LIMITS TO ATTENUATION (WITH COMMENTS ON TRUE FIELD PERFORMANCE VERSUS LABORATORY DATA)

摘要

With louder and louder weapon systems being developed and military personnel being exposed to steadynoise levels approaching and sometimes exceeding 150 dB, a growing interest in greater amounts ofhearing protection is evident. When the need for communications is included in the equation, thesituation is even more extreme. New initiatives are underway to design improved hearing protection,including active noise reduction (ANR) earplugs and perhaps even cancellation of head-borne vibration.With that in mind it may be useful to explore the limits to attenuation, and whether they can beapproached with existing technology. Data on the noise reduction achievable with high-attenuation foamearplugs, as a function of insertion depth, will be reported. Previous studies will be reviewed that provideindications of the bone-conduction (BC) limits to attenuation that, in terms of mean values, range from40 ? 60 dB across the frequencies from 125 Hz to 8 kHz. Additionally, new research on the effects of aflight helmet on the BC limits, as well as the potential attenuation from deeply inserted passive foamearplugs, worn with passive earmuffs, or with active-noise reduction (ANR) earmuffs, will be examined.