Dissecting sound of weapon fire may give soldiers an edge

By Rachel Ehrenberg

Web edition: April 28, 2010

Distinguishing enemy from friendly fire is a challenge in the confusing, stressful throes of combat. Turns out it’s a challenge even under the controlled conditions of a weapons acoustics study.

Listeners can tell handguns from rifles, but telling one rifle from another is harder, U.S. Army researchers reported April 19 at a meeting of the Acoustical Society of America in Baltimore. Investigating exactly what auditory information listeners tune into might eventually help soldiers discern one weapon from another.

Army scientists are developing a model of gunfire acoustics and a database of the sounds of different weapons, reported Jeremy Gaston of the U.S. Army Research Laboratory. The hope is that recognizing acoustic information can become part of formal training, he said, and give soldiers an edge in combat.

In addition to providing clues about who is doing the firing, sound information can reveal enemies’ whereabouts and give clues to their resources, said Gaston, of the Army’s Visual and Auditory Processes branch in Aberdeen, Md. Sound is an underexploited arena that “provides information on the environment and can cue soldiers to potential danger,” he said.

To investigate what auditory information is most useful for discriminating among weapons, Gaston and his colleagues recorded shots fired from several weapons commonly used in combat, including an AK-47, an M16 rifle, an M4 rifle, a CZ 75 pistol and an M9 pistol, the primary handgun of the U.S. military. The team recorded the shots at three different angles from behind the shooter and then played the shots back to listeners, who judged the similarity of the sounds.

Listeners could discern the pistols from the rifles, but telling the long guns apart was much harder, Gaston reported. He noted, however, that the study group was hearing only single shot events. Because an AK-47 is fully automatic, the rounds don’t stop coming until the clip is empty, while the M4 and M16 typically fire three-round bursts, producing noise that is followed by a pause as the gun is reloaded. Listeners typically focus on a gun’s loudness, but information is also embedded in the pauses between shots. Soldiers can tune into that information as well, said Gaston.

Sounds such as clicks or other background noise may also help listeners make decisions in harried situations. “Once you understand what is going on, you can figure out what information will lead to the best judgment,” Gaston said.