[chinsettawong]

  Hi everyone,
 
I have been following this forum for a few weeks now and wonder if one of you experts can assist me with some advice.
I have been using Sennheiser HE60 electrostatic elements in a medical research project.
However as you all will know these elements are now unavailable and so this led me to discover this forum when trying to find out a little more about these devices
.
My opening questions are.
 
1). What are the HE60 stators coated in to make them conductive?
As the whole assembly seems to be made of plastic (including the screws) I assumed they were some form of conductive plastic as my Xray of the element only shows up the connecting tags (sorry can't attach the Xray picture as I am too new!)
 
2). Just how conductive do the stators need to be?
I notice that constructors on this forum seem to make them out of copper clad fibreglass pcb.
Do they need to be such a low resistance?
My project cannot tolerate copper coated pcb as the stator, I have to replicate whatever Sennheiser did. (or some similar 'radiolucent' material)
 
3). The usual fault with the HE60's is loss of output why is this?
Reading between the lines it sounds as though it is loss of polarizing voltage on the diaphragm as I don't see any mechanism for the stator going faulty.
 
4). Are there any constructors out there that can supply CNC machined 'blanks' for the replication of these (or other) elements.
 
Thanks in anticipation
Dave

 
1.  The stators of HE60 are made from perforated metal.  I don't think they can ever go bad.  I have a few pictures to show you.  They were taken when I tried to recoat its diaphragms a few years ago.  
 

 

 

 
 
2.  I use copper clad PCB because it's very flat, cheap, and easy to work with.  You can, of course, use other conductive materials.  But, again I don't think you need to replace those stators on your HE60.
 
3.  The coating on the diaphragms has too high resistivity.  Recoat your diaphragms fixes the problem.
 
4.  Very unlikely.  
 
Wachara C.

 

[Dave1951]

Hi,
Thanks for your quick reply that was most informative.
 
However....are you sure that the HE60 stators are made of perforated metal as on the X-Ray image I have of a HE60 element only the solder tags show up as black (ie opaque to X-rays)
You would see if I was allowed to post the picture!
The rest of the element shows as a very hazy outline as if the rest of the material is just (see through) plastic or some radio-translucent material.
If the stators were perforated metal then they would definitely appear solid black with just the perforations showing as transparent!
 
So it would seem that the Sennheiser HE60's I have,  did not have solid perforated metal stators. Whereas the STAX elements I have in front of me do have solid metal stators but I haven't had these X-rayed yet.
 
As you say I don't need to replace the Sennheiser stators but was just wondering what they were made of that seemed transparent to X-rays. Looking at the pictures you posted it almost looks like they are gold 'sputtered'. A really thin coating such that they don't interfere with the X-rays?
 
1).
Does anyone know just how conductive the stators need to be?
I know the diaphragm can be Megohms/sqcm but can the stators be made say of plain fibreglass coated with DAG ( carbon colloid) or even carbon fibre.
So.... a few thousand ohms rather than solid metal (zero Ohms)?
For this medical application there can be NO (or only tiny amounts) of metal in the electrostatic element.
 
2).
So you are saying that the coating on the diaphragm wears out?
I sent quite a few elements back to Sennheiser in the past but of course this option seems no longer available
I have seen that constructors use something like Staticide to coat their diaphragms would this revive the failed HE60's I am using at the moment?
Do you coat both sides?
 
3). My main problem is that I need extra elements something like the Sennheiser HE60's which is why I asked if anyone supplied blanks. I don't have CNC capability here but maybe our Medical Physics Department do....
Are there CAD files available for constructors to cook their own stators/spacers I wonder?
 
 
This is a great forum BTW I have learned a great deal. I have some novel ideas about repeatably setting and checking diaphragm tension which when I manage to make some successfully I will share with you all.
 
Thanks in anticipation................
Dave

 

[chinsettawong]

Hi Dave,
 
You can post your pictures else where and post a link here.  That's how I do it.
 
I'm quite sure the stators are metal.  If you absolutely want to confirm it, I can open mine up again to check.  
 
Anyway, the easy fix for you would be to recoat your diaphragms.  Staticide is a good coating material.  Please try it.  You only need to coat on one side.  When you open your elements up, you'll see that you can only coat on one side anyway. 
 
It would be difficult for you to make the exact replica of the HE-60 stators and spacers.  
 
Aren't there any other headphones that you can use in your lab?
 
 
Wachara C.

 

[chinsettawong]

I'm looking at my HE60 right now.  There are many metal parts in the headphones.  The grills on the back of the headphones, the springs on the headband, the screws, and the cables are all metals. 

 

[Dave1951]

Hi,
Yes there are many metal parts but I would just buy the HE60/HE70 system then strip the HE60's down and throw everything away except the electrostatic element.
I then built the elements into a totally non metallic headphone for our application.
As I say the Sennheiser elements didn't seem to have metal stators as they don't show up as metallic on the Xray
here:-
https://dl.dropboxusercontent.com/u/81104063/x-ray.jpg
As you can see only the solder tags show up as metal. There is just the faintest image of the slotted periphery of the stators if you look closely, so the ones I have can't be solid metal!
The STAX headphone range are the next least expensive headphones to source elements from, but they have LOADS of metal in them which is useless.
So I need to 'roll my own' hence my plea for help on this forum.
 
Question.
When you make your own diaphragm how do you get a connection to it. I see you make a copper clad pair of rings but surely the glue insulates the diaphragm from the copper?
Do you coat the diaphragm after assemble and bridge the insulating glue with Staticide?
Or do you use conductive glue?
 
Dave 

 

[Dave1951]

Aw...I can't even link you to an offsite picture, not enough permissions. ...Sorry
Dave

 

[Dave1951]

Yes I bought HE70/60's strip everything out and bin it, I only use the electrostatic elements and the amplifier.
The next least expensive headphones are STAX and they are full of metal in the elements so no use.
Dave

 

[Dave1951]

Hi,
You can link to the X-ray now the administrator has kindly allowed the posting containing the dropbox link.
Dave

 

[chinsettawong]

The X-Ray picture looks interesting.
 
There are many ways to make a stator.  You can make it from a piece of plastic then paint the surface with a conductive paint, for example.  
 
You can cut a piece of plastic to make a spacer.  You glue a diaphragm on it and then coat the diaphragm with antistatic gel.  Then you make a small conductive connector on the other spacer to connect the cable and use it as a bridge to connect the cable with the conductive diaphragm when you sandwich them together.  Something like this:
 

 

[Dave1951]

Ah!......
So you take the side of the diaphragm that doesn't have the spacer glued to it, and coat it right to the edge painting over the conductive tag too.
Then glue the second spacer over the coated diaphragm and tag..
is that correct?
 
Do you have to solder the wire on to the tag really quickly? i.e does soldering iron heat affect the Staticide connection?
This is what I was always worried about with the Sennheiser units I was using, though I never damaged one. As I remarked before they just went low output after about 18 months of continuous use.
At least now I know how to fix one when it dies,
Thanks.
 
The stators will have to be non metallic and coated as you say with some 'radio translucent' conductive paint.
I have no feeling as to how conductive the stator has to be compared to the diaphragm, have you seen any constructors experimenting with this aspect?
I don't suppose it matters for normal audio enthusiasts, they can use copper clad pcb.... I will have to experiment.
I wonder if the rule is something like:-  as long as the stator resistance is 10 times lower that the diaphragm it will work ?
 
Sorry for all the questions but I would rather learn from the 'Elmers' as I have a mountain of other things to do on this project.
I really appreciate your taking time to tolerate a 'newbie'.
Dave

 

[chinsettawong]

Hi Dave,

Since you already have headphones that don't work well, opening them up and seeing how they're put together for yourself would answer a lot of your questions already. I don't glue the other spacer to the diaphragm. In my later builds, I use plastic screws to clamp everything together.

Sent from my SM-N9005 using Tapatalk

 

[n3rdling]

Pretty sure the HE60s use conductive paint on plastic stators.
 
Don't think you want a high resistance on the stators, they should be very conductive.
 
Is this for use in a MRI room?

 

[davidsh]

I can calculate the effects of adding a resistor in series with the stator if you like. Mainly loss of sensitivity and high frequency roll off

 

[Dave1951]

Hi
Yes that's a good idea and having now read most of this forum I feel much more confident in daring to disassemble my electrostatic elements.
At the moment I don't have any low output elements and the headphones are all in daily use so I don't have any to experiment with either
Thanks for the information about your assembly of the diaphragm and making the connection.
I was interested to hear that you now bolt the elements together just like my Sennheisers....LOL!
 
I am assuming you use the "Staticide ESD Safety Shield" version of the Staticide products, as they claim this is a 'permanent' coating?
Their other fluids and wipes appear to only be a temporary ESD 'fix'.
 
Finally, I notice you show the glue you use as UHU POR.
Reading the instructions for this glue it says it is a 'contact adhesive' i.e. you coat both surfaces and let them dry for a while before bringing the two parts together.
Do you use the adhesive in this way?
I couldn't decipher from your text exactly how you employ it when gluing your diaphragms.
 
I am surprised that the adhesive holds the diaphram's tension with a spacer glued to only one side.
I have no experience of this adhesive, but you describe the glue as 'rubber' glue (rather than a hard setting epoxy) which to me would suggest there may be some 'give' in the joint once the external tension is released?
Presumably you don't see any 'creepage' or relaxation of the tension once the adhesive is cured?
 
Many thanks for your advice I am overwhelmed by your helpfulness.
I now need to try to find someone who can convert your pictorial dimensions off this forum into a CAD file and then see if our Med Phys Dept has a CNC router.
What CNC machine do you have BTW are those cheap ones on Ebay (approx £400) good enough in case I have to go it alone?
 
Thanks again.......
Dave

 

[Dave1951]

Hi N3rdling 
 
Yes these headphones are used in an MR environment hence the requirement for them to contain no metal and my X-raying them in the first place. (Picture attached)
I suspected that the Sennheiser stators were plastic but having never dared to take one apart didn't know whether they were conductive plastic or coated with a conductive (yet low metallic content) paint.
I am battling with making new headphones that are much slimmer to fit in a 7T scanner which has a lot smaller bore, hence my appearance on this forum. Because I am almost certainly going to have to 'roll my own' electrostatic elements!
 
And Davidsh
Yes I can understand the effect of putting a resistor in series with the stator which using a resistive coating (rather than metal) is in effect.
I suppose the critical factor is what the effective capacitance of the element presents that will decide how resistive the stator can be to keep the frequency response in the 'sonic' window.
 
This is a great forum, thanks for your input chaps..keep the comments coming
Dave