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My DIY electrostatic headphones - Page 92

Quote:
Originally Posted by jcx

one sided coating, the thickness of the diaphragm hardly matters to the E field, the force, balance since it is a small fraction of the spacing and the e_r of the Mylar even reduces the small effect of the thickness of the diaphragm more  - do you really get the spacing/centering/flatness within few microns?

Here is the paper that outlines the concept of isolated coatings on each side: http://douglas-self.com/ampins/wwarchive/wwarchive.htm#diel

I went through the math a while back and it seems to be a correct assessment. Intuitively it seems absurd though, so possibly some math trick going on I fell for.

Quote:
Originally Posted by dude_500

But just right is better than too much

Do you have an idea of this tension in Newtons/unit of surface ?

Quote:
Originally Posted by ondesx

Do you have an idea of this tension in Newtons/unit of surface ?

If that's just how much weight do I hang from a unit area circle of mylar, it'd be about 1.1kN/m^2 (approximately 13 pounds divided amongst 16 weights hung from a 10" diameter circle).

Quote:
Originally Posted by dude_500

-I think we mostly do one-side on the DIY ones. Hard to know what retailers do. If you run the math, coating both sides versus one is the same situation. What mathematically would greatly reduce distortion, at least in theory, is having both sides coated but insulated, and both having a few meg-ohm resistance to the bias supply. It'd be very difficult to implement this, I don't know if anyone ever has. I can't find the paper that talks about this at the moment, it's somewhere in this thread.

I probably missed something here, because it doesn't appear very difficult to coat each side of the diaphragm, since after coating one side, the spacer with the copper track for polarization and the corresponding stator are glued on this side. Then the diaphragm and this ensemble (i. e. spacer/stator) are flipped and the coating of the other side is easily done. Afterwards, the spacer with the copper track facing the diaphragm and the second stator are glued on this side.

Thus, each spacer have a track connected to a small "ear" with a hole, where the wires for the polarization are attached. I suppose that the same polarization wire can be connected to both "spacer tracks"...

Of course, all the holes and the soldering/connections must be done before gluing all these pieces all together, in order to preserve the diaphragm.

The only unknown is the electrical quality of the glue : will be good enough the contact of the "spacer track" and the membrane, through all glues ?

Did Stax normal bias have both sides of the diaphragm coted?

Quote:
Originally Posted by ondesx

I probably missed something here, because it doesn't appear very difficult to coat each side of the diaphragm, since after coating one side, the spacer with the copper track for polarization and the corresponding stator are glued on this side. Then the diaphragm and this ensemble (i. e. spacer/stator) are flipped and the coating of the other side is easily done. Afterwards, the spacer with the copper track facing the diaphragm and the second stator are glued on this side.

Thus, each spacer have a track connected to a small "ear" with a hole, where the wires for the polarization are attached. I suppose that the same polarization wire can be connected to both "spacer tracks"...

Of course, all the holes and the soldering/connections must be done before gluing all these pieces all together, in order to preserve the diaphragm.

The only unknown is the electrical quality of the glue : will be good enough the contact of the "spacer track" and the membrane, through all glues ?

I doubt contact cement will conduct at all. Also, if going for the full effect of isolating the two sides with high resistance connection to bias, it would be necessary to keep the coating away from the edges or charge current could flow across the two sides that way. I think that would be the hardest thing.

Quote:
Originally Posted by jgazal

Did Stax normal bias have both sides of the diaphragm coted?

I recently repaired some SR-X MK3 and they appeared to be coated on both sides but it was hard to be sure. I didn't want to touch them with anything to try to measure them.

Quote:
Originally Posted by dude_500

I doubt contact cement will conduct at all. Also, if going for the full effect of isolating the two sides with high resistance connection to bias, it would be necessary to keep the coating away from the edges or charge current could flow across the two sides that way. I think that would be the hardest thing.

I recently repaired some SR-X MK3 and they appeared to be coated on both sides but it was hard to be sure. I didn't want to touch them with anything to try to measure them.

So although both sides of the diaphragm may be coated, there are no two bias input pins for each channel, right?

Did normal bias amplifiers have two separate bias regulators?

Quote:
Originally Posted by jgazal

So although both sides of the diaphragm may be coated, there are no two bias input pins for each channel, right?

Did normal bias amplifiers have two separate bias regulators?

Even doing what I described (which I don't think any retail headphones ever have, and probably no DIY either), you'd only need one bias supply and one bias wire from the amp to each side. You could take one wire into the headphones and have two high value resistors inside each side to break the wire out to each side of the diaphragm.

The headphones coated on both sides just connect the same bias line to each side, so they also only need one line/supply.

I'm used to using heat to shrink plastic film, the kinds used for covering airframes and wings of model aircraft.

I used the heat gun a long way away from the mylar film to keep the temperature low and controllable. At first the film sagged, then tightened as I moved the heat closer VERY slowly. As soon as the wrinkles disappeared I removed the heat. I haven't been able to test the result yet tho.

w
I don't see why coating both sides should make any difference, it's just a static charge after all.

I wondered about the effect of coating both sides of the diaphragm, however I put this aside as I attempted the practicality of assembling my first pair of phones.

It's not easy perhaps to visualize the exact arrangements inside the electrostatic headphone capsule until on starts to construct one from scratch.

I discovered that, for me, the contact to the film sorts itself out like this:-

1. You take one spacer, coat the copper area carefully with an even film of contact adhesive, set it aside to dry. Start to tension the mylar with the bicycle pump. When the mylar looks good, drop the spacer onto it, adhesive side down. Press with the fingers all round the edges to ensure adhesion, before removing the ring from the surrounding mylar with a scalpel, carefully removing any rags. The copper on this spacer plays no role in connecting to the diaphragm, it's just there for symmetry.

2. Now the antistatic can be applied to the film, on the opposite side from the spacer.

This means that when the diaphragm is assembled with the second spacer, the copper on this spacer butts up against the coated side of the diaphragm, and is available to provide a consistent, low-ohmic connection to the periphery of the high-resistivity diaphragm. Usually protruding tabs are formed at the edge of PCB of both spacer and stators to allow connection.

w

I wish that I was good at DIY. I think it would be so cool to build a pair of electrostatic headphones. What a life experience . Some of you guys/girls should go into engineering!
A heat gun can't shrink the diaphragm enough to make it stable, in my experience.

Sent from my SM-N9005 using Tapatalk

Heat shrink of most PET film is about 2% in x/y direction and 1.4% in z according to all the datasheets I've looked at.  The only one I've seen with a much different spec is the special heat shrinkable Hostaphan which is something like 20%, but way thicker than what we use (12 micron minimum).  Probably best to use mechanical tensioning and then heatshrink after if needed.

Edited by n3rdling - 5/28/14 at 11:19pm
Could someone please give me some details about how the Stax Pro Bias headphones are constructed? I think I might try my hand at building an electrostatic and I plan on using the SRM-252S as the amp. I know from reading this thread that the spacers should be 0.5mm in thickness (for Pro Bias), but how thick should the stators be? Also if I want to make a rectangular driver (long side vertical, like Stax), what driver dimensions should I be using? I would appreciate any help I can get .
Edited by ToddTheMetalGod - 5/29/14 at 3:01am
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