That I also need to do with my current perf Aluminum powder coated stators, as sensitivity + arcing threshold are greatly weather dependent, is that only by me?
Another two topic:
1) Would there be any disadvantage in "sandwiching" the conductive copper layer within the PCB stator instead of having it on the PCB's surface? If not, why didn't Quad do it (for the sake of increased safety, if not for any other reason) ?
2) What's that story going around about Elvamid, claimed to provide too high a surface resistance as a diaphragm coating in "normal" ESLs, as opposed to the QUAD '57s? What makes the '57s so different? Would Elvamide truly not work in my ESLs?
1) Would there be any disadvantage in "sandwiching" the conductive copper layer within the PCB stator instead of having it on the PCB's surface? If not, why didn't Quad do it (for the sake of increased safety, if not for any other reason) ?
2) What's that story going around about Elvamid, claimed to provide too high a surface resistance as a diaphragm coating in "normal" ESLs, as opposed to the QUAD '57s? What makes the '57s so different? Would Elvamide truly not work in my ESLs?
Hi,
1) No, I suggest You might want to read the afore mentioned patent of Beveridge. Also Roger Sanders got granted a patent in 2005 (! ... with no new and patentable worth in as it is basically a copy of the Beveridge knowhow).
2) a) rubbish b) Mr. Walker´s ESLs are brilliantly engineered. I still regard the ESL63 a misconception from its basics, but admittendly its brilliantly engineererd. ;-)
jauu
Calvin
1) No, I suggest You might want to read the afore mentioned patent of Beveridge. Also Roger Sanders got granted a patent in 2005 (! ... with no new and patentable worth in as it is basically a copy of the Beveridge knowhow).
2) a) rubbish b) Mr. Walker´s ESLs are brilliantly engineered. I still regard the ESL63 a misconception from its basics, but admittendly its brilliantly engineererd. ;-)
jauu
Calvin
Hi
1) There is also the 1969 British patent of Bowers and Greenwood (B&W) that is prior art for the PCB encapsulated stator. Sanders certainly filed a Patent - was it actually granted? I'm not sure. If yes, then he certainly should not have. The concept of the encapsulated stator goes back at least to Janszen, 1950ish, and it would be a tough job counting the different people who have suggested it.
2) Elvamide is a DuPont-made soluble Nylon. Like all nylons, it absorbs moisture from the air, and the water is a major factor in its conductivity. It is therefore very sensitive to humidity. However, there is no obvious reason why it would work on one ESL and not another. To Quote Calvin "rubbish".
1) There is also the 1969 British patent of Bowers and Greenwood (B&W) that is prior art for the PCB encapsulated stator. Sanders certainly filed a Patent - was it actually granted? I'm not sure. If yes, then he certainly should not have. The concept of the encapsulated stator goes back at least to Janszen, 1950ish, and it would be a tough job counting the different people who have suggested it.
2) Elvamide is a DuPont-made soluble Nylon. Like all nylons, it absorbs moisture from the air, and the water is a major factor in its conductivity. It is therefore very sensitive to humidity. However, there is no obvious reason why it would work on one ESL and not another. To Quote Calvin "rubbish".
Thanks for your comments Calvin and golfnut, so the question still remains: Why didn't Walker "sandwich" the conductive copper layer within the PCB stator? Surly he had the brains to consider that.
Calvin I promise to read all recommended literature, I'm just too eager to read your opinions, and sometimes (always) can't wait.
Calvin I promise to read all recommended literature, I'm just too eager to read your opinions, and sometimes (always) can't wait.
I suspect a combination of cost of multilayer PCB, and the possibility of much cheaper alternatives.
On the ESL-63 and successors, the copper is on the outside face of the PCBs, which will make it more immune to dielectric breakdown than Cu on the inside (for the same field strength). The breakdown is further inhibited by polyurethane spray coated over the copper.
The ESL-63s also use ~ 2 mm circular holes, and if you work out how many holes are required (about 250,000 on the larger ESLs), you can see that there is a manufacturing problem there too. The solution is to use a fibre-glass free PCB and gang punches, punching hundreds of holes in one hit. I understand the PCB is also heated before hand to soften the PCB making the punching easier and breakage less likely. I imagine multilayer FR4 would chew through punches.
On the ESL-63 and successors, the copper is on the outside face of the PCBs, which will make it more immune to dielectric breakdown than Cu on the inside (for the same field strength). The breakdown is further inhibited by polyurethane spray coated over the copper.
The ESL-63s also use ~ 2 mm circular holes, and if you work out how many holes are required (about 250,000 on the larger ESLs), you can see that there is a manufacturing problem there too. The solution is to use a fibre-glass free PCB and gang punches, punching hundreds of holes in one hit. I understand the PCB is also heated before hand to soften the PCB making the punching easier and breakage less likely. I imagine multilayer FR4 would chew through punches.
If you are getting arcing , then the powder coating did not properly cover the sharp edges of the perforation.
Calvin may be able to provide you some tips.
Another reason for needing to adjust HV with changes in humidity is surface leakage currents (ie leakage paths bypassing the stator-diaphragm charging path). For example, many Sound Lab ESLs have substantial leakage paths thru the multitude of foam facet dividers that increase with humidity. The result is the need/ability to run a higher HV setting in humid weather than in dry weather for the same air gap break-down threshold…a counter-intuitive situation until you think about it.
Concerning patents and encapsulated PCB stators:
When I think of encapsulated stators, I envision stators constructed with modern multi-layer PCB manufacturing techniques like the current Sanders panels.
- The B&W GB patent uses the word "encapsulate" but only covers PCB stators with a varnish dip or spray coating over the copper side not multilayer PCB construction.
- A little known JansZen US patent covered similar construction but used an adhesive film rather than a coating.
- The Beveridge US patent figures appear to cover encapsulation by PCB construction, but reading the text it only mentions covering the copper with a layer of polyamide coating like nylon not another PCB layer.
- The Sanders US patent application for encapsulated PCB stators has not been approved. It does specifically mention using PCB construction methods to encapsulate copper layer between PCB layers. However, seeing how it is has not been approved in the 13 years it must have been deemed insufficiently unique relative to approved patents, or just common construction practice at this point in time.
Thanks to you all for your comments! bolserst, reading through the Sanders paper I see that he praises "the excellent electrical insulation of PCB material", while from our correspondence I understand that it should be good but not excellent (a bit leaky that is).
Regarding this issue of electrical insulation, you mentioned that FR4 PCB is "not as leaky as PVC, but pretty close", which I take as a figure of merit (please correct me if I'm wrong). I also noticed that Sanders suggests the encapsulated copper layer should be closer to the inner side of the stator, which makes sense, but how close? What would be the optimal thickness of the "inner side" insulating layer?
Regarding this issue of electrical insulation, you mentioned that FR4 PCB is "not as leaky as PVC, but pretty close", which I take as a figure of merit (please correct me if I'm wrong). I also noticed that Sanders suggests the encapsulated copper layer should be closer to the inner side of the stator, which makes sense, but how close? What would be the optimal thickness of the "inner side" insulating layer?
Actually, smaller holes are better.
If you think about the mass of air in the hole you get the right idea. With bigger holes, the air mass extends further out from the stator - very very crudely, think of a cylinder of air the diameter of the hole and length the same as the diameter.
Sound waves propagating through the holes have to shake these masses of air about, and at high frequencies, the stators do not transmit so well.
So smaller holes are better. Also holes are better than slots. Thinner stators also better.
Possibly the best stators around from this perspective are the ESL63 family with 2 mm dia holes on 0.5 mm PCB with nearly 60 % open area.
If you think about the mass of air in the hole you get the right idea. With bigger holes, the air mass extends further out from the stator - very very crudely, think of a cylinder of air the diameter of the hole and length the same as the diameter.
Sound waves propagating through the holes have to shake these masses of air about, and at high frequencies, the stators do not transmit so well.
So smaller holes are better. Also holes are better than slots. Thinner stators also better.
Possibly the best stators around from this perspective are the ESL63 family with 2 mm dia holes on 0.5 mm PCB with nearly 60 % open area.
Hi,
I partly disagrree with ´smaller holes are better´
One can calculate the cutoff frequency quite well if the parameters are known.
Afair those formulas parametrize open percentage not hole diameter.
Also, depending on the stator material and coating the hole wands not necessarily form a cylinder .... punched metal thickly coated certainly does not.
With PCB material on the other hand it´ll be almost impossible to not have cylindrical holes ... besides mechanical weakness the most serious issue with PCB materials.
The reffort for rounding the wall shape will probabely be much higher than one would want to accept.
Still though such stators could be manufactured very precise and should be very safe against flashovers and ageing.
jauu
Calvin
I partly disagrree with ´smaller holes are better´
One can calculate the cutoff frequency quite well if the parameters are known.
Afair those formulas parametrize open percentage not hole diameter.
Also, depending on the stator material and coating the hole wands not necessarily form a cylinder .... punched metal thickly coated certainly does not.
With PCB material on the other hand it´ll be almost impossible to not have cylindrical holes ... besides mechanical weakness the most serious issue with PCB materials.
The reffort for rounding the wall shape will probabely be much higher than one would want to accept.
Still though such stators could be manufactured very precise and should be very safe against flashovers and ageing.
jauu
Calvin
Smaller holes are better down to the point where the effective of the air mass is overtaken by the acoustic resistance of the hole, about 1 mm at 20 kHz if I recall correctly.
Bolserst and I did some work on this a while ago and published a paper "Acoustic Transparency of Electrostatic Loudspeaker Assemblies"
- see AES E-Library >> Acoustic Transparency of Electrostatic Loudspeaker Assemblies
For those who want a copy send a PM with email address. We explain how the effect of the entire stator assembly can be modeled using LTSpice.
As Calvin says, rounding the edges of holes also reduces the effects, but we have not researched this in any detail.
Bolserst and I did some work on this a while ago and published a paper "Acoustic Transparency of Electrostatic Loudspeaker Assemblies"
- see AES E-Library >> Acoustic Transparency of Electrostatic Loudspeaker Assemblies
For those who want a copy send a PM with email address. We explain how the effect of the entire stator assembly can be modeled using LTSpice.
As Calvin says, rounding the edges of holes also reduces the effects, but we have not researched this in any detail.
Nylon is a Trademark, Elvamide is a Trademark. Both of DuPont. Both are polyamides.
https://dupont.materialdatacenter.com/profiler/N73zv/material/pdf/datasheet/Elvamide8061
There are uncountable grades of nylon/polyamide at DuPont alone.
Nylon (Generic per say), used to make clothing, is not soluble in alcohols but does in 5% phenol solution: https://dupont.materialdatacenter.com/profiler/G7BZ7/material/pdf/datasheet/Zytel101NC010
https://dupont.materialdatacenter.com/profiler/N73zv/material/pdf/datasheet/Elvamide8061
There are uncountable grades of nylon/polyamide at DuPont alone.
Nylon (Generic per say), used to make clothing, is not soluble in alcohols but does in 5% phenol solution: https://dupont.materialdatacenter.com/profiler/G7BZ7/material/pdf/datasheet/Zytel101NC010