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Homework Help: Question on waves and vibrations

  1. Nov 30, 2009 #1
    1. The problem statement, all variables and given/known data

    this is part of a problem sheet and is the last question i have left to work out. i have been given solutions of 105dB and 86dB.

    A person is in a room in which two sources of sound of loudness 100 dB and
    98 dB are emitting the same frequency. The sources form a standing wave pattern in the room. What are the maximum and minimum loudness the person will be subjected to as he moves about?

    2. Relevant equations

    3. The attempt at a solution

    not to sure i understand the question. i think it asks what is the constructive and destructive superposition that can occur. if so, what is my next step
    i'm guessing that the Standing wave ratio formula is a part of this but what is the amplitude reflection co-eff?

  2. jcsd
  3. Nov 30, 2009 #2


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    Staff Emeritus
    Science Advisor
    Gold Member

    If the two sound waves interfere entirely constructively, their amplitudes (intensities) will simply add together. If they interfere entirely destructively, their amplitudes (intensities) will subtract. Therefore, these are the extremal conditions, i.e. the represent the maximum and minimum possible sound intensities the person can hear. Of course, first you have to figure out what the individual amplitudes are, then add or subtract them, then see what the result is in dB.
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