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Striving for optimum transparency and resolution in an ESL
Striving for optimum transparency and resolution in an ESL
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Old 9th April 2017, 12:40 AM   #1
Bondsan is offline Bondsan  United States
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Default Striving for optimum transparency and resolution in an ESL

Besides being a fun worthwhile DIY project, one of the main reasons for building an ESL is their effortless transparency and resolution in the reproduction of music. Their holographic imaging can be uncanny at times. However, some are more capable than others in clarity and I'm trying to understand the 'how and why' of these differences. I'm not talking about major-no doubt about it differences, but very subtle ones; ones that if you had never heard the subtleties before, you would not be aware that your speakers were lacking some of the delicacies in the music. It's not necessarily that the music it missing, just that the detail could be better.

My present ESL's are all around the best speaker I have ever made, and probably the best I've ever owned. I'd be very happy to live with them for a long time. They do a wonderful job at transparency and resolution, but I must confess I've heard better(Quad ESL57 a long time ago) and I've actually made a more resolving ESL.(Will get to those later)

Usually it's the faint background information that might be missing details: backup voices to a soloist, orchestral works where the loud instruments are overpowering the softer ones, the separation of instruments and chorus in a large complex symphony, a soft drum roll that sounds slightly smeared, room ambiance, a particular twang on a banjo string, and so forth. Sometimes the subtleties have nothing to do with the music: a conductor humming along with the music, the clear crisp jingle of cocktail glasses at a live nightclub recording, background conversations, etc.. Sounds on the disc waiting to be heard if your speakers are up to the task. These are delicate nuances that ESL's, probably better than any other type of speaker, are truly capable of.

But how to ensure optimum capability. Most threads that I've read seem to concentrate on FR, efficiency, and db output, with little mention of resolution. I guess there is an assumption that transparency and resolution will result automatically since it's an inherent quality of an ESL's DNA(to a certain degree). I guess it basically boils down to the diaphragm construction, since its vibrations are creating the music. Below are a few of my layman thoughts on diaphragms. Please forgive if any are completely off base:

1. Membrane thickness. Usually 3um- 12um, with the thinner mylar offering better resolution, but more difficult to work with.

2. Conductive coating. As Calvin mentioned in an older thread, you want to add as little mass to the diaphragms as possible in order to reproduce the subtleties.

3. Tension. I don't know but I would think that if too high the stiffness would hinder the delicate movement necessary for subtle nuances. My speakers seem to have become more resolving since the tension has relaxed a bit over time.

4. Size. Not sure about this but perhaps a larger diaphragm would be more compliant at its center?

So, if a person was striving for optimum transparency and resolution, can it be designed with predictable and measurable results? Calculations and formulas are a language I do not understand, but I am fascinated how many of you are able to jumble a few figures on a piece of paper and come up with a workable solution. I don't understand French either, but enjoy listening to it spoken. So if you engineers could throw in a few english words now and then, much appreciated.

Well, I've rambled on enough. Hope it makes some sense. I'm an old audiophile(late sixties) looking forward to going to bed at night with a big smile on my face with the satisfaction of knowing that I've heard all the music that can be heard coming from my speakers.


BTW; That very resolving speaker I made(many years ago) was made with styrene panels, aluminized mylar, and bare aluminum welding rod stators. Couldn't play very loud due to unwanted lightning flashes, but boy, they could resolve the music. Ideas on what was going on?
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Old 9th April 2017, 01:21 AM   #2
anji12305 is offline anji12305  United States
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A great deal of the resolution presented by panel speakers is down to room placement. Verify this, to get the most out of what you have made.

I had a pair of Quad ESL63 rebuilt and they did many things well, including bass response.

See: Sumiko master set and Cardas dipole calculator.

Sent from my Nexus 6 using Tapatalk
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Old 9th April 2017, 08:01 AM   #3
Calvin is offline Calvin  Germany
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I agree with most of Your points.
The richness in detail contributes to a great deal to a natural authentic sonic image.
Against many dome tweeters -and seemingly more so ribbons- that often add a artificial glacing shimmer in spite of real resolution a esl can present highs and mids with utmost resolution of detail in a real appearing way.
1: positive
2: positive
3: positive ... as tension allows for higher efficiency and increased force/mass factor. While this shouldn´t play a role at all ... theoretically (as long as the panels upper bandwidth limit falls above the audible range) it seems to play a role in praxis. Maybe its just a sideeffect in that typical highly efficient panels can be driven with lower voltages hence lower U trannies.
It could well be that indeed the better low-U trannies are the true and most influencing reason behind that sonic effect.
The higher tension doesn´t make the membrane ´harder´ or less responsive to a signal. It just raises the lower bandwidth limit and as such the useable frequency range.
4: positive ... in part larger panels cover a larger area of nearfield condition, which can be regarded as an area of almost only membrane sound and nearly no reflected ´room´ sound. Even if the reflected sound waves arrive at the cochlea with sufficient delay they still influencing on the direct sound pressure response and the brain needs to do more signal conditioning (or ´thinking´) to extract the reflections from the pure direct signal.
Highly directive speakers like esls and horns and headphones (direct sound only) appear to have higher resolution.
Larger panels also enter the frequency range where the acoustic impedance becomes real towards lower frequencies. Real acoustic impedance means optimal coupling of the membrane to air. No power wasted in a complex part of the impedance. But that is just a wild guess in the early morning hours half awakened

I guess it basically boils down to the diaphragm construction, since its vibrations are creating the music
Not entirely. The stator construction plays an important role also.
With punched metal smaller holesimprove matters over larger holes ... under the condition of same opening factor. There have been discussion here about the optimum openness factor range.
And don´t forget that some esls apply mechanical damping measurements.
While printing mesh seems to not affect resolution, cloth or felt mats certainly do.
But the imho most affecting factor is still the amplitude response.
A speaker with prominent mids and highs will always appear more open and resoluting at first glance.
Lifting the bass response can already change that impression.

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Old 9th April 2017, 10:24 AM   #4
geraldfryjr is offline geraldfryjr  United States
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Hello there,

Here are a few things that I seemed to have notice while I was building and testing my little panels.

#1 Diaphragm

Even 6um (.25 mil) can be a pain to work with, I had a hard time getting enough tension with no stretching and using only heat on my wider 7.5" to 9" wide panels, But I did finally get them to work without the diaphragm collapsing in to a stator.

But I always strive for the lowest tension I can get that will still maintain stability for my given width, bias voltage and diaphragm thickness.

I have never worked with anything less than 3um except for some 2.5um, 1.5um, and .06um stuff that I have for making ES headphones.

The thought has come across to me too try a Tweeter type 1"-2" wide strip using those materials, But I haven't got that far yet.

#2a Stator Coating's....Well I have certainly done my home work here mostly in Stator coatings.

Yes, they will work and work well without it, But IMHO A stator coating is required if you want to get the most performance you can without having the risk of arcing and burn't diaphragms.

With a decent and proper stator material and thickness you can still have ionization but the current flow will be so low as not to cause any punch through or burn't diaphragms due to the increased DC resistance of the coating.

I have stated this before in other threads as I have found this out First hand in my crazy extreme testing.

In the case of losing efficiency due to the very high resistance of a stator coating you just simply raise the bias voltage to make up the difference.

Also choose a coating that has a high dielectric constant ( K ).

If you had to choose from different types of coatings over the dielectric strength (volts per mil), choose the one with the higher K even if it has a lower V-mil rating.

I was told this by our GuRu Roger Sanders, He said this actually increases the efficiency of the panel.
Knowing what I know about capacitors this make a whole lot of sense!

An ESL is Two capacitors in series, and with a coating it becomes Four capacitors in series as there are now two different types dielectric materials in involved.

So the higher the Constant (K) is for the coating it raises the the capacitance of the coating, this lowers the overall series impedance (AC resistance, Not DC resistance) of the stator coating to the diaphragm.

Thus this lessens the amount of AC voltage drop across Stator coating to the air gap from the stator surface to the diaphragm along more Ac voltage in the air gap.
Basically an AC voltage divider.

#2b Diaphragm Coatings

There are many types that work and there is lots of info in these threads on that.

I just happened to be luckly in 2003 and stumbled upon Licron as it came out at the very same time I built my very First ESL.

What a Godsend that was as I was trying to work with Graphite as a coating, it was a PITA and was just a mess to deal with, not to mention dirty frames the ended up shorting out the bias voltage.

Licron has always worked and never failed me so I stuck by it.

After all of the diaphragms I had made and replaced I still had 2/3 of a can when just recently a rusty pinhole form releasing the rest of its contents all over the top of my dresser. :/

The newer Crystal Licron is all they carry now and it is a much improved product although I haven't had an ESL made around long enough to test its longevity.

Halt...oh wait!!!.... Yes I do have a set, I have Mavric's Panel's that are now 7 years old and they do still work!!

Anyhow getting back to my point, it has been shown that having a very high diaphragm coating resistance reduces the THD on the low end and pretty much overall the whole bandwidth.

Being that Aluminized mylar does work it can have a higher THD due to it not running in constant charge mode and problems with charge migration.

I have some of that stuff and I want to try it for when I start playing the Direct Drive circuits later this year just to see how it will perform.

#3 I agree with completely, I have read it stated that a higher tension will increase the efficiency. this is utter BS!

All it does is raise the diaphragm resonance into a range that it becomes a nuisance.

At the high end the increased tension may not have any effect at all due to the extremely small amount of excursion at those frequency's.

At the low end, I think like you do, If the tension is too high it can limit the amount excursion with X amount of voltage swing and bias.

I haven't actually tested this fully, But logic tells me not to waste my time with such laboring efforts.

The closest thing I got to experimenting with this is that due to the construction method I use, I am able to vary the tension (lower it) by loosening the sandwiching bolts, Squeeze the sides of the frame and re-tighten them, And Wala, I have a lower tension!

I have never found any difference in the efficiency, just a lower resonance.

I do understand where Calvin is coming from but there is not enough mass in the diaphragm to make a difference in the efficiency, if there is, it would be a very insignificant amount.
Peak SPL is basically ruled by displacement alone

#4 Size

That is just a matter of the rules of physics, There are many spreadsheets and calculators available now that can accurately predict an ESL's Performance, SPL, Dispersion and Efficiency.

This I have tested using my own DIY panels and I must say that they are very close and quite accurate.

Electrically Segmented or not, it has been proven many many times the ES is the way to go, But not necessary if you are making little panels like mine.

However, I will be testing my newest electrically segmented desktop panel ( Built 3 years ago) this summer (finally) so stay tuned for my results on that.

My Hats off to those of whom who have created the software tools for ESL design!

Not mentioned,

#5 Bias Voltage

I can not stress enough how important this is and it refer's to Stator Coating Performance.

The better your stator coating is the higher you can run your bias, Although there are practical limits!

Say you are running 3kv of bias, and every time you double the bias you gain +6db of efficiency.
This also gives you a theoretical extra +6db of headroom.

This does not effect the overall peak SPL due to the limits of ionization breakdown of the air (more on this when I test my new panel that can handle my crazy extreme voltage testing), so I have read.

But the true benefit is the increased sensitivity and Dynamic range that the panel can produce is like night and day!!!

So, For every +6db of Bias gain, the amp has to drive half of the voltage it would normally have to produce a certain SPL, this is 1/4 of the power that it would normally have to produce.

Ohms law says 1/2Volts=1/4watts or W=V^2/R

I did an experiment starting at my original bias of about 1.5KV when I first started (using my PC coated stator version), and did a listening test to see how the bias effected the sound quality every time I doubled it all of the way up to 12kv of bias.

Like I said there are limits and 12kv is were leakage limit was for my Panel it was the highest voltage I could get out of my Powersupply that is capable of 14kv in just a .072" gap.

I was able to get my measurements and do my listening test at about 87db for every bias level I tried in order to save the panel.

Typically 10kv was the highest I could run safely at +100db, but I did get it to behave for a little while at 12kv (before I burned running full tilt with my DC300a).....Um yes it was quite impressive!

From 1.5kv to 12kv is a +18db jump.

The amp was an Awia 80watt CDstereo and was finicky as heck!!!
Yes, The amp loved it every I rose the bias as the power requirement was cut by 4 every time I doubled the bias.

What I heard was even better!

Raising the bias gave more control over the diaphragm, as I had explained before, drums had more authority at higher levels of bias.

I don't mean that they were louder as I kept within my 87db limit to keep my ears from fatiguing to early in the listening test due to the sheer volume that the panel could actually produce at .5 meter and 1 meter away.

The extra headroom put those peaks in proper perspective for a change.

With having the extra +18db of gain and headroom you can just imagine what it did to the micro detail as I found relevant while I was listening to ELP's Lucky Man and From the Beginning also in Spandau Ballet's True, and Crowded House.

Sadly The panel gave out later and I wasn't able too do some more detailed listening to really confirm what I was hearing and get used to it.

But, I did notice a change as I raised the bias and it wasn't about coloration as that just did not exist!!

#6 coclusion

You may ask what does this mean compared to an uncoated stator?

Well I was going to build one but as it turns out my earlier painted stator ESL's (exact same size as my High Performance panel) were basically that since I couldn't get the bias or drive signal much over 2kv to 3kv without them arcing and burning holes in the diaphragm.

Now Granted, Being that my panels are tiny compared to what everyone else has, They were impressive, But I was forced to use higher than normal voltages due to the small surface area to match the efficiency of the woofer.

I can't even imagine what my bigger system is going to be like (once it gets built later this year) using the techniques that I have learned and discovered.

I have Twelve 10's waiting for the low end in order to keep up, they are decent driver for dirt cheap ($15), but will work great in a line array dipole (OB) with some proper dampening.

They will work long enough for me to wear them out and then I'll get some quality Dayton RS series drivers for the low end in a few years.

Cheers !!!


Last edited by geraldfryjr; 9th April 2017 at 10:36 AM.
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Old 9th April 2017, 01:08 PM   #5
lowmass is offline lowmass  United States
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I cannot speak to the ESL directly as I have no experience, however I have a fair amount of development time with ribbons, quasi ribbons, and planer magnetics.

After 30 yrs of work I have concluded that the better units took care of two areas that are often dont get enough attention. Diaphragm and support structure resonances.

Yes all the other details matter. Especially when dealing with very thin light films, BUT I suspect taming resonances is the biggest issue by far.

My quess is that when you have a stat that seems to work better than the others you have one whos stator framework and its diaphragm are nice and quiet.

BTW just a word on the Quad. I have built planer magnetics that were driven from the center out in similar fashion. I can tell you that although dynamics are softened a bit by this approch, the resonances that play hell with full range planer type diaphragms are reduced noticably AND I believe this effects the sound more than we know. Theres also the concentric drives dispersion at play. Ive built planer mags with concentric MRT and compared directly to same panel but with same MRT to the side. The cconcentric design consistantly sounds better focused and interestingly less "bright". It just sounds "right" in compare.

I understand we have a well damped diaphragm BUT it will dance with standing waves at various feqs. AND the stator structure may have some modes in areas that can blur the sound??

yes this is a bit of a guess BUT I have seen far too many ribbons and planer magnetics both heavy weights and 4 micron versions that have had a particular region where frame and or diaphragm are not behaving as expected and they often sound less than great as a result.
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Old 9th April 2017, 05:47 PM   #6
CharlieM is offline CharlieM  United States
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Originally Posted by geraldfryjr View Post

The newer Crystal Licron is all they carry now and it is a much improved product although I haven't had an ESL made around long enough to test its longevity.

Halt...oh wait!!!.... Yes I do have a set, I have Mavric's Panel's that are now 7 years old and they do still work!!


Jer, I didn't know you ended up with Mavric's panels... you mean these: (?)

As I recall, Mavric liked the color of the primer coating so he opted to omit the color coat!

Click the image to open in full size.

Last edited by CharlieM; 9th April 2017 at 05:50 PM.
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Old 10th April 2017, 05:27 AM   #7
Bondsan is offline Bondsan  United States
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I should emphasize that my present speakers are fully capable of the nuances I have described, just the degree of the nuances. As an example, I'll use THE recording that got me started on this resolution quest; Erich Kunzel and the Cincinnati Pops playing Sousa's "Stars and Stripes Forever'. In this version the drums rolls are soft and slightly smeared sounding. In other versions of this march, the drums can be distinct and the beats clearly heard. So you would think that it's just the recording on the pops CD, since it also sounded slightly smeared on my little Dynaudio's and even my KHorns. But on my 'lightning' speakers, the separate beats were soft but clearly heard....and it's the last time I've heard that resolution. I wish they were still around so I could compare them to my present ESL's. But fortunately, the aluminum coating failed and the speakers died. Otherwise I would probably have had to write a letter; "Dear Farmers Insurance, sorry to have to inform you, but my speakers burned the house down".

Hi anji12305,

I have moved the speakers around, but logistics limits their placement. I have lived in the same house for nearly 40 years, and while the furniture has changed over the years, the layout remains pretty much the same. My present speakers are in a similar location as the 'sparkers'. Thanks for the suggestion.

Hi Calvin,

Forgot about the openess factor. Mine are around 50%. I also have a substantial amount of felt on the back stators to lessen boominess. Have tried different combinations, but will tinker some more. From what I gather on a few of your earlier posts, you're not a fan of Licron spray, but I am thinking about using it on 3um mylar to replace my 6um graphite coated membrane. Would the total mass be about the same? My older panels were mostly midrange to tweeter speakers, while my recent ESL's are driven as full rangers, so as you mentioned that could be affecting my perception also. Thanks for your comments.

Hi Jer,

My graphite coated diaphragms seemed to be happiest between 2.5 to 3kv. The bias supply tops out at 4kv so even if I replace the diaphragms to low resistance ones, I'm not sure I will be able to benefit from your higher bias recommendations. Makes sense, though. On a similar path, I replaced my 45:1 trans with 90:1 ones and all of a sudden there was a snap to the sound that brought new life to the panels. Surprised me on how much of an improvement it made. Unfortunately I forgot to heed Bolserst's advice on wiring them up, and fried one of them before I could play my Sousa CD. Been looking for another Scott trans, but they've become rare and expensive. Thanks for your comments.

Hi Lowmass,

I'm sure I have a resonance problems, probably several. My ESL's are constructed using 10 different sized diaphragms, each with its own resonance. In theory they are supposed to augment each other, but who knows. Interesting thought on concentric drives. Although a completely different sound, I've always enjoyed Tannoy speakers. Have also enjoyed following your recent thread. Informative and entertaining. Thanks

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Old 10th April 2017, 06:50 AM   #8
Calvin is offline Calvin  Germany
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I have read it stated that a higher tension will increase the efficiency. this is utter BS!
After so many years of good agreement in teaching our disciples You call me a BSer? Quite disapointing, but maybe I deserved it, as I should have explained more precisely.
Increased mechanical tension alone shows merely no effect on efficiency.
It mainly raises the lower bandwidth limit and allows to drive the panel harder (at least when unfiltered).
But then it allows for possibly higher bias, resp. increased field strength, and reduced stators distance .... both of which increase efficiency.
What do You do when the membrane's tension is too low and there's dynamic instability?
You raise the base resonance by putting spacer dots into Your panel!
The same effect as if You raise mechanical tension.
No different You design a tweeter .... which btw is the theme of this thread, not wideband esls .... notice the difference, jer?
You don't tension as soft as possible, as You don't make the s/s distance larger than required.
In fact, there's an old thread or posts from me about a design utilizing foam mesh as spacers.
The resonance became so high and so low in Q that it resulted in a clean soft rise and a smooth transition into the working range above fs, similar to a good dome tweeter.
Finalizing, yes, the raised mechanical tension alone doesn't affect efficiency considerably in itself, but it allows for more efficient panel designs.


ps. and no, lower mechanical tension doesn't give You more resolution

Last edited by Calvin; 10th April 2017 at 06:53 AM.
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Old 10th April 2017, 02:21 PM   #9
lowmass is offline lowmass  United States
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I did a test once just to explore the "no tension" thing.

Basically I hade 3 plainer magnetic designs intest. All the same materials and mass. All were heavyweights by lectrostat compare.

Two had frames that could tension the diaphragms easily on the fly. The third was same diaphragm BUT it was basically just held in place with no tension. Normally this would have produced a very noisy uncontroled crinkly diaphragm BUT it was built with materials and certain construction details ( mostly high mass and damping) That allowed it to just hang there.

The results were interesting, the one with zero tension had bass , mid bass dynamics very similar to a well damped sealed box cone. The tensioned ones did not. They had the proper rise in bass to work with the dipole arraingment BUT they were always a bit "fuzzyer" and less sharp in there attack and they simply had overhang the untensioned on did not. And the mids were more believeable on the untensioned unit. Just less background noise??

Now understand, These were unusual planers that were a bit higher mass than usual. They were VERY inefficiant! But the dynamics of the untensioned unit was obvious above the tensioned ones.

All the whys and ins and out of the reasions I cannot be sure, BUT I suspect, at least with diaphragme heavyer than the typical stat that resonances associated with tension can blur and soften, or muddy the sound a bit.

I have recently been awarded a patent on a ribbon design that attemps to overcome some of the resonance issues associated with these units. In use you notice two things. 1- they sound different than traditional ribbons.Less confused even under hard drive at lower than usual x overs. 2- under the strobe they show considerably less standing wave activity than traditional designs of same mass.

The point is this, with past experaments and the latest ribbon work it seems to me we often have issues with planers that are simply not as well behaved as we think and tension can at least in some areas amp up the problems...

Last edited by lowmass; 10th April 2017 at 02:26 PM.
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Old 10th April 2017, 04:39 PM   #10
Bondsan is offline Bondsan  United States
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"The bias supply tops out at 4kv so even if I replace the diaphragms to low resistance ones,"

Meant to say, "high resistance ones"
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