I had a Howard's, loud but a little high pitched for my taste. It was fun to put my hand over the air horn and make it wail. Do a search on Stebel. What you will find is Stebel makes the HD horn and several other aftermarket horns. So before you invest over $100 for the same horn and a fancy cover check out the guts.
You can buy a compact Stebel exactly like the HD version for about $25 -$50. It even comes with the relay which you MUST use. The biggest problem is mounting the damn thing. It's compact but it won't fit under the cowbell. If you have room, you can separate the horn from the compressor and hide the compressor. There is also one made by Wolo that looks exactly the same.
Try these:
http://www.twistedthrottle.com/trade/productview/2757
http://www.adventurersworkshop.com/M...e=STEBEL_HORNS
This one details how to wire and separate the horn from the compressor on a sport bike. Would be easy to hide either one under the cow bell.
http://www.sportbikes.net/forums/fz6...n-install.html
This will take you directly to the Stebel site where you can hear the sound.
http://www.stebel.it/stebel/index2007.htm
I really liked the compact truck horn but I heard they had problems with them. Very important to mount the compressor vertically.
Hope all that helps. In any case don't spend $100+ unless you just like to waste $