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Evaluation of the Communications Earplug in the H-53 and CH-46 Helicopter Environments.

Abstract : Noise levels inside military helicopters generally exceed noise exposure limits established by DOD Instruction 6055.12, "Hearing conservation" (1991). Noise levels in helicopters with higher load capacities such as the CH-47, CH-46, and H-53 are extremely high and sometimes exceed the helmet's capability to provide adequate hearing protection for crewmembers. Noise compromises communication because of inadequate speech signal to noise ratio at the ear (Mozo, Murphy, and Ribera, 1995; Ribera et al., 1996; Mozo and Murphy, 1997; and Staton, Mozo, and Murphy, 1997). Use of combination protection, earplug in addition to the helmet, does provide the necessary hearing protection, but further compounds the problems associated with communications capability. While active noise reduction (ANR) provides exceptional low frequency hearing protection, it does little or nothing to improve protection for frequencies above 800 hertz. A U.S. Army Aeromedical Research Laboratory (USAARL) report (Mozo and Murphy, 1997) shows ANR does improve speech intelligibility when worn alone, but both hearing protectiOn and speech intelligibility are degraded when worn with ancillary equipment such as spectacles and chemical biological (CB) mask. Aircraft modification, system cost, lateral impact, weight, and others factors should be evaluated carefully when considering the use of ANR in the helicopter environment. The communications earplug (CEP) shown in the figure is a device which incorporates a miniature earphone with foam earplug and can be worn in combination with the aviator's helmet. Calculations show the CEP provides adequate hearing protection for 8 hours duty even in the high noise levels found in the H-53. The device also provides voice communication intelligibility which approaches asymptotic limits near 100 percent in those high noise environments. The system is lightweight, cos