Free Oscillations of Acoustical Resonators and Pressure Effects on Damping and Amplification

The effects of sound‐pressure amplitude and static pressure are studied, primarily from experimental text results. Oscillograph records of the transient response of both Helmholtz and pipe resonators are analyzed to determine the damping, decay decrement, and relaxation time of the free oscillations. Damping is determined to be inversely proportional to the static pressure. Damping is found to be a function of amplitude and to decrease as the oscillating pressure amplitude decreases, although at a lesser rate. Since the pressure amplification at resonance is proportional to the reciprocal of the damping, very high amplifications are realized for systems with light damping and low pressure inputs. It is shown that seashells are pipe resonators that respond continuously in the audible range to inaudible inputs. Experimental data and theoretical analyses are used to make a plot of amplification at resonance versus input sound‐pressure level.