I needed to replace a diaphragm in my Quad ESL 63s during the recent rebuild. I have been experimenting with some weakly conductive coatings and found one that seems to work quite well (though it remains to beseen if it works for several years).
I was recently cleaning up a woodburning stove so I coiuld sell it so I picked up some stove-black at the local hardware store. The stuff is a wax + black pigment (carbon?) paste. I figured the pigment might be carbon and so the stuff may be conductive so...
I stretched a diaphragm and applied some of the goop to it with a paper towel. It goes on smoothly and it's easy to control where it goes. It can be softened further by putting a few drops of water on the paper towel. When the coating dries (about 30 seconds after application) it looks very much like the original Quad coating.
After applying it to the film I put a couple coins on it and measured the conductivity using my DMM. Depending on where I put the coins, it read between .1nS and 0.5 nS (that's equivalent to 10 Gohms - 2 Gohms. I let is sit for a few days to make sure it was fully dried and checked again and the results were the same.
I have installed that diaphragm in my ESL63 and it is working perfectly.
Stove-black costs about $2 for enough to coat about 1000 speakers.
I_F
I was recently cleaning up a woodburning stove so I coiuld sell it so I picked up some stove-black at the local hardware store. The stuff is a wax + black pigment (carbon?) paste. I figured the pigment might be carbon and so the stuff may be conductive so...
I stretched a diaphragm and applied some of the goop to it with a paper towel. It goes on smoothly and it's easy to control where it goes. It can be softened further by putting a few drops of water on the paper towel. When the coating dries (about 30 seconds after application) it looks very much like the original Quad coating.
After applying it to the film I put a couple coins on it and measured the conductivity using my DMM. Depending on where I put the coins, it read between .1nS and 0.5 nS (that's equivalent to 10 Gohms - 2 Gohms. I let is sit for a few days to make sure it was fully dried and checked again and the results were the same.
I have installed that diaphragm in my ESL63 and it is working perfectly.
Stove-black costs about $2 for enough to coat about 1000 speakers.
I_F
It's good to find relatively common household products for use as diaphragm coatings, but one is never sure of stability, the effects of humidity, temperature and added mass, etc. I live in coastal Florida where it can be pretty humid (despite AC) in the summer, but we also have some pretty dry air days in the winter. So the effects of humidity are important to me. My ESL-63s seem to perform consistently however.
Perhaps this will interest some folks: I came across U.S. patent #5,590,3212 granted to Sony engineers for an ESL coating they developed. Take a look at it at www.uspto.gov. The inventors give several formulas, but they all have in common a water solvent solution containing a conductive high-molecular weight monomer, a chemical oxidizer and a dopant. Choices for these various compounds include some commonly available chemicals, some even household chemicals. The diaphragm is dipped in the coating (for varying times depending on desired conductivity) and then rinsed and dried. In other words, no painting or rubbing required.
So what? The coating is said to be extremely uniform on the surface, adds little weight, but most importantly, the resultant conductivity varies very little due to humidity, aging and temperature (curves are presented in the patent for these variables). The conductivities shown in the patent are higher than I’d typically want, at around 10^5 ohms/square, but one should be able to vary the solution concentration and dipping times to control the conductivity. While one can’t use the patented formula for commercial projects without Sony’s permission, this might be worth trying for home projects. I haven’t mixed one of these formulas yet, but may try it soon.
Perhaps this will interest some folks: I came across U.S. patent #5,590,3212 granted to Sony engineers for an ESL coating they developed. Take a look at it at www.uspto.gov. The inventors give several formulas, but they all have in common a water solvent solution containing a conductive high-molecular weight monomer, a chemical oxidizer and a dopant. Choices for these various compounds include some commonly available chemicals, some even household chemicals. The diaphragm is dipped in the coating (for varying times depending on desired conductivity) and then rinsed and dried. In other words, no painting or rubbing required.
So what? The coating is said to be extremely uniform on the surface, adds little weight, but most importantly, the resultant conductivity varies very little due to humidity, aging and temperature (curves are presented in the patent for these variables). The conductivities shown in the patent are higher than I’d typically want, at around 10^5 ohms/square, but one should be able to vary the solution concentration and dipping times to control the conductivity. While one can’t use the patented formula for commercial projects without Sony’s permission, this might be worth trying for home projects. I haven’t mixed one of these formulas yet, but may try it soon.
ESL Diaphragm Coating
Brian,
The nominated coating resistivity appears low for all but ESL tweeters.
Regards,
Zvon
The conductivities shown in the patent are higher than I’d typically want, at around 10^5 ohms/square, but one should be able to vary the solution concentration and dipping times to control the conductivity.
Brian,
The nominated coating resistivity appears low for all but ESL tweeters.
Regards,
Zvon
The conductivities shown in the patent are higher than I’d typically want, at around 10^5 ohms/square, but one should be able to vary the solution concentration and dipping times to control the conductivity.
Yes, you are right; I typed an extra number digit in my posting. Just checking to see who is paying attention 
Thanks
By the way, I find that patent searching at the US patent site is a great, and underused, way to learn about anything technical. I frequently search for audio-related patents. I have tried to print out every patent related to electrostatic speakers, but now my stack of patents exceeds 3 inches (ok, make that 76 mm). We often must relearn what the inventors were trying to teach us decades ago. In particular, one lesson that needs to be taught over and over again has to do with not over-insulating stators. If the insulation has too much resistance, it will consume all of the electric field, depriving it from the air gap. This is why that when wire stators are used, PVC insulation is preferred over, say, Teflon. The speaker will simply play louder with PVC! I’ll bet Martin Logan’s black stator “paint” is somewhat conductive. If course, it can’t be too conductive if it is to limit potential arcing currents.
ThanksBy the way, I find that patent searching at the US patent site is a great, and underused, way to learn about anything technical. I frequently search for audio-related patents. I have tried to print out every patent related to electrostatic speakers, but now my stack of patents exceeds 3 inches (ok, make that 76 mm). We often must relearn what the inventors were trying to teach us decades ago. In particular, one lesson that needs to be taught over and over again has to do with not over-insulating stators. If the insulation has too much resistance, it will consume all of the electric field, depriving it from the air gap. This is why that when wire stators are used, PVC insulation is preferred over, say, Teflon. The speaker will simply play louder with PVC! I’ll bet Martin Logan’s black stator “paint” is somewhat conductive. If course, it can’t be too conductive if it is to limit potential arcing currents.
Many of the chemicals mentioned in the Sony patent are reasonably dangerous... I didn't read it all yet, there may be a unique combo that is only moderately dangerous and perhaps suitable for DIYers...
But if you wouldn't set up a plating line or anodize line in your work area, don't even think about this bit...
The Martin Logan "paint" is obviously "powder coating" - being black it contains a fair amount of what? Carbon.
The story from Jim Strickland is that he tried teflon(R) wire for the insulators and this permitted higher voltages, and better sensitivity, but that the speaker ceased to work in extremely dry climates! He teaches that leakage is required, and without leakage due to the moisture in the air, the field is decreased. Thus the use of PVC which is nicely leaky...
Which should tell us electronic builders something of interest too...
_-_-bear
But if you wouldn't set up a plating line or anodize line in your work area, don't even think about this bit...
The Martin Logan "paint" is obviously "powder coating" - being black it contains a fair amount of what? Carbon.
The story from Jim Strickland is that he tried teflon(R) wire for the insulators and this permitted higher voltages, and better sensitivity, but that the speaker ceased to work in extremely dry climates! He teaches that leakage is required, and without leakage due to the moisture in the air, the field is decreased. Thus the use of PVC which is nicely leaky...
Which should tell us electronic builders something of interest too...
_-_-bear
The problem with those coatings is adhesion- without treating the film surface, getting them to stick permanently will be nearly impossible. In order to get really good adhesion to Mylar or Saran, you need to do something like corona or plasma treatment to get the surface energy up to 45 dyne or higher. It can also be done chemically, but it involves VERY nasty stuff like chromic acid.
SY said:
Yeah, stability is always questionable until someone tries it. I also used double stick tape to secure the diaphragm to the stator in that one, another experiment, but based on some experience- my stretcher table has tape that was put on it 15 years ago and it still works fine!
Quad originally cemented the diaphragm to the stator using a super-glue type adhesive that doesn't really bond with the film. I am amazed they were able to ship the things without all of the diaphragms busting loose.
My rebuilt speakers (rebuilt ESL-63 ) allow easy access to the driver panels, so it won't be any problem to replace a diaphragm if needed. All I have to do is bust open the dust cover, unsolder the connections, and remove the driver from the frame. In the original frames it would take a couple hours just to get to the darned things! Now I can have a driver out, re-diaphragmed, reinstalled, and a new dust cover in place in about an hour with most of the time used to install the new dust cover.
I_F
Brian Beck said:
I am not surprised that they perform consistently. The dust covers seal them up pretty tightly. I don't know how permeable polyester film is but probably not very- they use the stuff for helium balloons that manage to hold helium for weeks or even months at a time. If polyester can contain helium, it will act as a barrier to almost anything.
I_F
The Quads do seem relatively well sealed, but certainly are not hermetic. But there are bound to be small leaks which will allow slow air exchange. During a long humid summer, the interior humidity has got to rise to match the ambient average level. And likewise fall in the winter. The Quads must use a coating which is fairly well behaved over humidity changes. The coatings I've seen are black, as in carbon bearing. I know that early Quads used dissolved nylon, but I'm not sure what the 63s used.
I assume you're referring to the Sony patent. I'm no chemist, so I wonder if you can tell by looking at the ingredients if anything there would work to ensure (or preclude) a good bond. We certainly don't need a thick layer. The patent is encouraging in that it shows thoroughness by testing several parameters, so if adhesion were a problem, you'd think they would have caught it.
My concern too. Hey, I don't even like solder flux vapor, and I use a suction system to draw that stuff out the window. I do see some chemicals in the Sony patent that I use already but I treat carefully, such as ferric chloride. Used outside in fresh air, perhaps with a ventilator, and some caution, I'm thinking of trying one of the easier and less toxic choices from the patent. The advantages touted in the patent are very tempting. Grinding graphite is no fun either, that's for sure!
Actually, the patent is more of a shotgun, with essentially no data on adhesion or longevity. I was referring to coatings in general on Mylar or Saran.
There's really no good reason to use conductive polymers rather than filled polymers as coatings and quite a few good reasons not to: expense, stability to air and moisture, mechanical ruggedness, toxicity...
That SONY patent...
I got a few minutes today to read the SONY patent...
It seems like this is a possibly do-able DIY "coating." It actually converts the surface of the poly chemically, so there is no "adhesion" issue.
There is some degree of danger using the least difficult of the chemicals. Two of the "oxidizers" are fairly easy to get - ferric chloride and ammonium persulfate are both commonly used to etch PCBs... so if you have experience with PCB etching, ur probably ok here...
The other part, the aniline I'm not so sure of... I know about aniline dyes, and I don't want them on or in me, but the dyes are sold for all sorts of things, including wood staining... dunno enough to determine the relationship between the quoted chemicals and the dyes. We would be lucky to have the dyes work here...
The process seems fairly straightforward bathe for a few hours then bake/dry. Rinse in hyper clean water. Done.
Any chemists out there who can identify the aniline compounds quoted??
Seems interesting...
Of course the stupid graphite method seems to work in many cases indefinitely and almost never less than 15-20 years done right and not soaked in humidity all the time...
If you live in southern FLA or Louisiana, the rainforest, this SONY method is clearly for you!
_-_-bear
I got a few minutes today to read the SONY patent...
It seems like this is a possibly do-able DIY "coating." It actually converts the surface of the poly chemically, so there is no "adhesion" issue.
There is some degree of danger using the least difficult of the chemicals. Two of the "oxidizers" are fairly easy to get - ferric chloride and ammonium persulfate are both commonly used to etch PCBs... so if you have experience with PCB etching, ur probably ok here...
The other part, the aniline I'm not so sure of... I know about aniline dyes, and I don't want them on or in me, but the dyes are sold for all sorts of things, including wood staining... dunno enough to determine the relationship between the quoted chemicals and the dyes. We would be lucky to have the dyes work here...
The process seems fairly straightforward bathe for a few hours then bake/dry. Rinse in hyper clean water. Done.
Any chemists out there who can identify the aniline compounds quoted??
Seems interesting...
Of course the stupid graphite method seems to work in many cases indefinitely and almost never less than 15-20 years done right and not soaked in humidity all the time...
If you live in southern FLA or Louisiana, the rainforest, this SONY method is clearly for you!
_-_-bear
Bear, as it happens, I'm a coauthor on the first definitive paper on polyanilines (Synthetic Metals 121, 173 (1985)). And I've got a handful of patents on using the materials in electronics manufacture. They are potentially suitable (though not optimal) as coatings, but you can't make the diaphragm out of polyaniline, then dope it into conductivity- the films don't have great integrity. It's a gimmick and absolutely not suitable for diy.
Forgot- thanks for the update. let's see how long we get out of this...
Forgot- thanks for the update. let's see how long we get out of this...
SY said:
Man, I now feel entirely inadequate in all respects...
Heh.
Anyhow, I didn't quite follow your comment above... the SONY patent calls for using it as a coating layer on a poly film, not the film itself as I read it, no?
Are you saying the SONY method, or similar will not have "great integrity"??
And, what is the "polyaniline" part's basic chemical make up - any relationship to the aniline dyes??
signed,
.... still curious
_-_-bear
You just accidently picked door number 3!
Polyaniline is, as you might expect, a polymer of aniline, that is, a bunch of aniline sub units hooked up in a long chain. It exists in a variety of forms depending on the oxidation state and the degree to which the nitrogens in the chain are protonated (that was the basis of the paper I referenced). The perchlorate is an oxidizing agent, which in an acidic environment will cause the aniline monomers to chemically link up and form the polymer. That's the perchlorate's only role; generally, you wash it out of the polymer before doing anything else.
The polymer needs to be partially oxidized and then protonated (e.g., from an acid treatment) to become electrically conductive. In the unprotonated (free base) form, the polymer doesn't conduct but it can be dissolved and cast into a very cool-looking coppery film. That film then gets treated with an acid (protonating agent) to "dope" it. The conductivity varies enormously with humidity, and the polyaniline needs to be somehow amalgamated with another polymer in order to make a coating that won't flake off.
Polyanilines of various sorts were known as byproducts of the aniline dye industry, but the relationship between oxidation state, acidity, structure, and conductivity weren't really sorted out until the 1980s. I note that the principal author of this paper, Alan MacDiarmid, received the Nobel Prize in 2000 for his work in conductive polymers.
There. This is much more than you wanted to know!
Polyaniline is, as you might expect, a polymer of aniline, that is, a bunch of aniline sub units hooked up in a long chain. It exists in a variety of forms depending on the oxidation state and the degree to which the nitrogens in the chain are protonated (that was the basis of the paper I referenced). The perchlorate is an oxidizing agent, which in an acidic environment will cause the aniline monomers to chemically link up and form the polymer. That's the perchlorate's only role; generally, you wash it out of the polymer before doing anything else.
The polymer needs to be partially oxidized and then protonated (e.g., from an acid treatment) to become electrically conductive. In the unprotonated (free base) form, the polymer doesn't conduct but it can be dissolved and cast into a very cool-looking coppery film. That film then gets treated with an acid (protonating agent) to "dope" it. The conductivity varies enormously with humidity, and the polyaniline needs to be somehow amalgamated with another polymer in order to make a coating that won't flake off.
Polyanilines of various sorts were known as byproducts of the aniline dye industry, but the relationship between oxidation state, acidity, structure, and conductivity weren't really sorted out until the 1980s. I note that the principal author of this paper, Alan MacDiarmid, received the Nobel Prize in 2000 for his work in conductive polymers.
There. This is much more than you wanted to know!
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