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Electrostatic Loudspeakers



esl3


General discussion

Electrostatics are by no means mainstream in the hifi world and as a consequence enthusiasts who do not own a pair seem to have some fanciful ideas about them. Depending who you speak to, you may hear:

One aim of this page is to dispel all the above myths, with the exception of the last one, which is profoundly true.

The other aim of the page is to promote the concept of DIY in the construction of electrostatic loudspeakers and to offer guidance and services  to assist would-be constructors. The contents of this page have been kept as low-tech as possible. There are numerous references to more detailed information in the links section.  

The principle of electrostatic loudspeaker operation is extremely simple, which is very handy from a DIY point of view. The basic concept is that a thin diaphragm is suspended between two perforated metal sheets. If the diaphragm has an electrical charge applied to it, then, when an audio signal is applied to the metal sheets, they will attract or repel the diaphragm depending on the polarity of the signal. The diaphragm is then the source of the sound waves which becomes the equivalent of the cone in a normal loudspeaker. The following sketch shows the basic details:

esl graphic


This is of course a simplification of the process, but the reality of a working system is scarcely more complicated and is largely governed by the parts used in the construction.

There are two basic routes available for DIY constructors. The first would be to start from scratch, design the speakers, acquire all the parts, and then construct the system. If choosing this route, it is highly recommended that you purchase, read, and fully understand one of the technical books on the subject. One of the best is Roger Sanders 'Electrostatic Loudspeaker Design Cookbook' (Refer to Links).

The second route would be to construct a system from a kit. This route obviously avoids the tedious issues of design and locating parts, and to a large extent avoids the need to understand any of the technical bits.

Both routes should allow the constructor to end up with a piece of 'high end' hifi that should stand scrutiny against the most esoteric and expensive speakers that can be bought. Obviously, the kit method is less risky.

Building

The following discussion relates to the ESLlll full range electrostatic kit from ER Audio. The photograph at the top of this page shows a finished version of the ESLlll speaker system. The methods described generally apply to any design  but specifically relate to the ESLlll kit.

Panels

Panels are constructed in two halves, each half panel, front and back, consisting of the perforated metal sheet (stator). The diaphragm must be sandwiched between these two half panels without actually coming into contact with them. Some design philosophies suggest mounting spacers directly onto the stators while others prefer to mount the stators on a support frame which has the spacers attached. It is generally accepted that thinner stators produce the best sound which suggests the mounting frame method. This choice, however,  may be dictated by whatever metal sheet is available.

The ESLlll system comprises of six electrostatic panels, three for each speaker, all of which are 4' tall. Each speaker has two 8" wide panels , positioned either side of one 3" panel.

Photos show half panels with frames, spacers and stators - click to enlarge

panel1 panel2 panel3


Diaphragms

Diaphragms are generally Mylar sheet (similar to cling film food wrapping) which can be 3 - 10 microns thick. The diaphragm is applied to 1 half of the panel during construction whilst under tension. There are a number of methods used to tension the film, ranging from exotic jigs to simple shrinking with a heat gun. Once applied, the film must be processed to allow it to hold an electrical charge. This again can be achieved by a number of methods, principal of which include rubbing powdered graphite into the film, or painting the surface with a semi conductive fluid. Mylar sheet can also be obtained with a metalised surface to remove the need for this processing.

Stretching and painting diaphragms - click to enlarge

dia1 dia2


Electrical connections

Electrics for electrostatic speakers couldn't be simpler. Consideration must be given to actually attaching electrical connections to the panel parts, the diaphragms and stators. Stators can have tabs soldered to them or even threaded posts for screwing standard terminals. Completed panels can be drilled to allow connection to the diaphragm, or, as in the photographs above, a copper conductive strip can be sandwiched between the panel halves.

Wiring can then be connected as per the basic configuration shown in the schematic in the general section. Transformers used are readily available audio standard with a turns ratio between 1:50 and 1:100 and high voltage supplies are available off the shelf at reasonable prices. Both items are simply wired into the circuit as indicated.

Typical wiring detail - click to enlarge

wire1 wire2


Cabinets.

Electrostatic cabinets are far simpler to construct than those for normal loudspeakers. There is no need for sealed enclosures or tuning of ports, damping materials or precise holes to cut. The examples shown are simple box crate construction and with rudimentary skills and equipment (table saw and router) can easily be constructed in one day. Finish can be as exotic as required and is only limited by available skill and time.

cab1 cab2


Footnote.

With a little patience and attention to detail, speakers similar to those shown above can be constructed at a fraction of the cost of commercial units. Furthermore, they can sound every bit as good, or even better, than the commercial systems.

Links

The Electrostatic Loudspeaker Design Cookbook - Roger Sanders - Audio Amateur Press ISBN 1-882580-00-1

ER Audio for details of the ESLlll and other full range Electrostatic kits

DIYAudio Forum with a wealth of DIY and electrostatic information

Mark Rehorst for detailed information on building Electrostatics

Sheldon Stokes Superb DIY walkthrough