Tomthiel wrote:
"Just a thought. I suggest running the 3.5s wide open with no EQ. I remember the bass loading as critically damped, so it should approximate 12dB / octave. (But that's old memory) If you can match that rollout with a sub, the sub HF will operate in the directionality range, so 2 subs is better than 1. I for one am most in your progress."
Now we have here a subject very dear to my heart and experience. Both my Thiel O3a and CS3.5 had equalizers. I found the O3a to sound much better with a subwoofer crossed over EXACTLY to the same curve as the EQ, with no filter to the main speakers at all
The CS3.5's equalizer was a gigantic improvement, which I found to sound just as good as no eq at all. Never-the-less, there is the original Stereophile test still on the internet, which shows its EQ curve. Take out the equalizer, add one or two subwoofers, adjust their crossover frequency and slope to match that curve, and run the main Theils with no filter at all. This purist approach works and sounds like a charm. The 10" woofers and main power amp are no longer taxed, so theoretically, distortion should be much less, and power handling much better.