I did say they were Kevlar-impregnated fiberglass, not Kevlar alone--huge difference. My EVX180Bs have Kevlar cones are are pretty rigid, but the Bassmaxx cones are like the hull of a boat in terms of stiffness. I can't stress enough, the point that it's the cleanest driver I've ever tested. Its THD performance is more akin to high end amplifier ratings than woofer ratings.
I know that the paper cone version of CGN's 1808 goes for $695. But that's not a Bassmaxx ZR18. I'm sure the Bassmaxx are a bit more, due to the Kevlar-impregnated fiberglass cones and custom suspension components. Also, the motor is a bit different, with a longer pole piece. Since I bought mine as demo models (prototypes, actually), I don't know what the same configuration would cost as new.
I too considered the Tumult, but was offput by the low efficiency, same as with the Acoupower driver. Although the latter LOOKS impressive, with it's huge heatsink around the magnet assembly.
To my knowlege, the Bassmaxx SPL sensitivity rating is in the bass range. It's sensitivity at 30Hz and below is higher than any other driver that I have auditioned. And the only driver I've tested that's totally free of audible THD. As a result, the room makes more audible noise than the driver, when the test frequency is below 20Hz.
Resonant Technologies makes a driver with a 54mm Xmax, but the sensitivity is so low that you'd need 6,000W of power into it to get what I get with 1500 into the Bassmaxx driver. And my cabinets were not designed expressly for the Bassmaxx. They were designed around a pair of Altec 3184s in 1982. I'm currently drafting a design for a much more suitable cabinet, with a port area that is equal to the sum of all the cones' area, for increased room coupling of port output. I'm going to be building a scaled-down convertable prototype with 6" drivers for testing the old and new designs via realworld response measurements.
It should be interesting to see what sort of gains can be achieved with a vent over 700 sq in over a long enough path to achieve the same tuning I get with a 96 sq in vent of shorter length.