I installed a Stebel airhorn, fit right behind the cowbell, the compressor is mounted under the seat.. can't even tell it's there. and it's loud.

 

I have a Stebel too, very loud. I would also recommend this wiring harness for a really simple install.
http://www.easternbeaver.com/Main/Pr...horn_kits.html

 

Air horns... none louder than BJ's http://www.bjspecialties.com/airhorns.html

 

I had the HD Air Horn put on as one of the many extras and so far, I have had 3 times to use the air horn. Each time I have had to use it, the intended recipient was definitely startled into reality and either didn't finish making the move they were going to make, or stopped short of making my life stupid (again).

For me, the HD air horn is plenty loud. If I wanted to go louder, I'd probably look to Howards Horns.

 

The look is not for everyone, but they have saved my life.

 

+1 to the Mini Beast! I love Mine...definitely gets the attention of people when needed!

Ride Safe, Mike