Honrmassive is a 2000 watt horn sound system that can "project 'content'" up to a kilometer. It's been seen heard at Burning Man, the Coachella Valley Music Festival, and a few other big blow-outs. From Hornmassive.com:
HORNMASSIVE (2004) (Matt Hope) is a 2 Ton (4500 Lbs US), 3.5 M by 3.1 M by 4 M mobile 2000 watt steel and aluminuim horn sound system, all powered from a commercial 12" speaker driver. It functions as a mobile audio input station… (and is) designed to be the ultimate monophonic sound projector intended to catalyze social activities in multiple settings.