This paper presents experimental measurements of the static and dynamic behavior of an edge‐supported circular membrane electret earphone. It is shown that the measured value of static capacitance and sound pressure level generated in a cavity agree well with theoretical predictions. The experimental results dramatize the nonlinear dependence of the earphone sensitivity on many of the transducer parameters. The effects of fluid loading of the foil electret and damping are considered. It is shown that the air surrounding the foil electret can significantly increase its apparent mass, and that damping effects may be ignored below the system fundamental resonance.