I've actually been trying to figure a way to mount a sub in the cross sections of the xb frame under the driver seat. If you get a half way decent sub set in that frame real good it should put out some pretty powerful sound. Sound doesn't all come from the speakers, a good majority of the sound and sound quality comes from the sound enclosure and how the cone is mounted. You gotta think, sound is vibrations, vibrations travel better through solid objects, the stronger the enclosure the bigger the sound. So naturally the strongest point on the bike would be the massive xb frame.