Formation of Beats
Beats (periodic rise and fall in intensity) are produced when two waves of nearly equal frequency are added. The beat frequency is the difference of the two frequencies, while the resultant waveform itself varies at the mean of the two frequencies.
In this applet, the two waves are emitted from two near point sources.
The original two, the combined or none of the waveforms will be displayed when the pattern is clicked repeatedly.
The reciprocal of the number "difference in freq / mean frequency" is the number of cycles between two consecutive points of zero intensity.