Sound Energy Density

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 is easily mixed with the sign (omega), therefore we choose the letter E.

In opposite to the sound intensity I, which gives the sound power 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 unit of measurement for sound energy density is N/m2, also known as 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
= 2 · · 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.

Famous quotes containing the words sound and/or energy:

    “If man is reduced to being nothing but a character in history, he has no other choice but to subside into the sound and fury of a completely irrational history or to endow history with the form of human reason.”
    —Albert Camus (1913–1960)

    “Just as we are learning to value and conserve the air we breathe, the water we drink, the energy we use, we must learn to value and conserve our capacity for nurture. Otherwise, in the name of human potential we will slowly but surely erode the source of our humanity.”
    —Elaine Heffner (20th century)