Hearing Protection for Bone-Conducted Sound
Abstract
The high-noise environments in and around modern military jet aircraft can impair voice communications and cause permanent damage to the hearing of pilots and maintenance crews if adequate hearing protection is not worn. With external noise levels of some aircraft approaching 150 dBA, adequate hearing protection must provide better than 50 dB of attenuation. In order to reach such a high level of attenuation, sound transmission routes that bypass the ear canal must be attenuated in addition to the ear canal transmission routes. These bone- and tissue-conduction paths limit the maximum attenuation that can be achieved, even if all air-conducted sound in the ear canal were eliminated. An investigation of bypass sound transmission mechanisms is presented. The aim of this investigation was to characterise the transmission levels of bypass sound to the cochlea and to determine the effectiveness of different hearing protection components in attenuating this sound. Measurements were made with a head simulator as well as with human subjects. In order to make detailed measurements of the vibration of skull bones in an intense sound field, we developed a head simulator. The simulator was built from a human skull, with silicon gel used to model internal organs and silicon and latex used to model the skin. Accelerometers attached to the skull bones were used to measure the skull vibration response. Mechanical point impedance measurements on the simulator were compared to results reported in the literature for humans, cadavers, and skulls. Reasonable agreement with these results served to validate the simulation. The relationship between skull vibration measured on the skull simulator and bone-conducted sound at the cochlea of a human subject was determined by comparing mechanical point impedance measurements recorded from the skull simulator and from human subjects, with the latter including psycho-acoustic responses.
Document Details
- Document Type
- Technical Report
- Publication Date
- Apr 01, 2005
- Accession Number
- ADA454449
Entities
People
- Anthony J. Dietz
- B. S. May
- Darin A. Knaus
- Hard P. Greeley
Organizations
- Creare, Inc.