Sound energy flux

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The sound energy (symbolized as q) results from the integral particle velocity v of the surface A , whereby only the portions perpendicularly to the surface acoustic velocity are important.

The sound energy flux marks the volume of the transmitting medium (air), which - caused by the excess sound pressure - and flows per time unit (1 s) by a surface A.

The sound energy flux is the average rate of flow of sound energy for one period through any specified area.

In a medium of density ρ for a plane or spherical free wave having a velocity of propagation v, the sound energy flux through the area A corresponding to an effective sound pressure p is

J = (p²A / ρ v) cos θ

where θ = the angle between the direction of propagation of the sound and the normal to the area A.