Abstract
This paper describes the optimal design of a foil electret earphone for use in telephony. The sensitivity (ratio of the sound pressure generated to the signal supplied) was maximized while meeting material, geometric, and performance constraints. First, a generalized reduced gradient optimization scheme based on the leading order approximations to the diaphragm motions was used. Second, the region of the approximate optimum was examined and an exhaustive search conducted for the optimal design based on exact numerical solution for the diaphragm motion. The results indicate that it is theoretically possible to design a foil electret earphone suitable for telephony which produces a sound pressure level of just over 90 dB in response to a 1‐V rms signal. The optimum earphone has a center circular portion surrounded by an annulus and uses thin, highly tensioned Mylar as a diaphragm. The electret material is mounted on the back electrode.
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