Estimation of otoacoustic emission and excitation force of bone conduction actuator by combined lumped parameter model

In sound presentation system using actuators which excite the surface of the pinna or head, both otoacoustic emission and vibration transmission inside the body contribute to the perception of the sound. The contribution of these pathways is affected by both the location of the excitation and mechanical characteristic of the actuator, leaving the optimal output level of the actuator to mask environmental sound or to present information yet to be estimated. This study, therefore, proposes a simplified model which combines an acoustic equivalent circuit of ear canal and a mechanical equivalent circuit of the tissues of the head. The model enables to estimate both otoacoustic emission component directly corresponding with the loudness for air conducted sound and the component of the transmission inside the head which requires the measurement of the loudness level individually by each excitation location. As the preliminary investigation preceding the establishment of the proposed model towards the human, these two components were calculated using the known parameter values for artificial ear and artificial mastoid. The results indicate that the stiffness of the excited soft tissue and the type of the actuator strongly affect the cutoff frequencies, resonances, and anti-resonances observed within the audible range.