Thanks Kevin. I spent some time working my conical midbass / upperbass horns yesterday, and they're really shaping up. I thought of a nice high-strength way to mount the driver cabinet to the cone. I attached "wings" near the throat that will attach to the driver cabinet. Now that's looking more like a rocket ship than a horn!
I'll post my build process (and calculations) in the next few weeks if anyone wants to try building multi-sided conical horns. I could see smaller (350Hz) compression driver conicals being way easier to build than the midbass horns. The larger ones are tough to assemble properly.
http://diyfirefly.blogspot.com