please answer with clear writing. 1. Most speakers (one that puts out sound, not

Question

please answer with clear writing.

1. Most speakers (one that puts out sound, not the person speaking!) at big events only need to put out sound in a certain direction facing the crowd. Imaging a speaker used at a graduation ceremony, where it essentially only puts out half a sphere (more properly called a hemisphere) of sound in the direction away from the speaker. At the ceremony the intensity level at your position is 95 dB a) What is the intensity of the sound I, in W/m2, at your position? b) If you are 20 m from the speaker, what is the power output of the speaker? c) If you moved twice as close to the speaker, what is the new intensity of the sound, in dB, that you would hear?

Explanation / Answer

(A) sound level = 10 log (I / I0)

95 = 10 log (I / 10^-12)

I = 3.16 x 10^-3 W/m^2

(B) I = P / (4 pi r^2)

3.16 x 10^-3 = P / (4 x pi x 20^2)

P = 15.9 W

(C) I = 15.9 / (4 xpi x 10^2) = 0.0126 W/m^2

SL = 10 log(0.0126/10^-12) = 101 dB

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