I have a fire truck horn installed on Deerslayer and witesses say it's unparalleled in volume. However it's not an easy install - though the air system is nice for other reasons, like air shocks and filling tires. The air tank is under the swingarm - not compatible with belly tanks.
So for now I installed a Wolo on Jade, which has a belly tank now. And designed and put in production a permanent and lightweight, easy to install lift adapter which is compatible with all known aftermarket accessories that occupy the space under the swingarm, including belly tanks and BigBF's quad horn. Works with or without the belly tank.
Not too expensive, at $58, and in stock. Gave away a couple of them at Inzane. Drop me an email, PM, or call... Horseapple.com
http://www.valkyrieforum.com/bbs/index.php/topic,84220.0.html