Characterization of the Dominant Structural Vibration of Hearing Aid Receivers

Results are presented of an analysis and characterization of the mechanical vibration of hearing aid receivers, a key electroacoustic component of hearing aids. The function of a receiver in a hearing aid is to provide an amplified sound signal into the ear canal. Unfortunately, as the receiver produces sound, it also undergoes vibration which can be transmitted through the hearing aid package to the microphones, resulting in undesirable feedback oscillations. To better understand and control this important source of feedback in hearing aids, a rigid body model is proposed to describe the essential dynamic features of the system. The receiver is represented by two hinged rigid bodies, under an equal and opposite dynamic moment load, and connected to each other by a torsional spring and damper. A method is presented to estimate the parameters for the proposed model using experimental data. The data were collected from translational velocity measurements using a scanning laser vibrometer of a Knowles ED-series receiver supported on a complaint foundation. Excellent agreement is shown between results obtained using the analytical model and the measured translation and rotation of an independent receiver. It is concluded that a dynamic model of the receiver must account for both rotation and translation of the structure in order to properly describe its motion due to an input current.