An experiment was conducted to explore the correspondence of earmuff attenuation data obtained under two physical procedures, each utilizing the microphone in real-ear (MIRE) technique and two psychophysical procedures, each utilizing the real-ear attenuation at threshold (REAT) technique. The primary impetus was to determine if attenuation testing techniques that could be implemented in the field yield attenuation data which approximate those from standardized 1/3-octave REAT tests on the same earmuffs and test subjects. Ten subjects were fitted with each of three earmuffs and three cap-mounted muffs and tested in counterbalanced fashion in six sessions. Four metrics, consisting of MIRE insertion loss, MIRE noise reduction, pure-tone REAT and 1/3-octave band REAT, were obtained for the same fit of the earmuff on each subject and three separate fitting trials were conducted. The transfer function of the open ear (TFOE) was empirically determined and used to correct the noise reduction MIRE data. For the REAT values collapsed across protectors, differences between the pure tone test and the ANSI S3.19-1974 (or S12.6-1984) 1/3-octave method ranged from 0.5 dB to 3.5 dB, with the 1/3-octave method revealing greater attenuation. The MIRE measures of insertion loss and noise reduction, the latter corrected for TFOE, were demonstrated to be equivalent quantities. Both MIRE measures exhibited significant differences when compared to the standardized REAT method; across earmuffs, the absolute differences ranged from 0.3 dB to 6.0 dB and the direction of the difference changed with frequency. At 125 Hz, the physical metrics yielded slightly lower attenuation, while from 500 to 6300 Hz, the 1/3-octave REAT method yielded lower attenuation. In any case, a comparison of the attenuation means from the laboratory standard 1/3-octave REAT technique and either the pure tone REAT or noise reduction technique (both of which are implementable in the field), appear to be small enough to allow either of the techniques to be applied in situ for estimation of on-the-job attenuation. In the case of the pure tone REAT results, estimates of protection should be made conservatively. In the case of noise reduction, the values should be corrected for the TFOE.
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