I've had my CLS IIz for 16 years (started out as CLS II) and I've had 3 different bass augmentation systems with them: Wilson Puppy 2 (excellent), Kinergetics SW-800 towers (awful) and now a single ML Depth (the best!)
Stacking two pairs of panels vertically is a ridiculous idea for the II, IIa, or IIz panels because they radiate different frequencies at the middle (mid-range), top and bottom (highs) and of course bass along the inner and outer edges - so you can see by stacking a pair, you'd have a "super-high frequency panel in the middle (vertically), a midrange radiator above and below that, and a single high frequency radiator at the very top and very bottom -- PRODUCING AN UNCONTROLLABLE PATTERN OF FREQUENCY CANCELLATION AND REINFORCEMENT!!!
Now, the ORIGINAL (CLS) panels MIGHT work becase they are evenly divided (and only) vertically, and not side to side (no bass sections on each edge) but to me, it's a total EXERCISE IN FUTILITY, and as someone else pointed out, won't extend the bass any lower -- you'll just get more output at 80 Hz (which is where the CLS starts its rolloff to bass oblivion!)
If you want the ultimate great sounding CLS system, look at mine. The first EXCELLENT improvement I made to them in 16 years (and LONG OVERDUE) was to finally put them up on Sound Anchor stands. The joy of hearing what they could really sound like was overwhelming. Imagine, even better transients! (because of the rock-solid panel bracing provided by the stands.) And cleaner bass (what bass there is) because of eliminating the floor boundary, and wider sweet spot -- just an amazing transformation - I almost forgot to be angry for not trying (even concrete blocks for God's sake) sooner.
Then there's the bass issue. If you just let the CLS's bass response decay naturally -- i.e. run them full range with no hi-pass filter, then all you need from a sub is to bring it in at 35 to 45 Hz (depending on the source material) ant a gentle 6dB/octave slope. The ML Depth with its omnidirectional radiating pattern, and its 3 very lightweight long throw 8' drivers is so FAST, that you have NO IDEA the bass isn't coming from the panels themselves. Just set one sub smack in the middle, set the phase angle to 90 degrees (to reinforce the effective phase of the dipole panels,) and you're all done.
Less is more gents. Those panels were not designed to be part of a line array. Just get 'em up off the floor, add just a dash of the fastest little non-directional sub on the planet, and gloat!!
BTW, a brand new pair of SA CLS stands from Larry at High-End palace in Miami, shipped, is only $500, and a used Depth in good condition is $1300. Plus $100 to $400 for a pair of RCA ICs from preamp to sub and you've given a whole new life to an already classic speaker system for what? $2000? Do it!
PS: Look at my system for before and after pics.
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