Assume that a loudspeaker broadcasts sound equally in alldirections and produces

Question

Assume that a loudspeaker broadcasts sound equally in alldirections and produces sound with a level of 109 dB at a distance of 1.66m from the center. (a) Find its sound power output.
1 W

(b) If the salesperson claims to be giving you 170 W per channel, he is referring to the electricalpower input to the speaker. Find the efficiency of the speaker --that is, the fraction of input power that is converted into usefuloutput power.
2% (a) Find its sound power output.
1 W

(b) If the salesperson claims to be giving you 170 W per channel, he is referring to the electricalpower input to the speaker. Find the efficiency of the speaker --that is, the fraction of input power that is converted into usefuloutput power.
2%

Explanation / Answer

a) The intensity level is                        = (10 dB)log(I/Io)                     I = Io*10^10.9                     I = (1.0*10-12 W/m2)*10^10.9                       = 0.0158 W/m2 The sound output power is              P = I(4 R2)                 = (0.0158 W/m2 )(4 (1.66 m)2) b) the efficiency of the speaker is                 e = P/Po Here Po = 120 W Substitute the values.

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