Jon... I finally received a response from Mark Longley @ Sublime Acoustics!!! He has a 2-3 week back log at this time and I am going to order the K231 Stereo 3-Way Active Crossover from his company momentarily... but first... I need your answer to a very important discrepancy! In a past post/thread, you recommended these frequencies for the active XO: Sub xo @ 80 Hz/24dB Slope & Mid/High xo @ 300 Hz/24 dB Slope for the Monolith3's. HOWEVER, Mark @ Sublime Acoustics recommends: Sub xo @ 50 Hz/24dB Slope & Mid/High xo @ 120 Hz/24 dB Slope. I have no idea of Mark's actual reasoning, but this is HIS crossover. I also know you have a very extensive background/history with these speakers and putting them through various testing. Therefore, whose opinion should I accept? Or should I simply order the XO unit with 4 frequency modules (it comes from the factory with 2) to cover all four frequency recommendations (50, 80, 120, & 300 Hz/24dB Slope) and experiment with them??? Thanks!
Hi Mike, good to hear you two hooked up and that you can source a unit.
As for why I think Mark suggests his XO points is that he went and read the specs for a stock Monolith III
However, the measurements I've made on the bare Monolith panel showed that 120Hz is too low an XO point, as it was already several dB down relative to 300Hz. And since an XO is not a brick wall but a slope, you are asking the panel to still put out some serious sound at 80 to 90Hz, even with a 24dB slope.
One of the reasons I go with the higher XO point to the panel is to move it out of the worst of the dipole cancelation range. At 120Hz, there is significant cancelation from the rear wave on top of the already diminished output. So why bother pushing the panel when the output at the listening position will be down relative to the upper regions?
If the unit were to be converted to monopole operation (which I eventually plan to do to mine), then for sure, I would test at lower XO points but still above the output drop-off point.
The other reason for the 300Hz XO point is the power curve. At 75 or 85dB, sure the panel might have decent output below 300Hz, but at 100dB+, no way. Panel resonances build up and THD goes well over 1%.
So to have a consistent power curve (same frequency response at varying output levels), keeping the panel at 300Hz and above is what works best, at least per measurements and my experience.
This brings us to the recommendations for XO points.
I'll stick with my 300Hz @24dB/Octave for the panel high-pass.
The woofer to sub should be a bit higher than Mark recommends, as ESLs are typically placed in locations (multiple feet away from walls) that are not conducive to great low-end in-room output.
So I'd say 60Hz is the lowest I'd go, and 70 or 80Hz might be better. But some measurements of the current units in the locations you have them now might reveal room modes you might want to avoid. So if the current placement has a big null @70Hz at the ML (with no sub), then you definitely want to go higher than 80Hz for the XO to the sub.
So if you do not have a big null @70Hz, then I'd use that for the low-pass to the sub, high pass for the woofer.
Low pass for the woofer would be the same 300Hz as the HP for the panel.
Cheers.