[wppk]

thank you both,Kerry an Georg, well, as I said, I am not intending to do it myself, I was just imagining a possibly new idea. Not knowing if it was really new.
Maybe it is because I am french,  but there is something I don't understand, Georg, when you talk about the FR4. What is FR4 ? if it is not too long to explain.
yes, I feel like reading the whole thread.
 
there is also something very interesting for me in what you say here, and it brings a question or more, because I succeeded in repairing several of my stax lambda pro headphones ( I have a recording studio, giving french dubbing for movies lessons and my students are happy to work with these, which I really want them to do, to give them an idea of what quality is, and then, make them feel like making quality in their acting) but, couldn't on some.I started to read on head-fi about it, but couldn't find any thread where people had done what I did to repair them, and how to make it when their is a persisting problem. To explain : My stax ( BTW the lambda pros are far better than the 007 or 009 for monitoring, and my favorite is a (very rare) " spirit lambda pro" for that) had, of course, because they were old, the usual static issue caused by the protective membrane teared off by aging, and, after a while, the "heat" of my head made condensation, microscopic , but important enough to reach the stator and make little short circuits. and then static noises.
I noticed that, because they worked perfectly well when I had not used them for a while, and, after one out two hours, started to make these disturbing static noises. most people say that no one can repair these, because the parts are glued, and then, opening is destroying them. Also, that the smallest dust particles can also give these static problems, and when opening them, dust gets in it and the driver is wasted. Well, I had nothing to loose, indeed, with those among my stax which didn't work well anymore, and I decided to try to mend them by myself. I had tried before to have it done by someone who said he was a specialist, but when I received my headphones back, nothing had changed.
well, I had to find Mylar to replace the damaged one, and a good glue. That is what I did. Opened the driver, not until the membrane that make the sound, but only reaching the protective one, and made it so that a new protective membrane was here and couldn't move. It worked really great, and effectively completely repair 4 lambdas, like that. But for those which had an imbalance, I didn't find a way to mend. And for some, too, I still had static after that (not on the four ones I mentioned, that are definitely repaired) . probably because of dust on the central membrane. dismounted the driver completely, and changed the membrane, which was damaged, with the same Mylar I used for the protection membrane. It worked, but the sound was weak, like I already thought that it would, and I was even surprised to have any sound, because the Mylar I had found was not conductive. Tried, then, to cover the Mylar with a very very thin gold leaf, the kind of gold leaf which is used by painting menders, you know, to fill holes in gold, and platter the frame of paintings with gold. I had that because my mother used that when she was still on earth... but I had no better result. Bought a conductive spray, had no better result. Now, what you say :"you only want the active area of the membrane conductive on the stator." is something new for me. Do you think that it could have worked if I had not made that on the complete membrane ? I have seen other people on head-fi saying that to recoat a membrane, one could use a simple anti static liquid... Would that be true ? I am quite lost now in my mending, for I would like to repair my other stax, and have been stuck for days now at this point. Left a classified to find a lambda with only one driver working, and I just found one form a very nice dutch man and head-fier. Will receive it soon. But I have other stax lambdas to repair, and so, I would like to know how to make a complete repair in any situation. to re-balance unbalanced drivers. To avoid the statics. And to change the membrane.
Maybe all the solutions are on head fi, but not all together in one post and thread, and I think that would help to have it in an easy to find place, with all necessary details.
many people have an old damaged lambda pro, I think. Maybe they would be happy to repair it you don't need too much apparatus and machines, just a cutter, soldering iron, soldering lead, glue, also another kind of glue, which has to be heated to melt to be used ( sorry can't think of the right expression in English) long lasting Mylar, observation and patience.
and the knowledge that I don't have about when the repair cannot by completed with my system.  
Does anyone have experience and solutions for that ?

 

[GvTT]

Hello wppk,
 
although I think others like Wachara can answer your questions better, I will try to fill your questions.
First of all I have to mention that I have not yet built or repaired any ESL speaker. I have the tools and material ordered, started building a Mylar stretcher (inner tyre stretcher).
 
When I spoke of FR4 I was referring to the glass fibre reinforced epoxy plates use for makeing PCB's in electronics.
 
As for your tries to make the membare conductive: you need a very low conductivity, in other words a very high resistance. This is mandatory to keep the static charge from moving on the surface of the membrane when the membrane if moving (making sound). Hence gold, conductive sprays, etc. are not the prime choice. Some people rub carbon in, use Elvamide and other used antistatic clearners, like Wachara. His choice sound logic to me, is prooven, so I will use this method in my first trials.
 
There was a french magazine in the 70th?, publiched by Hiraga, the L'Audiophile. One of their articles covered the built of an ESL headphone by Philip Hiraga. Maybe you can loan it via a library. The description is not as complete as in this thread, but might be easier for you to read, as it is in French and much much shorter.
 
As glue to fix the membrage Wachara uses "UHU contact", what you should be able to get easiely. It is available here in Germany, and UHU is marketed in France as well. As Mylar is not easy to glue, I recommend this too.
 
When making the membrane assembly, the trick seems to me to get the right tension. I will try to measure it's frequency response on tab with a microphone prior to gluing it. As to this tread it sould be somewhat between 100 and 150Hz, and mainly affect the bass, as long as the membrane stays stable.
 
As for the active area of the stator:
an ESL speaker presents a capacitive load to the amplifier. This load is defined by the spacing of the stators and their conductive area. By reducing the conductive area to the area where the membrane can actually move, you minimize the capacitive load withpout loosing sound pressure. The amplifier just has to do less work. (leaving the stator conductive everywere is just like adding a resistor in parallel to a conventional speaker. You can still listen, but your amp has to work harder, probably not increasing sound quality by this).
 
Greetings
Georg

 

[wppk]

WOW ! that's an answer ! thank you very much for all your so nice explainations. so nice  of you !

 

[GvTT]

Hello,
 
a link for those that like math:
http://www.high-amp.de/html/electrostatic-principle.html
On this page it is explained in more detail why the membrane should have a high resistance.
Andreas Rauenbühler is referring here to a membrane staying flat while moving.
This assumption simplifies the math but reflects the general situation.
 
You find his main page at:
http://www.high-amp.de/html/frame.html
 
Greetings
Georg

 

[wppk]

oh dear ! it 's far too simple for me ! 
seriously, the concept is easily understandable, but the math..... I always had problems with math.. Happily, people like Andreas exist for people like me to put the result in their ears only, nor even passing thru the head. Too bad, I would have liked to be able to do so excellent work.
thanks georg

 

[chinsettawong]

Looking at the formula, my head is already starting to swell.  

 

[Muamp]

Hi chinsettawong,
 
I came across your blog entry by chance, and that made me decide to become a member of Head-Fi forum.
So far what I have read of the 135 pages is awesome information, and I love your latest ESHS designs, professional finish!
I have been DIYing my own ESHS for about a year now in my spare time, and would love to post some photos of my still prototype panels and energiser, but as a new member I am not yet allowed to post photos, just text posts. I will be allowed to post photos after a while as a member.... that's if your interested in seeing them?
But, I will also want to pick your brain, especially on matters like the mechanics. I have a home CNC for copper clad drilling and cutting and PCB making, but not much to produce / mould / print plastics etc.
I guess that many of my questions will be answered by the time I have read all 135 pages in this thread....
I will keep reading, and probably asking some questions real soon....
 
David (Muamp).

 

[chinsettawong]

Hi David,
 
I would love to see your work.  Please do share your pictures (lots of them) and your experience with us.  I'm sure that we can learn from each other.
 
Wachara C.

 

[chinsettawong]

I managed to cut some parts today.  They didn't turn out as good as I would like to, but let's see how they'll make sound.
 
The stators are cut out from 1 mm PCB and spacers are 0.5 mm.  I'll try to cut some stators from a 0.6 mm PCB tomorrow.  The holes are 0.5 mm and the gap between two vertical holes is 0.25 mm.  The active area is 8 mm.  Now I need to find some really small cables to with the earphones.
 

 

[GvTT]

Hello wppk,
hello all,
 
I found the link I promised wppk: http://www.amateuraudio.fr/images/audiop1.pdf  (Philippe Hiraga, L'Audiophile 1989)
This article started my interest in ESL Headphones.
 
@Wachara: I think you should go much thinner with spacers and the stator, considering the small diameter.
The deflection of the membrane is going to be far less than in a full sized headphone. The resonance frequency of the stator is much, much higher, you will not need the thickness of the plates as machined. I would expect the sound not to pass freely through there. I don't have the formulas at hand, but for doing the scaling, I would try to keep the resonance frequency of the stator in the range of a full sized one (or choose then thinnest material I dare to work with if this is the limiting factor).
 
I would not be surprised if you can go with 0,2 to 0.25mm spacer thickness and the same for the stator. The required membrane tension is probably much lower then in full sized headphones. But this is just a feeling, I am curious to read on your results.
 
The parts look really nice. Congratulations to your CNC. Drilling 0.5mm that close is not everybody's favorite. Form the picture I can only guess some missalignments. Did you pre-drill with a sturdy centering drill prior to drilling the 2xD with 0.5mm?
 
Greetings
Georg

 

[chinsettawong]

Hi Georg,
 
I know I should go with much thinner materials.  However, I don't have those on hand at the moment.  
 
I was really surprised that my DIY CNC could actually do a pretty good job on such small parts.  There was no misalignment.  It's just that my CAD, for some reasons, did not allow me to cut the circle and the tab in one go.  So, I had to cut the circle and the tab afterword.  It turned out that the cuts were overlapping.  
 
Anyway, let's make them sing first and then we can do some modifications later. 
 
Wachara C.

 

[ThePCWizard]

Interesting Design you have for your headphones, I don't have access to the materials needed to make electrostatic headphones, but I now have some design inspiration for a pair I've been planning!

 

[GvTT]

Hi Wachara,
 
as for the scaling of the speakers to find the right dimensions for you "in ear" I came up with this:
 
Full size speaker (headphone)
diameter: ca. 80mm
spacer 0,5mm
=> membrane displacement +20% safety = 0,5mm => displacement = 0.4mm
 
In Ear:
diameter: ca. 10mm
membrane displacement = 0.4mm * 80mm/10mm = 0,4/8 = 0,05mm

If you reduce the spacer to 0,2mm you increase the electrostatic forces by factor 2.5.
This will increase the membrane displacement by a little less, not knowing how much, I assume it being proportional.
=> Membrane displacement expected: 0.125mm (0,05mm * 2,5)
Adding 20% safety, I come up with 0,15mm
 
(spacer 0.175: factor 2.86 => 0.05 * factor * safty =  0.17mm)
 
So I would try 0.2mm spacer thickness.
 
You could try to machine the spacer down or mill a recess in the stator.
If you recess the stator you need to find a different way to connect the stator electrically.
One way could be to drill a hole, insert a copper pin from the rear, almost flush with the surface and solder it. Afterwards you have to grind the solder spot flat, flush with the surface.
 
As for the stator thickness: a plate stiffness is proportional to the power of 3 of it's lateral size. => Half the diameter of the plate means a stiffness increase of 8, mass going down by 4 => Eigenfrequency increases by factor 32. And this is just for halfing the diameter.
And again, for those who like math:
https://en.wikipedia.org/wiki/Bending_of_plates
https://en.wikipedia.org/wiki/Vibration_of_plates
 
In other words, the stiffness of the stator should not be any issue. As long as you can handle the material you will (most likely) be fine.
Have you thought about etching the stator from a metal-foil?
 
Greetings
Georg

 

[Muamp]

I still cannot add photos to threads or to change the default avatar. How do I get permissions to do this?
 
David.

 

[wppk]

hello there
I want to thank you very very much indeed, because owe to your explaintations I was able to change the main membranes of all my stax lamdbas and they work perfectly now. Well, just finishing the last now but there is no reason why it should not work.
I couldn't control the tension of the mylar, but the two ways sound identical, evenif not scientificly measured. didn't use the same glue as you did, had no opportunity to find it yet, will tell you, if you whish, if it is tille working well after a while
i am very happy to have been able to do that. Thanks to you again !