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Sound question

  1. Sep 23, 2008 #1
    In my homework, I was assigned a question,
    If two firecrackers produce a sound level of 95dB when fired simultaneously at a certain plance, what will be the sound level if only one is exploded ( hint: add intensities, not dB?

    My immediate guess is to divide 95 in two, but it seems too simple, plus if it is only one fire cracker, would the sound level be 1/2 ? I don't think I am right, but can someone help me?
    thanks
     
  2. jcsd
  3. Sep 23, 2008 #2

    LowlyPion

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    Welcome to PF

    What is the definition of a db?
     
  4. Sep 23, 2008 #3
    a decible (measured in hertz)
     
  5. Sep 23, 2008 #4

    LowlyPion

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  6. Sep 23, 2008 #5
    sorry, I got mixed up between frequency and dB...I guess my question is, is it possible to just divide dB by the amount of objects a noise is coming from?
    ie. 3 sirens = 30dB
    therefore 2 sirens =20dB?
     
  7. Sep 23, 2008 #6

    LowlyPion

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    The sound intensity may be half in your example but that doesn't change the db's by half, because what is the a db?

    It's a Log base 10 of the ratio of sound intensity to some reference.

    So if Log10(P1/Po) = 95,
    then Log10(1/2*P1/Po) = your answer.
     
  8. Sep 23, 2008 #7
    thank you for the help,
    I was able to solve for Intensity (P1) as .0031622777w/m squared
    I then inputted this into the formula that you gave me to come up with the answer of 92, and I also double checked the formula and got the original answer of 95 for both firecrackers. Thank you so much!
     
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