A short blast of sound with frequency 335 Hz is created by a speaker that projec

Question

A short blast of sound with frequency 335 Hz is created by a speaker that projectsn the sound equally in all directions. The sound was measured to be 84.8 dB at a distance of 1.35 meters from the speaker.

1. what was the power of the blast?

2. what intensity is measured at a distance of 75 meters from the speaker?

3. At how far away (assuming no obstacles or energy loss due to damping) would you need to be to have the intensity level drop to 20 dB?

Pls. help and explain your answers. Will rate high for correct answers. Thanks

Explanation / Answer

1.    B = 10log I/Io

84.8 = 10log(I/1 X 10^-12)

I = 3.02 X 10^-4 W/m^2

P = IA

P = (3.02 X 10^-4)(4pi)(1.35)^2

P = 6.92 X 10^-3 W .............Ans

2.    I = P/A

I = (6.92 X 10^-3)/(4pi)(75)^2

I = 9.78 X 10^-8 W/m^2


3.    20 = 10log(I/Io)

I = 1 X 10^-10 W/m^2

P = IA

6.92 X 10^-3 = 1 X 10^-10(4pi)(r^2)

r = 2347 m

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