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My DIY electrostatic headphones - Page 115

post #1711 of 1719

Hey Folks,

 

Just thought I'd check back in with my latest ES headphone driver build.  No grand new ideas here, but I was able to get access to a CNC machine capable of cutting rather accurately, so am pleased with the build quality.  I am still having some difficulty finding the best way of stretching the Mylar, but was able to get a taught set of diaphragms on the third or forth attempt.  My general impression is that they sound rather good: not very bass-heavy, compared to my last pair -- probably because the diaphragm is stretched tighter -- with clarity throughout the midrange.  

 

I still have yet to build a case, and am listening to them strapped on the front of the hollowed plastic shells of some cans from the 1970s.  An open backed case would give me a better sense of how they should sound, I believe.

 

 

I would like to understand more fully how each of the variables we can alter in making these headphones affects the output level and quality.  See below the variables I know and do not know for this current build.  IT is quite likely that some of these variables do not affect sound quality (stator thickness and hole shape seem unlikely to make much difference), but I would eventually like to know exactly which variables affect sound in what ways.  If anyone can suggest reading on the subject, or has thoughts, please let me know.

 

For the time being, I'll keep chugging away on these designs if you all keep chugging away on your designs.

 

Happy Building,

OnyxOcelot

   

 

 

SPECS:

 

KNOWN VARIABLES:

DIAPHRAGM AREA.......................................................3.5in x 2.5in

DIAPHRAGM MATERIAL...................................1.4 Micron Mylar film

DIAPHRAGM COATING.........................Static Guard anti-static spray

DIAPHRAGM-STATOR SPACING..........................................0.021in

DIAPHRAGM SHAPE................................................................Oval

 

STATOR THICKNESS..........................................................0.021 in

STATOR HOLE SHAPE.................................................vertical slots

 

POWER SUPPLY...........................Stax SRD-7 (Self-Biasing) Adaptor

 

UNKNOWN VARIABLES:

STATOR OPEN AREA 

post #1712 of 1719

You might want to use thicker PCB for your stators on your next attempt and also change the long slots to holes.  With such thin stators and those long slots, I imagine you're getting some stator resonating while music plays, which increases the distortion.  I think I remember somebody trying the slots before and saying they weren't getting much bass also. 

 

Output level depends mainly on spacer thickness/bias voltage/driving voltage, with some smaller influence from open area % of the stator design.

post #1713 of 1719
Thread Starter 

Nice looking stators.

 

How do you stretch your Mylar now?  To get good bass, you need to tension your diaphragm just right - good stability and not too tight or loose.  It's not easy.

 

For me, stretching the Mylar to the exact right tension is still a problem.  I have to do and redo it many times until I'm satisfied.  Maybe it's time that we focus on experimenting the best diaphragm stretching method.  If you guys have any thoughts, please share them.  

 

 

Wachara C.

post #1714 of 1719
Thread Starter 

I made this design a long time ago, but never tried to make it.

 

 

However, my CNC machine works better with drilling than routing.  So, I stick with drilling holes on the stators.

 

Wachara C.

post #1715 of 1719

Perhaps a non-workable idea, but the way a screen is tensioned on a screen door or a screen is tensioned on a silk screen, if the stator (or perhaps one of the spacers) had a groove around its perimeter, with an o-ring (rubber or metal) placed over the mylar (over the groove), when the assembly is bolted together, it would pull the mylar tight. Experimentaion would be required. Just a thought.


Edited by marsupialx - 2/12/15 at 5:16pm
post #1716 of 1719
Quote:
Originally Posted by n3rdling View Post
 

You might want to use thicker PCB for your stators on your next attempt and also change the long slots to holes.  With such thin stators and those long slots, I imagine you're getting some stator resonating while music plays, which increases the distortion.  I think I remember somebody trying the slots before and saying they weren't getting much bass also. 

Yes, I made slots instead of drilling to reduce machining time (I am working on borrowed machine time), but there have been some issues of stator stability -- no resonance yet, but a certain amount of bending as they are fit into the (makeshift) case.  

 

Wachara, on this pair of drivers, I tried a couple methods of stretching the diaphragm:

 

                  1. I built a rectangular frame with a bicycle inner tube stretched around the outside.  I would use gaffer's tape to attach the mylar around this frame, then inflate the inner tube.  I never quite achieved a high enough tension before the Mylar ripped using this method.

 

                  2. My most successful stretching methods have been the simplest.  I stretched the Mylar using many pieces of gaffer's tape on a flat, clean table.  This allowed me to progressively stretch the diaphragm by moving each piece of tape outward a bit at a time.  This method is in no way repeatable, but without a proper stretching jig, this has been quite successful.

 

I have noticed that I occasionally get a very high pitched whine in one or both drivers.  It does not sound like a noise issue in the signal, but something else: perhaps a repeated partial discharging of the diaphragm's static charge to the stator.  Perhaps something else.  It may or may not be humidity dependent.  Do any of you have any experience with this particular issue?

 

Best,

OO

post #1717 of 1719
I have read that a whine might come from corona discharge. Especially forms at sharp edges on the stator
post #1718 of 1719
Thread Starter 
Hi OO,

I'm not sure why you can't get enough tension on your diaphragm using inner tire method. As for me, I really have a hard time not to put too much tension on the diaphragm. It's so easy to pump too much air into the tire and that the diaphragm is too tight.

About the noise in the drivers, it's very common. Most of the time it's dust in the driver. You have to clean your stators and diaphragm very well before you put everything together. It takes a lot of patience to clean. Even a very tiny piece of dust can cause this annoying noise.

Wachara C.
post #1719 of 1719
I plan to use dishwashing liquid for coating. How much is needed, give or take?
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