Measuring impulse insertion loss of hearing protection devices using high-level impulse noise

The American National Standard, ANSI S12.42-2010 (R2020), specifies how to measure the impulse peak insertion loss (IPIL) for a hearing protection device (HPD) using an acoustic test fixture (ATF) with impulse levels of LPeak = 132, 150, and 168 dB peak sound pressure level (dB pSPL). The acoustic test fixtures (ATF) described in ANSI S12.42 have ear simulators that are limited to peak levels below 172 dB pSPL. Two GRAS 45CB ATFs (with 40BP and 40BH 1/4” microphones) were used to measure the impulses. Impulses were generated with a .223 caliber Colt AR-15 rifle (160 dB pSPL) and a .300 caliber Browning A-Bolt Medallion rifle (167 dB pSPL). Each fixture was at the same location relative to the firearm muzzles. The IPIL values for the Hocks Noise Braker earplug were measured between 28.8 dB and 33.8 dB. The ANSI S12.42-2010 standard yielded a single IPIL for just the impulses used in the measurement. In the proposed revision to S12.42, the complex transfer function is estimated and can be applied to arbitrary impulses. This paper compares the spectral impulse insertion loss and IPILs using measurements from the two ATFs.