Got M&K MX-150 THX for Maggies... feelings?

Panel speakers tend not to go very low (ie most Maggies and almost all stats) and therefore they have a natural bass roll-off when run full range. In other words, no need to use any high-pass filters with them to "relieve" them of bass duties.

So run the sub (and its amp -- internal or external) from another pair of preamp main outs (if your preamp has two pair) and set it 10 - 20 Hz below the spec'd low limit of your panel. Then slowly bring up its volume until you can just barely hear the additional low end.

If you're buying just one sub (an excellent solution with panels IMO) place it exactly between the speakers (L/R/F/B) and if it has a phase adjust, set it to 90 degrees.
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That article and M&K's test tones look to be a fantastic resource, Bob. Thank you so much for the response!

-Steve

P.S. One quick question... could placing the sub behind my left 1.6QR cause conflict with the sound radiating from the rear of the panel? There is a good amount of breathing room back there (more than 3'), but I'm not sure what the end result of that interaction would be.

Bob, I made it very clear that my remarks applied to panel speakers, which do not have increasing SPL in the bass and (for this reason) do not exhibit bass distortion since you can't have distortion where you have no response.

The bass response in (almost) all panel speakers (along with the SPL) tends to roll off smoothly starting between 40 and 80 Hz (depending on the speaker) at a slope similar to that found in a high pass crossover circuit anyway.

The object (again, with panels) is NOT to assign bass and mid-bass to two separate devices but rather to BLEND the outputs of the two devices as if they were part of a single enclosure/crossover system. Attenuating (sloping off) the sub starting at 10 to 20 Hz below where the panel initially begins ITS natural roll-off insures a nice flat response across the point where the two speakers' acoustic response overlaps, sort of a "natural" blending (ie in the air) of crossover slopes.

As for locating the sub, the dipole radiation pattern of panels produces sound waves between the front and back of the panel that are at approximately 90 degrees out of phase with the original signal (ie 0 degrees at the front, 180 degrees at the back, 90 degrees in between) so locating a single sub exactly between the speakers F/B/L/R, and adjusting it's phase (if you can) to 90 degrees, will make it virtually disappear and be indistinguishable from the panels.

Again, these comments apply to pure full-range dipole speakers (ie not hybrids with cone drivers as in many Martin Logan speakers.) Examples would be ML CLS's, Maggies, Quad 57's, etc. Soundlabs do qualify, but shouldn't need subs anyway ;--)

Some of your remarks DO apply to typical two or three way monitors or full-range box enclosure speakers; and I have certain other ideas about those applications. I'm quite familiar with M&K bass management system. I know Ken quite well (in fact I designed their logo back in 1970) but his recommendations apply (primarily) to multichannel systems with conventional speakers, LFE processing, etc. I still stand by my advice as to using subs with dipoles.
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Although most planar speakers aren't capable of the excursion necessary for low bass reproduction(and hence: roll off the bass)- It doesn't mean they aren't trying(not to mention the wasted wattage). The sound of your Maggies will benefit greatly if you use a GOOD high-pass filter(BEFORE your power amp). I've been actively bi-amping planars for the last 26 years, and have found they ALL sound cleaner/less strained/more dynamic with the bottom handled by another amp/sub system. The corner sub not only energizes the room and lays an excellent foundation for your music, but- the driver has much less work to do having the reinforcement of the room boundaries. The drawback is in the time domain. Three feet will add up to a lot of mS in delay. I'm using a TacT 2.2X which delays the mains to compensate(along with a multitude of other neat tricks).