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My DIY electrostatic headphones - Page 43

post #631 of 1522
Quote:
Originally Posted by chinsettawong View Post

 

 

How can you blame the coating for your diaphragm instability?  confused_face.gif

 

Well, I have done my part.  It's all up to you now.  I won't give you anymore comment.

 

Wachara C. 

 

Quite simply, one coating causes instability while the other doesn't, when applied to a stator of the same tension. Since most coatings go unstable at said tension (like soap and PVA/graphite) I can only assume it's because elvamide has a bit higher of a surface resistance preventing the charge from quickly spreading to where it is contacting the diaphragm. The differences between the coating is massive in stability performance, but seems to have no effect on sound (so long as you're willing to wait for the elvamide to charge for a couple of minutes, which I couldn't care less about - I've heard even some retail headphones take some time to charge up).

post #632 of 1522

Dude500, I finally got around to make vibration simulation of your recent omega clone stator. I was surprised by the result but essentially the smaller size of perforated area did not seem to increase the effective stiffness of the stator and both versions exhibit resonances at similar frequencies. It does not mean stator resonances are not an issue in absolute sense, but at least, it doesn't seem to be the cause of your current issue with the old stator... Else something went awfully wrong with my simulation lol.

 

Examples below with the first 2 stator resonances at about 750Hz and 1400Hz, left is the old stator, right is the new one with smaller perforated area. In both cases I ignored the copper trace / etching so this is assuming 1mm FR4 (also I used isotropic average properties for the material even though its mechanical properties are actually somewhat direction dependent):

 

Mode 1 (730Hz for both stators):

 

 

 

 

Mode 2 (1460Hz for old stator, 1350Hz for new stator):

 

 

I will probably try to investigate acoustic resonance within the DS gap next, have to think of the most efficient way to model it...

post #633 of 1522

Terrific thread, thanks for all the useful information everyone.

post #634 of 1522
Thread Starter 

For those who are interested to learn about the diaphragm coating:  http://www.diyaudio.com/forums/planars-exotics/109789-esl-diaphragm-coating.html

 

Wachara C.

post #635 of 1522

Here's some potentially interesting data, although I'm not sure what to make of it.

 

Made new stators today with 0.042in holes, with 0.055 hole-to-hole spacing.

 

 

 

Red is the new smaller hole stators, blue is the old large hole stators. This is with no damping fabric anywhere, so it's a bit more peaky than previous FR's I've posted recently. I was wondering if the huge narrow peak in the large-hole stator FR is something like the ~30th harmonic of the diaphragm resonance. If the resonant geometric diaphragm pattern matched up with the holes in the stator, I could see that creating some pretty serious resonances.

 

 

My ears can not notice any difference between the two.

post #636 of 1522
Dude500, it's very difficult to see the consistency with your measurements. Last week, you show us results from the new smaller diameter perforated zone which alleviated the 1kHz or so peak / lack of bass. Yet the results today with smaller holes but same "reduced" perforated area seem to show again the same problems as your original stator. Am I missing something?

Also, a couple pages back you showed some comparisons of 2 diaphragms tensioning with very large variation above 5kHz or so (which might be as much due to microphone placement variation as it is to diaphragm change). Hence, I am wondering how repeatible your narrow band measurements really are. From experience with simulation, you don't need more than a few mm shift in mic placement to get 5-10dB shifts in narrow band response above a few kHz (past the first few acoustic resonances in the earpad cavity).

Results today (small perforated area, small vs large perforation holes): http://www.head-fi.org/content/type/61/id/702419/
Previous result (small vs large perforated area, large perforation holes): http://www.head-fi.org/content/type/61/id/700423/
Older result (large perforated area, large holes, change in diaphragm tensioning): http://www.head-fi.org/content/type/61/id/697112/flags/LL
Edited by arnaud - 10/17/12 at 9:03pm
post #637 of 1522

I agree it is quite strange how the bass rolloff seems to be coming back. All measurements and comparisons I do on one day I do many times with microphone placement adjustments to ensure repeatability against major FR changes or random measurement glitches. Day to day, I really can't claim repeatability.

 

My diaphragms seem significantly lower in tension today than last week, which may be one explanation. This may or may not be related to the fact that the temperature has increased substantially in my room since, and humidity is much higher today than the last FR I posted.

 

 

Moving the microphone around does seem to change the treble peaks, but not hugely or on the scale of the difference between the two traces. There is no doubt in my mind that the larger holes result in a sharp peak. Tomorrow, who knows confused_face(1).gif... Maybe I should just start tuning to sound and personal preference.

post #638 of 1522
Quote:
Originally Posted by notloc View Post


 

I have been interested in building my own electrostatic headphones for a while (most of my information coming from this page: http://gilmore2.chem.northwestern.edu/projects/showfile.php?file=radford1_prj.htm )

 

This link has now gone down, just curious if it is the same article as this one: http://headwize.com/projects/cmoy3_prj.htm

 

Thanks

post #639 of 1522
Quote:
Originally Posted by J-Pak View Post

 

This link has now gone down, just curious if it is the same article as this one: http://headwize.com/projects/cmoy3_prj.htm

 

Thanks

 



changed to:      http://headwize.com/projects/radford1_prj.htm

post #640 of 1522

The cause of the inconsistencies in bass roll-off day-to-day seems to have been how well I was sealing to the detector panel. What's strange, is the better I push it down to seal it, the more roll-off I get. The relative flat FR pictures I posted before are reproducable by basically setting the headphone onto the detector, if pressing at all then with very light force.

 

Do Stax headphones or the ones you guys DIY have any sort of vents on the earpad side of the driver? It almost seems as though very slight leakage is preferred. Mine are so sealed that if I push them into my head while wearing them, the diaphragms are slammed into the outer stators for a few seconds due to the air pressure.

post #641 of 1522

Mine DIY ES are air-tight as much as possible, just like the SR-404. With better seal (=more pressure towards detector panel), there is LESS rollof: with 2kg force pressing towards detector panel, there is -10dB rollof at 10Hz (white curve) compared to flat range between 50Hz and 500Hz.

 

BTW, does anyone have STAX SRM-006t amplifier? I'd like to check some parameter on another amp - I think mine is "not all right". frown.gif

 

EDIT: link


Edited by AmarokCZ - 11/5/12 at 8:22am
post #642 of 1522
Thread Starter 

The diaphragm slamming on the outside stator is normal.  With such a large diaphragm diameter to stator thickness ratio such as Omega's, this problem is quite unavoidable.  However, the diaphragm must be tensioned enough so that it will never stick to the stator.  It should just touch and bounce right off.  The diaphragm touching the stator for a few seconds is a sign that the tension isn't enough.

 

Wachara C.

post #643 of 1522
Thread Starter 

The HE-6 to Omega clone conversion is finally done.  wink_face.gif

 

 

 

post #644 of 1522

Very nice! Are those 80 mm diameter stator?

post #645 of 1522
Thread Starter 

The active diaphragm diameter is 80 mm, and the diaphragm thickness is 3 microns.

 

Wachara C.

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