Sound Level: an Enclosed Chamber with Sound Absorbing Walls Has

Multiple Choice

Sound level: An enclosed chamber with sound absorbing walls has a 2.0 m × 1.0 m opening for an outside window. A loudspeaker is located outdoors, 84 m away and facing the window. The intensity level of the sound entering the window space from the loudspeaker is 56 dB. Assume the acoustic output of the loudspeaker is uniform in all directions and that acoustic energy incident upon the ground is completely absorbed and therefore is not reflected into the window. The threshold of hearing is 1.0 × 10^-12 W/m². The acoustic power output of the loudspeaker is closest to

A) 0.035 W.
B) 0.070 W.
C) 0.18 W.
D) 0.35 W.
E) 0.70 W.