what causes CLS sway?

[zaphod]

partly for diversions from wedding planning, and partly from peaked curiosity, i'm toying with some designs for my own set of CLS stands.

to stop sway i'll use a brace from the base to the mid/top of the frame that will create a triangular support. this means that the frame will not sway relative to the bases

but will that stop sway relative to the floor/room? the electronics will sit on the bases of the stands (unattached from the CLS frames) to weigh down the frame, but is that enough to stop the whole thing (frame, base, electronics) from swaying as a unit?

i guess what i am wondering if CLS frame sway is due to flex in the frame or not. if it is, then bracing fixes things. if not, then bracing just means that more is swaying in addition to the frames.

 

[C.A.P]

ZAP , when I did my stands the rear brace was a MAJOR thought out design. Not only does it hold the panels rigid it stabilizes the image much better as there is very little resonance going on. They don't sway per say but they sure tend to vibrate without braces. This along with Neoprene foam tape in the wood V groov that the panel rests in was a HUGE improvement.

 

[User211]

Quad have latched onto the triangular bracing idea... kind of makes you wonder why ML didn't... it's fairly obvious. Good luck with it Zaphod! It takes a bit of nerve to physically mess with the speakers. Be VERY careful before you do ANYTHING

 

[MiTT]

When I began working on my stand project for the CLS (somewhat on the back burner right now because of demands at work), I had modeled the speaker in our Finite Element Analysis program (COSMOS). There is some amount of deflection in the upper panel portion of the speaker, but it was actually less than .030". The biggest contributor with regards to sway at the top of the speaker when you consider the whole assembly of the panel and the electronics enclosure, is actually the deflection of the sheet metal on the bottom of the electronic enclosure. The sheet metal is only about .062 thick and there is a mechanical grounding point smack dab in the middle of it at the bottom where the rear spike attaches. As this point is fixed, the base of the enclosure deflects. When you consider that the base is now the anchor of a moment arm that extends upwards 58", it's easy to understand how this deflection translates into significant sway at the top of the speaker. The important thing to remember is not to interpret this "sway" as actual "deflection" of the panel as the panel itsel is fairly rigid as already stated above.

There are two factors to consider when designing a good base for the CLS. (Edit - three actually, see comment about height below)

One is to either make that electronics box more rigid, or to remove it from the mechanical circuit altogether. This latter is what is done in both the Arcicci and Sound Anchor stands - as well as what CAP did with his great interpretation of the Arcicci design.

The second factor has to do with the removal of resonant vibration, and that is the function of the arms that you see in these designs. Even with the electronics box out of the equation you still need to deal with the resonant vibrations of a very large planar surface that, while somewhat rigid, is hardly inert. If it were truely inert it wouldn't function very well as a transducer, I mean it's really an incompatable set of requirements isn't it? We need the speaker to vibrate in order to generate sound, yet we need it to be rigid in order that it generate only those sounds that we want embodied in the music. Martin Logan did a pretty good job actually in their method of constraining the active portion of the speaker (the panel) in a nice rigid frame - it's both highly functional and very aesthetically pleasing; almost archetypal actually in a Jungian sense. But there is still resonant vibration within the frame and if you doubt it simply walk up to a pair of them while they are playing and touch the top bar of the frame. It may be very slight, but it is present and since it is present it makes a contribution to all of the other vibrations in the room. I've talked here before about my thoughts on spurious vibration. Vibration can be dealt with in two ways basically. You can change the resonant frequency of a vibration to ultra sonic or sub sonic levels or you can reduce it's amplitude. Either can be accomplished by means of either mass loading or mechanical grounding or both. The use of some sort of rigidly attached arm to the planar surface of the frame on the CLS serves both of these purposes, but the method of attachment may yield differing levels of effectiveness. I'm not quite ready to "spill the beans" on my proposed method yet - but hope to do so sometime in the fall when I can devote more time to it.


Edit - I forgot to mention height. As you design and build your stands you'll discover that the best height will position the vertical center of the elcetrostatic panel (not the overal speaker as the frame is asymetrical in this axis), at the center of your ears. The problem here is that people and listening chairs come in all sizes. In my opinion, given my stature and the listening chair I have in my room the Arcicci and Sound Anchor stands are a little too tall. Check out some of Neil's posts recently about putting some blocks under his listening chair to deal specifically with this issue. Take the time to experiment with this because it will pay dividends.

 

[DTB300]

Either can be accomplished by means of either mass loading or mechanical grounding or both. The use of some sort of rigidly attached arm to the planar surface of the frame on the CLS serves both of these purposes, but the method of attachment may yield differing levels of effectiveness. I'm not quite ready to "spill the beans" on my proposed method yet - but hope to do so sometime in the fall when I can devote more time to it.

Excellent post MiTT.

Mass Loading of the electronics box and/or the stator/frame does yield some very good results at minimal costs - one of those great tweaks for little cost.

And as you know from your testing, the type of connection, and where this connection is on the frame also has an overall affect. For those not wanting to "screw" into their frames, there are other alternatives but without some testing and modeling, it is hard to tell which may have greater benefit.

Edit - I forgot to mention height. As you design and build your stands you'll discover that the best height will position the vertical center of the elcetrostatic panel (not the overal speaker as the frame is asymetrical in this axis), at the center of your ears. The problem here is that people and listening chairs come in all sizes. In my opinion, given my stature and the listening chair I have in my room the Arcicci and Sound Anchor stands are a little too tall. Check out some of Neil's posts recently about putting some blocks under his listening chair to deal specifically with this issue. Take the time to experiment with this because it will pay dividends.

I have always agreed and preached the "Center Spar" at ear height for stands.

http://www.martinloganowners.com/forum/showpost.php?p=77826&postcount=14

This can be an "issue" with other stands - you then have to make a "Neil Chair" or platform. Homemade stands can address this issue for each persons home seating height issues.

Also remember that the forward/backward tilt, along with toe-in/out amounts also greatly affects the results.

 

[zaphod]

hmmm, so we have some people wanting to raise their CLS and some people wanting to raise themselves. colour me confused

as for attaching the spar to the CLS frame, i have a clamping idea in mind, or an insert nut on the back of the frame. just ideas.

Tim - the problem of the frame moving relative to the electronics box due to the thin metal of the box never occured to me. hmmm i wonder how far a stiffer connection would towards getting the sway removed. hmmmm.

 

[Jeff Zaret]

The issue of sway is an interesting topic to say the least. I am not sure it can be classified as sway as much as it is vibration caused by the excitement of the panel. I am sure technically it can be called sway but my simple minded thought/definition is that sway would be more of an even back and forth movement. If I understand acoustics and the physical nature of sound, i.e. reproduced musical notes, are symmetrical in their unique existence are not when combined and reproduced in a musical representation. That being said, there are many (sound) cycles being reproduced by music which IMHO create multiple wave factors and patterns that will not produce an even type of wave form which produces a typical even sway of back and forth.

What I believe is being produced is a vibration of many auditory cycles. I have put my hand on the top of my CLS frame when playing music with heavy content and I only feel a slight vibration. My electronics box is mass loaded and I have built my own stands. Playing the same music, at the bottom of my frame, there is no vibration that can be felt at all. I believe, like Dan has said, this is due to mass loading of the electronics box and in my case my stand which has sand filled legs and on carpet. My CLS are spiked on my stands! Does my solution work, definitely!! Is it better? Well that is a matter of interpretation, cost and satisfaction.

I would not tell anyone how to build their stands or which one to buy. It is a matter of choice and many variables for the correct decision. Do the Sound Anchors and Arcici stands work, yes. They isolate the electronics box but do not mass load it. This isolates the box and the frame. The frame will still "resonate" and that is where the brace comes in to isolate or actually reduce the resonance of the frame. The electronics box will still resonate but will not "transfer" this to the frame and "alter" the sound of the panel.

Again, it is a matter of economics and choice. There are methods of isolating panel resonance and electronic box resonance besides these choices. This is what makes this hobby enjoyable. To reach a satisfactory point by different methods is what is desired is part of the fun and in reality who really cares how you get there!


Jeff

 

[zaphod]

good points, it's all about the enjoyment. when the experiments become obsessive, less fun is to be had.

i also mass load my electronics box, with the 25lb mono amp (spiked of course sitting on it. of course, the frame is still attached to the box, so i think that i'll just have to force myself to sit and listen and check for frame vibration.

ah, the gruelling work of listening and improving

 

[nirvanaseeker]

just a thought.

I know you guys don't know me since I don't usually partake in these forums, but here's another view from an outsider:

The basic thing you have to remember about squelching vibration in any physical system is that mass and structure play a role. If you could add as much mass to the CLSs as needed, then you could just shut it out. This can be seen in machine shop equipment and is why mills, lathes, etc. are so heavy. However, if mass isn't possible, then structure must be used. Triangles, as I'm sure most know, seem to be the most stout - such as those structures seen in railroad bridges, etc. It seems to me with the CLS approach, a combination of both damping and structure is used, with a resultant system "Q". Given such an approach, a maximum damping figure is wanted - but the question is: What is the system that would give a proper Q? Perhaps keeping these things in mind might provide a little better guidance and a slightly different way of looking at things. Trying to come up with a brace that acts like infinite mass probably is more likened to banging one's head up against the proverbial concrete wall. I see the brace commonly used going from the frame's mid-top to the bottom rear being more of a shock absorber of sorts with a damping factor. Perhaps building a bracetype structure with a built-in shock absorber might be worth thinking about. Remember statics and dynamics and structural systems?? Wish I had paid more attention..

I don't have any stands or frames built for my CLSs, but have given it some thought, and am no further along than anyone else.