Measurement of impulse peak insertion loss for five hearing protectors.

Abstract

In 2009, the US Environmental Protection Agency proposed an impulse noise reduction rating (NRR) for hearing protection devices. The impulse NRR is based the American National Standard, ANSI S12.42-2010, and requires measurements with an acoustic test fixture for three ranges of impulse noises: 130–134, 148–152, and 166–170 dB peak SPL. Five protectors of each of five models (The Combat Arms Linear, Combat Arms Nonlinear, EAR Pod Express, Etymotic EB1, and Bilsom 707 Impact II, all in passive mode) were evaluated per the levels specified in the ANSI standard. Impulses were generated by an acoustic shock tube in the laboratory and by a 0.223 caliber rifle in the field. At each peak impulse level, protector samples were fitted on the test fixture five times and for each insertion, at least three impulses were measured. The impulse NRR increased with peak pressure and ranged between 20 and 38 dB. For some protectors, significant differences were observed across protector examples of the same model and across insertions. Relationships between the continuous noise NRR, the impulse NRR, and the increase in allowable impulse exposures due to the protector will also be presented.