# Sound energy density

Not to be confused with Sound pressure.
Sound measurements
Characteristic
Symbols
Sound pressure  p, SPL
Particle velocity  v, SVL
Particle displacement  ξ
Sound intensity  I, SIL
Sound power  P, SWL
Sound energy  W
Sound energy density  w
Sound exposure  E, SEL
Acoustic impedance  Z
Speed of sound  c
Audio frequency  AF
Transmission loss  TL

Sound energy density or sound density is the sound energy per unit volume. The SI unit of sound energy density is the pascal (Pa), that is the joule per cubic metre (J/m3) in SI based units.

## Mathematical definition

Sound energy density, denoted w, is defined by

$w = \frac{p v}{c}$

where

The terms instantaneous energy density, maximum energy density, and peak energy density have meanings analogous to the related terms used for sound pressure. In speaking of average energy density, it is necessary to distinguish between the space average (at a given instant) and the time average (at a given point).

## Relationships with other quantities

Sound energy density is related to sound intensity:

$w = \frac{I}{c},$

where

Sound energy density is related sound power:

$w = \frac{P}{Ac},$

where

• P is the sound power;
• A is the area.