Laboratory Attenuation of Earmuffs and Earplugs Both Singly and in Combination

For very high-level noise exposures, especially when 8-hour, time-weighted averages are greater than 105 dBA, the attenuation of a single hearing protection device may be inadequate. For such exposures, double hearing protection, i.e. muffs plus plugs, may be called for. It is well recognized that double hearing protection does not simply yield overall attenuation equal to the sum of the individual attenuation of each device due to the bone-conduction flanking paths and the acoustical-mechanical interaction between two such closely spaced devices. The incremental performance to be gained by double protection was investigated experimentally by measuring the real-ear attenuation at threshold for a number of combinations, according to ANSI S3.19-1974. All tests were conducted on 10 subjects, three replications per subject. Devices included foam plugs (partial, standard and deep insertion), fiberglass down, V-51R earplugs, medium and large volume commercially available earmuffs, and an experimental large-volu...