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Homework Help: Interference of rock music at a concert

  1. Dec 9, 2009 #1
    1. The problem statement, all variables and given/known data
    Two loudspeakers at an outdoor rock concert are located 2.4 meters apart. You are standing 17.7 meters from one of the speakers and 20.7 from the other. During a sound check, the technician sends the exact same frequency to both speakers while you listen. The technician starts at 20Hz and slowly increases it to 30,000Hz.

    What is the lowest frequency where you will hear a minimum signal ?

    2. Equations

    y(t) = Acos(wt) + Acos(wt)

    3. Attempt at the solution

    I am not sure how to go about this one. But here is my thoughts on it. Since you are at a different differences from each of the speakers, the waves will arrive out of phase and will interfere constructively or destructively. I am thinking that this is related to beats. Any help?
  2. jcsd
  3. Dec 9, 2009 #2


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    Homework Helper

    Re: Interference

    It isn't related to the beats, but the path length has to be an odd multiple of a half-wavelength in order for there to be a minimum. That's because such a path length difference ensures crests overlap with troughs and cancel.
  4. Dec 10, 2009 #3
    Re: Interference

    So would I just find how much of the 20Hz signal would fit on each distance?
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