Active and Passive Reduction of Noise Caused by Bone Conduction to the Head of U.S. Navy Deck Crew Personnel with Helmets

"The goal of this project is to characterize the magnitude and transmission paths of bone-conducted noise, and then to use this information to design an effective Noise Reduction System (NRS) for use in crew helmets. US Navy personnel working on the decksof aircraft carriers operate in a very high noise environment and are at considerable risk for hearing damage. There is no technology available to reduce engine noise levels without significant performance penalties. Further, noise levels will notimprove with the next generation of aircraft, where noise levels for deck crews will exceed 150 dB. At these levels, sound conducted to the cochlea via bone and tissue conduction may inflict damage despite complete attenuation of air-conducted sound inthe ear canal. The phenomenon of bone conduction is not well understood. During the Phase I project, we plan to use two new innovative audiometry techniques, supplemented by laboratory tests, to characterize this phenomenon. We will then use these datato model the noise conduction mechanism in order to design an effective countermeasure. During the Phase II project, we will fabricate and test prototypes of the NRS. The results of our unique tests on bone/tissue conduction to the cochlea will be ofbenefit to those setting hearing protection guidelines as well as to designers of hearing protection systems. The Creare Noise Reduction System (NRS) will reduce the effects of this potentially