Austin has several large (chaotic) monthly rides, and one time my friend rigged his speaker system up to his bike. Sufjan Stevens blared the entire way there and back. Not the safest setup, but they were all pretty baked at the time, if you know what I mean.

He was one-upped wattage-wise, though, by a guy that strapped a speaker hooked up to a car-battery powered amplifier onto his back rack.