COMPARISON BETWEEN SUBJECTIVE AND OBJECTIVE MEASURES OF ACTIVE HEARING PROTECTOR AND COMMUNICATION HEADSET ATTENUATION

A masked-threshold and a loudness-balance method have been developed t o estimate the attenuation of communication headsets and hearing prote ctors with built-in active noise reduction (ANR) systems. Both methods are used to estimate the attenuation of tile ANR systems and the mask ed-threshold method is also used to estimate the total attenuation (ac tive plus passive) of the device. The procedures are designed to be us ed in the presence of environmental noise, and to minimize the noise e xposure of subjects during the measurements. For comparison, physical measurements of insertion loss have also been performed using a miniat ure microphone in the concha. Experiments showed that the masked-thres hold method tends to give increased estimates of the attenuation if th e noise reduction of the left and right earcup ANR systems differs, as commonly occurs In practice. In contrast, the loudness-balance method reduces the estimates of the active attenuation. Insertion loss measu rements may be influenced by the position of the microphone, owing to the spatial variability of the sound field under an earmuff when the A NR system is operating. Differences between physical and subjective me asurements of up to 20 dB have been obtained in this study at frequenc ies of 250 Hz and below for a device in which the sound pressure varie d substantially near, and within, the ear canal.