Level Dependent Nonlinear Hearing Protector Model in the Auditory Hazard Assessment Algorithm for Humans
Abstract US Army Research Laboratory technical report ARL TR 6748, Using the Auditory Hazard Assessment Algorithm for Humans (AHAAH) With Hearing Protection Software, Release MIL STD 1474E, includes AHAAH with a Hearing Protector Module (HPM) modeling all hearing protector devices (HPDs) as level independent linear devices. Listed HPDs include several level dependent nonlinear (LDNL) earplugs. These are modeled linearly, based on Real Ear Attenuation at Threshold (REAT) measurements in closed and open modes. When analyzing auditory hazards with LDNL HPDs applied as linear devices based on REAT measurements, results are generally overly protective, since REAT measurements do not reflect increased attenuations for higher waveform pressures. Several MIL STD 1474E Working Group members felt LDNL HPD performance must be accurately described and incorporated into AHAAH cited in the MIL STD. Consequently, a nonlinear pressure amplitude dependent model for performance of LDNL HPDs was created and added to the HPM of version 2.1 of AHAAH (Release MIL STD 1474E) We describe LDNL modifications to AHAAH s HPM and validate the LDNL HPD model by comparing predicted and measured insertion losses (ILs) and waveforms under the HPD, for increasingly intense waveforms. A LDNL HPM will more accurately predict ILs and waveforms under HPDs and support more accurate auditory hazard assessments for complex impulsive waveforms encountered in real situations.