Martin Logan CLS panel distortion


Dear Audiophiles,
My original Martin Logan CLS speakers developed harsh distortion at higher spectrum of frequencies (mostly audible at high pitched soprano voices). Distortion disappears at low volumes of sound. Are my panels getting too old (they could be 10 years old, I am a third owner)? Is there a way to clean/tighten them (the panels, not owners ;-)? Your comments and suggestions will be appreciated. Thank you.
meta
I a re-posting Jim Power's advice which I think is already in the archives - see below. You can ruin the panel...but it is already broken you may have nothing to lose. Also, you can call ML, give them the serial # on the panels and they can tell you when the panels were built.

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There are a couple of possibilities that may be occurring. One would be that the panel is simply resonating because it has perhaps lost a bit of tension. The other possibility is that the clear 'damping strips' have come loose from the backside of the panel. There is a difference in performance between the two.

A resonating panel will only buzz on certain notes and at somewhat higher volumes.
A loose damping strip will buzz at almost any frequency and at any volume.

From your description, I believe that you are hearing a resonance. We fondly refer to the phenomena as "Kazooing" because it sounds like a kazoo. This can usually be improved by heat treatment. All CLS panels are heat treated initially before they leave the factory. Some times with age, they will stretch themselves slightly loose. They need heat to re-tension them. There is a very specific technique to heat treatment. If you wish to try it, Here are the instructions.

CAUTION!!!!
There certainly is the risk of damaging the panels by melting a hole through the membrane. Bad thing. If you are careful however, I think you will do just fine.

The heat can be applied with a strong hair dryer. A heat gun may be too extreme. I recommend starting with the heat source about 12 inches away from the speaker. Complete the entire procedure and if it has no affect, move the heat source about 2 inches closer and repeat the entire process. Patience is required.
The heat must be applied ONLY to the side portions of the panel, never in the center zone indicated by the horizontal spars or ribs. The side sections are the 'bass' sections that are about 6 inches or so wide and run from top to bottom on each side of the panel.
The heat must be applied from a constantly moving heat source but at a very slow steady rate of movement. Specifically, start applying heat from the dryer at the top of the panel along the edge of the wood frame moving toward the bottom. Keep the heat source moving at the rate of 1 foot per 3 seconds. Next start at the top again but this time, move inboard just slightly, about 2 inches and make another slow downward pass. Repeat until you are near the vertical spar defining the beginning of the center section.
If you first treated the left bass zone, now do the right bass zone.
If you have a good light source on the membrane, you may be able to determine if it is receiving enough heat to have a good effect. You should be able to see a slight shimmer of the membrane directly under the heat if light is so that you can see the reflection of the light. As you move the heat past, the area that was shimmering will draw tight. I hope this helps.
If all else fails, you can purchase new panels and receive an new 5 year warranty on everything. New panels are $890 including shipping within the US. We accept Visa, MC. Call me if you have any questions or need new panels. (785) 749-0133.

Happy listening!
Jim Power
service manager
Here's a related question - I just bought a pair of used CLSII, they were advertised as new panels, but when I called ML, I discovered that the panels were built in 1989.

I'm also getting distorion, but not sure if the problem is low power, old panels or a combination of both (I'm using 80 watt mono GTA tube amps, this is the low end of ML recommended 80-200 watts). Not sure if I want to invest in both new amps and new panels...any recommendations for inexpensive amps that I could try out with the old panels before upgrading them? or should I just go ahead and replace the panels? Jim at ML said that very few panels of that age are still in use...which might be a good argument for replacement?
Hello Tonnesen - thank you for your answer and forwarding of Jim Power's e-mail. I will attempt "tightening" of the panels in few days.
I will also test my amplifier - need to borrow something more powerful. I am using VAC Renaissance 70/70 so our problem could be related to not sufficient power supply.
Try to examine tubes in your amplifier. If it's old than upgrade or replacement of passive components should probably take place to bring your amp back to tolal balance.
Any opinions on the Anthem Amp 2 200w/channel hybrid for the CLSII? These are available for about $1k (I'm looking for a higher power amp to try out the CLSII).

Thanks,