Development and validation of a computational model of bone-conducted sound transmission for improved hearing protection design.

Bone-conducted sound is the limiting factor in current hearing protection for very high-noise environments such as those encountered by maintainers of military aircraft. The University of Illinois has developed a three-dimensional acoustic wave propagation model for the computation of sound transmission into, around, and through fluid and solid-shell bodies. Creare has implemented experimental techniques to validate the computational results. Three cases are presented. The first is a fluid sphere, for which experimental, computational, and analytical results were obtained. The second is a solid-shell, fluid-filled sphere, for which experimental and computational results were obtained to determine the effect of the solid shell. The third is a representative human head with and without passive hearing protection. For this case, the computational model and an experimental head simulator were both developed from a computed tomography scan of a living human head. The head simulator was built around a rapid-prototype instrumented skull using silicon organs and simulated tissue. Experimental, computational, and analytical results were all in good agreement for the fluid sphere test case. While general agreement was obtained for the other two cases, specific discrepancies in the results are outlined and limitations of the models are discussed.