Look forward to hearing more about this one Duke!
And most importantly: Listening impressions!!!
Typical bandwidth is 30 Hz to 20 kHz (-3 dB), in-room. This assumes some boundary reinforcement, but not a great deal. In a large room and/or where boundary reinforcement is scarce, the -3 dB point moves up closer to 35 Hz. With generous boundary reinforcement and/or with a low-damping-factor tube amp, and re-tuning the enclosure accordingly, we should get down into the mid-to-lower 20's (without boom).
Crossover point is about 1.4 kHz.
The 2.83-volt sensitivity is about 90 dB, which means that it'll be comparable in loudness to a 90 dB, 8 ohm speaker, when driven by a solid state amp. I won't know for sure what the impedance curve looks like until the final tweaking is done, but my guess is that the system impedance will probably be a little higher than 8 ohms. It will definitely be tube-amp-friendly, but not SET friendly. (A SET-friendly system is also in the works.)
Note that I base my efficiency and voltage sensitivity claims on the woofer's T/S parameters, which is a fairly conservative yardstick. I once had an amplifier manufacturer compare a set of my speakers side-by-side with a competitors' which were 8 dB more efficient "on paper", and he said they behaved as if they were the same efficiency.
I do most of my tweaking in mono because stereo imaging can be distracting from the task at hand. Then the final fine-tuning is done in stereo, and since you're looking at the only two such woofers in the US, I haven't been able to do that yet. The US importer should be getting some within the next several weeks, at which point I'll be able to get a second pair and finish the fine-tuning.