I have a Fiamm Roadblaster mounted in this manner under the tank. It actually has a "horn" shape to it, I pointed that end out from under the front of the tank, just between the spark plug wires as the exit the coil.
Here's a picture of the horn:
It's louder than stock (but not by much), and with the open end pointing out it doesn't seem to be muffled too much.
http://www.aerostich.com/catalog/US/...n-p-17137.html
I bought mine at the local auto parts store for about $12-15.
