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The sound energy density or sound density (symbol E or w) is an adequate measure to describe the sound field at a given point sound nergy. The letter "lower case w" sign <math>w<math> is easily mixed withe sign <math>\omega<math> (omega), therefore we choose here the letter E.
In opposite to the sound intensity J, 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 obout the sound energy which is at a definded place of room.
The sound energy density E (or w) for a even proceeding sound wave is:
- <math>
E = \frac{J}{c}
<math>,
where J 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 J (Joule ) = W·s = N·m.
You will find also W·s/m3 or N·m/m3.
You get N/m2 = Pascal, what is - alas - the unit of a 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 in general, 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:
<math>
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{J}{c} = \frac{P_{ak}}{c \cdot A}
<math>
where:
- ξ: particle displacement (particle amplitude), in m
<math>\xi<math> is the greek letter xi
- ω: angular frequency = 2π·f
- f: frequency, in Hz
- ρ: density of air, in kg/m3
- v: sound velocity, in m/s
- Z: acoustic impedance (characteristic impedance) = c · ρ, in N·s/m3
- c: speed of sound, in m/s
- J: sound intensity, in W/m2
- Pac: sound power or acoustic power, in W
- A: area, in m2
For digits of the sound energy density the RMS value will be given.
But you get also the level in dB. See sound energy sensity level.
See also:
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
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