Question

A loudspeaker has an output power of 85 WW and behaves like a point source emitting sound as a spherical wave.

Part A - The intensity of sound, II, is defined by which of the following equations

Part complete

PP is the power of the source, and aa is the area the power is spread over.

I=aPI=aP

I=PaI=Pa

I=PaI=Pa

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Correct

Part B - How far fromt he speaker would you need to stand (under ideal circumstances) for the intensity of the sound to be barely audable (i.e. equal in intensity to the human threshold of hearing)?

Part C - Sound intesnity level is calculated from the intensity using which of the equations below?

Part complete

β=(10dB)log10(I/I0)β=(10dB)log10(I/I0)

β=log10(I/I0)β=log10(I/I0)

β=(10dB)log10(I∗I0)β=(10dB)log10(I∗I0)

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Correct

Part D - What is the sound intensity level in dB at position found in part (b)

Answer 1

Part B - How far from the speaker would you need to stand (under ideal circumstances) for the intensity of the sound to be barely audable (i.e. equal in intensity to the human threshold of hearing

SOLUTION

human threshold of hearing, I = 1e-12 W/m2

so,

we know

I = P / A

I = P / 4r2

4r2  = P/I

4r2  = 85 / 1e-12

4r2  = 8.5e13

r = 2.6e6 meters

__________________________

Part D - What is the sound intensity level in dB at position found in part (b)

= 10log ( 1e-12 / 1e-12)

= 0 dB