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Homework Help: DB question

  1. Mar 6, 2006 #1
    hi, i need help in understanding something on sound. if admam works near a jet plane that is taking off and experiences the sound level of 150dB. then the protectors to reduce the sould level to that of a chain saw, what decrease in dB is needed? i think it's 40 but i am not sure.
    and also if Adam hears something that sounds like a whisper then what would a person w/o protectors hear? is there even a difference....
  2. jcsd
  3. Mar 6, 2006 #2
    The decibel is a logarithmic scale. The decibel level can be calculated by

    where [tex]I_{0}[/tex] is a constant reference intensity = [tex]10^{-12}W/m^{2}[/tex] This is roughly the intensity of a just audible sound.

    Your problem can be solved only if the intensity of the chain saw is known.
    I don't understand your problem .... sorry ....

    who are those protectors??? and how can they reduce the sound of an aeroplane?? :wink:
    Last edited: Mar 6, 2006
  4. Mar 6, 2006 #3


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    Your book should have a table with some common sound levels. Wikipedia has a table that is probably virtually identical with the table in your book (and, yes, that is a 40dB decrease).

    Do you understand the relationship physicsprasanna gave? If you do, then you'll realize why decibels come in so handy. They turn a multiplication problem into an addition problem (i.e. - if the sound is the same as a barely audible whisper (0 dB), then a person without ear protection will hear a sound 40dB louder).
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