A bit more information on the use of the hypersonic soundbeam (LRAD) in the military.
“LRAD (Long Range Acoustic Device) has been quietly deployed to Iraq. And there the story gets a little strange. LRAD is basically a focused beam of sound. Originally, it was designed to emit a very loud sound. Anyone whose head was touched by this beam, heard a painfully loud sound. Anyone standing next to them heard nothing. But those hit by the beam promptly fled, or fell to the ground in pain. Permanent hearing loss is possible if the beam is kept on a person for several seconds, but given the effect the sound usually has on people (they move, quickly), it is unlikely to happen. LRAD works. It was recently used off Somalia, by a cruise ship, to repel pirates. Some U.S. Navy ships also carry it, but not just to repel attacking suicide bombers, or whatever. No, the system was sold to the navy for a much gentler application. LRAD can also broadcast speech for up to 300 meters. The navy planned to use LRAD to warn ships to get out of the way. This was needed in places like the crowded coastal waters of the northern Persian Gulf, where the navy patrols. Many small fishing and cargo boats ply these waters, and it’s often hard to get the attention of the crews. With LRAD, you just aim it at a member of the crew, and have an interpreter “speak” to the sailor. It was noted that the guy on the receiving end was sometimes terrified, even after he realized it was that large American destroyer that was talking to him. This apparently gave the army guys some ideas, for there are now rumors in Iraq of a devilish American weapon that makes people believe they are hearing voices in their heads.”