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Homework Help: Sound intensity Help!

  1. Jan 18, 2009 #1
    1. The problem statement, all variables and given/known data

    A concert loudspeaker suspended high off the ground emits 36 W of sound power. A small microphone with a 1.0 cm^2 area is 48m from the speaker.

    What is the sound intensity at the position of the microphone?

    What is the sound intensity level at the position of the microphone?

    2. Relevant equations

    I don't know where to begin. Which formulas do I use?
    * I=P/4(pie)r^2 ?
    *B(beta)= 10log( I/ Io)?

    But it says the microphone is 1.0cmsquared area is 48 m? What does the distance x=48m fall into any of the formulas?

    3. The attempt at a solution

    I Cannot solve this problem...help!
  2. jcsd
  3. Jan 18, 2009 #2


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    Science Advisor
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    hello hello kitty kitty! :approve:

    (have a π: and a beta: ß or a different beta: β :wink:)

    I don't know what the definitions of sound intensity and sound intensity level are :redface:, but the 48m is obvously the r in 4πr2.

    The reason for the 4πr2 in the formula is that it's the surface area of a sphere of radius r …

    the power P is spread over the whole surface area, so the power per area is P/4πr2. :smile:
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