Sound attenuation evaluation of four prototype helmet-integrated ANR systems

Abstract

Current Navy flight helmets do not provide sufficient passive sound attenuation of the high-intensity, low-frequency noise present in some naval aircraft. As part of a program to provide improved hearing protection for aviators and aircrew personnel, the Naval Aerospace Medical Research Laboratory conducted sound attenuation evaluations of four helmet-integrated active noise reduction (ANR) systems. Sound attenuation measurements (passive attenuation and combined passive/active attenuation) were obtained on Navy and Marine Corps student aviators wearing the prototype helmets in a laboratory noise environment. A Knowles miniature microphone was used to obtain sound levels at the subject's ear. Three sets of measurements were obtained on each subject for each of the prototype systems. A comparison of the combined passive/active attenuation measurements with the passive attenuation measurements reveal increased sound attenuation at 125,250, and 500 Hz and decreased attenuation at 1000 and 2000 Hz. Speech intelligibility measurements obtained on one of the prototypes demonstrated improved speech intelligibility at high sound pressure levels (105 dB and 115 dB) in the ANR “on” mode. [Work supported by the Naval Air Development Center.]