A new approach to a damage risk criterion for weapons impulses

Existing damage-risk criteria for weapons impulses suffer from their lack of a theoretical basis, thereby limiting their generalizability and utility. Furthermore, a number of studies now indicate that they may be inaccurate for impulses with energy in the low frequency region (Dancer & al., 1985; Patterson & al., 1985; Price & al., 1989). We have approached the problem by modeling the ear mathematically as a means of gaining insight into the loss processes. In the model, the external and middle ears are linear at lower intensities; however, the stapes displacement is limited to 20 microns, as would be expected on anatomical/physical grounds. Susceptibility, in the inner ear, is modeled as mechanical stress, a function of basilar membrane displacement and number of flex cycles. The model, which is executable on a PC-based computer, reproduces the data on the ear that can be measured at lower intensities. It also ranks the known hazard from impulses in the correct order, explains the finding of loss in mid-cochlea regardless of spectral location of the weapons impulse, and suggests that the greatest hazard comes from that portion of the acoustic wave in which pressures cross through ambient and at a rate consistent with energy in the mid-range. Because the model is theoretically based, it has the potential for use as the basis for a damage risk criterion for impulse noise as well as for a design criterion for weapons.