G. Richard Price
Human Res. and Eng. Directorate, US Army Res. Lab., Aberdeen Proving Ground, MD 21005
It is commonly observed in impulse noise experiments that hearing loss data are highly variable. The explanation implicitly accepted is that the ear is just inherently variable at very high sound pressures. However, calculations of hazard with a mathematical model of the ear [G. R. Price and J. T. Kalb, J. Acoust. Soc. Am. 90, 219--227 (1991)] indicate that the details of pressure histories of the impulses themselves may be the source of much of the variability. The model calculates the transfer of energy from the free field to displacements of the basilar membrane. ``Hazard'' is modeled as the sum of the peaks of upward displacement of the basilar membrane (in microns) raised to the 2.5 power. Weapons impulses (105-mm howitzer) with the same peak pressures and highly similar pressure histories (which would be rated as equally hazardous by traditional damage-risk criteria) nevertheless produced hazard calculations that varied by a factor of 2 or 3 in a completely deterministic ``ear.''