Bone-Conducted Sound Transmission and Attenuation

Hearing protection for personnel working in high-noise environments presents an important challenge for the scientific and engineering community. Air Force maintenance personnel working in close proximity to operating jet aircraft can be exposed to sound levels approaching 150 dBA. At these levels, the attenuation provided by hearing protection devices (HPDs) is limited by bone-conducted sound that bypasses the ear canal and its associated protection (earplugs and earmuffs). An improved understanding of the transmission mechanisms for bone-conducted sound is required to enable the design of improved active and passive hearing protection devices. Creare and the University of Illinois at Urbana-Champaign propose a three-pronged approach to investigate the transmission of bone-conducted sound and design-improved HPDs. The approach involves (1) computational modeling, using an acoustic wave propagation model; (2) experimental simulation, using an instrumented physical model of a human head; and (3) human subject tests, using innovative objective and psychoacoustic test techniques. In Phase I we demonstrated the feasibility of each of these techniques. In Phase II we will further develop and validate the computational model and we will investigate bone-conduction nonlinearities using human subject tests. We will then use this method to evaluate and improve the performance of hearing protection designs.