My DIY electrostatic headphones
Jan 15, 2016 at 12:26 AM Post #1,951 of 4,061
Yes, 4.32 mm is nice.  It'll be a lot better than 0.8 mm for 230V bias voltage.
 
As for using mic for measurement, I think it's better to use your own ears.  If you think they sound nice, then it's a success. 
beerchug.gif

 
Jan 19, 2016 at 2:44 PM Post #1,952 of 4,061
Hello,
 
I came across this thread several days ago. Reading the whole discussion took quite a while and was very informative. My compliments first to Wachara for his builds, his will to share so much knowledge and to tame and guide all the ideas in this thread. A big nod from my side!
 
I have been thinking about building my own ESL headphones since more than 20 years and never got to it -shame on me-. Many answers I had have already been answered here. What got me started was an article by Philippe Hiraga in L'Audiophile. Still being in school back than.
 
Now I own a Stax Lambda Signature and a SRM1/MK2 (thanks to Kevin G. here, he gave me the right advice how to repair it).
 
Reading the thread I gained a few ideas that I would like to share and discuss here, I also found some topics only described but not explained. Please correct me if I am wrong, I have just engineering knowledge, no building experience.
 
Please allow me a remark on the Resistance of the membrane:
The membrane gets moved by the voltage applied to the stator (Coulomb Law). The deflection of the membrane will be half-sine or parabolic like. If charges can move too easy on the membrane, they will be attracted by the stronger electric filed in the middle, where the distance is smaller. So the charge would shift to the center, reenforcing the pull in the center. This could lead to higher distortion and/or instability. Therefore you need to have a fairly high resistance.
 
For the stator I have the idea shown at http://up.picr.de/24335672lm.jpg
based on the following: (sorry, I have no permission to post pictures yet)
 
I do not understand the center hole on the Stax 009. To me it seems too small to significantly reduce the forces acting on the center of the membrane. On the other hand applying more force to the edge of the membrane might help to move it more uniformly.
(I think that the center-hole is truly for acoustic reasons. As the membrane movement is biggest at the center, it makes sense to me, to open up the center)
 
The stator itself has an eigenfrequency within the audible range. Getting the stator more stable will always be good. So I have to make it stiffer, where most of the bending takes place and/or reduce the mass where most of the motion takes place.
 
I want to control/reduce the forces on the center of the membrane.
 
So I chose an oval stator (minimizing the dominance of eigenfrequencies of circular objects), started the copper about 3mm away from the spacer (to keep capacity low) and increased the hole size toward the center.
 
The active membrane would be 78x102mm, open area is 32%. But increasing toward the center, where the membrane moves most of the air, so it's hard to tell, how it would compare to an equal spaced stator.
 
I am curious to read what you think about this.
 
Many greetings
Georg
 
Jan 20, 2016 at 11:00 AM Post #1,953 of 4,061
Hi Georg,
 
It's always good to see someone interested in building ES headphones.  I have tried to explained all of my knowledge in this thread.   But since I'm not an engineer,  there is a limitation to what I can share.  I am more into the actual making rather than going into too much about the theory.  It helps from time to time to have an engineer helping me out.  Thank you.
 
You have a good idea on how to make the stators.  Please go ahead and make them and share with us how they turn out.  That's the only way to prove what you think is true.
 
There is one thing that I would like to comment on the active membrane size you're proposing.  As you might have known, I've been making a lot of headphones, and I know for sure that with the width of 78 mm, you'll have a very difficult time getting the diaphragm to tension just right.  If I were to make another pair, my width on the active diaphragm for the oval shape headphones would not be more than 76 mm.  I think 74 mm is just right.  I would probably increase the length a bit to compensate for that.  So it might be around 110 x 74 mm.  
 
By the way, here is your stator picture:  
 


It looks really nice.
 
Have fun!
 
Wachara C.
 
Jan 20, 2016 at 3:56 PM Post #1,954 of 4,061
Hello Wachara,
 
thank you for the kind welcome.
 
I will follow your suggestion and go for 74 x 110 mm. Having no experience here and not really intending to start with a failure, I kindly accept your advice. I totally agree, that there is no way around building and listening.
 
I updated the stator, (copper not shown): http://up.picr.de/24345854bg.jpg
Next I will design the spacers, cable connectors, etc. The G-code needs to be created and I have to switch my CNC milling machine on (has been resting for a year now).
 
Before I start milling I want to find a way to measure the free air frequency, so I can generate membranes with different tensions to test.
 
Do you think one could test the membrane for stability before gluing it to a stator, on the strecher?
[As for a stretcher I tend more and more to an inner tire on a frame. I would coat the Mylar on the stretcher, bring a spacer and a stator in contact with it, so that the Mylar is stretched over the spacer. The stator connected to ground, the spacer to 580V + 280V (860V) [high valued resistor needed for safety!!!]. I think one could see if the diaphragm becomes unstable before gluing] 
 
Kind regards
Georg
 
Jan 20, 2016 at 10:57 PM Post #1,955 of 4,061
Sadly my first few attempts at CNCing my stator design ended in failure (Laminate PCB is just too weak a material to hold up to so many 1mm holes. I'll increase my my hole diameter to 1.6mm, my pocket depth will be reduced to 0.8mm, and I'll switch to the suggested triangular pattern (as opposed to hexagonal) to increase stability.
 
Anyone have experience with the machinability of FR-4 vs Laminate PCB?
 
The 1mm hole model performed quite well in analysis, but it just proved too difficult to machine. It might be worth re-visiting the design when I have access to electroplating equipment, as I could use stiffer materials such as stainless steel and then plate the stator in copper or silver.
 
I might be a bit ambitious for a first time EStat maker.
 
Jan 20, 2016 at 11:06 PM Post #1,956 of 4,061
  Hello,
 
I came across this thread several days ago. Reading the whole discussion took quite a while and was very informative. My compliments first to Wachara for his builds, his will to share so much knowledge and to tame and guide all the ideas in this thread. A big nod from my side!
 
I have been thinking about building my own ESL headphones since more than 20 years and never got to it -shame on me-. Many answers I had have already been answered here. What got me started was an article by Philippe Hiraga in L'Audiophile. Still being in school back than.
 
Now I own a Stax Lambda Signature and a SRM1/MK2 (thanks to Kevin G. here, he gave me the right advice how to repair it).
 
Reading the thread I gained a few ideas that I would like to share and discuss here, I also found some topics only described but not explained. Please correct me if I am wrong, I have just engineering knowledge, no building experience.
 
Please allow me a remark on the Resistance of the membrane:
The membrane gets moved by the voltage applied to the stator (Coulomb Law). The deflection of the membrane will be half-sine or parabolic like. If charges can move too easy on the membrane, they will be attracted by the stronger electric filed in the middle, where the distance is smaller. So the charge would shift to the center, reenforcing the pull in the center. This could lead to higher distortion and/or instability. Therefore you need to have a fairly high resistance.
 
For the stator I have the idea shown at http://up.picr.de/24335672lm.jpg
based on the following: (sorry, I have no permission to post pictures yet)
 
I do not understand the center hole on the Stax 009. To me it seems too small to significantly reduce the forces acting on the center of the membrane. On the other hand applying more force to the edge of the membrane might help to move it more uniformly.
(I think that the center-hole is truly for acoustic reasons. As the membrane movement is biggest at the center, it makes sense to me, to open up the center)
 
The stator itself has an eigenfrequency within the audible range. Getting the stator more stable will always be good. So I have to make it stiffer, where most of the bending takes place and/or reduce the mass where most of the motion takes place.
 
I want to control/reduce the forces on the center of the membrane.
 
So I chose an oval stator (minimizing the dominance of eigenfrequencies of circular objects), started the copper about 3mm away from the spacer (to keep capacity low) and increased the hole size toward the center.
 
The active membrane would be 78x102mm, open area is 32%. But increasing toward the center, where the membrane moves most of the air, so it's hard to tell, how it would compare to an equal spaced stator.
 
I am curious to read what you think about this.
 
Many greetings
Georg


Really amazing observation, and it explains why the large centre holes appear in high end Stax models.
 
In your design, is every layer of holes a different diameter, or are you using a few set diameters for several layers at a time?
 
Jan 21, 2016 at 8:05 AM Post #1,957 of 4,061
hi spritzer or chinasettawong wachara etc !! and all the rest k gilmore ,and all stat lovers!! sorry to but in , im new to the forums ,im  trying to rebuild my sr 404 sig membranes  with 1 micron .......phew, im at my wits end trying to get it wrinkle free and not to rip, i had it once the coated the mems with fine graphite ,once in the brass ring", and they arced so bad they burned some stator paint off!! any ideas how i can fix this?? and the + - connections came apart so i delicately soldered them to the same point but on the back of the stator, is any antistatic pc cleaaner gel good for membranes? and do you know what i can do with the burned stator? ,all the best ps whats the best glu im using evo stik contact but its hard to get off once a mistake is made is modellers cement glue better ps i use a srm3...cheers!! pps i just held the assembly together using a dry towel, what paint can i use to re paint the stator burn? its not near the holes nearer the brass ring edge 4 mm sq id say... and is it ok to solder the stator connections on the back of the  stator? i  ,i scraped a 2 mm sq patch on the same point and delicatly soldered them  is this ok im in the uk and finally is adding ink to the antistatic coating gel improve the charge sound etc ,i blame the damm grapthite causing the burn soz for long post, but im quite poor, and want them fixed, also have som n bias lambdas, but they sound crackily ,not bad but im a stikler for perfection!! as we all are!! any help from the really knowledgeable guys will be greatly appreciated will changin the thick dustcover material on my sr lambdas, to 1 micron help with openness or should i leave alone ..??? many thanks cheers guys and gals!!
 
Jan 21, 2016 at 1:49 PM Post #1,958 of 4,061
 
Really amazing observation, and it explains why the large centre holes appear in high end Stax models.
 
In your design, is every layer of holes a different diameter, or are you using a few set diameters for several layers at a time?

 
Hello Ghost Pack,
 
I just intend to use different drill diameters. My stator is goind to be flat.
 
I considered the option of a curved stator, giving more space in the center. But this would really be hard to machine. As I am a beginner I will go the route with only one unknown, for me the variation in drill diameters.
 
I seriously consider using copper covered UD-CFK as stator. I can get a young-modulus of the laminate (using pitchfibres) of 200 to 400 GPa, what is above steel, and this at 1/4 of the weight. Compared to glass fibers, pitch-fibre UD-CFK should be 4 to 10 times stiffer, at a slightly lighter weight. I think this could theoretically shift the 1.5kHz stator eigenfrequency out of the audible range, although I do not know if this would improve anything.
 
But: as I mentioned before, I will only change one parameter at the beginning. Need to define my baseline.
 
Many greetings
Georg
 
Jan 21, 2016 at 2:56 PM Post #1,959 of 4,061
It should show up on measurements if the stators really are resonating, I'd think. And if it doesn't it is probably insignificant. Interesting.
 
Jan 23, 2016 at 11:49 AM Post #1,960 of 4,061
Hi Scotsstax,

I'm sorry that I might not understand your questions very well, but I'll try my best.

If I'm not mistaken, the driver of SR404 is built by actually gluing the staors and spacers together. To open it, you actually have to rip everything apart, right? I've only opened up the SR507 drivers before, but they are constructed differently. For SR507, you only have to unscrew some screws of the deiver holder to disassemble it. The stators of SR507 look to be perforated matel with powder coating. If they are the same as SR404, you can use woman's finger nail clear paint to paint over the burnt area to fix it.

I personally don't like to use 1 micron Mylar as a diaphragm. I think it is too thin and it's very difficult to tension it just right. However, it certainly can work.

I always use the antistatic gel or the floor cleanser as my coating material. I prefer them to graphite or anything else.

I also prefer contact cement glue to any other type of glue.

Good luck!

Wachara C.






Sent from my SM-N9005 using Tapatalk
 
Jan 25, 2016 at 1:55 PM Post #1,961 of 4,061
hi chinasettawong!! love your work !! just awe inspiring!!., can i run a  frequency responce graph on my pc with a mic goin in to the usb port to get even membrane tension??? thanks as ever my freind in diying staxes and orpheous clones  take care !!
 
Jan 26, 2016 at 1:09 AM Post #1,962 of 4,061
  hi chinasettawong!! love your work !! just awe inspiring!!., can i run a  frequency responce graph on my pc with a mic goin in to the usb port to get even membrane tension??? thanks as ever my freind in diying staxes and orpheous clones  take care !!

 
I've never done that, but sounds interesting.  Please try it and let us know your results.
 
Wachara C.
 
Jan 26, 2016 at 8:00 AM Post #1,964 of 4,061
also maestro, can weak bass be a sign of  only using  washing up liquid as a coating on the membranes?? im gettin ok detail, but bass is weak any suggestions appreciated mate!! as in coatings tensioning , ps im in the uk!!
all the best  scotstax
 

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