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

The American National Standard, ANSI S12.42-2010, specifies the impulse peak insertion loss (IPIL) for a hearing protection device (HPD) using an acoustic test fixture (ATF) over a range of impulse levels nominally at 132, 150, and 168 dB peak sound pressure level (dB pSPL). The GRAS 45CB ATFs have ear simulators fitted with GRAS 40BP microphones (6.35 mm diameter) that have amplitude limits of about 169 dB SPL (172 dB pSPL). The open ear transfer function measured at the 168-dB level can cause the peak amplitude to exceed the design specification of the microphone. Accordingly, the standard directs the user to measure the 150-dB transfer function between the field microphone and unoccluded ear (HFF,TM) and apply it to the field microphone measurement at 168 dB. We have measured the HFF,TM with GRAS 45CB ATF and with the GRAS 45CB-S2 ATF equipped with GRAS 40BH microphones (193 dB/196 dB pSPL). Impulse peak insertion loss measured with both ATFs will be reported and compared.