Carolyn S. Bennett, Lt Col, USAF, BSC
Air Force Research Laboratory
Wright- Patterson, AFB, OH
The American National Standards, ANSI S12.6 - 1997, Methods for Measuring the Real-Ear Attenuation of Hearing Protectors, paragraph 0.2 states: "The need for a better human-factors model... experimenter-supervised fitting of HPDs...is intended to describe the upper limits of hearing protector performance...provide inadequate insight into the performance of HPDs when real-world human-factor considerations must be taken into account." In an attempt to provide more valid estimates of field performance, the working group responsible for the revision of the ANSI 1984 standard for measurement of real-ear attenuation developed the subject-fit method of ANSI S12.6 - 1997. Under the subject-fit method, subjects must be naive hearing protector users.
The Department of Defense (DoD) Hearing Conservation Working Group (HCWG) Memorandum For The Record, 31 March 97, paragraph 14 states: "Consensus was reached that DoD should use subject fit methods to determine NRR...consensus that subject fit data were most appropriate for both the purchasing process and for field evaluation."
Empirical data has not yet been presented, however, that validates a single HPD attenuation measurement method. The Air Force Research Laboratory, Wright-Patterson AFB has undertaken a group of experiments to determine empirically which method of hearing protector attenuation measurement will provide the most valid measurement of field performance. The present study, "A Comparison of HPD Attenuation Measurements Obtained with Subject and Experimenter Fittings" is a preliminary study in the investigation of the most valid method to predict hearing protector attenuation. Air Force Research Laboratory, measured attenuation values using ANSI S12.6 - 1997, Method B. Procedures followed were those specified in ANSI S12.6 - 1997, 9 Method B: subject-fit.
The study to be presented compared the attenuation values obtain using subject fit method with attenuation values obtained using the experimenter fit method previously employed by the Air Force Research Laboratory.