New to Martin Logan, but not to Electrostatic speakers

[ESLFan]

Hi, I joined this forum to get as much information on my Martin Logan speakers. I purchased them second hand, because I wanted to start off slow. They are what I consider entry level speakers, Electomotion ESL.
Unfortunately they arrived broken. It did not seem a big deal, as I found out that only the support brackets are broken. ML service is great to work with. After sending several picture, they knew what parts to supply and they already have been ordered.

For many years I owned the Dayton Wright Electrostatics, if anyone here is familiar with them.

So now to the technical question: Does anyone know what the capacitance reading of the panel should be? Both measure differently. Example, red-blue and red-black 280pF on one and 380pF on other panel. Maybe one of them is damaged?

 

[Jazzman53]

Hi and welcome to the forum. I'm just curious whether you are wanting to know what the stator-to-stator capacitance of the panels should be or what their stator-to-diaphragm capacitance should be.

The stator-to-stator capacitance is determined by the panel area and gap between stators, and should be measured with the diaphragm fully discharged, and between the two stator leads only. (to discharge the diaphragm, disconnect all three panel wires and short them together momentarily). I can't imagine this measurement having any diagnostic value.

To measure the stator-to-diaphragm capacitance you would need to fully charge the diaphragm. MLs have a sensor circuit that only charges the diaphragm when a music signal is detected, and having the transformers in circuit may affect the reading.

I've never felt the need to make these measurements, so what follows is speculation based on my understanding of panel construction.

The spacing between the diahpragm and front stator and diaphragm and rear stator are not symmetric on a curved ML panel by design (rear stator is purposely spaced farther away), so you wouldn't see equivalent capacitance to both stators, even in the same panel.

There is yet another variable at play: Charge tends to pull the diaphragm toward one stator--- it's a bit like trying to balance a pencil on its tip (charge is analogous to gravity affecting the balance) and so the diaphragm will tip toward one stator and then be ever-more-strongly pulled toward that stator. This could produce unequal diaphragm-to-stator capacitances.

Given the variables; I'm not sure whether measuring the panel capacitances will tell you whether the panels would play normally or equally.

 

[ESLFan]

What answer I was really after is that I would expect both panels to be the same if they are supposed to be a matched pair. Maybe no one ever measured the capacitance of this model. If they are working then of course there is no reason to dismantle them. I am an engineer, I'd like to know what state of performance my audio gear is.
Since one of them looked like it was stressed at the point where the wires are connected to the foil I was concerned about the damage. So I compared the capacitance of one with the other. Since the stressed one measures less, it could be that not all of the area is attached to the wire. Only when they are connected back to the woofer section, after I receive the brackets, will I know for sure. Attached are some pictures of the damage.
Has anyone ever just replaced one panel? Would a new and old one sound different? Do I need to replace them as a pair if there was a real problem? I don't know right now unless someone can tell me in this forum.

 

[Robert D]

Take a look at the panels and inspect them for a serial number. On here we have a decoder posted, it's a sticky, and you can figure out how old the panels are. The speaker cabinets should have their own numbers. Compare the two.
IMO, if something is wrong with one panel then you need to replace the pair. I don't think Martin Logan produces single panels anyhow. You'll want a pair so they are close in specs. I replaced my Prodigy speaker panels.
You can email Martin Logan and get a price quote on new panels. The price of course depends on the model.

 

[ESLFan]

I can't figure out the decoder for my serial number for the panels. They start with CBT0242 and have a two letter suffix.. Maybe someone else can figure it out. I don't really care about posting them here. Martin Logan service quoted me a price for a single and for a pair. So they do sell singles. Price of a pair is slightly cheaper than buying two singles. Replacing the panels negates the saving from buying them used.
Just so you know, shipping them in the factory boxes does not save them from breakage.

 

[Leporello]

Hi and welcome to the forum. I'm just curious whether you are wanting to know what the stator-to-stator capacitance of the panels should be or what their stator-to-diaphragm capacitance should be.

The stator-to-stator capacitance is determined by the panel area and gap between stators, and should be measured with the diaphragm fully discharged, and between the two stator leads only. (to discharge the diaphragm, disconnect all three panel wires and short them together momentarily). I can't imagine this measurement having any diagnostic value.

To measure the stator-to-diaphragm capacitance you would need to fully charge the diaphragm. MLs have a sensor circuit that only charges the diaphragm when a music signal is detected, and having the transformers in circuit may affect the reading.

I've never felt the need to make these measurements, so what follows is speculation based on my understanding of panel construction.

The spacing between the diahpragm and front stator and diaphragm and rear stator are not symmetric on a curved ML panel by design (rear stator is purposely spaced farther away), so you wouldn't see equivalent capacitance to both stators, even in the same panel.

There is yet another variable at play: Charge tends to pull the diaphragm toward one stator--- it's a bit like trying to balance a pencil on its tip (charge is analogous to gravity affecting the balance) and so the diaphragm will tip toward one stator and then be ever-more-strongly pulled toward that stator. This could produce unequal diaphragm-to-stator capacitances.

Given the variables; I'm not sure whether measuring the panel capacitances will tell you whether the panels would play normally or equally.

The capacitance of an ESL panel may indeed be more complicated than it appears at first glance. For example, when you apply voltage to a capacitor, charge moves from one electrode or set of electrodes to the other. When you apply voltage to an ESL panel charge moves from one stator to the other, but it also results in motion of the diaphragm, which also moves charge. That is why it's incorrect to think of an ESL as just a capacitor. The power factor may be crazy capacitive, especially at high frequencies, but it isn't purely capacitive. And even though the diaphragm movement may be tiny when using an instrument to measure capacitance, it scales approximately linearly. The cap meter itself, depending on the type, may be dependent on not having a voltage offset.

Nevertheless, it's difficult to see what could account for a 30% discrepancy between the two ostensibly identical panels. Making sure each panel is thoroughly discharged could be very important. Also, any conductive body close to either panel could affect the reading. Broken bracket? I agree that this measurement, unless done under very tightly controlled and well understood circumstances, doesn't have much significance for a properly functioning panel.

An RF bridge style capacitance meter that measures the resonant frequency of the capacitor and a known inductance should be independent of any charge present, and should not result in any significant diaphragm movement. The "Q" of the resulting circuit could tell you if there is anything funky like a high resistance short circuit. Unless there's reason to suspect one panel is defective there would be little point in going to that trouble.

 

[Leporello]

What answer I was really after is that I would expect both panels to be the same if they are supposed to be a matched pair. Maybe no one ever measured the capacitance of this model. If they are working then of course there is no reason to dismantle them. I am an engineer, I'd like to know what state of performance my audio gear is.
Since one of them looked like it was stressed at the point where the wires are connected to the foil I was concerned about the damage. So I compared the capacitance of one with the other. Since the stressed one measures less, it could be that not all of the area is attached to the wire. Only when they are connected back to the woofer section, after I receive the brackets, will I know for sure. Attached are some pictures of the damage.
Has anyone ever just replaced one panel? Would a new and old one sound different? Do I need to replace them as a pair if there was a real problem? I don't know right now unless someone can tell me in this forum.

ML does recommend replacing panels in pairs, and may only sell them in pairs anyway. When I bought my second hand CLS II's they came with the frames and two unopened new panels. Some time later, while hanging a carpet for acoustic treatment, I miscounted how many steps up the ladder I was and fell backwards onto a speaker. I was fine but the panel was trashed. They told me it was up to my ears whether I wanted to replace one or both panels. I went with the former, and they sounded fine to me. But they had aged less then a couple of years.. CLS panels are pretty expensive compared to the others that I have seen quoted on this forum. That may be one reason they were willing to sell me only one. It's a long wait for new panels, at least a couple of months.

You should certainly reserve any decisions about repaneling until you get the speakers functioning properly. If you like them but one definitely sounds off, and you're willing to put the money into them, I would just go ahead and replace both panels. Waiting months for one panel, then finding they don't match, and waiting more months for the other, even if they gave you that option, just wouldn't make sense. In your case you don't know the age of either panel, and they do diminish with age. I would replace both panels of my CLS II's in a heartbeat, when the time comes.

 

[Jazzman53]

The panel/stator surface areas would be identical so I'm thinking any significant capacitance difference could only result from different stator-to-stator gaps or a shorting path or some interaction with the diaphragm(s).

I recently replaced the diaphragm on a ML Theater center-channel speaker panel (my first foray into an ML panel), and I was surprised at the degree of non-uniformity I measured in the spacer thicknesses, affecting the stator-to-stator and diaphragm-to-stator gaps.

ML's periphery spacers are pliable foam tapes which compress in response to (and to accommodate) mating errors between the contoured stators.

On the Theater panel rebuild I also noted a ridiculously fat solder bead at the bias supply wire connection to the charge ring. That fat solder bead prevented the stators from fully mating and resulted in a much larger gap at that end of the panel. Additionally, the fat bead was compressed so deeply into the foam spacer tape that only its Kapton tape wrap kept it from shorting to the rear stator (I fixed this issue when I replaced the charge ring).

Even with the significant mating/gap errors I found in the Theater panel, it had played fine for two decades until the diaphragm coating had deteriorated so badly the panel lost output.

Based on what I observed in the Theater panel rebuild, it's not unreasonable to speculate that other ML panels may have similar gap issues which might account for any capacitance differences between them.

 

[Leporello]

I can't figure out the decoder for my serial number for the panels. They start with CBT0242 and have a two letter suffix.. Maybe someone else can figure it out. I don't really care about posting them here. Martin Logan service quoted me a price for a single and for a pair. So they do sell singles. Price of a pair is slightly cheaper than buying two singles. Replacing the panels negates the saving from buying them used.
Just so you know, shipping them in the factory boxes does not save them from breakage.

A speaker damaged in a Martin Logan shipping box obviously suffered abuse. Did you file a claim with the shipper? I can't imagine a shipment like that not being insured, unless you specifically declined it.

The price of used speakers plus new replacement panels exceeding the price of new speakers is not surprising. Under the circumstances, it might be worth replacing just the apparently damaged panel first, if you get no joy from the shipping company. If you do figure out the serial number it can give you an idea of the age of the panel you're keeping. My own personal experience is the mismatch between a new and two year old panel is insignificant.

I've had trouble receiving expensive items in a timely manner, but never damaged in a factory shipping box. Lucky, I guess. I've had damaged items incompetently packed, including a Martin Logan Descent i subwoofer.

 

[Robert D]

A speaker damaged in a Martin Logan shipping box obviously suffered abuse. Did you file a claim with the shipper? I can't imagine a shipment like that not being insured, unless you specifically declined it.

The price of used speakers plus new replacement panels exceeding the price of new speakers is not surprising. Under the circumstances, it might be worth replacing just the apparently damaged panel first, if you get no joy from the shipping company. If you do figure out the serial number it can give you an idea of the age of the panel you're keeping. My own personal experience is the mismatch between a new and two year old panel is insignificant.

I've had trouble receiving expensive items in a timely manner, but never damaged in a factory shipping box. Lucky, I guess. I've had damaged items incompetently packed, including a Martin Logan Descent i subwoofer.

Great advice!

 

[ESLFan]

I am pretty good a repairing anything audio equipment. My favourite is recapping old audio gear. \
I see a small whitish looking area that is less transparent than the rest. I assum this area has arced over?
Then there is another problem. I opened up the one cabinet where the wire to the panel was ripped off the 3 terminal connector. I followed ML instructions on opening the bottom of the woofer box. It turns out now that the wire that goes from the transformer to the panels has been pulled so tight that there is not enough slack to open the bottom wide enough to do any repair. There is just enough room for my hand. I have no idea if I can lengthen it and if I can get the wire from ML.. The reason for the investigation is how to replace those garbage binding posts. I can't believe they have spring loaded connections.
I replaced the broken brackets already. This is becoming a project. I am hoping the result is worth it. I live near Atlanta, but the closest ML dealer is quite a drive and they certainly would use much different equipment hooked up to them. So I decided to buy used and resell if they don't work for me.

 

[Jazzman53]

I am pretty good a repairing anything audio equipment. My favourite is recapping old audio gear. \
I see a small whitish looking area that is less transparent than the rest. I assum this area has arced over?
Then there is another problem. I opened up the one cabinet where the wire to the panel was ripped off the 3 terminal connector. I followed ML instructions on opening the bottom of the woofer box. It turns out now that the wire that goes from the transformer to the panels has been pulled so tight that there is not enough slack to open the bottom wide enough to do any repair. There is just enough room for my hand. I have no idea if I can lengthen it and if I can get the wire from ML.. The reason for the investigation is how to replace those garbage binding posts. I can't believe they have spring loaded connections.
I replaced the broken brackets already. This is becoming a project. I am hoping the result is worth it. I live near Atlanta, but the closest ML dealer is quite a drive and they certainly would use much different equipment hooked up to them. So I decided to buy used and resell if they don't work for me.

Hey, didn't know you were in GA.

I doubt ML uses a special wire for the transformer leads-- the Theater center channel speaker I recently rebuilt had standard 300V wire and the leads were even twisted. If you have to replace a transformer lead in, any speaker wire would do. If you have to replace a transformer lead out (HV lead), you could get by with standard 18GA 300V wire if you overwrap it with electrical tape or shrink tube. I use a 5kV rated silicone jacketed wire for my ESL builds.

BTW, I'm in Savannah so if you're ever down this way, give a yell and drop by. I have some interesting wire-stator ESLs you might like. I don't build them anymore, but I still have an unsold/unused pair I would let go for cheap.

Charlie

 

[Leporello]

The reason for the investigation is how to replace those garbage binding posts. I can't believe they have spring loaded connections.

I guess that's their "entry level" option. I have little Motion series bookshelf speakers--an eBay special--that I use for surround, having not taken the plunge for serious surround speakers. They have spring loaded terminals. They're pretty decent but still, spring loaded. The CLS II's came with good quality standard 5 way posts. The Ascents came with posts I really like: oval shaped, for good tool-free tightening. I use Blue Jeans Cables locking banana plugs on both ends on the CLS, which wouldn't have been an option on the Ascents, but I wouldn't have minded because they're easy to get down tight on spade lugs. I always crimp and solder spade lugs.

 

[ESLFan]

Thanks for all your replies. I like projects. Looks like the third set of brackets are being shipped. Maybe I can listen to them this weekend.
Since I always dabbled with electrostatics, I have some 15Kv wire, probably 50ft I bought cheap 15 years ago, If I can find it.
Talking about cables, I have two sets of Kimber Kable speaker wires. One 4TC and another custom 16TC. I was using my new LCR meter, same one used to measure ML panel capacitance, I verified that the cable capacitance was much higher than a standard zipcord, which makes sense since positive and negative cables are braided together. What is important is that the series inductance is lowered since electrostatic speakers present a capacitance at higher frequency. You want to make sure that that capacitance and speaker inductance does not create a filter and roll off the highs. This could be some of the reasons why people seem to hear differences between different speaker cables..
So during this testing it turned out that the resistance of the cable kept changing and none of the four connections were thew same. Turns out that after 30 years the crimping lets go. Sorry for rambling.
I contacted Kimber Kable and they were surprised I still had them. In spite of all the forums I read saying crimping is better than soldering, Kimber Kable now solders all they crimp connections on the bigger cables.
To get to the spade lug connection I had to cut off the heat-shrink with their Logo on them. They were kind enough to send me new heat-shrink to replace all the cut ones
The only reason I had the 16TC cable was that the Dayton Wright speakers could sustain an input of 500W per channel and I was driving them with a 300W per channel MOSFET amp I designed and build by myself back in the late 80s.

 

[Leporello]

Thanks for all your replies. I like projects. Looks like the third set of brackets are being shipped. Maybe I can listen to them this weekend.
Since I always dabbled with electrostatics, I have some 15Kv wire, probably 50ft I bought cheap 15 years ago, If I can find it.
Talking about cables, I have two sets of Kimber Kable speaker wires. One 4TC and another custom 16TC. I was using my new LCR meter, same one used to measure ML panel capacitance, I verified that the cable capacitance was much higher than a standard zipcord, which makes sense since positive and negative cables are braided together. What is important is that the series inductance is lowered since electrostatic speakers present a capacitance at higher frequency. You want to make sure that that capacitance and speaker inductance does not create a filter and roll off the highs. This could be some of the reasons why people seem to hear differences between different speaker cables..
So during this testing it turned out that the resistance of the cable kept changing and none of the four connections were thew same. Turns out that after 30 years the crimping lets go. Sorry for rambling.
I contacted Kimber Kable and they were surprised I still had them. In spite of all the forums I read saying crimping is better than soldering, Kimber Kable now solders all they crimp connections on the bigger cables.
To get to the spade lug connection I had to cut off the heat-shrink with their Logo on them. They were kind enough to send me new heat-shrink to replace all the cut ones
The only reason I had the 16TC cable was that the Dayton Wright speakers could sustain an input of 500W per channel and I was driving them with a 300W per channel MOSFET amp I designed and build by myself back in the late 80s.

That's the trade-off: decreasing the conductor spacing raises the capacitance but lowers the inductance. I'm not sure how important either is at loudspeaker impedance, though. Both reactances are much smaller than the resistance, normally, at audio frequencies. Yes, a crimp that has gone bad would make way more difference!

When I worked in broadcast engineering I built many crimped BNC cables. There's no question the tool used for crimping creates very high pressure, and a gas tight connection. The metal junction is as one piece. I've seen crimped BNC connectors that have lasted decades, sometimes outdoors, and still work fine. I'm not so confident about a spade lug crimped with a normal electrician's crimping/stripping tool. The fact that solder does flow into the wire says something.

 

[Leporello]

I was trying to refresh my memory about Dayton Wright electrostatic speakers. Were they the ones that worked inside an inert gas with secondary diaphragms to the outside world, or was that Beveridge?

I turns out there was an aircraft company which Orville Wright lent his name to, but nothing else, founded in 1919, called Dayton-Wright. No relation, apparently.

It was indeed the Dayton Wrights that were gas filled. Beveridge used a different intermediary between the ESL diaphragm and the world, namely acoustic lenses. There's a review by Gordon Holt, a huge ESL fan, pretty well panning them. Haven't yet found out what he thought of Dayton Wrights.

IMO, the ESL diaphragm directly driving the air is the way to go, especially now that people understand how to build them without arcing out. Putting a curve on them to address the dispersion problem, as ML does, is all the better.

Before the CLS's I was using Ascents, before that Acoustat 1+1's. So I have an ESL history myself. Never designed and built and amp, though. Good for you. I'm sure it's "blameless".

 

[ESLFan]

I know this is off topic, I think I will create a new thread because there is so much engineering involved in the design of those electrostatic elements it would be a shame to loose all that. I havea non-working pair now I owned since 1978.
The Dayton Wright speakers were not origionally designed for consumer use. They were designed to provide the sound for the original IMAX theator on Toronto Island, an island seperated by about a mile of water from Toronto harbour in Lake Ontario,
So it was designed to produce prodigious amount of sound and accurate loud bass which is possible with 18 sq ft of operation area and up to 1/4 inch excurion. The gas solved 2 things. It allowed 16kV of bias voltage. Every time you bouble the voltage you get 6dB more output. As you move the stator plates away from the diaphram for more output you need to increase voltage to gain back the efficiency. The gas provided the breakdown capabilty, it is the same gas used by all electric companies around the world to estinquish arcs on their high voltage circuit breaker.
What I find also interesting is that one of the original founders of ML lived in Ontario, and so did Mike Wright. In addition Mike's speakers were build in Guelph, a short ddistance from Toronto, I visited the facility once. Now ML has a factory in Missisauga, which I hope to visit this year

 

[ESLFan]

I know this is off topic, I think I will create a new thread because there is so much engineering involved in the design of those electrostatic elements it would be a shame to loose all that. I havea non-working pair now I owned since 1978.
The Dayton Wright speakers were not origionally designed for consumer use. They were designed to provide the sound for the original IMAX theator on Toronto Island, an island seperated by about a mile of water from Toronto harbour in Lake Ontario,
So it was designed to produce prodigious amount of sound and accurate loud bass which is possible with 18 sq ft of operation area and up to 1/4 inch excurion. The gas solved 2 things. It allowed 16kV of bias voltage. Every time you bouble the voltage you get 6dB more output. As you move the stator plates away from the diaphram for more output you need to increase voltage to gain back the efficiency. The gas provided the breakdown capabilty, it is the same gas used by all electric companies around the world to estinquish arcs on their high voltage circuit breaker.
What I find also interesting is that one of the original founders of ML lived in Ontario, and so did Mike Wright. In addition Mike's speakers were build in Guelph, a short ddistance from Toronto, I visited the facility once. Now ML has a factory in Missisauga, which I hope to visit this year

Talking to ML service, mine were made in 2014. He said that there were no changes and a new panel should blend well with the original. I should have the remaining bracket early next week at the latest. So no firing them up (I hope not literally) this weekend. The seller is very nice, he will re-imburse me for all the costs including a new panel. I don't mind assembling them as I like to take apart audio gear I buy. Since I already looked inside, I think I can replace the binding post with ones that will take spade lugs or banana plugs.

 

[Leporello]

there is so much engineering involved in the design of those electrostatic elements it would be a shame to loose all that.

I can well imagine. The space between the outer diaphragms would form a distributed acoustic resonator, particularly as the half wavelength approaches the spacing. Not insurmountable, just complicated. At low frequencies, though, the three diaphragms would move approximately in unison, and the wide spacing would allow for large excursions, ideal for a separate bass panel, if one wanted to go that route. If you create the thread I'd be interested in following it.