Bone-conducted Sound Transmission and Attenuation

Hearing protection for personnel working in high-noise environments remains an important challenge for the scientific and engineering community. The sound levels close to certain modern military weapons platforms approach 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 propose a three-pronged approach to investigate the transmission of bone-conducted sound and design-improved HPDs. The approach involves (1) calculation, using an acoustic wave propagation model implemented in finite element analysis software; (2) simulation, using an instrumented physical model of a human head; and (3) human subject tests, investigating the nonlinear response of the cochlea to bone conduction stimulation. In Phase I we propose to demonstrate the feasibility of each of these techniques, and in Phase II we will conduct a detailed investigation of the phenomena using these techniques and apply the results to the next generation of hearing protection devices.