Intensity Level and Loudness

• I=Pav/area

• area of sphere = 4?r2 => I ? 1/r2

• sensation of loudness is not directly proportional to intensity

• varies as log(I) eg. log(100)=2log(10)

• define sound level SL=10 log(I/I0) in decibels (dB)

• I0 = 10-12 W/m2 is the hearing threshold

• hence for I=I0 , SL= 10 log(1) = 0

• pain threshold is I= 1 W/m2 or SL=10log(1012)=120 dB

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