Resonance Mode and Sound Pressure of a Push–Pull Electrostatic Speaker Based on Elliptical Diaphragm

Abstract

This study modeled an elliptical diaphragm in a push–pull electrostatic speaker using the average displacement, specific impedance, and equivalent radius to predict the frequency response in terms of sound pressure level (SPL). We also fabricated a prototype of an electrostatic speaker based on an elliptical diaphragm with a fixed rim measuring 32 mm (semi-major axis) by 30 mm (semi-minor axis). The speaker was then used to analyze the frequency–response characteristics associated with resonance modes and displacement curves using optical measurement and obtain the SPL curves in an anechoic chamber using acoustic measurements. The experiment results revealed that the predicted curves were in good agreement with the measured displacement and SPL curves. These curves of the electrostatic speaker were strongly affected by air radiation impedance. The study provided a designed guide for the electrostatic speaker of the elliptical diaphragm by theoretical analysis and experimental measurements. When our speaker was implemented in an over-ear electrostatic headphone, we obtained a solid bass response and a frequency response typical of high-fidelity headphones.