If you look up car horns on wikipedia, you'll find an explanation of how the horn part of it is critical to really conducting the audio energy to the air. The vibrating surface by itself is not very efficient in this regard, the horn is required to really get a large volume of air moving, rather than just super-compressing air in a small volume and turning a lot of the energy into waste heat. Sometimes there's just no substitute for something that's large and substantial.
__________________
Work: the 8 hours that separates bike rides.