[chinsettawong]

Wow, that's an extremely high resistivity.  I doubt if your diaphragms can really be fully charged.
 
If I were you, I would go for a bit thicker spacers, and put on a less resistive coating. 
 
For my Float clone, I couldn't get the right tension and stability when using 0.5 mm spacers.  In the end, I cut a piece of 0.1 mm thick plastic sheet as extra spacers.  It's amazing to see how the extra 0.1 mm can help stabilize the diaphragms.
 
Wachara C. 

 

[OnyxOcelot]

So, I built a set of rectangular drivers today, sized around 75x90 mm.  I'm using .5 mm spacers with Stax normal (230V) bias, and a static-guard spray as coating.
 
The most obvious negative characteristic is that low-end distortion begins at higher volumes (a high, but not untoward listening volume).  The high end does not seem to distort, or is masked by the more prominent low-end rumble.  The distortion is unnoticeable at lower volumes, or with more mid-range heavy music.
 
What might be causing this distortion at relatively low volumes?  
Any suggestions for how I might overcome it?  
 
I'm finding the headphones fairly inefficient to begin with, so I may give a second coating of static-guard to begin experimenting.  
 
Thanks in advance for any tips!
OO

 

[chinsettawong]

  So, I built a set of rectangular drivers today, sized around 75x90 mm.  I'm using .5 mm spacers with Stax normal (230V) bias, and a static-guard spray as coating.
 
The most obvious negative characteristic is that low-end distortion begins at higher volumes (a high, but not untoward listening volume).  The high end does not seem to distort, or is masked by the more prominent low-end rumble.  The distortion is unnoticeable at lower volumes, or with more mid-range heavy music.
 
What might be causing this distortion at relatively low volumes?  
Any suggestions for how I might overcome it?  
 
I'm finding the headphones fairly inefficient to begin with, so I may give a second coating of static-guard to begin experimenting.  
 
Thanks in advance for any tips!
OO

 
Can you show us some pictures of your phones?
 
With 0.5 mm spacers, you can already use Stax pro bias voltage of 580V.  Your headphones will be much more efficient too.
 
I'm not sure what is causing the distortion, but I'm guessing that your current bias voltage is too low and you have to crank up your volume too much that your amp is running out of juice.
 
By the way, how do you drive your headphones?  Do you use step up transformers or do you use an electrostatic headphones amp?
 
Wachara C.

 

[OnyxOcelot]

   
Can you show us some pictures of your phones?
 
With 0.5 mm spacers, you can already use Stax pro bias voltage of 580V.  Your headphones will be much more efficient too.
 
I'm not sure what is causing the distortion, but I'm guessing that your current bias voltage is too low and you have to crank up your volume too much that your amp is running out of juice.
 
By the way, how do you drive your headphones?  Do you use step up transformers or do you use an electrostatic headphones amp?
 
Wachara C.

Sure.  I will attach a photo of their current test set-up (attached by rubber band to an old pair of earpads).  As with my previous pair, they are plagued with some build-quality issues that have more to do with my CNC than the design.  Fortunately, I think all build-quality issues on this pair are purely cosmetic.  
 
I am driving my headphones with a stax energizer with only normal bias.  Eventually, I would like to build a dedicated amp, but for the moment, this will have to do.   Perhaps the distortion is coming from the amp driving the energizer, but I did not have this issue on the previous pair, so I think it might be some unique quality of this shape of diaphragm...
 
In any case, I'll try to increase efficiency with another coating of static-guard and see what happens.  

 

 

[dude_500]

That is very odd if there is audible distortion at low amplitudes only. Are you testing this on a pure sine tone and distinctly hear a distorted tone with harmonics? Or do you just "hear distortion" listening to music?
 
The only thing I can think of would be crossover distortion in a crappy power amp. There aren't a lot of forms of distortion that would become less audible at higher amplitudes, but that one could.

 

[chinsettawong]

Maybe your diaphragms are unstable and are stuck to one of the stators.




Sent from my iPhone using Tapatalk

 

[OnyxOcelot]

  That is very odd if there is audible distortion at low amplitudes only. Are you testing this on a pure sine tone and distinctly hear a distorted tone with harmonics? Or do you just "hear distortion" listening to music?
 
The only thing I can think of would be crossover distortion in a crappy power amp. There aren't a lot of forms of distortion that would become less audible at higher amplitudes, but that one could.

Sorry, I guess I wasn't clear.
 
I only hear distortion in the bass at higher volumes.  I *am* using a very crappy integrated power amp, but did not experience this problem on my first set of round drivers.  I added a pre-amp to try and take some strain of the power amp, which seems to have only somewhat reduced the problem.  I am listening to music rather than a sine wave or sweep, but the distortion is patently obvious.  Audiophile headphones, these ain't, unfortunately.
 
Wachara is probably right that .5mm is too thick a spacer for the normal 230V bias.  Perhaps my first round drivers were small enough that it didn't matter.  
 
I will try ordering some thinner spacer material and keep on building.
 
Thanks!

 

[dude_500]

  Sorry, I guess I wasn't clear.
 
I only hear distortion in the bass at higher volumes.  I *am* using a very crappy integrated power amp, but did not experience this problem on my first set of round drivers.  I added a pre-amp to try and take some strain of the power amp, which seems to have only somewhat reduced the problem.  I am listening to music rather than a sine wave or sweep, but the distortion is patently obvious.  Audiophile headphones, these ain't, unfortunately.
 
Wachara is probably right that .5mm is too thick a spacer for the normal 230V bias.  Perhaps my first round drivers were small enough that it didn't matter.  
 
I will try ordering some thinner spacer material and keep on building.
 
Thanks!

 
If it's bass at higher volumes, that definitely points to clipping. Indeed your efficiency is probably very low with 0.5mm at 230v, causing the power amp to clip to get enough volume out. 
 
That said I took apart the drivers of my standard bias SR-X mk3 for a repair, and the diaphragm spacers appear to be approximately 0.5mm (unfortunately I didn't have any calipers with me). They could be a little smaller, but certainly not by much. 

 

[n3rdling]

When I get that problem (low efficiency and lots of bass distortion) on Stax I've had, usually the problem is that the driver stack is loose and there's a little gap as a result.  Usually at an angle.

 

[jgazal]

I am not certain if this is the right place to ask.
 
Are there eddy currents (foucalt currents) inside the aluminum earcup of a SR-009 or SR-Ω? Can I assume that the more mass in the earcup the more induced eddy current inside the earcup? 
 
Is there a dope or an specific aluminum alloy that reduce free electrons in the earcup?

 

[nikongod]

  I am not certain if this is the right place to ask.
 
Are there eddy currents (foucalt currents) inside the aluminum earcup of a SR-009 or SR-Ω?

 
Anywhere current flows, there are eddy currents.

  Can I assume that the more mass in the earcup the more induced eddy current inside the earcup? 

 
No, you can assume that the lower the electrical current the smaller the induced eddy current. Since electrostatic headphones operate at current levels small enough to be imaginary, you can estimate the eddy currents to also be imaginary.
 

  Is there a dope or an specific aluminum alloy that reduce free electrons in the earcup?

 
You made this up. I'm declaring shenanigans.
Lets just say for a second that you did not make this up. Why do you think it would be worth trying? Do you have any indication that "reducing free electrons in the earcup" would have any positive effect? Do you have any indication that it would have any effect at all? 

 

[jgazal]

 

 
No, I have no indication that "reducing free electrons in the ear cup" would have any positive effect.
 
Just think about a naive student that have no deep knowledge of electronics and is just learning how transformers work. He has just read what eddy current is and asks if this happens in metallic ear cups.
 
I understand that to a have little knowledge is worse than having no knowledge at all. Sometimes I assume things that are not correct simple because I have no deep understanding of electronics. On the other hand, I admire your knowledge.
 
I would never claim it has a negative effect.  It was really a naive question. I should not have mentioned any models specifically. I concur with you that it probably does not have any effect.

 

[wakibaki]

If you mean 'reducing the free movement of electrons in the material of the cup itself', you could use a dielectric instead of a conductor for the cup, but of course there will be displacement currents.

w

 

[jgazal]

Warning: long post.
 
  

Spoiler: Warning: Spoiler!

Thank you for the responses. I was not only thinking in headphones. I just want to better understand ferromagnetic, paramagnetic, diamagnetic and dielectric materials down atom level. This doubt follows me since my younger ears, but unfortunately I have chosen a profession that is far away from this field of knowledge.
 
Particularly in the metallic ear cups I have doubts like:
 
1) When the material creates a magnetic field and when it creates an electrostatic field. Now I see that aluminum is diamagnetic so it may actually increase a magnetic field. And thanks to nikongod now I know eddy currents in the ear cup are on smaller order of magnitude than I was imagining. So any magnetization of the aluminum is a faint force and coincides with the stator generated force, so it is an irrelevant doubt.
 
2) How the electrostatic field of the stator interact with the metallic ear cup. The thick anodizing skin isolates the ear cup. Suppose I earth the ear cup so the internal lattice can suck and loose electrons from and to the ground. Would that increase the electrostatic field over the diaphragm? Will it be a relevant force, since the ear cup is more distant than the stator itself? Probably it would be a faint force so it is an irrelevant doubt.
 
3) What is the magnitude of the magnetic field created with the paramagnetic stator? Is the Mylar diaphragm driven by two fields of force (electrostatic and paramagnetic)? Is there any difference between a paramagnetic field and the electrostatic field? Is one related to spin alignment and the other related to the simple accumulation of charges? What are their orders of magnitudes?
 
I was recommend to buy a book of solid state physics, but there are a quite a bit of authors and they seem to be expensive books. And chances are I am not going to have the mathematical skills to understand the subject.
 
Probably no one is interested in theory. The headphone is just built and it works and measure well so there is no real evidence that magnetic field play a significant role. It is just that I am curious about the subject.

 

[dude_500]

   

Spoiler: Warning: Spoiler!

1) When the material creates a magnetic field and when it creates an electrostatic field. Now I see that aluminum is diamagnetic so it may actually increase a magnetic field. And thanks to nikongod now I know eddy currents in the ear cup are on smaller order of magnitude than I was imagining. So any magnetization of the aluminum is a faint force and coincides with the stator generated force, so it is an irrelevant doubt.
 
2) How the electrostatic field of the stator interact with the metallic ear cup. The thick anodizing skin isolates the ear cup. Suppose I earth the ear cup so the internal lattice can suck and loose electrons from and to the ground. Would that increase the electrostatic field over the diaphragm? Will it be a relevant force, since the ear cup is more distant than the stator itself? Probably it would be a faint force so it is an irrelevant doubt.
 
3) What is the magnitude of the magnetic field created with the paramagnetic stator? Is the Mylar diaphragm driven by two fields of force (electrostatic and paramagnetic)? Is there any difference between a paramagnetic field and the electrostatic field? Is one related to spin alignment and the other related to the simple accumulation of charges? What are their orders of magnitudes?

1) Yup, eddy currents don't do anything of relevance for milliamps at audio frequencies
2) The field between the stators is fixed regardless of what's in the surroundings outside the inter-stator gap. The stators set fixed voltage potentials, so the field between them is just voltage/distance. You can potentially change the fields outside the gap, possibly substantially, using metal. But this region does not affect the diaphragm which is in an isolated world due to the fixed potential stators.
3) I have not run the math, but I would be absolutely shocked if the magnetic effects are anything more than many orders of magnitude lower in force than the electrostatic forces. If they were on the same order, then electrostatic headphones should make a good bit of sound with no diaphragm charge voltage.