Why Do Sound Waves Cancel Each Other Out?

AI Thread Summary
Sound waves cancel each other out through a process called destructive interference, which occurs when the waves are out of phase. The discussion revolves around the confusion regarding the timing and distance for cancellation, specifically how the wave's travel time relates to its frequency. The user initially miscalculated the relationship between wave period and frequency, mistakenly considering both odd and even multiples of the half-wavelength. Clarification reveals that for cancellation to occur, the distance must be an odd multiple of the half-wavelength, confirming the principle of destructive interference. Understanding this concept resolves the confusion regarding the conditions for sound wave cancellation.
Spyder22
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I'm confused by this problem: http://myspace.homelinux.com:32123/sound.jpg
Can someone explain the solution and what's wrong with my reasoning?
It takes 1.7/340 = .005 sec for the wave to travel the 1.7m. So for the waves to cancel woudn't .005 = T * 1/2 * n (where T is the period of the wave and n is an integer)? Since T= 1/f, we have f = 100n. But then f could be 200hz, 300hz, or 400hz, so that must be wrong... :frown:
 
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For destructive interference, the distance must be an odd multiple of the half-wavelength. If it were an even multiple, that would be constructive interference.
 
oh wow duh that was obvious :blushing: thanks!
 

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