# Intensity of a sound wave

1. Jan 13, 2009

### Pastel

1. The problem statement, all variables and given/known data
I need the formula of the intensity of a sound wave at distance r from the source. The wave is spherical, and we know $$\rho$$, c, the speed of the wave, $$\omega$$, the pulsation, and A, the amplitude of the wave.

2. Relevant equations
The problem text specifies that intensity is the energy $$\Delta$$W that passes, during one unit of time, the unit of surface perpendicular to the direction of the propagation of the wave.

3. The attempt at a solution
I don't know how to calculate $$\Delta$$W.

2. Jan 13, 2009

### Delphi51

A google search for "sound wave intensity formula" yields a large number of hits.
http://www.ajdesigner.com/phpsound/sound_wave_equation_intensity.php has one.

The main feature of the formula will be 1/distance squared dropoff in the intensity as the energy of the wave is spread over the surface area of an increasing large sphere centered on the source.

3. Jan 13, 2009

### Pastel

Thanks, but that doesn't really help. Believe me, I've tried Google. The link you offered has a formula that might be useful, were I to know the sound power, which I don't. What I do know is amplitude and pulsation, as I've said.