The Theory of the Operation of the Howling Telephone with Experimental Confirmation

A general theory of the sustained oscillations of electromechanical systems is presented in the paper. The electrodynamical properties of the telephone transmitter and receiver are described and sufficient numerical data are given to enable one to calculate the intensity and frequency of howling for various types of systems. Detailed consideration is given to the following three systems, namely, one where the transmitter and receiver disphragms are coupled together mechanically by a lever system, one where they are coupled by a small box of air, and one where they are coupled by a long tube of air. The type of electrical circuit to use with each of these systems depends upon the type of performance desired.