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Old 4th January 2007, 01:38 PM   #1
danielm is offline danielm  United States
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Default Conductive coatings

Would India Ink work as a diaphragm coating?
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Old 4th January 2007, 10:34 PM   #2
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Default depends....

on the exact type of carbon black used in the ink. Some carbon black are such that the particles of carbon are actuallly coated and are then are not conductive. You only need to obtain a small sample to find out. Have fun. When people find out what you want the ink for they are usually fastinated and are almost always happy to lend a hand in the name of musical science. Regards Moray James.
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Old 6th January 2007, 03:50 AM   #3
Geoff H is offline Geoff H  Australia
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Why not use Aquadag? Its a product used for coating the back of TV picture tubes, for grounding purposes.

It was suggested as a conductive film for ESLs in an article I read years ago.

http://www.achesonindustries.com/doc/pds/Aquadag.pdf

Good luck with the project. I can never decide between ES or Ribbon. I have a lot of respect for those who roll their own, either way.

BTW, on reading this thread, I glanced at my laser printer. That fuses carbon to the paper doesn't it? No go. Reads open circuit on my digimeter.

Regards,
Geoff.
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Old 6th January 2007, 04:27 AM   #4
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Quote:
Originally posted by Geoff H
BTW, on reading this thread, I glanced at my laser printer. That fuses carbon to the paper doesn't it? No go. Reads open circuit on my digimeter.
Regards,
Geoff.
Plastic, not carbon.

How about Licron? Works well, readily available.

I_F
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Old 6th January 2007, 04:56 AM   #5
Geoff H is offline Geoff H  Australia
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Thanks for the correction I F. Tell that monkey I get the message.

Cheers,
Geoff
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Old 6th January 2007, 07:26 AM   #6
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Quote:
Originally posted by I_Forgot


Plastic, not carbon.

How about Licron? Works well, readily available.

I_F

I can't understand the the persisting promoting of Licron. It may be good, but not in all cases as I will explain.
I have seen it and I have measured it. A homogeneous layer is more than five times as heavy as the EC-coating. The thinnest result I could get was more than twice as thick. Now this surface looked a bit spotted but resistance still was reasonable uniform, not good. Resistance of this thinnest as possible layer wasn't higher as 100 Mohm.
Adhesion to Mylar is good, but thicker layers have tendency to crack.
Because of the milky (not transparant!) appearence, the use in open esls like audiostatic, martin logan, final is out of question.

If you use speaker grill cloth to hide the Mylar and are taking care to spray a very thin, slightly spotted, layer you will have a system which adheres well and is easy to use. Added mass is not the best, but acceptable for most amateurs. Same is for the resistance which is on the low side. So it is an option which should be seriously considered, but there are limitations.
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Old 6th January 2007, 08:29 AM   #7
Calvin is offline Calvin  Germany
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Hi,

I have to admit to Martin´s words. I won´t use Licron any more. First its quite expensive. Than is it nearly impossible to get an even coating with this spraycan. The appearance is milky-greyisch and not even. It dries out very quick. In fact so quick that You can´t correct for any failure. It adds considerable mass, such that You can hear a distinct difference in resolution and attack of the panel. It sounds like the difference between a 12µm and 3µm diaphragm. Its resistance is low. That will work for hybrids and small panels but probabely not very well for fullrangers.
There are other coatings that are better suited to this application.
Aquadag, EC, Hobby-glue, Pedot, which all four have proven to me to work better than licron. Especially the Hobby-glue is a good solution with respect to price, flexibility of resistance, handling, safety, transparency, longtime stability and added weight.

jauu
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Old 6th January 2007, 09:30 AM   #8
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Hi,

Among the HC-systems, the dissolved hobby glue is the best you can get, also very cheap. Transparent as well. So Calvin is right here.
The only disadvantage is the very high resistance in the Giga-ohm range. Depending on temperature and humidity the resistance increases and may be at the same order as the 'leakage' resistance so the charging process will be affected. This is the reason that pure hobby glue will not work as well in every esl. The same thing for methylcellulose / hypromellose
Some people are trying to lower the resistance by doping the glue with ionic substances such as stearates or small ions like ammoniumsalts. This may work, but resistance will increase over time again.
Hobby glue should be properly diluted to achieve low added mass.
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Old 6th January 2007, 05:01 PM   #9
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What is "hobby glue"?

I_F
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Old 6th January 2007, 06:12 PM   #10
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Default Hobby glue...

for the most pat they are talking about PVA (white glue) there are all kinds of brands and versions. In America you can buy Weldbond or other white glue usually sold as wood glue. If you dilute it five parts of water to one part glue you can apply it with a mister bottle in a very fine layer. You can dope it wit Quats or conductive carbon powder. You can also try our clear floor polish (diluted) which will work fine. The trick to making this stuff stick is to dilute it. You can probably dope it with just about any brand of antistatic compound. Regards Moray James.
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