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Q & A: sound gone

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Most recent answer: 10/22/2007
Q:
When I say "K" (at time 0)- a disturbance starts from my throat and travells in air in all the directions. Suppose the disturbance reached a point "x" after 0.1 second in a particular direction. At this moment, do the disturbance at all the preceding points which are nearer to me in that direction than "x" ,still exist or not? Many people say "yes". If it is yes, than a man standing at a point should hear the sound "K" many times instead of just once.
Please give your idea.
- Hindu
Delhi, India
A:
The speed of sound in air is about 344 m/s but depends a bit on temperature, pressure, and humidity.   Now when you speak the letter "K" it is not an instantaneous sound but takes few milliseconds, say 10 to give an example.   So there exists a sound pressure wave train corresponding to the spoken letter K that has a length of  L = VT = 344*.01 = 3.4 meters.  This wave train travels outward at the speed of sound.  But that's it.  Once it's gone by, it's gone, unless there are echoes involved.    So a listener hears it only once.
 
Lee H

(published on 10/22/2007)

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