An enclosed chamber with sound absorbing walls has a 2.0 m x 1.0 m opening for a

Question

An enclosed chamber with sound absorbing walls has a 2.0 m x 1.0 m opening for an outside window. A loudspeaker is located outdoors, 78 m away and facing the window. The intensity level of the sound entering the window space from the loudspeaker is 79 dB. Assume the acoustic output of the loudspeaker is uniform in all directions and that the acoustic energy incident upon the ground is completely absorbed and therefore is not reflected into the window. The threshold of hearing is 1.0 x 10-12 W/m2. The acoustic power entering through the window space is closest to

Explanation / Answer

Power is given by

P = A I

where A is the area and I is the intensity of sound in watts

intensity level = 79 dB

therefore,

79 = 10 log (I/Io)

solving we get

I= Io x 107.9

I= 1 x 10-12 W x 107.9

now,

P= 2 x I= 158.86 x10-6 W

P = 160 W

option A

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