Beats

When two sound waves of different frequency approach your ear, the alternating constructive and destructive interference causes the sound to be alternatively soft and loud - a phenomenon which is called "beating" or producing beats. The beat frequency isequal to the absolutevalue of the differencein frequency of thetwo waves.
Arising from simple interference,the applications ofbeats are extremelyfar ranging.

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Wave envelope for two tonesApplications of beats
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Traveling wave concepts
 
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Applications of Beats

Subjective tones
Missing fundamental effect
Police RADAR
Doppler pulse detection
Radio applications
Mulitphonics

Origin of beats
Two tone generators
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Traveling wave concepts

Doppler concepts
 
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Envelope of Beat Production

Beats are caused by the interference of two waves at the same point in space. This plot of the variation of resultant amplitude with time shows the periodic increase and decrease for two sine waves.

The image below is the beat pattern produced by a London police whistle, which uses two short pipes to produce a unique and piercing three-note sound.

Sum and difference frequencies
Index

Traveling wave concepts

Doppler concepts
 
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