October 23rd. "The crossover board just arrived and so did new sample face plates. Those for the Model 3, 3SE and 4 are 10mm, those for the Model 1 and 2 6mm thick. Now I just have to cut the tinted windows and after that it's only a few minutes of assembly. It's a far more expensive solution than before but it saves me a few hours and a lot of extra work.
"The crossover polypropylene caps are measured, sorted and paired to within 0.5%. The FET-input op amps are low-noise OPA1652 smd types which are best for active filters. All the new premium op amps come in surface-mount packaging only. I'm against funny rolling with socketed parts where golden ears add some additional oscillation, mismatch or new kinds of distortion with a wrong type or sub-optimal op amp to get their 'right' sound.
"I'll soon have the frequency response and FFT measurements to see what we will hear."
October 25th. "For your planned usage, I didn't implement the optional stereo/mono mixer for a monaural sub, extral low-pass shelving and standalone power supply. But here are the frequency response and distortion spectra. The crossover works fine, distortion is around 0.001 – 0.002%, about the same as my generator's own distortion. The frequency response is exactly as it should be, -6dB at 40Hz, 24dB/octave. It shouldn't have any self sound, just the effects of steep attenuation."
Here are the crossover response curves:
Now the filtered monitors would start to roll off gently at 100Hz, be down -6dB/40Hz, then -24dB/20Hz. Perfect.