Humming Notes 1/2-lambda apart

  1. A question my friend gave me the other day:

    If I start humming a constant note and, once 1/2 a wavelength exits my mouth, I start humming the same constant note starting at the same point along the wave while somehow managing to produce both of the same note, what will you hear?

    His logic is that destructive interference would occur and I wouldn't hear anything. This confused me. How can someone just conclude that someone is totally deaf to a sound is coming just because "I'd hear 1/2 a wavelength and THEN they'd cancel each other out.". Why is my friend wrong? Any ideas?

    Thanks in advance! :)
     
    Last edited: Jan 25, 2013
  2. jcsd
  3. Oi, that wasn't the other day, that was today! :)

    Though my argument was that you'd hear 1/2 a wavelength and THEN they'd cancel each other out.
     
  4. Which is what I meant to say. Thanks for clearing it up though! I'll edit.
     
  5. sophiecentaur

    sophiecentaur 13,569
    Science Advisor
    Gold Member

    Of course, in some other direction is space (off axis), the two waves would add constructively and the power that didn't go in the forward direction would cause the power in that direction be quadrupled (2 squared). There is no way that the power coming from the sources would 'disappear'.

    You could do this much easier with two loudspeakers.
     
  6. sophiecentaur

    sophiecentaur 13,569
    Science Advisor
    Gold Member

    Actually, you don't hear "a 1/2 wavelength" because that is a distance. You could say that you would hear one half of a Cycle of oscillation.
    I'm not sure what the original description means - now I read it again.
     
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