Analysis of Sound Pressure Level of a Balanced Armature Receiver Considering Coupling Effects

A balanced armature (BA) receiver has the advantages of small size and high sound quality, which appeal to today's trend of portability and better acoustic quality for hearing aids and earphones. Previous studies on BA receivers have usually used the lumped parameter method or the equivalent magnetic circuit method, but they are not sufficient to describe the complicated behavior of the coupling effects of the electromagnetic, mechanical vibration, and acoustic behavior, especially in the high frequency range. Furthermore, the sound pressure level (SPL) cannot be predicted accurately at high frequency due to the vibration mode of the membrane. This paper proposes a new simulation method based on the 3-D finite-element method (FEM) and the 3-D boundary-element method (BEM) for a BA receiver. FEM was used to analyze the electromagnetic circuit and the mechanical modal analysis, while BEM was used in the acoustic analysis. The results show the trends of nonlinear parameters, such as the cogging force, inductance, speedance, and force factor in consideration of the nonlinear permeability of soft magnet materials. The coupling effects among the electromagnetic, mechanical, and acoustic behaviors are considered in the analyses. The simulation results were experimentally verified and showed good matchings. This simulation method provides a tool for predicting the SPL in the design process of a BA receiver.