I'm converting my 1x10 mini slant cab to use round cab using a Keller drum shell. I'm not sure on how deep to cut the shell to at the moment - it will be 6-12" tall (and 12" diameter). The slant cab was "OK". It was my first build since I did 2x18 subs 35 years ago. I should not have just used left-over 3/4 Cherry ply for one thing (normally I fabricate with metal/fiberglass). At 6" tall the volume is 580cu.in. It will be ported with a 4" hole on the underside and then the gap between the floor will be a tapered port. With 1" tall feet the underside taper port starts at roughly the same area as the 4" hole = 12sq.in and increases to the outside of the 12" diameter = 37sq.in. Will be fun to play with - I can make the feet height variable to tune the port. Might even try aperiodic with a restriction in the 4" hole. I've given up trying to model the tapered port using Helmholtz - so trial and error from here on out. My one fear is that the round wall is equidistant from the driver (given they're concentric). I have room to offset it a bit (10" driver in a 11.5" round baffle) but that might look like a mistake or poor workmanship... Maybe it's not a concern. I'll post back as I proceed.