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Homework Help: Resulatant intensity level

  1. Aug 8, 2014 #1
    1. The problem statement, all variables and given/known data
    A source prodeuces sound of intensity level of 30dB .If another source prodeuces sound at the same time , what's the resultant level?

    2. Relevant equations

    3. The attempt at a solution

    the ans is 10 log (2##I_1## / (##I_0##)) = 33dB , but why not = 10 log (4##I_1## / (##I_0##)) .. beacuse when 2 sound waves superposed , the resultant amplitude is A+A= 2A , I is directly proportional to (A^2) ...
    Last edited: Aug 8, 2014
  2. jcsd
  3. Aug 8, 2014 #2


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    Science Advisor

    Are the two sounds correlated (e.g., in phase) with each other? The sum of the two will only have amplitude A + A (and therefore +6 dB) if they are perfectly in phase with each other. In general they're assumed uncorrelated (they have nothing to do with each other), and so you add the intensities and get +3 dB.
  4. Aug 8, 2014 #3
    it's not 3db am i right? the intensity now it's 2I ?
  5. Aug 8, 2014 #4


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    Science Advisor

    33 dB is +3 dB relative to the original 30 dB, right?

    Hint: log102 = ?
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