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:
- extremely expensive
- extremely complicated
- extremely fragile
- extremely unreliable
- extremely good
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:
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 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.
Panels.
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.
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.
Electrics.
The coated mylar must be connected to the high voltage supply. This can best be acheived by running an adhesive backed copper strip around the stator frame that will mate with the coated side of the mylar on the corresponding opposite frame. This can then be connected to a readily available voltage step-up unit. Voltage step-ups can be bought off the shelf or built on the bench and usually step from something like 6v to 2-3000 volts. The stators must be connected to the secondary winding of an audio grade transformer with a turns ratio between 1:50 and 1:100. These transformers are generally advertised as being suitable for electrostatic loudspeakers.