[n3rdling]

If you don't have access to a vacuum hold down table, you can level the spoilboard and use double sided carpet tape to hold down the PCB pretty flat.  A more expensive option is to use a floating head.
 
There are two programs I know of to do what you describe:
http://www.pcbgcode.org/
http://www.autoleveller.co.uk/

 

[jgazal]

Okay, no feedback, I must have said something nonsense. More down to earth, how much reduction in efficiency (at 30Hz, 300Hz, 1kHz and 10Khz) one would expect adopting a semi-coated, single-side, diaphragms like these:
 

 
I know you can say “go and build one yourself to test it”, but right now I do not have the practice you guys have…

 

[dude_500]

  Okay, no feedback, I must have said something nonsense. More down to earth, how much reduction in efficiency (at 30Hz, 300Hz, 1kHz and 10Khz) one would expect adopting a semi-coated, single-side, diaphragms like these:
 

 
I know you can say “go and build one yourself to test it”, but right now I do not have the practice you guys have…

 
Rather than "go build one", I'm going to say go simulate one for yourself. It would be tremendously difficult to conceptually analyze what any of those patterns would do. There are so many dynamics at play here.

 

[jgazal]

You are right. The patterns may alter the vibrations modes itself. Perhaps a coating pattern that match the exactly the holes in the stators. But then one would have half the coated area and probably a strong decrease in sensitivity. (no constant charge effect...). Thank you for your response! 

 

[chinsettawong]

I received a few pieces of these car speaker grills from a friend.  So, I put them to good use. 

 

 

 

[wink]

Your artisan streak shows up again.  Well done.

 

[OnyxOcelot]

jgazal, do you have a plan for how to coat a diaphram as such?  Perhaps a stencil held on top of diaphragm with your coating material sprayed or brushed on through?
 
A hopefully quick question with a long explanation:
I put together another set of rectangular drivers yesterday.  These have very thin spacers(.015 in or .381 mm), which unfortunately are double sided copper plated board.  I say unfortunately because I have been having trouble isolating one side from another.  Inevitably, with the number of screw holes around the outside, and the very little isolating material between the two copper plates, there are some very small burrs or strings of copper connecting one side to another, even after a considerable effort at their removal.  After my very best attempt at removing any and all burrs, I measured a resistance of ~250 mega-ohms between the top and bottom of the spacer.* 
 
Assuming that perhaps this level of resistance between stator and diaphragm (once the unit was put together) might not affect the unit's performance, I put the unit together and tried it.
 
Question 1: will this very high resistance connection between stator and diaphragm cause a detriment to performance in the unit?  Should a stator and diaphragm be completely isolated?
 
Once I put the unit together, it seemed to work.  However, when I put the driver down and increased the volume, it began sparking along the sides (where the copper of the spacer and the copper of the stators are exposed and close to one another).  I don't know if this is because the gap is so much smaller than my previous set (both because the spacer is thinner *and* double sided) or because the edge is not covered in tape (as were my previous sets, which didn't use screws).
 
Question 2: do your drivers spark along the edges and is there a way that you avoid this (electrical tape, hot glue, etc.)?  I suppose this all could be due to my double sided copper board, so if anyone knows where to source thin copper plated board that is single sided in the USA, let me know.
 

Thanks for the advice,
OnyxOcelot
 
 
 
 
*I should specify that my multi-meter would jump back and forth between a very high resistance and Open Loop. 

 

[chinsettawong]

I think you still have some copper dust sticking to the side of your spacer.  I always use a sand paper to sand the edge of the spacer.  Sanding at an angle also helps remove some copper near the edge.  If all else fail, you can still etch out the copper on one side of the PCB using chemical.
 
About the PCB supplier in the USA, there is one that I've bought PCB from:    http://www.ebay.com/itm/FR4-Copper-Clad-Laminate-PCB-Printed-Circuit-Board-Material-FREE-SHIPPING-USA-/120802756087
 
The material is pretty good.
 
Please show us your drivers.
 
Wachara C.

 

[OnyxOcelot]

Also, I would like to solicit criticism for this stator design.  It has slots rather than holes, and I made it simply to cut down on machining time.  On my CNC, it took over 20 mins to cut each stator with holes.  With this design, it took less than 10 mins.  How might it affect the sound produced?
 

 
Thanks,
OO

 

[chinsettawong]

  Also, I would like to solicit criticism for this stator design.  It has slots rather than holes, and I made it simply to cut down on machining time.  On my CNC, it took over 20 mins to cut each stator with holes.  With this design, it took less than 10 mins.  How might it affect the sound produced?
 

 
Thanks,
OO

 
Slots are fine.  I don't see any problem with that at all.
 
If I were you, I would paint the stators.  You want them to be well insulated.  That way you won't get spark so easily.
 
What is the measurement on your stator?
 
Wachara C.

 

[jgazal]

  jgazal, do you have a plan for how to coat a diaphram as such?  Perhaps a stencil held on top of diaphragm with your coating material sprayed or brushed on through?

 
I have never built an electrostatic headphone. It is just a theoretical exercise, because I overthink things a bit. I just want to better understand how the transducers work. Please follow Wachara and dude_500 advices. They have built fully operational units.

 

[OnyxOcelot]

   
Slots are fine.  I don't see any problem with that at all.
 
If I were you, I would paint the stators.  You want them to be well insulated.  That way you won't get spark so easily.
 
What is the measurement on your stator?
 
Wachara C.

I figured as much.  The slotted stators should have an equal amount of open and conductive area as one with holes.
 
What type of paint do you use?  And do you cover them entirely or just the edges where they touch the spacer?
 
The stators are ~ 88 x 76 mm.  I would like to make larger ones for the next attempt.

 

[chinsettawong]

  I figured as much.  The slotted stators should have an equal amount of open and conductive area as one with holes.
 
What type of paint do you use?  And do you cover them entirely or just the edges where they touch the spacer?
 
The stators are ~ 88 x 76 mm.  I would like to make larger ones for the next attempt.

 
Since you don't try to etch away any copper, I would paint the whole stator.  Acrylic paint is what I always use.

 

[davidsh]

It is ofc quite important to leave an area unpainted so you can solder wires etc.
How do you connect a wire to the diaphragm without making a gap between the stators and diaphragm?

 

[n3rdling]

The wire doesn't connect directly to the diaphragm.  It connects to the inner side of one of the spacers (which is why single sided PCB is used here) which then presses up against the coated side of the diaphragm, acting as a "charge ring".  By using tabs on the spacers there is no extra gap at the connection point.