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Home Q & A Board Science-Related Homework Help Physics
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11 years ago
I have two problems but I can't find the equations to solve them, the first is "a sound system produces 90dBSPL at 4 feet with 1 watt of input. How much power will be needed to produce 105dBSPL at 75 feet?"

And the second problem is "A sound system produces 90dBSPL at 4 feet with 1 watt of input. At 5,000 watts, what will the sound level be at 100 feet?"

I would be thankful for any help.
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#1
11 years ago
I would use this equation:

Lp = Lw-20*log(r)-0.5

where:
Lp = sound pressure level (dB)
Lw = sound power level where Lw = 10*log(W/Wreference) where Wreference = 10^-12 watts
r = distance from the source in feet

and all of these logs are base-10 logs.

One thing I'm not sure of is whether sound power level can be equated to the input power in the problem statement (both are in watts)
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