There are any number of “concept” weapons in developmant out there that use sound or some variation of air pressure for effect. Most are simply demonstrations of “Gee Wiz” scientific odditites, but one or two have potential to actually be useful, in limited circumstances.
The problem with using sound as a weapon is that air is a crappy medium for transfering energy.
There are two concepts that currently look somewhat promising, although they have a long way to go before becoming practical, and even then will only be useful in very limited conditions:
A controlled, directed vortex device, which basically creates a high-subsonic ‘smoke ring’, which can apply a fair bit of force over short ranges, and might be useful in hostage or crowd-control situations.
A combination high-frequency - low frequency device that can make you puke or crap yourself. This works by using rapid-fire detonations (Gasoline or Natural Gas) in the chamber of a directional device, which produces a fairly well-directed beam of high frequency sound. You take two of these devices, separated by 10 or 15 feet, and aim them at the same target. Where the two beams of sound intersect, they produce an Ultra Low Beat Frequency the intersection, where they heterodyne. If a person happens to occupy that intersection, the ULF sound may cause nausea or uncontrolled defecation. Or maybe not. If it works at all, this system allows fairly tight control over the area of effect, allowing rather precise targetting. Wouldn’t that be a politico’s dream? He’s on stage, speechifying, when a heckler starts harrassing him from the crowd. What to do? No problem! The security team leader just takes aim, and Blammo! The heckler craps himself in public, while all around him, no one else is affected. Problem solved!
Just call me cynical
The second system looks like it might have more real-world use, but is still quite limited in application and range.