Instrumentation Techniques for the Measurement of Gunfire

Abstract

The peak sound pressure from near-field small arms gunfire is commonly used when assessing a shooter's hearing damage risk. Close to a shooter's ear, the peak sound pressure level from a rifle or pistol can be 155-to-160 decibels with a pulse rise time on the order of ten microseconds. Standard dosimeters equipped with conventional measurement microphones significantly under-report the true peak levels from proximate gunfire; hence, the shooter's exposure is either unknown or underestimated. The U.S. Military has established exposure limits for small arms gunfire; however, the specified properties of the measurement instrumentation are more prescriptive than performance-based. The implication is that the practitioner is responsible for pre-qualifying his or her own instrumentation. For near-field gunfire, the leading cause of measurement error occurs when the wide-band signal from the acoustical transient is transduced by a relatively large-diameter measurement microphone having limited bandwidth. Secondary measurement errors include the finite bandwidth of the microphone signal amplifier and its slewing limit, the characteristics of the anti-aliasing filter used, and the sampling rate of the digital recording device. The paper discusses these instrumentation constraints and recommends minimum performance requirements to help attain reproducible measurements of small arms gunfire.