Measurement of the Mechanical Impedance of Ear Cartilage and Development of a Coupler for Vibrator Evaluation of Cartilage Conduction Hearing Aids

Cartilage conduction hearing aids (CCHAs) are new devices that have attracted attention in recent years for external auditory canal atresia. In these devices, a vibrator is attached to the ear cartilage to transmit sound through vibration. In this study, we measure the mechanical impedance of the ear concha auriculae, which represents the mechanical load on the vibrator. To evaluate the output of the CCHAs, we develop a coupler simulating the ear cartilage that measures the sound pressure corresponding to the eardrum sound pressure of the normal ear. Consequently, the mechanical impedance of the developed coupler is several times larger than that of the human ear cartilage measured in this study; however, it is an acceptable value considering the difference in the contact area. The output sound pressure of the vibrator with the coupler simulating the ear cartilage roughly simulates the sound pressure in the ear canal with normal hearing (with the ear canal sealed). In this study, the measured mechanical impedance of the human ear cartilage is approximately 20 dB less than that of the mechanical coupler specified in IEC (International Electrotechnical Commission) 60318-6 for the evaluation of the bone conduction vibrator.