Beats
The periodic volume fluctuation or throbbing sound produced by the interference of two sound waves with slightly different frequencies.
Governing formula
f_beat = |f1 - f2|
SI unit
Hz
In depth
The two sound waves alternate regularly between in-phase constructive interference (loud) and out-of-phase destructive interference (soft) at frequency f_beat.
Examples in the real world
Musicians tuning instruments by adjusting string tension until audible beating fluctuations disappear entirely.