by

where

p is the sound pressure,

v is the particle velocity.

Acoustic impedance

Main article: Acoustic impedance

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

${\displaystyle Z(s)=\frac{}{}}$

where

${\displaystyle {\hat {p}}(s)}$ is the Laplace transform of sound pressure^{[citation needed]},

${\displaystyle z(s)={\frac {{\hat {p}}(s)}{{\hat {v}}(s)}},}$