I have all three varieties of the Orange isobaric cabs, the SP210, SP212, and SP410, and I reviewed the SP210 and SP212 (along with the original Terror Bass) back in Bass Gear Magazine issue #6.. Mine all have neo drivers, but I believe some of the earlier production cabs had ceramic drivers, which would make for exceptional weight in a small package. These things do have some very impressive qualities, and the ability to throw out gob tons of volume and low end heft for their size, but they are definitely limited in terms of higher frequency response (and they are tweeterless, to be clear). I didn't care for them a ton, initially, but when I learned to dial things in a bit more, I have been able to gig with them quite happily. Of course, this was in a context where I was going for a more "vintage" tone with a bit of grit/grind/dirt. They do that pretty well, but they don't do a very balanced, clear/clean tone, IME/IMHO. I actually really do like adding the SP410 on top of an OBC410, though (typically with an AD200 on top). It keeps the overall rig height at a more manageable level, but still delivers a massive wall of sound.
Euphonic Audio also played around with isobaric loaded cabs. I have an EA IL-110, which features a front-facing 10" driver, with an 8" feeding an isobaric transmission line. It is an impressive feat of engineering, but it adds bulk and weight, and in its final form, the VL-110 was able to match the low-end and overall output (with enough watts behind it), and was both lighter and smaller.
