at a rock concert. a dB meter registered 130dB when placed 2.8 m infront of a loudspeaker on the stage ( a) what was power output ofthe speaker, assuming uniform spherical spreading of thesound and neglecting absorption in the air? (b) how far away wouldthe sound level be a somewhat reasonable 90 dB? at a rock concert. a dB meter registered 130dB when placed 2.8 m infront of a loudspeaker on the stage ( a) what was power output ofthe speaker, assuming uniform spherical spreading of thesound and neglecting absorption in the air? (b) how far away wouldthe sound level be a somewhat reasonable 90 dB?
Explanation / Answer
Intensity level of sound = 130 dB distance from the speaker r = 2.8m = 10 log ( I1 / I0 ) 130 = 10 log ( I1 / 10-12 ) 13 = log ( I1 / 10-12 ) ( I1 / 10-12 ) = 1013 I1 = 10W /m2 Power o/p of the speaker P = I *A = 10W /m2 *4(2.8) ( since spherical spreading Area of sphere is 4r2 ) = 9.85*102W b) If the intensity level is 90dB 90 = 10 log (I2 / I0 ) 90 = log( I2 / 10-12 ) I2 = 10-3 W /m2 Power o/p is P = I *A 9.85*102W = 10-3 W /m2* 4 r2 calculate the above to get solution r = .......... m