Mini Beast here. Its cover is devoid of style, but it's no uglier than the cowbell and is plenty loud.

 

http://www.bjspecialties.com/airhorns.html I had BJ's dual trumpets installed at Wildwood Bike week a few two years ago. I've had no problems at all. 127 decipals loud! Chrome plated brass. Great horns!

 

Bear with me guys. My bike is having some upgrades done to it, it's still under warrenty. As soon as I get it home, I'll take some pictures if the bracket and horn setup. I should have taken the pictures last spring when I installed them. Dan

 

These are not air horns, but they are very LOUD. They are made by FIAMM and sold by most auto parts stores. I bought mine at Advance Auto. I know NAPA has them too. I paid $16. They are a direct bolt on, that fits under the cowbell.

http://www.fiammamerica.com/Product.asp?ProductID=156

 

Went to NAPA and picked up their BK 7301056. It is made for them by FIAMM. Made in USA. Also known as the Freeway Blaster.

$16

130 db at 4"

Fits under the stock Harley cowbell and requires no changes to wiring.

Works for me.

 

here's one idea for that mounting: http://www.doofclenasmc.com/8-Ball/Air_Horn.html