Thanks Nathan & all.
The Forsman VSS has a similar design to my sub, but the K-tube concept is properly attributed to snkby. He turned me me on to the Forsman site which I studied, but I can't translate Norwiegen nor are Norway's patents available on-line. I studied snkby's shape and designed the sub. Due to the size, I had to develope alternate construction techniques.
Anyway, the basic shape of the sub is an h-baffle with inward curving wings that create a bit of load. I suspect the loading is akin to horn loading given the eliptical opening each driver sees (a 2-D horn), but I have no idea how to determine that. As an H-baffle, I get an effective 2 meter wide baffle in less than a sq. meter of floorspace. Very little eq is needed and the single sub pounds out relatively high SPLs of solid bass.
The offset of the drivers combined with the eliptical profiles virtually eliminates the normal dipole bump. Forsman claims that the quasi-horn loading makes the transients 40% faster than with an unloaded OB. He might be right about that.
Form follows function.
My lexan baffles play solidly down to about 160 Hz, and have usable output down to 80 Hz. The bass they provide is not deep, but is very articulate and has excellent tone. I have the sub crossed over with a 2nd order lowpass at around 80 Hz. This seems to fill out the bottom and provide a bit more heft the the lexan's upper bass, which is not a bad thing. I've considered high-passing the lexan baffles to provide for more SPL, but unfiltered they blend nicely with the sub so that's the way they'll stay (for now).
Ya gotta know I love bass if I would go to this effort just to strengthen the lower two octives!
Overall the speaker system sounds very nice. Certainly more balanced than my old Newforms. Large soundstage and great depth. Nice, but not yet great. These are all very much works in progress, and will improve as I learn more and apply what I've learned. Can the sub fly? You should see they way the wings flap as a frequency sweep drops down to 30 Hz and below! This can be solved with some internal bracing. I had left the inside of the wings unfinished figuring I'd need to make some adaptations after I assembled and tested the main pieces. And there's always a new crossover topology to try with the lexan baffles.
More work, not enough time. And the speakers are quite pleasant to listen to as is...
