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Sound as longitudinal vibrations of air

  1. Jan 26, 2007 #1
    Sound is just Longitudinal vibrations of air that are detected from objects like the ear. Hence it originates from a vibrator.

    For humans this vibrator is in the neck in the form of a vocal cord. So sound from humans really comes from the neck and the vibrations of air ascend up the neck and comes out from our mouth and nose.

    The question is I am able to hear someone's voice even if I am right behind them. Does this occur because of the diffraction of sound which is a wave as it passes through that person's nose and mouth? What is the difference in intensity of sound between someone standing 1m in front and 1m behind a person producing sound?

    Another question is sound waves interfere just like any other wave but when minima occurs, the sound dosen't neccessairly cancel (i.e. you would still hear some sound? Whereas light would, ie. dark fringes.
    Last edited: Jan 26, 2007
  2. jcsd
  3. Jan 28, 2007 #2
    It's not necessarily a diffraction through their nose and mouth. Keep in mind also that air is not the only carrier of sound waves. If I close my mouth and plug my nose, I can still make audible noises.

    Air diffracts sound quite a bit, and the room you're in probably reflects sound fairly well. Both of these are the reason that sound spreads in many directions.
  4. Jan 28, 2007 #3


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    Just like light, you can consider every point on a sound wave a source of new waves. The sound diffracts through the air.

    Sound waves do interfere exactly like light. I have been in orchestra halls where in some seats you could hear almost nothing. Similarly, those fringes are where the intensity is reduced, not where there is no light.
  5. Jan 28, 2007 #4
    When I try to do that, whenever I make a sound, it's because I haven't closed my mouth and or nose properly. When they are completely shut, isn't sound from the vocal cord impossible?
  6. Jan 28, 2007 #5


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    You can puff your cheeks out while your mouth is shut and your nose is plugged, right? Try humming as you puff them out.
  7. Jan 29, 2007 #6

    Again when I make a hum noise, it's because I haven't closed by mouth or nose properly.
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