Experiments on modes of resonant vibrations of telephone receiver diaphragms

(1) The well-known phenomenon of the ¿howling telephone¿ is extended by the insertion between the microphone and the receiver of a valve amplifier. (2) The extended phenomenon is used to measure the velocity of sound. (3) An investigation is made as to which member of the complicated mechanical-electrical system determines the pitch of the ¿howl.¿ (4) Sand figures are obtained of some of the various modes of vibration of a receiver diaphragm. (5) The frequencies of the various modes are compared with those predicted by theory. (6) Conclusions; that the characteristic note is determined by the telephone receiver, and that the receiver diaphragm overtones are substantially in accordance with the plate theory.