However, the army has recently been taking the same idea into account for a new(ish) type of nonlethal weapon. A long range acoustic device (LRAD) is used to direct infrasonic waves to a specific area and is capable of causing hearing damage from hundreds of feet away with no damage to the person standing behind the device operating it. An LRAD was even used back in 2005 to deter pirates from attacking a cruise ship, the Seaborn Spirit (if you want to learn more about that particular incident, that link is to the BBC story).
Unlike the speakers in your car, which use one giant speaker to move back and forth and produce sound, an LRAD works by moving thousands of teeny tiny little cells (like mini speakers) at a time. This winds up being much more effective as all of the small waves stack together to make a huge amplitude sound wave.
If you'd like to learn some more about how an LRAD works, this how stuff works article has some great visuals and explanations: How LRAD Works