Psychophysical and Physical Techniques for Measuring the Attenuation of Hearing Protectors in the Field

Abstract

A field-implementable measure is needed to estimate the attenuation workers achieve with their hearing protectors in the field. Manufacturer-supplied values overestimate in-field attenuation and reliance on these values could result in greater noise exposure, thus contributing to hearing loss. Alternative measures for assessing a hearing protector's effectiveness were evaluated through comparison to the standardized real-ear attenuation at threshold (1/3-REAT) method (ANSI S3.19-1974). These measures, termed microphone in real ear (MIRE), used miniature microphones underneath and outside of the hearing protector to physically measure the attenuation of the protector using both insertion loss (IL-MIRE) and noise reduction (NR-MIRE) techniques. Results indicate that the MIRE measures differ significantly from the 1/3-REAT method (a psychophysical technique) for attenuation collapsed across protectors, with absolute differences as great as 6.6 dB and the direction of the difference changing due to frequency. At 125 Hz, the MIRE metrics yielded lower attenuation, while from 500 to 8000 Hz, the 1/3-REAT method generally yielded lower attenuation. These differences may be due in part to the occlusion effect and the bone conduction of sound. The size and consistency of these differences across HPDs suggest that these measures hold promise for providing quick and relatively accurate estimations of an HPD's attenuation in the field.

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