Quad  ESL-57 loudspeaker

From Hi-Fi World - October 2007 issue

ANOTHER THING!

One Thing Audio now offer an even better upgrade to Quad's original ESL-57 loudspeaker. Is this the electrostatic for you, wonders Noel Keywood?

As I waved my Tannoy Yorkminsters goodbye, tear in my eye, I was dreaming of my next affair. There’s always another, different experience around the corner. The notion of a perfect electrostatic was on my mind and, as if reading it from afar, a pair of revamped, tuned Quad ESL-57 electrostatic loudspeakers arrived in the office from One Thing Audio. The large spaces left by the outgoing Tannoys were promptly filled and my tears vanished...

The ESL-57 was Quad’s first ever electrostatic loudspeaker. Introduced in 1957, it is still popular today, retaining value as a classic. However, the ‘57 was always a little fragile and most around today, with a good forty years use under their belt, are barely working. One Thing provide a unique rebuild service for this loudspeaker: they equip it with new, improved panels, and revamp it to provide a level of performance considerably better than the original.

If you already have a pair of 57s, the upgrade costs an affordable and highly reasonable £1,450. To that, add £235 per pair for the Rupert wooden stands you see in our pictures, and £79.95 per pair for Widgets (yes, that’s their official name) that make the loudspeakers a friendlier load for transistor amps. You end up with a loudspeaker that’s not only a classic but, we have found from past experience, frighteningly good by today’s standards. Which is why I was dreaming of electrostatics again when the Tannoys went...

If you are wondering why the ESL-57 looks like a radiator - a common accusation - it’s because it is a panel loudspeaker. To be precise, each one uses three sheets of Clingfilm - or something like it in truth - to produce sound. One sheet, tensioned in a frame to form a panel, sits vertically at centre, radiating high frequencies. Either side of it are bass panels - hence the oblong proportions of the composite whole. The louvred metal covers let sound out, front and back, whilst preventing inquisitive little fingers from getting in, because lethal voltages exist inside; these speakers are mains powered.

I had a long talk with One Thing about what they do with the ESL-57 and its technology in general because, as you might imagine from someone who dreams about such things(!) I am more than a little interested. I did, after all, run ESL-63s for many years, modifying them heavily and finding there was always more to come.

One Thing can accept just about any ESL-57, irrespective of condition, and renovate it fully. If you don’t already own a pair, then they should cost around £400 per pair second hand, but having said that some ask for much more, up to £1,000. One Thing recommend people buy tatty ones cheap, as good ones are likely to be good looking rather than good sounding, and One Thing replace all important parts and can even fit new grilles. All you need to be aware of is that models predating 1960, with a Serial Number below 1200, are balanced for mono, having less treble energy due to fewer turns on the audio transformer’s high frequency secondary winding. So pairs should have similar Serial Numbers to avoid a pairing of old and new models, which sometimes happens, and which One Thing cannot rectify, as the audio transformers are different.

The ultra light film diaphragms of electrostatics follow musical waveforms with unnerving accuracy, magically banishing screechy violins caused by the wayward cones and dome tweeters of conventional box loudspeakers. The lighter the film, the less energy it stores to colour the sound, and the faster it accelerates and decelerates, to better follow the music. In this respect electrostatics are way ahead of cone loudspeakers, something that is audibly very apparent.

Whilst Quads and other electrostatics traditionally used difficult to obtain special DuPont films, One Thing went to Germany and ordered an industrial quantity of a specially manufactured film 2.8microns thick, compared to 6microns of the original. This is coated with a highly resistive conductive film so the surface holds charge, resisting charge migration. I was surprised to learn that One Thing also fit high voltage secondary protection circuits of the sort used in later ESL-63s, which from experience I know work well. So their upgraded ESL-57s are all but bullet proof, which is good to know because I remember the originals being prone to arcing when overdriven. Additionally, they fit improved front electrodes to better disperse mid and high frequencies, and stronger rear electrodes. All in all then, this is a very modern electrostatic, to the pattern of the original, but otherwise broadly updated. Only the audio transformer is retained.

Some solid-state amplifiers find electrostatics difficult to drive - meaning they blow up! Mindful of this, One Thing offer a Widget that makes the Quad an easier load (it is a reactive network, not just series resistance). This, they find, improves sound quality with solid state amplifiers. With valve amplifiers it has least affect, they told me. With the Almarro valve amplifier I used, it offered a small subjective improvement, adding just a little body to voices. All the same, with it or without it the ESL-57s sound bright in their balance, due to a +5dB lift at high frequencies our measurements show, which is quite a lot. I would be tempted to equalise them flat. One Thing said many listeners prefer this balance, and it does mimic the lift found in many modern loudspeakers. I am used to a ‘flat’, neutral balance that is gentler with DVD-A, which tends to sound brittle in any case; the 57s were also bright with much SACD, even though it has subtler treble than DVD-A, but they were better balanced with most LPs.