Characterization and modeling of the internal vibrations of a balanced armature receiver

Abstract

The balanced armature receiver is a miniature loudspeaker used in hearing aids. When the receiver produces sound, it also exhibits structural vibrations that propagate as both sound and vibrations within the hearing aid structure. These are picked up by the microphones, resulting in feedback. For the first time, a multi-mass lumped element model, representing the mechanical vibrations of the balanced armature receiver, is presented in the literature. The model distinguishes the internal, moving components to capture how their movement propagates to the chassis structure. Component mass is assigned to model their movement, while their mechanical couplings are captured by spring-damper connections. The (ideally) static components (chassis etc.) are lumped into one mass, whose movement represents the structural vibrations that propagate to the hearing aid shell. The model captures the overall behavior of the mechanical system, which means that with physically sound parameter input, we can predict how parameter changes will impact the response. The thorough treatment of the interplay between the components provides a detailed model response that is completed by parameter properties determined through measurements and analytical methods. Validation against the measured electrical and mechanical response, shows that all main features including resonances are explained by the model.