Comparison of subjective and objective methods for the measurements of hearing protector devices attenuation and occlusion effect

With the increase popularity of individual fit testing and miniaturization of electronic components, the Field-Microphone-In-Real-Ear approach (F-MIRE) is becoming more appealing and well suited for estimating hearing protection devices (HPD) attenuation both in laboratory and in "real world" occupational conditions. The approach utilizes two miniature microphones to simultaneously measure the sound pressure levels in the ear canal under the hearing protector, as well as outside of the protector. In this study, experiments on several human subjects were carried out in order to examine the various factors relating the subjective and objective attenuation values. The subjects were first instrumented on both ears with miniature microphones outside and underneath the protector. They were then asked to go through a series of subjective hearing threshold measurements followed by objective microphone recordings using high level diffuse field broadband noises. Earmuffs, earplugs and double-protection were tested for each subject and attenuation values were compared. Additionally, an objective scheme to measure the occlusion effect was developed and tested using subjects' voice as the excitation and the same microphone setup. Results obtained for the attenuation values as well as the occlusion effect levels are presented and discussed.