lecture21-sound-levels-

# lecture21-sound-levels- - What you will be able to do a/er...

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What you will be able to do a/er today … how sound waves propagate sound waves vary according to distance from the source Explain … power and intensity intensity levels in dB Calculate … mathema>cal manipula>ons of log Apply …

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Intensity of waves in three dimensions At a distance R away from the source, power P will be uniformly distributed over a spherical shell of area 4 π R 2. So the intensity of the sound at this position is 2 4 R P I π = R I = Power Transmitted Area = P A
For three waves in three dimensions, the intensity of a wave at a point is inversely proportional to the square of the distance of that point from the source I 2 = P 4 ! r 2 2 I 1 I 2 = r 2 2 r 1 2 I 1 = P 4 r 1 2 r 1 r 2

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Worksheet (from Monday) Assume that sound wave fronts are three-dimensional spherical shells, how should intensities compare if located 1.0 m and 3.0 m away from a sound source? A. I 1 /I 2 = 2 B. I 1 /I 2 = 3 C. I 1 /I 2 = 9 D. I 1 /I 2 = 1/3 E. I 1 /I 2 = 1/9 I 1 I 2 = r 2 2 r 1 2
Intensity of Sound b Loudness ` : Energy deposited by the sound wave on the ear drum per unit time ( b intensity ` , unit: W/m 2 ). Perceived loudness (1 phon = 1 dBSPL at f = 1 kHz) is not proportional to intensity: à Sound appears twice as loud when intensity increases by 10 . Human ears can detect sound waves over a very large

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## This note was uploaded on 01/15/2012 for the course PHYS 101 taught by Professor Bates during the Winter '08 term at UBC.

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lecture21-sound-levels- - What you will be able to do a/er...

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