Shock waves and the sound of a hand-clap - A simple model

The aerodynamics of the impact between two human hands in a hand-clap is examined, in particular in relation to the hand profile which may be either nearly complementary between the two hands, giving a nominally flat impact, or else domed so that there is a significant enclosed volume. It is shown that shock waves are generated in nearly all hand-claps, with the addition of a Helmholtz-type resonance in the case of domed impacts. As can be judged by simple listening, a flat clap produces broad-band sound that typically extends to about 10 kHz while the spectrum of a domed clap usually has a subsidiary maximum somewhere below 1 kHz and then declines with frequency more rapidly than does the flat clap.