ASA 129th Meeting - Washington, DC - 1995 May 30 .. Jun 06

3pNS5. Comparison of impulse noise effects generated by two rifle muzzles.

Linda L. Pierson

G. Richard Price

Joel T. Kalb

Pamela A. Mundis

Visual and Auditory Processes Branch, Human Res. and Eng. Directorate, U.S. Army Res. Lab., Aberdeen Proving Ground, MD 21005-5425

The current impulse noise standard for US military uses a combination of peak sound pressure level and envelope duration to rate hearing hazard. There is general agreement that this procedure tends to overestimate the hazard from impulses that are broadly peaked at the low frequencies. One possible correction would be to frequency-weight the energy, giving less emphasis to the low frequencies. The current study, using the cat as a model, compares the physiological effect (auditory brainstem response threshold) of one rifle impulse generated either with the standard or an experimental muzzle device. The pressure from the standard muzzle device (N=9) (157.1 dB Peak, 9.62 ms B-duration, 0.9 J/M[sup 2]) has a peak 13 dB ``below'' the pressure generated by the experimental muzzle device (N=10) (169.9 dB peak, 6.88 ms B-duration, 9 J/M[sup 2]). It would be expected that the animals in the normal muzzle group would incur substantially less threshold shift than animals in the experimental muzzle group. However, group mean threshold were not significantly different. This finding challenges the current criterion. Furthermore, although both impulses contain essentially the same spectrum, because the energy composition of the impulses was very different, frequency weighting alone does not solve the problem.