Measuring sound attenuation capabilities of helmets using a KEMAR manikin

Sound attenuation measurements were made on three Army helmets and one headset. A Knowles Electronic Manikin for Acoustic Research (KEMAR) was instrumented to read the sound pressure level of one‐third octave band filtered white noise. Sound pressure levels were measured using two different procedures. The first procedure employed a Zwislocki coupler microphone responding as a human eardrum and the second procedure used a probe tube located at the ear canal entrance of the manikin. All measurements were taken with the manikin in a diffuse sound field in a sound isolation room. Attenuation values were calculated by subtracting the sound pressure level measured with the helmet on the manikin's head from those sound pressure levels recorded without the helmet in place. These attenuation values compare favorably at most frequency bands with similar measurements made using human subjects in the same sound field wearing the same helmets. [Work supported by U.S. Army, Natick Laboratories, Contract No. DAAK 60‐80‐C‐100.]