Numerical and experimental investigation of the sound transmission delay from a skin vibration to the occluded ear canal

Abstract

High-level impulse noise can permanently damage the ear and protection is therefore essential. Using hearing protectors to occlude the external ear canal, reduces air conduction but provides only partial attenuation. This is because the pinna converts airborne sound into mechanical vibrations, which propagate through body tissues to the occluded ear canal. To better understand the propagation pathways and mechanisms, which remain unclear, we simulated a preliminary two-dimensional transient model of the external ear in COMSOL Multiphysics. It shed light on how the waves travel through the tissues to reach the occluded ear canal, illustrating phenomena that are usually not visible experimentally. We also conducted an experimental evaluation of the time delay of wave propagation between the external ear tissues and the auditory canal air to confirm the numerical observations. Thus, we measured delays to reach the ear canal during stimulation with a transducer at the back of the concha and at the tragus of 0.37 ms and 0.32 ms respectively. This matched the numerical simulations and corroborated transmission through the skin. The model also highlighted coupling between the skin and the plug leading to pressure transmission in the ear canal. These preliminary results pave the way for the improvement of hearing protection devices by demonstrating the impact of the protection device’s material and coating on the radiative phenomena resulting from the tissue conduction.