If you prefer a better tone and a little more sound without the big trumpets or the other problems folks have mentioned, get a high/low horn set meant for automotive use and either mount one horn in the stock location and the other in the fairing, or just mount both in the fairing. Harley used to sell a kit to add a second horn in the fairing on the batwing bikes, but it's no longer offered. It wouldn't take much to fabricate a simple bracket and run a couple wires to do it yourself though.
BTW, unless something has changed in the past few years that I don't know about, RIVCO makes good stuff. Check the link smkblwr posted.
Jerry