Noise and Pure-Tone Attenuation of Hearing Protectors

Abstract

The acoustic attenuation characteristics of five ear muffs and four ear plugs were measured. Ten experienced listeners performed threshold shift determinations using pulsed pure tones and 13-oct bands of noise at 0° and 90° incidence in anechoic conditions and the same bands of noise in semireverberant conditions. Sound field diffuseness was determined by a directional microphone technique and subjectively. Ear muff attenuation at 1 and 4 kHz was significantly lower (p<0.05) for the noise bands in diffuse field than for frontal incidence pure tones in free field. This difference was not observed for ear plugs. The subjects agreed that threshold determinations were no more difficult with noise bands in diffuse field than with pure tones in free field; variability was somewhat lower for the noise band stimuli. Physical measurements of ear-muff attenuation on an “artificial head” test fixture exhibited statistically significant rank correlation with diffuse field subjective measurements at test frequencies of 2 kHz and below, although absolute attenuation values showed only fair agreement. The diffuse field subjective method and the “artificial head” method are being recommended for ANSI standardization. [This research was sponsored by DHEW, Public Health Service.]