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Why does an open ended column reflect sound?

  1. Aug 27, 2005 #1
    I am reading about how sound waves travelling down a column that is open at one end (clarinet, vocal tract etc). Apparently when they reach the open end some are reflected and interfere constructively or destructivly with subsequent waves in the column. My question is why are the sound waves reflected at all at the end of the column, its not like there is a thick solid to bounce against.
    Thanks
     
  2. jcsd
  3. Aug 28, 2005 #2

    Tide

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    In effect there is an impedance mismatch at the end of the column. Basically, it means that the pressure variations at the end of the column end up pushing and pulling a noticeably larger mass of air.
     
  4. Aug 28, 2005 #3
    Can you please explain more, I don't understand. Thanks
     
  5. Aug 28, 2005 #4

    Tide

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  6. Aug 28, 2005 #5
    Whenever the pipe changes shape or ends, the pressue and velocity ratio
    of the moving gass changes. At such a change there will always be
    some energy reflected backward. In free space this is how radars work,
    and in pipes this is why you hear stange echoes from very long pipes.

    The only way to prevent a reflection is to have the open end presented
    with the same conditions as occurr when you place another identical pipe
    to the end, i.e. extending the pipe.
     
  7. Aug 29, 2005 #6
    Link was excellent, thanks Tide
     
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