At a rock concert, a dB meter registered 128 dB when placed 2.6 m in front of a

Question

At a rock concert, a dB meter registered 128 dB when placed 2.6 m in front of a loudspeaker on the stage. The intensity of the reference level required to determine the sound level is 1.0 times 10^-12 W/m^2. Part A What was the power output of the speaker, assuming uniform spherical spreading of the sound and neglecting absorption in the air? Express your answer to two significant figures and include the appropriate units. Part B How far away would the sound level be 81 dB ? Express your answer to two significant figures and include the appropriate units.

Explanation / Answer

Part A

we know that

128dB = 10 log I/I0

12.8 = log I/10^-12

I = 6.3095 W/m^2

Power = I x 4pir^2

Power = 535.989 W

part B

81 = 10logI/I0

I = 0.000125892

P/4piR^2 = I

R = 582.067 m

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