Free-field attenuation of earmuffs and earplugs both singly and in combination

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Free-field attenuation of carmuffs and earplugs both singly and in combination

This article deals with subjective measurements of attenuation characteristic of three earmuffs (A, B, C) and two earplugs (foam and molded). The measurement was carried out through the real-ear attenuation at threshold (REAT) under freefield condition. The five devices were examined singly, and four of them in combination. The performance of double hearing protection (earplug plus earmuff)were investigated experimentally using the same method for a number of combinations. All tests were conducted on 7 subjects, and two replications per subject. The obtained data of the earmuffs tested show that earmuff (A) posscsses the lowest attenuation and is characterized by highest standard deviation. On the other hand, the foam plug provides the higher attenuation and the lower standard deviation. When the foam plug was combined with either carmuff (B or C) an improvement of attenuation was similar, i. e. the choice of earmuff is not important. This combination yields higher attenuation than that produces for either device alone, but does not simply yield overall attenuation equal to the sum of the individual of each device. However, when situation was reversed, the combination of either earplug (foam or molded) with single earmuff yields variation in attenuation below 2 kHz. At and above 2 kHz, the combination results were comparcd to the bone conduction limits which was reported by different authors. At these frequencies, all tests of plug plus earmuff combinations that were studied provided attenuation approximately equal to the bone conduction limits of human skull. Finally, the attenuation estimates derived in this study werc less than comparable data published by the respective manufacturers.