Quantifying the insertion loss of hearing protection using a compressed gas shock tube

Compressed gas shock tubes provide a method of generating repeatable and consistent blast overpressure waves similar to those observed in combat and military training. Shock tubes of different diameters and lengths have been used to evaluate the level dependence of various types of hearing protection devices (HPDs) for sound pressure levels ranging from 132 to 192 dB. Insertion loss data was generated using mechanical test fixtures, post mortem human surrogates, and animal models in order to compare the respective auditory responses at these high pressures. The inclusion of animal models was possible since gas driven shock tubes can be housed in mobile laboratories and trailered to vivarium for physiological and behavioral observations. Measurements were conducted on a variety of HPDs and indicate that the responses of many advanced hearing protection devices are nonlinear at these sound pressure levels. Models of hearing protection and auditory injury have been updated and improved based upon quantificat...