Has anyone tried double CLS

I had posed this question before because I had two pair of CLS11Z speakers in a Home theatre set up that I wanted to find a way to stack.I had just been feeling a loss of music after I sold my stacked pair of esl 57, and was curious about stacking the CLS. Would the bass improve as much as it did when the Quads were stacked?The similarity between the two speakers was that each speaker was bass shy and that attempts at sub-woofing never really were sucessful even after trying the Depth.So after seeing coverage of the RMAF and of the Kimber/Soundlab set up I decided that if they could double up the Soundlabs side by side,why couldn't the CLS be run that way?I was also bolstered by the fact that when my friend Tony went from three to four panels per side the sound from his Acoustats really improved.It is a shame that Martin Logan gave up on the CLS and went the hybrid route,because all they needed to do was increase the panel size.If Mr Saunders can get his hands on a couple of pair of CLS and wires them to a good amp in series he will hear that a lot of problems with the original CLS disappear.Maybe it will even change his priorities,so that great uncompromised sound and not floor space rules.


Its interesting to talk about the CLS in a stacked configuration to get better bass. I do not believe this will work due to the design. From what I can remember the best configuration for the CLS I had heard was from the designer who produced the American Hybrid phono stage.

He used a tube amp in place of the CLS's own transformer/power supply. This approach borrowed from the old Acoustat designs, a direct drive amplifier configuration. The efficiency was better and CLS played with High SPL in the bass. I was in shock.
I'd be more curious to hear them back to back.
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.
You guys are all talking unproven nonsense. I am reporting the facts as I actually am living with doubled CLS11Z at the moment.Not a flight of fancy.Until you hear or try this you are just speculators.Now to get back to the real facts and truthful description of what is happening with double CLS.To begin with there are no cone speaker matches for any Stat that do any more than add disconnected bass.This is where things can really get nasty.Way back when, Harry Person substituted the Hartley cone subs for the panel Magnepan Tympanis,he got more realism and a better match to the speed of the stacked Quads.I used to own single esl 57, heard a stacked pair in Montreal, realized what I was missing and found another pair ,made the stands and away you go.It is all about the radiating area of the speaker.Anyone out there remember the Acoustat with the servo tube amps? The more panels you added,( up to 6 per side per amp)the easier the amp ran the more bass you got and the more effortless sound,the only limiting factor was room size. These are not stacked arrays,but multiple panels, side by side.This is what Kimber did at RMAF, they are not stacked,the speakers are 8 feet tall un stacked.
I have been at this game for over 30 years and I have owned the stacked 57, single 63, Acoustat 3 panel(unamplified)ML sequel and single CLS, CLS with Depth sub and now double CLS.I can tell you from real exposure to all these combinations, that the sound I have now is light years ahead of anything I have owned.Forget the subs and stands,for what you are spending you could have bought an extra pair of CLs and then know what I am talking about.
No Rube Goldberg for me, sorry Lacee. My system does EVERYTHING just the way it is. And besides, I don't have 20 ft ceilings ;--)
Everytime you mention it, I consider what you have done. Pelase send me a photo or two of your speaker setup. Offline is fine...maybe even better for me! duke@mesls.org

I am considering doing the same thing as you have, so please send a photo.

BTW, I get a 3dB to 5dB suckout from 160Hz to about 200Hz at my current listening position. Do you get that at all?
Well! Let us start then by saying the original Quad was stacked not for bass extension but to increase thier limited output which remains Quads Achilles heel.
Then vertical stacking of the Quads made sense. Theoretically you doubled the output. Moreover since the Quad beamed vertically by stacking them you created a line array of sort.
Neither of these is necessary with the CLS. Just ask my neighbors if the CLS has sufficient output.

While intuitvley you may think that having two speakers instead of one that say are 3db at 60 hz may improve your bass response. In fact you will just have 2 speakers that are 3db down at 60 hz.
No I have not tried that but it would be interesting to try if a person had two matched pairs.

Since the CLS panels are mirror imaged you would not want to stack them but put them side by side. One right channel with one left channel edge to edge (side to side).

I would put the narrow side of the panel side by side (to the inside of the stereo channel pair) so that they would physically be the center of the double pair.

Then what you would want to do since you would now have two power supplies per side is to wire them in series for the speaker connection from the power amp (amps).

The hot connector from one of the speaker terminals connected to the ground of the other speaker terminal on each power supply for that pair. A long jumper could be used for this purpose.

Then you would want to connect the speaker cable (from one channel of) the amp (amps) to the hot (red terminal) on one power supply and the ground of the speaker cable (from one channel of) the amp (amps) to the ground terminal on the other power supply.

This would raise the impedance of the CLS speaker PAIRS up to about 3 0HM’s and should make it fairly easy to drive for tube power amps or whatever you are using.

Both power supplies would of course need to be plugged into the wall for AC connection for each speaker pair.

I think that it would work but the only drawback is a wide room would be necessary to accommodate both stereo pairs.

If you are not familiar with series wiring here is a link that shows how it is done with raw drivers.


If you do try this report back and report the results.
Greg, allow them their fun. It will be a time consuming and expensive learning experience. And I'm charmed by their enthusiasm:
Since the CLS panels are mirror imaged you would not want to stack them but put them side by side. One right channel with one left channel edge to edge (side to side).
Good grief!
I must repeat, the double CLS are not stacked so you do not need ceilings any higher than you need for a single pair. The speakers are wired in series exactly as the gentleman has described and the load to your amp is not as severe as with one pair.You only need to find a used pair of CLS and 1 extra speaker wire per channel( I use 6 separate 3 foot wires)This is a very inexpensive,upgrade that anyone can perform. There is no external crossovers, no extra sub woofers and interconnects, no pain in the ass positioning of a sub to where it sounds best( like I have done trying to get The Depth to disappear)no soldering wire, replacing or upgrading internal parts or connectors,no power supply upgrades,no power cord upgrades.None of the things audiophiles spend small fortunes on trying to improve their sound.If you find a used pair in the $1000.00 range that is the least amount of money for the most improvement you will ever make to a single CLS system.No expensive time consuming learning experience here.The fun and the proof is in the pudding. And in putting together a double pair.I would feel grief to those who spend five times as much money and effort futzing around with power cables and speaker wire upgrades in a vain attempt to better the sound of their single pair.Good grief, don't knock what you don't know and have no hands on experience with.Do you still think that if man was meant to fly he would have been born with wings?
Sorry Lacee, I would never do that. The CLS (Curvilinear Line Source) is designed to provide a single, uniform, wavefront. Good dispersion, not generally a feature of flat electrostatic panels, is achieved using the (single line) curved driver. (Soundlab achieves a similar result using many smaller flat drivers in a curved array.)

Placing two (curved) lines side by side will create addition and subtraction nodes resulting from combining the two offset wavefronts, and will produce reinforcement and/or subtraction nodes all the way out in to the listening space. This cannot possibly reproduce an accurate soundstage hologram, rather just a "wall of sound".

Nor will adding more panels change (extend) the bass response lower than that of a single panel as Greg points out. If you are not getting adequate performance because the amp is having trouble driving an admittedly difficult load, then get a different amp, or perhaps try using an autoformer like the one made by Paul Speltz.

This subject has been covered ad nauseum for years. If you want confirmation of the points I've made, I suggest you speak with Jim Power or one of the other senior technical people at Martin Logan. It's a dead issue for me ;--)

As for stacking the old Quad 57s, that's an entirely different matter. The (individual) electrostatic drivers (1 bass in the middle 3 HF each side) run vertically top to bottom. So stacking 2 of the them still results in a uniform wavefront, twice as strong. A good thing too because 57s didn't play very loud without arcing and burning up! Again, this arrangement didn't increase their upper or lower frequency response specifications, and when Mark Levinson designed his "Super Quad" system, it consisted of subwoofer and super-tweeter units as well.
The more panels, the more radiating area the more sound.Is this too hard to comprehend?The stacked Quads didn't magically have any different bass than they had before.They did not go lower.The bass just radiated into the room more so that you did not feel the need to augment it in any way.This is what I have found by doubling up on the CLS.My claim is that there is more bass, not deeper or different sounding bass.Just more bass power ,if that is easier to understand.The bass no longer feels like the poor country cousin.There is more bass loading the room.Would you have us believe that an Acoustat 2(2 panels per side) has the same bass energy as an Acoustat 4( 4 panels per side)?Yet this is your argument that an extra set of CLS will make no difference. The basic principal involved is air movement.More panels more air movement.More sound in the room is generated by 4 CLS as there is by 2.This is like saying that the panel sound from a pair of Aerius is no different than the sound generated from the Summit panels. It just isn't so in the real world, or in my listening. Larger panels, more sound.Four panels equates to more sound,and there are no problems.Addition and subtraction nodes?You should get some hands on experience and not postulate wild assumptions.What about the nodes created trying to pair up woofers and stat panels?Why do you think that most stacked or doubled up Quads systems don't have subs? I am sure there were a lot of people who said it was blasphemy and that it just wouldn't work as well.In any event,this set up works for me and it will for those who try it.
I think you don't know much about the Quad ESL.There is one treble panel in the centre of each ESL 57,flanked by a bass panel to either side. Three panels per speaker only.
So when you stack you get 2 treble panels and four bass panels per stack.You get more of the bass into the room this way and the result is you do not feel the need to add on subwoofers,neither do you need a super tweeter.When you add the subs and super tweeters you change the sound of the Quads and move into territory that is frought with problems,beaming tweeters, booming bass.Talk about room node problems. Doubling up on Quads or doubling up on CLS is not meant to change anything about the sound of either speaker, and I have never claimed it would.It is all about delivering more of the sound you liked about the speaker in the first place.
There is a difference between frequency response, dynamiccs loudness and volume. Frequency reponse will not be corrected by increasing loudness and or volume.

Many speakers bump up the bass to mask thier lack of low frequency extension. While your existing bass may get louder so does everytihng else. You get more volume but the same frequency curve.


You hit it right! That is what I heard. The volume went up 5 fold on the CLS 1. There was no added extension in the bass or in the highs, not possible with this design. The point here is the CLS and any speaker for that matter can be "tweaked" to load a room so there is the "appearance" of more bass or dynamics using tweaks like anchor stands or direct drive amplification or just using a "fast" sub.

By the way in my old set up I used a subwoofer comprised of 2x10" paper cones and 1 passive 12" cone driver. Clever mechanical roll offs, which helped with the integration in that 100hz area.

Fun times with that speaker, the most transparent midrange but not the sweetest, that honor goes to the Stax 81's.
I loved my eight years with the CLSIIZ's. I had 'em on Arcici stands and in the last three years, augmented them with a REL Stadium II sub. But I am very dubious that any amount of reenforcement in the bass can aleviate what I considered a major shortcoming: the lack of weight in the lower mids that tended to make instumentalists sound a bit disembodied.

Don't get me wrong, what the CLS does well, it does incredibly well and box speakers cannot match it for transparency and soundstage. But it does not have the instrumental weight and timbre of a good dynamic speaker.

At least, IMO.

"...it does not have the instrumental weight and timbre of a good dynamic speaker."

I have not heard a lot of the contenders but at this point the only speaker I would trade for cls is the von schwiekert vr 9se. At $70k it is not likley in this lifetime. I have neither the means nor the inclination.
With the right amplification the CLS has considerable weight and authority. It is even more so when those panels are relieved of thier duties at around 100hz. The panels however will eventually "bottom out".
Truth be told I have achieved about 80% of the CLS potential. I have said before the CLS will benefit form the best components availble today.
Lacee I am not so sure I am in agreement with you. To get louder sound you need more amplifcation which you are not getting running them in series. Neils claims about cancellation are valid. If you position them to avoid cancellation then you run into phase problems. Having two pair of CLS in my room is an extremley attractive proposition for me. Just not sure it makes sense.
To quote from issue 67 of TAS"a pair of(Classe) DR 8's sends 350 watts into 8 ohms,and 525 into 4 ohms"So I think my Classe DR 8's run in balanced mono are quite up to the task of driving my CLS even as a single run. Now when the amp sees the series set up the power output would drop some, but the increased wave launch from the extra panels makes watts a moote point and the amp sees an even more friendly speaker impedence.Forget the Speltz auto formers,not needed.I hate to beat this thing to death but I am the guy who lived with these without the sub, then with the Depth and now doubled up pair.The difference is amazing and the 80% acceptance factor goes up another 10% at least.The only time this makes sense is when you do it. Then you will insert your foot in your nether regions for not doing this before,and for trying all the "audiophile approved"expensive fixes.I am stating, you will never get a cone sub to mate with a stat.The closest the Quad 63 got was the Gradient dipole and it was not perfection.The Depth is a good sub ,I have one remember,but it is not a panacea for this or any other stat.Stats need planar bass panels to keep the music coherent.This is much more serious yet it appears not to mater to the naysayers here,who have not tried or heard a double pair,and have had little exposure to very many stats as is evident from the threads.There are NO Cancellation or Phase problems!The speakers disappear,it is a seamless integration,coherent,more music occupies the room, yet they aren't louder.More bass is present- not louder, deeper,out of phase,added on bass, but the true panel bass of a single CLS is increased. There is the same bass sound, but more of the room is filled by it so you don't notice that the speaker is bass shy.I have run out of ways to explain the benefits of a double CLS set up,and if I were wealthy enough I would fly the doubters here for a listen, because you have to hear the improvement for yourselves.
...and you have the last word!