Quad ESL 57 electrostatic loudspeaker
The speakers which we currently use for music are the classic Quad ESL 57. These speakers were well ahead of their time, being designed in the mid 1950s and originally sold singly for use with mono recordings before even stereo was popular.
The visual design of the ESL 57s is stylish but anachronistic. However, their internal design is still novel. Far from being a collection of off the shelf parts arranged in a wooden box, these speaker work on a different principle. Very high voltages are used to move a very thin plastic diaphragm using electrostatic principles - hence the name. The use of such a thin, light-weight and well damped diaphragm, and that the large area of the same has to move only very slightly to make sound are two of the reasons why the electrostatic speakers distort the signal significantly less than a normal speaker design.
When the electrostatics were designed, this was all cutting edge. The designer, Peter Walker, had to do much of his own research and in 1955 he wrote a fascinating article which explain the principles of operation. The work which he did was entirely on proper scientific and engineering principles. No fluff at all. These speakers were designed to have objectively the best performance possible at the time, providing what Peter's company, Quad, called "the closest approach to the real sound". The speakers still give a life-like sound.
The rear panel
To provide a high DC voltage across the stators, a mains power supply is built into each speaker. The voltage must be selected for that of your local mains supply. Select too high a voltage and your speakers will not be charged enough. Too low and the resulting voltage inside the speaker will be too high and may lead to corona discharge, a hissing noise, and creation of ozone.
Our speakers are numbers 37237 and 37246, which means my speakers were produced in 1975. The speakers were produced almost unchanged from 1958 until 1984.
The grill of the electrostatics is iconic. This pattern, in pressed aluminium, a beautiful bronze colour, tessellates across the entire front surface of the speakers which measure 84 cm wide by 74 cm tall (but only 22 cm front to back). The grill can be dented, but if you remove it and use a bottle to roll flat again from the back, most dents can be removed.
Our speakers are driven by the matching Quad 33 / 303 hifi amplifier. This was Quad's (and Peter Walker's) first transistor amplifier design. Again, it took a novel approach, but was designed to produce the smallest amount of distortion possible at the time. The amplifier still measures well, it is stable into any load, and it is not so powerful that it could damage the speakers.
People often have concerns about how much bass they are likely to hear from the ESL 57s. Actually these concerns are mostly unfounded. So long as the speaker is far enough from the rear wall, the bass performance is quite good. They stretch down to about 50 Hz and what you get is "honest" bass, not a boxy rumble. It's better than what you will hear from most smaller speakers. However, it is possible to extend the response with some care. That's why I built a subwoofer to match the Quads. On the right, you can see the frequency response in the bass for the ESLs on their own, for my home made subwoofer on its own, and the combination of subwoofer and ESL. All are real in-room measurements taken from the chair that I usually sit in to listen to music.
Commercial support for the ESL57
A number of companies offer a commercial service for maintaining and updating the Quad electrostatic speakers. Amongst them are the following:
Quad Electroacoustics is no longer really the company that it was (now owned by IAG), but they still have great products and they still offer the service of renovating their older products.
Quad Musikwiedergabe is a German company which owns some of the original tools used for making these speakers, and which still makes new ESL57s.
ESL Labs service Quad ESLs in the Netherlands
Sheldon Stokes does the job in the USA.
MAE Audio are in Belgium.
One Thing Audio are in the UK.
An interesting aside about using the Quad 303 with ESL 57s
The Quad 303 power amp has an output impedence which is a little higher than most modern power amplifiers. Normally, this would be expected to have no effect with normal speakers, but the complex load of the ESLs might be expected to have an effect on the overall response. As it happens, and as pointed out by Jim Lesurf, the Quad 303 output impedence interacts with the ESL, but does so in such a way that it slightly flattens the frequency response. Whether this was by design or merely a happy accident, I don't know. However, the 303 and the '57 really do work excellently together.
Quad resourcesGary Jacobson has an enormous amount of information about the ESLs. Sheldon Stokes also provides an enormous amount of information. Jim Lesurf on 303 and 57 interaction
Peter Walker's articles on electrostatic speaker design
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