@kazap: I will try that soon and report back!
I did some listening tests and measurement last week but didn't manage to make it sound good enough to be satisfied: the sound had more punch in the bass, but when switching the same esl with and without OB woofer, using several different filters with x-overs of 150-300 Hz, the conclusion was that the extra puch welcome for some recordings and the best sounding of all previous non OB attempts. But mid-bass sound quality was audibly lower when using the OB woofer compared to my esl in "full range" (no OB woofer) mode. I used only the left channel for testing, with and without OB woofer.
So tonight I made some measurements again, starting from zero. I hope you can help me finding some posibble errors / mistakes I might have made.
My idea was to first put the mic very close to the woofer, 3 cms, and measure it's response without any filtering:
This seems similar in response to the simulation from Edge in the previous post. I decided to add two notch filters to take care of the peak at 300 Hz and the dip at 180 Hz:
first notch at 180Hz, 3dB, Q=4
second notch at 300 Hz, -3dB, Q=6
Result (mic still at 3 cm in front of woofer):
After that I decided to correct the -6 dB/oct dipole roll-off by adding two low shelving filters:
first low shelving filter at 100Hz, 7dB, Q=0.8
second low shelving filter at 200Hz, 7dB, Q=0.8
After that I measured again at 3cm distance:
this looks like a +6dB/oct slope starting at 300 Hz and stopping at 55 Hz. I added a high pass filter at (only) 35 Hz, 48dB/oct LR, to prevent too large excursions (I constantly check cone excursions but they never make large excursions during my tests using a low power amplifier):
After this measurement I put the microphone close to the sofa / listening position, about 4 meters awai from the woofer and measured again, first with all filters active:
I didn't expect the boost between 100 - 150 Hz. Is this due to an error / mistake? I made another measurement without all parametric equalizer filters, only the high pass filter, again at 4 meters:
So my first question is: did I made a mistake as the response at 4 meters looks very rough?