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Brands

ESL Information eXch.
Haarustat
McMaster-Carr
Metrum Acoustics

Introduction

On the top of this page you can find an overview of all brands that supply stator material.

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Insulating stators

Frank Geissler (July 2002): I was offered from Renatech GmbH an isolating coating for stators with a dielectric rigidity of 90kV/mm (normally they have only 40kV/mm) and it's called:

  • ALTANA 1200/30 transparent or
  • ALTANA 1203/30 red or
  • ALTANA 1204/30C black

as a sample 1.2 litre for 48.-EURO within Germany. It was offered to a business and not as a private a person. Thank you, regards Frank.

Suitable construction materials

  • Aluminium
  • Styrene ( plastic)
  • Copper clad epoxy laminate
  • Steel

Aluminium

  • Needs to be perforated to 50 - 60% of the panel area and must not be thick, so as to avoid restriction of air from the diaphragm movement and any apparent "breathing" characteristics through the panel.Typically the maximum thickness would be about 1.6mm and be uniformly flat to avoid irregularities in field strength across the plate to the diaphragm. Burrs from perforations if any must be away from the diaphragm. (During preparation for the anodising process most burrs would be removed by chemical etching).
  • Anodising must be carried out after perforation. It would be possible to drill all holes in aluminium panels after first making a panel template (to save costs), however the time required will be considerable. The anodising could be replaced with high voltage insulating varnish but these chemicals do not adhere very well to Al. and in any event the anodising gives the desired colour and hence pleasing appearance.
  • Anodising insulates the plates well from the high driving voltage and renders them safe. A small area of anodising must be scraped away on the bottom of the panel for electrical connection.
  • Decorative anodised mesh is often available at a moderate cost and can be a suitable material as long as the previously stated requirements of thickness, openness and rigidity are met.

Styrene

  • This group includes high-impact and ABS types.
  • This material is a good, cheap option, comes in a number of colours (including black) and requires little or no preparation.
  • The styrene must be perforated and kept flat as with the aluminium.
  • The surface is first roughened with 220 grade oxide paper and then made conductive by applying Electrolube nickel loaded spray. In this case 0.002" thick gives a low resistivity. The base fluids are xylene and acetone, which provide a good key in the plastic for the metal. The cost of this preparation is about $55AUS ( $40 US) per 500ml can and will cover many panels.
  • The connection is made from the inside surface of the to panel bottom outside corner by a piece of very thin copper shim, window alarm tape or similar, to allow electrical connection. If the tape or shim is applied first the nickel is sprayed over the join to consolidate the connection.
  • The cost of a 4x3' sheet of styrene is about $10 AUS ($7 US).
  • Any burrs should be positioned away from the diaphragm.
  • The outside of the panel requires no further treatment for electrical safety.

Styrene is the author's choice as it does not dull tooling and when used as the spacer, the material bonds easily to the driven panel. Many adhesives are suitable for styrene and most bond well to this material. Various forms of epoxy resins have been used in the past for construction, but the author finds them brittle and only marginally satisfactory.

Copper laminate

  • Dulls tooling easily and does not perforate readily.
  • This material is reasonably costly.
  • Can be painted, but best results are with epoxy paint which is expensive.
  • Not the preferred material but is effective and requires no external insulation.

Steel

  • Material is heavy but stable.
  • Can be perforated but must be insulated on the outer surface.
  • Steel is of moderate cost.
  • Use only if other materials unavailable or a surplus is at hand.

There are other materials available but most of the materials that are suitable (most are metals and plastics) and available are either more costly or less suitable and less common than those listed above. Spacers: Styrene Polycarbonate Plexiglas

Wire stators

George Ingram (February 2001): Wire stator tip: Having seen some people saying how their wires weren't straight here's a really easy way of straightening coiled wire. fix one end to something solid, put the other end in a electric drill, pull on the drill trying to keep the wire straight and give a little spin, twisting the wire will straighten it out, this is done for straightening wires used for suspended ceilings, I'm not sure how well it would work on stranded, but it works brilliantly on solid wire.

Questions and answers

Frank Geissler (July 2002): Hi, I have access to 2000mm long and 1,5mm diam. straighted aluminium wire, and like to build ESL stators out of that. To prevent arcing, I like to laquer them. Someone knows what product is suitable? Is it better that it has high or low dialectric constant, and why? Thanks for answering. Frank

Answer: Please contact The Audio Circuit if you can provide an answer.

Mat : I am based in Brisbane Australia an I am building an electrostatic speaker - any comments on the suitability or otherwise of 1 mm thick steel stators? (51% open area, hole size 4.6 mm). I can get them coated in zincalume (90% aluminium, 10% zinc). All comments appreciated.

Rob Mackinlay : 51% open area 1mm thick steel is fine to use as a stator as long as the exit side of the perforations ie. the rough side of the sheet, point away from the diaphragm. The sharp edges caused during the perforating process will cause the insulation to migrate away from these points leaving only the thinnest coating. This will allow premature flashover and corona effects to occur.

It's not essential, but if you choose, you can overcome these problems by using a high speed wire brush in an angle grinder to erode the sharp edges away before coating. This works but is very hard work. The alternative is to acid etch the sharp edges away using dilute Hydrochloric acid. If using either of these techniques take precautions against injury by wearing safety glasses, gloves etc. Observe the usual rules for diluting acids, ie acid to water NOT water to acid.

Generally, ESL's with thicker grids do not have the same low level or spatial information as do the thinner ones. This is due to the roll off caused by the impedance of the air mass trapped in the holes.

If your panels are flat you probably need 1mm thick material to obtain the necessary stiffness, if they are curved, they can be made much thinner, say 0 .5mm, due to the stiffness created by the curvature. This does depend on the overall size of the panel, the curvature and any proposed support structure. Perhaps you could give a bit more dimension detail.

Zincalume may not be as good an insulator as you had hoped. I just measured the surface resistivity of the zincalume coating on my garage and got a 500 megohm per square reading. I'm not sure what the dielectric strength is but the fact that there is measurable surface conductivity is not a good omen. I think you will do better with a commercial powdercoat. Choose white or a light colour for best insulation. Black is loaded with carbon so avoid it. Ask the powdercoater to do a double pass.

An alternative is to visit a local electric motor rewind shop and get them to dip the grids into their tub of polyester insulation that they use to impregnate the coils of large motors and transformers. Most places have tubs big enough to do this. The insulation is heat cured after dipping and is very effective. Good luck with the project. Rob Mackinlay

Please contact The Audio Circuit if you can provide an additional answer.