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Adding dB - Cannot figure out logs!

  1. Sep 16, 2009 #1
    1. The problem statement, all variables and given/known data

    A family ice show is held at an enclosed arena. The skaters perform to music with level 80.0 dB. This is too loud for your baby, who yells at 75.0 dB.

    (a) What total sound intensity engulfs you?
    (b) What is the combined sound level?


    2. Relevant equations

    dB = 10log(I/1E-12)

    3. The attempt at a solution

    I am trying to convert back, but I have never been great with logs, and I cannot figure out how to get I.

    80=10log(I/1E-12)
    75=10log(I/1E-12)







    EDIT - it just clicked - anti-derivatives
    A)
    75db = 10^7.5/1E12 = I(b)
    80db = 10^8/1E12 = I(m)
    add them for total = 1.316E-4

    B)
    10log(1.316E-4/1E-12)
    81.19dB
     
    Last edited: Sep 16, 2009
  2. jcsd
  3. Sep 16, 2009 #2
    A hint: Use the fact that 10^log x = x
     
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