Sequential detuning of a drumhead with a lock-in amplifier

Abstract

Whenever a drumhead is tuned, a perturbation in the tension of the membrane induces the splitting of frequencies for the degenerated asymmetric modes (m, n), with m ̸= 0. With the use of a lock-in amplifier and piezoelectric sensors and actuators attached at the head, the amplitude of the signal generated by the sensors is recorded as the membrane is forced to vibrate over a range of frequencies, answering noticeably when mode’s harmonics are reached. The progression from uniform conditions where the modes are accessible, to the measure of frequency splitting when the drum’s lugs are symmetrically tightened demonstrates the functionality of the system and the behavior of non-uniform tension for a vibrating membrane.