From Air Raid Sirens site: Truck equipped with a lot of loud horns
Mark Frauenfelder
After BB reader Mark perused the sounds and movies from the fun-loving folks at the delightful www.airraidsirens.com website, he came across a picture of a truck loaded with many loud horns installed in the bed. Wouldn't it be wonderful to drive up alongside a pimplyfaced kid slouched in the seat of one of those cars that make thumpa thumpa sounds from its powerful bass speakers and give him a blast from these monsters? Link(thanks, Mark!)
Reader comment: Jeff Hirsch says: "Sure, the horn truck is cool, but you can't talk about horn/siren laden cars without discussing Hyler Bracey's 'The Big Horn.' An amazing art car covered in historical bells and whistles.
http://www.big-horn.com/ has pictures, details, and a fascinating history of not only the vehicle, but the different bells, pipes, etc that have gone into it.