Wave interference using sound: beat frequency for two sine waves with similar frequencies.

Wave interference using sound: beat frequency for two sine waves with similar frequencies. We introduce the sound of “beats“ which are caused by alternating constructive and destructive interference between to sinusoidal sound sources with frequencies that are very close. We listen to a 440Hz tone and view the graph of the amplitude as a function of time, then we listen to a 442Hz tone and view the graph of the amplitude as a function of time. Next, we view the two functions superimposed, and we see that they drift in and out of phase over time. This causes alternating constructive and destructive interference, giving us the phenomenon of beats! Finally, we view the graph of the sum of the two sound waves, and we see that the sum wiggles rapidly as the amplitude grows and shrinks slowly. In this case, the tone we hear from the rapid wiggling is 401Hz: the average of the two frequencies of the inputs, and the audible beat frequency is 2Hz: the difference of the two frequencies of the inputs.