Application of the probe microphone method to measure attenuation of hearing protectors against high impulse sound levels

Abstract The purpose of the present study was to develop a probe microphone method to measure the attenuation of earplugs, earmuffs and their combination against high impulse sound levels from military firearms. The field measurements were made on three earmuffs and one earplug. A probe microphone was supplied with a replaceable soft tube (outer diameter 1·5 mm) to transmit the sound pressure from the ear canal to the microphone. The tube was led between the skin and the cushion ring of the earmuff and through the earplug to the ear canal. A formula was developed to estimate the potential effect of tube length on the results. Subjective laboratory tests of earplugs showed good agreement with the probe microphone method below the 3·15 kHz octave band. The field measurements showed that earplugs may provide attenuation equal to that of large-volume earmuffs against low-frequency impulses from large-calibre weapons. It was also shown that a prominent increase of attenuation can be achieved by using earmuffs and earplugs simultaneously.