Need Help-Sound

1. Nov 8, 2005

Physic_Scholar

I need help for this problem. I tried applying the formula B=10log(I/Io) but I don't get right answer. Someone help me or give me suggestion/hint about what to do? The problem is as follows: At a rock concert, a dB meter registered 130gB when placed 2.8m in front of a loudspeaker on the stage. a) What was the power output of a speaker, assuming uniform spherical spreading of the sound and neglecting absorption of air? b) How far away would the sound level be a somewhat reasonable 90 dB?

2. Nov 10, 2005

big man

what answer do you get?
I would have thought that you would use the decibel equation you have to solve for I. Then once you have the intensity you can solve for $$P_a_v_e$$ given that you know the distance away from the source and that it is spherical spreading with no attenuation through air.

I=P/A

Where A is the surface area of a sphere: $$4(\pi)r^2$$

Does this give the wrong answer?