Hello ro7939,
Thanks for your post!
Okay, at this point you have more experience with that filter than I do! I'm not using anything quite like it in my own speakers, and I'm very glad to hear that it's offering an improvement even with your solid state amplifier.
For those wondering what we are talking about, high output impedance (low damping factor) amplifiers tend to deliver more power into a high impedance load than into a low impedance load, which is just the opposite of a solid state amp. Ro7939's speaker was "voiced" on a solid state amp, and has a nominal 8-ohm impedance but the impedance peaks up around 20 ohms in the crossover region. Assuming an output level equal to 1 watt into 8 ohms, a solid state amp will deliver less than 1/2 watt into that impedance peak but the Atma-Sphere OTL amp will deliver maybe 1.5 watts into that same impedance peak. Remember that the speaker was voiced on a solid state amp - meaning that the frequency response curve is as intended with only 1/2 watt going into the impedance peak. So with the OTL amp's increased power output into the impedance peak, we have maybe 4 or 5 dB too much energy in that region - giving the speaker a forward sound. The filter I made for RLC smooths the impedance in that region so that the speaker presents something much closer to a smooth 8-ohm load across the spectrum - well except for the bass impedance peaks, but that's another story.
I don't think I could duplicate the filter for speakers having more than one impedance peak unless I could take measurements as I went along, because that's too many things interacting for me to predict the outcome. And even with your filter, I think I included a couple of different resistors because I wasn't sure which would work best.
As for the polarity of the filter, again ro7939 you are in new territory for me. In theory, I don't think the polarity should make a difference... but then either the theory or my understanding of it may well be incomplete.
I would expect only a minor improvement from "burn in" of the elements in the filter, but some improvement is possible.
Duke