# Sound level from a loudspeaker

1. Jan 21, 2007

### ultimateguy

1. The problem statement, all variables and given/known data
A loudspeaker uses 65W of electrical power at 1kHz and converts this electrical power into acoustical power with an efficiency of 0.75%. Determine the distance at which the sound level is a) at the threshold of pain (120db) and b) 60db. Assume the loudspeaker emits sound waves uniformly in all directions.

2. Relevant equations
beta = 10log(I/Io)
I = P/4pir^2

3. The attempt at a solution
I know how to solve this usually, but what is throwing me off is the inclusion of the frequency of the electrical power.
In the second equation, I used a power of 0.0075(65)=0.4875W. And did the calculations. I obtained 0.197m for a) and 197m for b).

Is this right, or do I need to include the frequency somehow?

2. Jan 21, 2007

### Mindscrape

Good question. I don't think that the frequency comes into it because I don't see any sort phase information, which I think you would need if there was some kind of frequency dependence. So yeah, I think you are right in just using the amplitude.