THE COMBINED SOUND-ATTENUATION OF EARPLUGS AND EARMUFFS

This research was conducted to measure the attenuation that may be achieved by wearing an earplug and an earmuff in combination. The specific aims were to delineate the relative contributions of each type of device to the outcome and to test various mathematical models of the process. Two plugs (E-A-R expandable foam and Bilsom Soft) and two muffs (E-A-R 3000 and Bilsom 2315) were tested both singly and in the four possible muff/plug combinations in 16 normal-hearing subjects. Hearing thresholds were measured with the ears unoccluded, and fitted with each of the eight protector alternatives at seven one-third octave noise bands with centre frequencies ranging between 500 Hz and 8000 Hz. For each subject, attenuation scores for each device or combination of devices were obtained by subtracting the unoccluded from the protected outcome within frequency. The results showed that the combined attenuation fell short of the sum of the attenuation scores achieved with each device worn separately. For frequencies below 2000 Hz, there was a significant gain in wearing double protection. However, the amount of benefit was determined exclusively by the choice of plug. For frequencies at and above 2000 Hz, the outcome was no better than the limit imposed by bone conduction of sound to the cochlea.