Investigating the source characteristics of gunshot noise

Characterization of gunshot source noise is important in areas including, but not limited to, military hearing loss prevention, community noise from firing ranges, and counter-sniper detection. Gunfire noise is a difficult quantity to measure for many reasons. The noise emitted from a firearm, both the bullet shockwave and the muzzle blast, is high-amplitude and non-linear. This makes it difficult to measure gunfire noise with typical microphones and data acquisition systems which have limited frequency bandwidth, limiting accurate measurement of rise times and peak levels. Due to the high acoustic pressures, microphones historically have been placed at some distance, 3m to 100m, from the source. At these distances, environmental factors (ground reflection, refraction, absorption) limit the amount of source information available in the signal. In this study, rifles, pistols, and shotguns of varying caliber were evaluated. Environmental effects were minimized by recording 1m from the muzzle. To accomplish this, low sensitivity, high frequency (>500 kHz) blast probes, sampled at 500 kHz, were used in place of microphones. The data show much higher peak sound pressures (>177 dB for some firearms) than previously reported, due to accurate measurement of the non-linear portions of the source signal.