http://edition.cnn.com/2015/03/27/us/sound-fire-extinguisher/index.html
How long until we're putting out fires at the track with sound cannons instead of ultra-corrosive powders?
Edit: Also I'm surprised they released this video before they have even a provisional patent. Just using the video for reference, most of this system could be replicated before lunch in a good workshop, the tricky part may be figuring out the the best shape for the "barrel."
