Measurement of hearing protector insertion loss at ultrasonic frequencies

The preferred method for assessing the attenuation of hearing-protective de vices (HPDs) involves real ear attenuation at threshold (REAT) determinatio ns, usually obtained in accordance with ANSI Standard S12.6-1997 or ISO Sta ndard 4869-1, where measurements are normally made in the range 125-8000 Hz . In certain circumstances, the use of an acoustic test fixture (ATF) with built-in artificial ears is an acceptable substitute for subjective testing . In this case, the metric obtained is "insertion loss"; the difference bet ween the open-ear and occluded-ear sound levels measured using the ATF micr ophone. REAT attenuations are not generally interchangeable with insertion loss measurements; however, their similarity often promotes data comparison . Experience has shown that subjective thresholds obtained above 8000 Hz ar e highly variable due primarily to decreased hearing sensitivity and to the complexity of high-frequency wave patterns. With an ATF, measurements may be carried out over an extended frequency range while minimizing the proble ms associated with subjective evaluations. In this study, the high-frequenc y insertion loss of two earmuff and three earplug HPDs was measured objecti vely at frequencies up to 22.4 kHz. One of the earplugs provided consistent ly better performance than the other devices for both grazing and direct so und incidence. In addition, two lightweight materials (copier paper and foa mcore sheeting) were evaluated for high-frequency noise reduction when plac ed in the direct path between the sound source and the artificial ear of th e ATF. Of these, the foamcore was the more effective barrier. Crown copyrig ht (C) 2000 Published by Elsevier Science Ltd. All rights reserved.