Thanks for your kind words. Yes I wanted a "no compromise" loudspeaker just to see what is possible, especially for low frequency capabilities.
I think you are right about dipole / OB woofers, although I'm a bit afraid about sensitivity and maximum output. But maybe I will just give it a try, I think it's nice to not have cabinet coloration.
I added frequency response images (brown line is freq. response) together with distortion graphs. The first picture is measured at listening position (microphone about 3 meters from the loudspeaker), but unfortunately only at about 70 dB output and with an external equalizer.
After that I did several new measurements at 1 meter distance and higher output (picture #2 and #3), without external equalizer. There is some heavy distortion below 200 Hz and I think this is caused by undamped resonance: when I attach a damping screen at the back stator this distortion is much lower. I'm using a UMIK-1 microphone so I have no idea about distortion of this microphone, so these graphs have to be taken with a grain of salt.