Evaluating harmful acoustic impulses

Abstract

Noise-induced auditory impairment is widespread, despite many successful efforts to reduce sound emitted by technical equipment. Using accumulated acoustic energy as an indicator for health hazard, as in ISO1999, is insufficient to describe the hazard for impulses. While stimulating a system with many vibrating parts, like the ear, it is more important how the energy is fed into the various components than how much is applied. The Human Ear Model (AHAAH) uses the pressure-time-history of impulses which is much better. It is based on theoretical assumptions, but it has serious deficits that lead to results that can be extremely wrong. Within another long-term approach the effects on hearing of accidents caused by impulses have been collected and documented. The harmful situations were reenacted thoroughly, to obtain acoustic measurements that can be correlated with the auditory damage, if present. All told, impulses cause three types of notches, at different frequency ranges. Hence, harmful impulses show characteristic footprints in carefully recorded audiograms, and the type of notch depends upon details of the causing impulse. This EPI approach (Effects of Powerful Impulses) applies to most cases of auditory damage, and it is useful to prevent and understand such injuries.