The Acoustics of the Telephone Receiver with a New Earcap

Abstract

The invention of a new earcap for the telephone receiver is described incorporating a resonatory body which consists of a channel-formed room made up of a number of tubes open at both ends. The development of this invention has been based on investigations of the actions from the resonatory body of the violin and through studies on a new type of an organ pipe. It has been found by subjective tests that this new earcap compared to the standard earcap, now in general use, reproduces sounds with less “singing” mechanical vibrations from resonance in the diaphragm. Consequently an improvement in making speech clearer and music more mellow has been accomplished. It is believed that the acoustical improvement obtained by the new earcap is due to the interaction between the vibrations excited in the diaphragm and the interfering standing waves generated thereby in the tubes. This action reaches an optimum by the formation of a differential wave which is one octave below the excited fundamental if the tubes have such dimensions in relation to one another that their resonance frequencies build a series of numbers, the terms of which have the proportion 2 : 3. The aural impression of a more true reproduction of sound with the new earcap has been confirmed by tests supplying electric currents of a single sine wave and of combined waves to the same telephone receiver alternatively equipped with the two different types of an earcap, the standard one and the new earcap, the sound intensity produced accordingly being measured and recorded with an oscillograph.