Some of you requested that I keep you updated on progress with my new FRs. I started by using the system in its stock configuration, with passive crossover and using the interface boxes with their transformers for bass and for midrange. I biamplified with four channels of 250 watt ARC tube amplification using their 4-ohm taps. That actually works pretty well, but erring on sounding overly ripe in the bass. Impressive, but big-bottomed.
So then I skipped the bass transfomer and directly drove the ~1.8 ohm woofer panels from the tube amps. I tried both the 1-ohm taps and the 4-ohm taps (2-ohm taps not being available, unfortunately). Direct drive completely changes the bass character of these speakers, more than I imagined it would. Bulbousness gave way to tightness. Fatness became leanness. My first reaction was that I missed the bass sock. But I am still balancing the relative gain settings between bass and MR/TW using various familiar recordings. I think if I can find the right balance, direct drive will be preferable for its tighter control and (perhaps) better pitch definition in the lower registers. Interestingly there was relatively little difference in the sound whether I was direct driving with the 1-ohm taps or the 4-ohm taps. I have to readjust the gain balance each time I change them of course. Either tap seems unflappably capable of producing high amplitudes without distress. It will take me some time to decide which bass tap to use. Both have a two-to-one impedance mismatch (from a theoretical ideal) in opposite directions, but in practice they sound more alike than different. And both sound radically different than when using the interface transformer. So, how do you like your bass? You have choices with the FR.
I also tried driving the MR/TW with 1-ohm taps knowing that the tweeter dips to about 1-ohm on top. That set-up seemed more analytical and perhaps constrained. Depth seemed to diminish. I went back to the 4-ohm tap for the MR/TW path. Of course I used the interface box for the MR/TW in all cases because the MR’s brutal ~0.15-ohm resistance requires a transformer (for now anyway). I will spend some time with this direct drive bass configuration, using the 4-ohm taps for both bass and MR/TW. I will get familiar with it on many recordings before making other changes. In my experience it pays not to change too many variables too quickly. Nevertheless this configuration does play music beautifully.