Hi
Has anyone found retail 3 to 6 microns thick plastic film (ideally Mylar) that maintains 10^8 - 10^9 ohms/sq without any surface coating? I know of Kapton XC, but it has 25 microns minimum thickness Kapton® XC Black Anti-Static Polyimide Film----[[LIREN ELECTRICAL INSULATION MATERIALS]].
Some manufacturers order such films for internal use, like Cadence Audio's tweeter for Siltech (supposedly teflon / indium oxide) - 6moons industryfeatures: Siltech's Pantheon 25.
Has anyone found retail 3 to 6 microns thick plastic film (ideally Mylar) that maintains 10^8 - 10^9 ohms/sq without any surface coating? I know of Kapton XC, but it has 25 microns minimum thickness Kapton® XC Black Anti-Static Polyimide Film----[[LIREN ELECTRICAL INSULATION MATERIALS]].
Some manufacturers order such films for internal use, like Cadence Audio's tweeter for Siltech (supposedly teflon / indium oxide) - 6moons industryfeatures: Siltech's Pantheon 25.
No, even if you use plastic stator spacers it will dramatically increase the shunt capacitance to have the resistive coating run up to or under the stators. This does not mean that the speaker will not work it will just not as well as if you applied your resistive coating so that there is a gap between it and your stators/frame. If you look at the construction of an Acoustat panel you will see that the resistive coating is applied to the diaphragm such that there is about a 1/2" gap all the way around the diaphragm and the coating extends out onto the frame (about 1/2" wide) at only one point where it makes contact to the HT supply. That is your best option.
Acoustat panels have over many many decades proven to be among the most robust and reliable of all electrostatic loudspeaker panels in the world. Why not simply copy what has been proven to work best? The Acoustat panel can be improved upon by using improved materials (at increased cost) but the design is very close if not perfect. Thanks to Jim Strickland and the other good people at Acoustat who designed and built these amazing loudspeakers.
Acoustat panels have over many many decades proven to be among the most robust and reliable of all electrostatic loudspeaker panels in the world. Why not simply copy what has been proven to work best? The Acoustat panel can be improved upon by using improved materials (at increased cost) but the design is very close if not perfect. Thanks to Jim Strickland and the other good people at Acoustat who designed and built these amazing loudspeakers.
The stator spacers are always plastic. Shunt capacitance will not increase at all, as there is no stator overlapping the film at the edges in my case. And with contemporary materials things can be done way better than 50 years ago.
There is no need to turn this into a design discussion though. The only question is if anyone has found a film that does not need surface coating.
There is no need to turn this into a design discussion though. The only question is if anyone has found a film that does not need surface coating.
IT's also nice to be able to only coat the areas you need to minimize leakage. IF you were to use a film with an impregnated conductive material, you'd have to be careful of the edges and insulate them appropriately. Where if you don't have a coating on the edges of the mylar it matters a whole lot less. If you are building a set of ESL's from scratch that's pretty easy to do, but if you were say rebuilding a set of quad ESL's, that's a bit harder. Even then, a layer or two of kapton tape is your friend.
Sheldon
Sheldon
I guess a bit more information is needed. So, I am planning to build something myself, but only if I find film that does not require coating. I do not want to deal with sound degradation as a result of the coating being affected by atmospheric conditions, cleaning, aging, cracking, etc. Soap, ink, floor or screen cleaners, and any other anti-static gunk will have no place in the construction. Edges will be insulated with silicone tape (10kV per 0.2mm). Stators will be flat, initially from etched, and later from multi-layer PCB for insulation on both sides. There will be no stator overlap where I do not want it, so no need think about shunt capacitance as a result of the approach. I will be making small panel(s) that can handle 300Hz and up, so the film should be thin. Mylar will be ideal, but I would be happy to experiment with anything else with proper thickness and resistance. Kapton XC seems a good choice, but what I found was too thick.
I've never seen Kapton thinner than 1mil and thicker than 5mil. Pretty sure it doesn't exist.
Not all coatings are effected by atmospheric conditions, but the humidity of the air does effect the leakage from the bias supply, that's just a fact of life. Typically it doesn't matter
Vacuum deposition of a coating on mylar is a good way to get a very stable coating. It's not cheap though. I'm dealing with aluminized mylar for a project at work, where we want a thicker layer than is typically applied. A typical aluminum layer is about 20nm, which is enough to make it look shiny (OD 2 or so). That thickness is also WAY too conductive for ESL service.
Based on my ESL experience, I wouldn't get too wrapped up in the coating, the rest of the design matters so much more. Once you build a few and measure and refine the design, you can then worry about things like coating longevity.
I do think you are on the right track. Flat panels with segmented drive regions fabricated with multi-layer PCBs. The conductive regions will be buried in the inner layer insulating it on all sides. That's a recipe for success right there.
If it were me, I'd actively EQ the panel from the pressure rolloff (~1KHz or so depending on width) and cross over steeply to a dynamic bass driver at about 100-120Hz.
If you want to do a full range ESL, consider damping out the panel resonance mechanically with silkscreen screen.
Good luck with your project,
Sheldon
Not all coatings are effected by atmospheric conditions, but the humidity of the air does effect the leakage from the bias supply, that's just a fact of life. Typically it doesn't matter
Vacuum deposition of a coating on mylar is a good way to get a very stable coating. It's not cheap though. I'm dealing with aluminized mylar for a project at work, where we want a thicker layer than is typically applied. A typical aluminum layer is about 20nm, which is enough to make it look shiny (OD 2 or so). That thickness is also WAY too conductive for ESL service.
Based on my ESL experience, I wouldn't get too wrapped up in the coating, the rest of the design matters so much more. Once you build a few and measure and refine the design, you can then worry about things like coating longevity.
I do think you are on the right track. Flat panels with segmented drive regions fabricated with multi-layer PCBs. The conductive regions will be buried in the inner layer insulating it on all sides. That's a recipe for success right there.
If it were me, I'd actively EQ the panel from the pressure rolloff (~1KHz or so depending on width) and cross over steeply to a dynamic bass driver at about 100-120Hz.
If you want to do a full range ESL, consider damping out the panel resonance mechanically with silkscreen screen.
Good luck with your project,
Sheldon
Thank you for the suggestion Sheldon. I will try not to think about the price of vacuum deposition yet, but would you share with me the shop you are using for this? I will try to contact them, in case they have any suitable (lower resistance coating) leftovers from previous runs.
Regarding the setup - I am listening in a small room (my home office). Pretty soon I bumped into problems with the low end. To tame the resonances I switched to fully digital, running 8 channel nanodigi dsp, 3 of them handling subs with separate tuning per channel, then 4 for the mids and highs. Lots of freedom with configurations. I am switching occasionally speaker boxes and within a mouse click I have multiple EQ options available. So no problem to go steep and to even change EQ depending on material (4 pre-sets in memory, more if loading from storage).
I am traveling the next 2 months, so for now just planning and purchasing the materials. Until I get my own ESL running - the ERAudio 505 panels will fill the gap. Below them I will try this driver Scanspeak Discovery 18W/4434G-00, 7" Midwoofer, 4 ohm - I hope it sounds as it looks, +-0.5dB 120H-1kHz.
Regarding the setup - I am listening in a small room (my home office). Pretty soon I bumped into problems with the low end. To tame the resonances I switched to fully digital, running 8 channel nanodigi dsp, 3 of them handling subs with separate tuning per channel, then 4 for the mids and highs. Lots of freedom with configurations. I am switching occasionally speaker boxes and within a mouse click I have multiple EQ options available. So no problem to go steep and to even change EQ depending on material (4 pre-sets in memory, more if loading from storage).
I am traveling the next 2 months, so for now just planning and purchasing the materials. Until I get my own ESL running - the ERAudio 505 panels will fill the gap. Below them I will try this driver Scanspeak Discovery 18W/4434G-00, 7" Midwoofer, 4 ohm - I hope it sounds as it looks, +-0.5dB 120H-1kHz.
I am currently working with a place called Flagship Converters, but they don't have any mylar thinner than 1/2mil (48 gauge). Really thin materials are harder to find. But they do the metalizing in-house and may be able to help you.
My first DIY ESL's used Seas Excel 8" woofers, which are really great drivers. But a lot of the cost and complexity of those high performance units has gone into dealing with resonances and motor performance way up high where you aren't going to be using the driver anyway. Some of the cheaper metal cone Seas woofers look great for the bottom two to three octaves and are about 1/4 the cost.
good luck with your project
Sheldon
My first DIY ESL's used Seas Excel 8" woofers, which are really great drivers. But a lot of the cost and complexity of those high performance units has gone into dealing with resonances and motor performance way up high where you aren't going to be using the driver anyway. Some of the cheaper metal cone Seas woofers look great for the bottom two to three octaves and are about 1/4 the cost.
good luck with your project
Sheldon
you can get Kapton thinner than 1 mill but its not widely available and will likely cost a bunch. I have seen as thin as .3 mill and have some .5 mill in tape form.
Also not sure if its an issue BUT Kapton is a bit hydroscopic. I wonder if its tendency to absorb water will effect speakers capacitance or change resistance??
Also not sure if its an issue BUT Kapton is a bit hydroscopic. I wonder if its tendency to absorb water will effect speakers capacitance or change resistance??
Thanks, I found the 0.3 mil one, but it will still require coating it seems https://catalog.cshyde.com/viewitems/films/kapton-polyimide-film-type-hn.
I am hoping to find thin carbon loaded Kapton XC, but that one is 1 mil and up.
I live in California, high humidity the last years is rarely a problem.
I am hoping to find thin carbon loaded Kapton XC, but that one is 1 mil and up.
I live in California, high humidity the last years is rarely a problem.
Hi whsh93a, interesting, can you share a bit more - picture or dimensions of the panel, and what kind of video tape. I read they are 3 thicknesses, starting from 0.5 mil, and it seems a bit high. What is the uncorrected frequency response you managed to achieve?
Good quality ones will be 50 to 125 microns thick. Some cheap Chinese blankets are reportedly going down to ~12 microns. Most people gravitate towards 3 microns for tweeters, 6 for mid-range, 12 for bass sections. I will not be making bass sections, so something between 3 and 6 microns would be best. Removing the metallization is not a gentle operation on something that thin, no matter what approach we choose.
I am willing to play with it, I wonder where I can find something that is 3” wide and thin enough though. The closest I found was audio master tapes 2” wide, which is still not enough. And they were way too thick – usually 50 microns.
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