Anyone want to answer a stupid question about ESL's?

[jzh797s]

With power reaching and exceding 2,000vDC, wouldnt you get a hell of a shock if you touched your speakers while they were on?

[moray james]

ESL speaker panels are comprised of a symetrical pair known as stators (one fromt and one back) which are insulsted (for the most part, there are exceptions) so that when they are being charged and discharged there is no (very little) chance of you receiving a shock. That said if the diyer id not careful you can get quite a wallop (speaking from experience. does that answer your question? Regards Moray James.

[jzh797s]

Yeah, but now I have a new question. Is there a spray coat used for insulation?

[moray james]

high voltage dielectric coatings are available in spray cans and in liquid form to brush on. I don't want to make this sound daunting but the likelyhood of you achieving a uniform insulative coating on perf metal by hand is not very good and these products are very expensive. That is one of the reasons why insulated wire stators are so popular not only in diy circles but with manufacturers as well. Your bet bet for a perfect coating with a quality appearence is to take your perf metal stator panels to a local powder coat shop and have them lay as heavy as possible coating of Nylon66 powder coat on them. Nylon66 is the best choice powder coat as it builds up better on corners and edges than any other powder and it is an excellent dielectric. This is what Martin Logan use. There are of course many other powder coat materials you could use to do the job but Nylon66 is the best chioce. Hope that this helps, regards Moray James.

[Calvin]

Hi,

You´re Q is in no way stupid. Stupid are those who don´t ask themselves this question! As MJ already explained there is a chance to touch the stators, wether they are made from metal sheets, wire or other materials. So there is a potential danger of shocking Yourself.
And since the stators are usually connected to the audio transformer the possible voltages as well as the possible currents(!) can easily reach fatal values. So every DIYer and manufacturer has to think of appropriate ways to insulate the stators. Many prefer PVC coated wires (Kynar could be an alternative, as well as some magnet wire types) since this insulation comes in highest quality and sufficient insulative effect.
Perforated metal sheets should be powder coated by a professional coater with a polymere. This can be Nylon, but can be other polymeres too. PE for e.g. has a much higher insulative effect.
It is very difficult to coat such thick coatings as needed for ESL use in prime quality and its costs more than the wire solution.

jauu
Calvin

[jzh797s]

Do you coat the front and back of the stators?

[Bazukaz]

jzh797s:
Yes , you need to coat both sides of stators.

By the way , Calvin , could you please share your coating formula with me ? I will understand if you don't want to do that.

Regards,
Lukas.

[moray james]

of only coating the inside of the stators (the side facing the diaphragm) provided that you can insure that the outside of the stators cannot be touched in operation. This is however not a plan I would advise. As stated before if you do not want to go with insulated wire stator construction your best option and least expensive method is to build perf metal stators and then have them powder coated. When you assemble the stators into finished panels make sure that you orient the perf metal stators such that the panels present the smooth side of each stator toward the diaphragn. When perforated metal is made they take a sheet of metal and punch holes into it. The side of the metal panel that the punch goes into is smoother than the side that the punch exits. The smooth side needs to go toward the diaphragm so that there will be no sharp edges for corona charge to build up on. This means that you have to have some sort of identifying mark like a small bent corner on each stator panel prior to coating so that you can easily tell which side is which after the powder coating is done. This may seem like a small detail but you need to remember that your powder coater does not normally do coatings for this specific type of application often if ever. Should the coater not build up a very thick coating or a non uniform coating the small edges on the sharp side of the perf panel could well cause you a lot of grief and render the panel useless. Remember that once a panel is powder coated you cannot recoat it to further build up the insulation. This process is a one shot deal so you want to make sure that you stack the odds in your favor. You need to remember that almost all powder coating and electrostatic spray coating is done for either cosmetic and or corrosion purposes and coating for high voltage dielectric insulative purposes is a very specific application which must be perfect and uniform the first time every time. I hope this helps. Regards Moray James.

[I_Forgot]

Originally posted by jzh797s
With power reaching and exceding 2,000vDC, wouldnt you get a hell of a shock if you touched your speakers while they were on?

A couple notes:

2000 VDC is a voltage, not power. There is a huge difference in the meaning of the two terms. Electrostatic speakers use HVDC bias supply that supply 2000-5000VDC at extremely low current. If the bias supply is properly designed and built, it is perfectly safe for you to touch the bias supply output while it is energized, just don't have you other hand on the CPU of your new computer while you do it. You will get a small shock similar to the one you get walking across a carpeted floor and touching a door knob.

The danger in ESLs comes from the HVAC (high voltage alternating current, not heating, ventilation, and air conditioning) that drives the speaker. ESLs can hit peaks of 5000 volts, depending on the transformers, amplifier, and the volume level at which you are playing the system. All commercial ESLs are designed to prevent electric shock by covering the stators one way or another. Unfortunately, not all amateur-built speakers are made that way.

It is not difficult to make a mechanical barrier that covers the speaker to protect curious people from sticking their fingers where they don't belong. Of course, the guy building the speaker has to be careful before the cover is in place...

I_F

[Calvin]

Hi,

I have mine powdered with a Nylon powder, but I think I´ll change to PE or POM, since this s cheaper. The reason for using Nylon is threefold:

1) excellent stability: Rilsan (one of the brand names) is used in offshore oil station applications as well as in dishwashers. Apart from heat it can nearly considered indestructable in normal use

2) Epsilon is quite high for a polymere --> low losses. The polymere coating forms a capacitor for the music signal that is series connected with the ´air-filled´ capacitor in which the diaphragm moves. To keep the voltage losses low the coating should be either very thin and /or the dielectric constant should be high. Since the thickness of the coating has a lower limit which is stated by the min. flash over voltage You can only vary Epsilon, i.e the material. You can see that effect well with the very thick (8mm) stators of a Beveridge. They used a very high dielectric material to be able to go this thick without too much loss within the stator. Because flashover treshold rises with thickness this kind of stator should be very safe against flashover.

3) The resistance of the material is relatively low for a polymere (~10^14Ohm/cm). In case of an overload condition with the diaphragm touching one stator, charge from the membrane is deposited on the stator. With high ohmic values of the material the charge will decay very slowly. While this doesn´t conflict with safety aspects it simply reduces the SPL at the touched area. The SPL recovers to normal levels as the charge decays. With values below 10^14Ohms recovery time can be less than a second. With high ohmic values (PE: 10^17Ohm/cm) the time constant can be several thousand seconds!

Other polymeres with similar parameters are PVC and PU.

I had my panels powder coated and laquered them additionally with an PU top coating since the powder thickness was too low for my taste. It will be very difficult -maybe even impossible- to find a coater who is able to coat more than 300µm and up to 600µm on a RV3-4 perforated sheet!
In the moment I´m thinking about alternatives.
The high resistance values of PE could be used for thinner coatings. So it should be easier to find a coater. If You add a thin top coat of PU-laquer on You have the advantage of the lowloss material and the highly resistive material.
The idea came to my mind when I read datasheets about Magnet wires. The better wires all use 2- or even 3-layer coatings, especially when they are intended for high corona resistance.
The other alternative I think of is using this corona resistant magnet wire for a wire stator. The coating is very thin, controlled for high corona resistance and flashover voltages and manufactred with tight tolerances. Possibly the best You can use for higly efficient panels if the wire and the insulation can withstand the straightening procedure. Too bad this wire is specially and seldomly manufactured
As I learned You have to order at least 200kG of it (~10-20km)

jauu
Calvin