G-20 Protest Sept 24, 2009

Amid blasts from a Long Range Acoustic Device, designed to break up crowds with piercing noise, demonstrators ducked down a side street in what would become a day-long chase

Sonic weapons have been used by the US military overseas, notably against Somali pirates and Iraqi insurgents but not until now on its own citizens.

I suspect the volume used was not high enough to cause permanent hearing damage damage for two reasons: (1) this was an area with a mixed residential and business area so there were others present besides the protesters and (2) this is a first use they are figuring out how high they can go.