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Would you hear nothing if you struck two tuning forks of the same

  1. Aug 21, 2014 #1
    1. The problem statement, all variables and given/known data

    Would you hear nothing if you struck two tuning forks of the same frequency at the same time or if you struck one some amount of seconds after the other which would result in one fork's sound wave to be exactly pi out of phase of the other?
     
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  3. Aug 21, 2014 #2

    phinds

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    that would depend on where you held them relative to your ear. Even if you got the best cancellation possible I think you'd likely still hear at least something. Real-world wave cancellation of this type is likely to be a bit messy
     
  4. Aug 21, 2014 #3

    mfb

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    Did you ever note interference effects with two speakers at a computer? You can let them play a sinus wave to simulate your experiment. Are there regions where you hear nothing?

    Hint: think of reflections
     
  5. Aug 21, 2014 #4
    phinds Oh ok plus because the sound would probably reflect off of other surface and eventually reach your ear. No mfb unfortunately I cannot try that experiment now b/c I'm at a laptop which has a single source of sound. I'll try to do that if I ever gt my hands on a desktop computer though. Thank you both for your replies
     
  6. Aug 21, 2014 #5

    phinds

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    I think you are missing his point. You only NEED a single source of sound since most browsers will play sound from two different windows at the same time. Since the sounds are mixing electronically, you can get perfect cancellation.
     
  7. Aug 21, 2014 #6
    Oh I thought you meant to play two separate sounds from two separate speakers, but what you're saying makes sense. I tried it with opening this in two separate tabs but I didn't get any cancellation. I heard some beats though or at least I think I did.
     
    Last edited by a moderator: Sep 25, 2014
  8. Aug 21, 2014 #7

    phinds

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    The problem seems to be that you can't control where the tone is in its cycle when it starts in the different windows. I guess you could try opening the second window over and over until you got cancellation but it would likely take a boringly long time and wouldn't really prove anything new anyway.
     
    Last edited by a moderator: Sep 25, 2014
  9. Aug 21, 2014 #8

    haruspex

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    Yes, you'd need the sources to arrive exactly out of phase at each ear, preferably in an anechoic chamber.
     
  10. Aug 21, 2014 #9

    nsaspook

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    Even if they were exactly out of phase and equal in amplitude at each ear in isolation the ear/brain interface still does the processing so much of what we hear is preconditioned and is a bit of an illusion of reality that can somewhat be changed with practice and concentration. Above 1khz we lose the ability to phase discriminate signals and mainly only sense frequency so full sound cancellation with stereo hearing is limited.

    http://www.philomel.com/musical_illusions/
     
  11. Aug 22, 2014 #10
    The cancellation is almost complete if you put your head exactly the right position.
    Try playing the attached mp3 (in a zip file) through a device with stereo-speakers,
    (not headphones), whilst slowly moving your head , e.g. rocking back and forth , and/or turning your head.
     

    Attached Files:

  12. Aug 22, 2014 #11

    mfb

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    It works very well, nice. You can even hear the influence of moving a hand around close to the ear or between ears and speakers (yes it can make the sound louder).
     
  13. Aug 22, 2014 #12

    haruspex

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    I don't see how cancellation can be annulled by perception considerations. If there's no net movement or pressure change of the air molecules, there's nothing to perceive.
     
  14. Aug 22, 2014 #13

    nsaspook

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    Last edited: Aug 22, 2014
  15. Aug 22, 2014 #14

    haruspex

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  16. Aug 22, 2014 #15

    nsaspook

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    Why? The separate conversion of acoustic energy in each ear to signals interpreted by the brain as sounds allows us to detect phase and aptitude differences across our head and normally we think of our ears as linked acoustically. Our hearing is not a simple algebraic mixer of two signals. You can be easily trained to listen to a voice in one ear and copy Morse code in the other for example. I often wore two set of headphones with each over only one ear to compare the signal quality of radio comm circuits transmitting the same signal when selecting which one to use. Changes in phasing due to HF skip were detected in my head as direction changes or beats not a null of the signals.
     
    Last edited: Aug 22, 2014
  17. Aug 23, 2014 #16

    haruspex

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    I repeat, you wrote:
    This means that, at each ear separately, the arriving waves completely cancel. Neither ear gets any signal. This has nothing to do with any subsequent processing by the nervous system.
     
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