Problems with dB

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  • #1
stumped23
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'The intensity level of sound in a factory is 93.0 dB when all seven of its machines are working. If four machines are shut down for maintenance, what is the intensity level of the sound from the remaining machines? Assume that all seven machines are identical.'

I know the answer is not just 3/7*93 as dB are similar to the richter scale. I found http://en.wikipedia.org/wiki/Decibel" [Broken] and am trying to apply the third formula under 'Defintion' but to little success. I'm very confused.

Could anyone explain a little clearer exactly what the dB is?
 
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Answers and Replies

  • #2
HallsofIvy
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Reverse your formula: all 7 machines are 7/3 as loud as only 3 so you must have 93.0= 10log((7/3)X) where X is the intensity of 3 machines.
 

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