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Wave interference in violins

  1. May 21, 2010 #1
    Why is it that when say 2 violins are playing the same tune at the same time, there is never any destructive interference and no sound is heard?
  2. jcsd
  3. May 21, 2010 #2
    Destructive interference(DI) does occur, it will have to but consider your self or your ears how far apart are they even if one of ur ear is at the point of D.I the sound from other ear masks it
    and to "hear DI occur" the detector has to be at the exact point, considering human dimensions it is difficult to get the exact point to lie at your ear. and also our ears are not so sensitive, thus you cant tell the differce unless its like a few decibels apart or roughly 25% drop, any musician would find such sudden dips a bit incoherent to hear unless they are well composed.
    Last edited: May 21, 2010
  4. May 21, 2010 #3


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    Interference does not occur with two separate sources, because the waves are uncorrelated. The phase difference between the waves is not constant.
    Interference could occur for two correlated lasers, but not for two violins.
  5. May 21, 2010 #4


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    Let me describe what it would take to get destructive interference in the case of acoustics.

    Take a tone generator or a synthesizer, any thing that generates a clean signal. Feed the electric signal to two speakers. Connect one speaker correctly, and connect the other with swapped wires.

    If you connect both speakers correctly, then they will vibrate in phase; they will move back an forth in unison.
    If one speaker is connected correctly, and the other with swapped wires, then the speaker's vibrations will be in counter motion. It's the opposite of being in phase, and it's called 'being out of phase'.

    (Incidentally, there is in fact no "correct" or "incorrect" here. If for both speakers the wires are swapped then the sound will be perfectly fine too. It's just that how you wire one speaker must match the other one.)

    If you place the speakers very close together then at a sufficiently large distance from the speakers there will be complete destructive interference.

    In the case of two violins there are several factors working against any possible destructive interference.
    As pointed out in an earlier reply, since two violins are separate sources it is extremely unlikely for the sound produced to be precisely out of phase.
    Also the sound of violins is extremely rich in higher harmonics, which again reduces the likelyhood of destructive interference enormously.
  6. May 21, 2010 #5
    If in a large open space so that no reflection (echoing) can occur, one should be able to perform a double slit experiment with one violin though, no?
  7. May 21, 2010 #6
    Thanks for the informative replies. In that case, how would the intensity of sound produced by 2 identical violins compare with the intensity produced by just 1?
  8. May 22, 2010 #7


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    The sound from one violin passing between two openings, or from two speakers could have dead spots at some angles. This won't happen with two separate violins.
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