Alternative field methods for measuring hearing protector performance.

Abstract

In comparison with the mandatory noise reduction rating (NRR) testing of every hearing protector sold in the United States, real-world tests of hearing protector attenuation are scarce. This study evaluated data from three potential field-test methods as compared with the subject-fit data from Method B of ANSI S12.6-1997 for the E.A.R(R) Express trade mark Pod Plug trade mark. The new field-test methods were the FitCheck headphone (FCH) method, FitCheck in sound field (FCSF) method, and bone-conduction loudness balance (BCLB) method, all of which can be administered in small single-person audiometric booths such as are commonly found in industry. Twenty normal-hearing and audiometrically competent subjects naive to hearing protector use were tested with the laboratory and the three field-test methods in a repeated-measures design. Repeated-measures models with structured covariance matrices were used to analyze the data. Significant effects were found for method, frequency, and first-order frequency-by-gender and frequency-by-method interactions. These effects and interactions were expected given the different psychophysical tasks. The FCSF and BCLB methods provided attenuations that were not significantly different from those found with Method B. Although the attenuations measured for the FCH method were statistically different (greater) than the attenuations from the other methods, the differences were within the magnitude of acceptable test-retest audiometric variability. The results suggest that the FCH and FCSF methods were both feasible and reliable methods for field testing. The FCH method is limited to testing earplugs, and the FCSF requires additional equipment to outfit the test booth, but could be used for testing all types of protectors.