Thundering bursts from M-16 assault rifles. Cursing as firefights begin. Explosions so powerful that troops don't just hear the deafening blasts, they feel them.
Battle, veterans say, is about sound.
"It can be very overwhelming to your senses," said Sgt. Maj. William Bennett, who has been serving in combat zones for more than two decades and now trains soldiers at Missouri's Fort Leonard Wood.
In an effort to help prepare troops for combat's auditory assault, researchers are turning a nearby warehouse into a surround-sound audio battlefield that they hope Bennett and other military trainers could soon use. The 64-speaker system wraps users in the sounds of fighter jets roaring overheard, tanks approaching, and cannons and guns firing from all directions. Loudspeakers hang on a truss system, and four 20-hertz subwoofers create that low bass that vibrates through a person's gut.
Combat veterans going through early tests suggested using the pulsing speakers under a raised floor to simulate the ground shaking during a bombing. Others told researchers at the Missouri University of Science and Technology, which is spearheading the project, that the volume doesn't match an actual battle.
The noise levels that troops experience in battle can reach levels nearly 25 percent louder than a rock concert _ enough to cause hearing loss and far higher than what researchers are permitted to use.
"One guy was saying, 'It's just going to be impossible. When real ordinance hits, it just sucks the wind out of you,'" said Steven Grant, a telecommunications professor conducting the experiments in Rolla, less than 30 miles from the Army base.
Still, researchers are incorporating the feedback with the hope of better preparing troops for the deafening sounds they'll encounter. Troops could, for example, practice huddling in tight groups to be heard or using hand signals to communicate while surrounded by voice-drowning noise.
The nonprofit Leonard Wood Institute is funding the $840,000 project, hoping researchers will eventually be able to create a portable audio battlefield where five to 10 members of a unit could drill together in full gear.
The first official training sessions will begin soon with university students.
The military can't endorse such projects, but the Army is excited about the work, said Joe Driskill, executive director of the Leonard Wood Institute, which uses federal money to support research benefiting the base.
"It's very, very promising," Driskill said, adding that it's vital for troops to be able to focus in loud environments. "They are really excited about it. It's important for soldiers to be good at this skill."
The military has long worked to prepare troops for the deafening sounds of combat, with current training ranging from detonating actual explosives in bombing ranges to relatively inexpensive video gaming facilities.
The audio battlefield has its roots in work done at the Army Research Laboratory's Environment for Auditory Research, a facility built in Maryland to study how helmets and other equipment affect troops' perception of sound. Tom Letowski, a senior researcher at the EAR facility, and his co-workers also see promise in the Missouri S&T research. Other researchers are having good luck with headsets that adjust the sounds a user hears by detecting head movements.
Training in the immersive audio environment is an altogether different experience from watching a movie in the typical theater. All but a handful of theaters rely on the audience facing forward to create the visceral effect that something is happening to the rear or off to the side.
In training, troops are moving around so that system doesn't work as well. That's why Missouri S&T is trying to take it a step further by developing a surrounding setup.
For the past year, university researchers have been setting up their audio battlefield in an 18-foot by 36-foot warehouse. They can focus noise on a specific spot with three-speaker clusters scattered around inside. By activating different trios, researchers can make the sound move, giving the impression that a tank is approaching or a helicopter is flying low overhead.
Although none of the systems could ever match what combat troops experience, the research and training helps, Bennett said.
"Everyone in combat is afraid," he said. "Training people and exposing them helps negate the fog of battle."