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My DIY electrostatic headphones - Page 104

post #1546 of 1552

I have been reading the SR-009 imbalance thread and I think it is better to post my questions here.

 

Humidity, diaphragm tension and diaphragm coating resistivity were already mentioned in this thread. But humidity is usually mentioned as a factor when using the drivers and I have not found any mentions of the relationship between humidity and the coating process.

 

This article describes the effects of humidity in very sensitive production processes: 

 

Quote:
 

By far, the most pressing need for humidity control in a semiconductor cleanroom comes from photoresist sensitivities. It's photoresist that demands the tightest (most expensive) control limits because its properties are so sensitive to relative humidity.

Actually, both relative humidity and temperature are critical for resist stability and precise dimensional control. Even at constant temperature, photoresist viscosity decreases rapidly with increasing relative humidity. Changing viscosity, of course, changes the thickness of a resist film spun-on by a fixed coating recipe. Reference 2 cites an experimental demonstration in which a three percent variation in relative humidity produced a thickness variation of 59.2 A (sic) in resist thickness.

In addition, resist swelling following a bake cycle can be aggravated by water absorption at high relative humidity. Resist adhesion can also be adversely affected by high relative humidity; low humidity (~30 percent) facilitates resist adhesion even without polymeric modifiers, such as hexamethyldisilazane (HMDS).

Relative humidity control in a semiconductor cleanroom is not optional. But, from time to time, it's good to review the reasons and bases for common, universally accepted practices.

"Why control humidity in a cleanroom?", Robert P. Donovan, Solid State Technology

 

Do you feel from your experience that coating the diaphragm in very humid days derives more drivers with imbalance? 

 

I see that DIY drivers use a FR4 ring to hold the diaphragm. What material the SR-009's ring is made of? Is it metal like the stators?

 

I wonder if, contrary to the use of a FR4 ring to hold the diaphragm, a metal ring worsens the dimensional control of the ring/diaphragm structure.

 

Anyway, if it is such a precise process, a 95% reject rate is not bad at all. And congratulations to all DIYers of this thread that achieve such stability!

post #1547 of 1552

I don't think humidity while coating will matter much for arcing, but it might have a slight effect on the resistance of the coating.  Humidity plays a factor in arcing because the voltage breakdown of air gets decreased with more humidity thus an arc in the small gap between stator and vibrating diaphragm.  Think of it like making the gap smaller.  Humidity while coating wouldn't really make the coating thicker (ie lessening the gap).  If it lowers the resistance this can lead to more current on the film and possibly more damaging arcs but it's probably not a big issue.  I believe Wachara lives in a very humid climate so maybe he's noticed a difference in summer/winter.

 

Whatever material Stax uses for spacers, it isn't something as conductive as metal.  That would assure constant arcing.  The reason FR4 is used is to isolate the voltage on the diaphragm from the voltages on the stators since FR4 has a high resistance.  There was one member here who had ants in his SR-009 a while back and he ended up making a thread with a bunch of detailed pictures of the drivers.  That's the only place I can think of that might show the spacers used.

post #1548 of 1552

Humidity affects the coating material while in use, not while coating (at least as far as I've experienced and can conceive of). It also seems to accelerate the wear on DIY coatings. The pros have it figured out well enough that the coating isn't going to just go bad... at least not for most, maybe the SR-009 does.

 

I'd say it's not so much about arcing as it is about stability. Well designed headphones will simply never arc. But diaphragm stability is much much harder to design for. 

 

In my building experience, it is very possible to make a diaphragm in November that will last the entire winter, and the first humid hot spring day it's shot forever, eternally unstable.

post #1549 of 1552
Thread Starter 

I too don't think humudity during the coating process has any bad effect on the coating material - my coating material is actually water base.

 

From time to time, my headphones do have some imbalance issue.  Most of the times when that happens, I find some small arc spots on the diaphragm.  The arc isn't severe, it just leaves spot marks on the diaphragm.  Recoating usually fixes it.

 

Wachara C.

post #1550 of 1552
Thread Starter 
Quote:
Originally Posted by jgazal View Post
 

I see that DIY drivers use a FR4 ring to hold the diaphragm. What material the SR-009's ring is made of? Is it metal like the stators?

 

I wonder if, contrary to the use of a FR4 ring to hold the diaphragm, a metal ring worsens the dimensional control of the ring/diaphragm structure.

 

 

Do you know that Stax also uses PCB as stators and spacers is their SR007?

 

In Stax Lambda series, the spacers are made of brass rings.

post #1551 of 1552

Thanks n3rdling, dude_500 and chinsettwong. 

 

I knew spacers need to insulate stators and diaphragm, but I did not know the Lamda series had brass rings. So do they use electrical insulating coating at the rings or stators?

 

I have been a fool trying to figure out what is happening, because there are too many variables…

post #1552 of 1552
Thread Starter 
Quote:
Originally Posted by jgazal View Post
 

Thanks n3rdling, dude_500 and chinsettwong. 

 

I knew spacers need to insulate stators and diaphragm, but I did not know the Lamda series had brass rings. So do they use electrical insulating coating at the rings or stators?

 

I have been a fool trying to figure out what is happening, because there are too many variables…

 

It's easier to just show you the pictures than to try to explain it.

 

 

 

The stator is glued to a piece of plastic.  The stator is perhaps powder coated.  So, it's insulated.

 

When put together, the different thicknesses of spacer and stator makes the air gap of around 0.4 mm.  There is about 1 mm of spacing between the outer diameter of the stator and inner diameter of the spacer.


Edited by chinsettawong - 9/26/14 at 9:08pm
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