On the Cutting Edge of Hearing Aid Research

Knowles took a multilateral initiative to develop transducer vibroacoustic models that are easy to implement and compatible with its hearing health customers. These models help hearing aid designs graduate from a prototype stage to a final product more efficiently without sacrificing accuracy. A significant breakthrough came when Dr. Daniel Warren introduced a 'black box' model in 2013. This model uses a minimum amount of simple circuit elements to capture the essential electroacoustic transfer function between voltage and output sound pressure level for balanced armature receivers, while leaving out factors that are unimportant to feedback control. The 'black box' and vibroacoustic models were tested and validated against realistic acoustic and mechanical attachments to the receiver using the COMSOL Multiphysics software and industry-standard tests. This collaboration between Knowles and its hearing health customers started in 2014 and involved measuring the acoustic output and vibration forces simultaneously using a structure that could be easily modeled in FEA. The COMSOL model revealed the dependence of the output pressure and mechanical forces on the applied voltage, frequency, and material properties, showing excellent agreement with physical measurements.