# Relationship Between Sound Intensity and Power?

1. Oct 26, 2011

### AimlessWander

I understand the inverse square relationship between sound intensity (I) and distance (r). There was a misunderstanding in physics class today about the mathematical and theoretical relationship between sound intensity and power according to the equation:

I = P/4∏r2

Sound intensity is defined as the acoustic power per unit area.

I know it's a stupid question, but can anyone clear this up for me?

2. Oct 26, 2011

### dacruick

Hi Aimless,

maybe I'm missing something but what's your question.

3. Oct 26, 2011

### AimlessWander

Hello :)

Is there a mathematical relationship between sound intensity and sound power?

4. Oct 26, 2011

### dacruick

Isn't that what you've just written?

I = P/4∏r2

5. Oct 26, 2011

### AimlessWander

I mean a direct relationship between power and intensity.
Two teachers were arguing on the relationship between sound intensity and power. In the end, they said something about a direct relationship between power and intensity. I was thinking that I misunderstood something.

Right now it seems they mixed it up with the inverse square law that exists between intensity and distance. Bunch of hooligans.

Thanks though :) All cleared up.

6. Oct 26, 2011

### nasu

The relationship that you wrote is valid for the special case of a point source that produces spherical waves. 4∏r^2 is the area of the sphere with radius r.
If you need the power received by a receptor, for example, you need to multiply the area of the receptor by the intensity at the receptor, assuming the intensity does not change much over the area. If it does, you will need to integrate IdS over the area of the receptor.

7. Oct 26, 2011

### AimlessWander

Okay, I see. So it seems that there is no mathematical direct proportionality between intensity and power then. Right?