Window tint film -> electrostatics

[schizeckinosy]

Somewhere I read of someone trying window tint film for an Electrostatic speaker membrane, so I went and got a piece. I found that the lightest shade of Centaur film (about 50% tint) gave a resistance of between 1.5 and 3 megohm . This seems great, especially considering that the conductive film is sandwiched between two thin layers of insulating mylar.

The problem is how to connect to the conductive layer reliably. I was thinking of scratching up the edge of the film and painting it with conductive paint.

Anyone tried this material, or have any ideas? I'm still working on mt ESL amp and transformers, so I can't do practical test right now

Cheers, Dan

[MRehorst]

Window tint film is pretty heavy stuff. Even if you manage to connect to the coating inside the "sandwich", the mass of the film might limit the high frequency response. Still, it never hurts to try it. I've heard of people using Saran wrap...

A lot of people fuss over diaphragm coatings for some reason. I've tried different things, from ink to soap to anti-static fluid, but I always come back to powdered graphite. I have test drivers and speakers with graphite coated diaphragms I made about 12 years ago and they still sing like new. I also have some test drivers I made using dish detergent and anti static fluid. They haven't fared so well, though they still play.

Graphite is cheap, readily available, and most importantly, long-term stable. Its only drawbacks are the labor required to apply it and the difficulty in making a really high resistance coating. I have found that the resistance of the coating is not really critical anyway, so the only real problem is the labor.

If you're going to make 100 speakers, then it would be a real pain to rub all that graphite onto the diaphragms. If you're just going to make a pair or two of speakers for yourself, rubbing the graphite in is no big deal. Graphite coated daphragms will probably outlive you.

I would put more effort into locating thinner film and quit worrying about the coating. Thinner film will make an audible difference. The diaphragm coating won't (unless it flakes off, or adds a lot of mass- neither of which will occur with graphite).

Do a web search for the ESL Circuit. You can find people there who will sell proper diaphragm material in small quantities.

MR

[Circlotron]

How about the conductive plastic they make anti-static bags out of? There seems to be a variety of thicknesses and colours available. Just a thought.

[MRehorst]

I've never seen a thin antistatic bag.

You can order 0.0005" polyester film from McMaster-Carr. 10' or 25' long x 27" wide. While you're at it, you can order the perforated stators and insulating plastics as well. They've really spoiled the fun!

For the film, go here: http://www.mcmaster.com/
Scroll down the screen to the bottom right and click on plastics under "Raw Materials and Springs". Then click on "PLastics". Then click on "Polyester". Then click on "Film", Then click on "0.00005". Then click on either 10' ($7.78) or 25' ($11.50) length.

Back when I was sourcing materials I had to do it in Japanese. This is just too easy...

MR

[Ilianh]

A friend of mine works in a videoclub, and they have those rolls of plastic film they use to cover dvds and cassettes for sale.

It is very thin (not sure how much exactly..) and shrinks alot with heat.

Any ideas? Would this work? I think they use the same stuff on cd's in music stores.

Or anyone has experience with saran wrap? I'm not too sure about it.

[SY]

Most shrink films are too thick, and many are designed specifically with poor tear resistance so consumers can get to the product they're shrunk arround. I'd love to source some half-mil Clysar, a great shrink material, but I've never seen it.

If it were me doing a diaphragm, I'd use quarter or half mil mylar, corona treated (you'd want a surface energy of 38 dynes or higher), then paint on some high resistivity carbon black based coating. I don't know if Acheson Colloids is still around, but if they are, they make some excellent candidate coatings. Saran should also work well, but again, corona treatment is key to getting coatings to stick well. One nice thing about Saran is that you can get excellent adhesion from Saran-based coatings.

The whole rubbed graphite thing gives me the willies. Difficult to do, difficult to control. I'm amazed at the crude state of ESL diaphragm technology, but I'm a polymer snob.