The sound energy density or sound density (symbol E or w) is an adequate measure to describe the sound field at a given point as a sound energy value. The letter "lower case w" sign $w$ is easily mixed with the sign $\backslash omega$ (omega), therefore we choose the letter E.

In opposite to the sound intensity I, which gives the sound energy per area A, the sound energy density E (also: sound density) describes the time medium value of the sound energy per volume unit; it gives information about the sound energy which is at a defined place in the room.

The sound energy density E (or w) for an even-proceeding sound wave is:

$$

E = \frac{I}{c} , where I is the sound intensity in W/m² and c is the sound speed in m/s.
The sound energy density is given in J/m³, where the joule J = W·s = N·m.
You will find also W·s/m³ or N·m/m³.
The sound energy density is N/m² = pascals, the same as the units of sound pressure.

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). More formulas for sound energy density for even proceeding sound waves:

$$

E = \xi^2 \cdot \omega^2 \cdot \rho = v^2 \cdot \rho = \frac{a^2 \cdot \rho}{\omega^2} = \frac{p^2}{Z \cdot c} = \frac{I}{c} = \frac{P_{ac}}{c \cdot A}

where:

Symbol	Units	Meaning
p	pascals	sound pressure
f	hertz	frequency
ξ	m, meters	particle displacement
c	m/s	speed of sound
v	m/s	particle velocity
$\backslash omega$ = 2 · $\backslash pi$ · f	radians/s	angular frequency
ρ	kg/m3	density of air
Z = c · ρ	N·s/m³	acoustic impedance
a	m/s²	particle acceleration
I	W/m²	sound intensity
E	W·s/m³	sound energy density
Pac	W, watts	sound power or acoustic power
A	m²	area

For digits of the sound energy density the RMS value will be given.
But you get also the level in dB. See sound energy density level.

See also

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• Particle displacement | Particle amplitude | Sound velocity | Particle acceleration | Sound pressure | Sound intensity | Sound power |

Or the level:

• Sound pressure level | Sound velocity level | Sound intensity level | Sound power level | Sound energy density level |

External links

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• Conversion: sound intensity to sound intensity level
  
• Ohm's law of the acoustics - calculations
• Connection of acoustic sizes for even progressive acoustic waves

Schallenergiedichte

Sound | Fundamental physics concepts