The Listener 1998

The Quadfather


In the beginning, there was the Quad ESL, the world's first full-range electrostatic loudspeaker.


An appreciation, by Chris Beeching


Quad ESL loudspeaker: available used for between $600 and $2000 per pair and up, depending on condition. Originally manufactured by Quad Electroacoustics, Huntington, England.Surely the venerable Quad speaker is one of the most enduring of all quality hi-fi products ever made.Since it took the audio world by storm in 1957, the Quad Electrostatic Loudspeaker or ESL has slowly gained acceptance as the benchmark in audio sound reproduction. Even its successor, the ESL?63. has failed to unseat the original design for a great many listeners. Bunt could be argued that what prompted its cessation of manufacture was nothing more or less than the quest for higher power handling, owing to the increasingly muscular amplifiers of the late 1960s and early 1970s.



The ESL is housed in a wooden frame which almost resembles an easel on much shorter legs. The frame is divided into three sections: The two outer ones are about twice the width of the central section, and these contain the two bass panels; the central, narrower section of the frame contains the treble panel.

In real terms the whole speaker is remarkably compact; the power unit (mains energiser and audio transformer) is located on the bottom of the speaker frame, at the rear behind the audio panels.

Internal wiring is cleverly routed through holes in the wooden frame and is almost as shot as it's possible to get within the design constraints.

In order to protect the unsuspecting public. children, or pets from the high potential within the speaker when in operation, a stout expanded metal grill with "attractive" styling covers the front aspect while a more utilitarian grill covers the rear. On older models the mains input was via a round Bulgin 3-pin connector, while later models have the more modern IEC socket. Audio input is courtesy of standard 4mm banana sockets.

To finish the ensemble off, the speaker is fitted with (in most models) beech end "caps" which tastefully set off the speakers' bronze or black front grill.

One commentator of the time noted that his cat took far more notice of this particular speaker when the review sample arrived than anything hitherto, and for many this fascination and recognition of its capabilities have remained its most endearing feature.


Why electrostatic?

One problem inherent in any design is the limitation of the drive unit, no matter how "well" it is loaded. The fundamental problems are:

  • A cone driver still has significant mass (compared with the air? it's trying to drive); and
  • at anything greater than minimal excursions a cone driver coil 'runs out" of effective magnetic field, and therefore for a given input voltage change, the excursion rate changes as well (i.e. it is not linear).
  • The idea of an electrostatic transducer tantalised engineers throughout much of the early part of this century, because if executed properly it could solve those problems and more.

Rather than using magnetic repulsion and attraction to transform electrical energy into physical motion, the electrostatic speaker uses - unsurprisingly - electrostatic repulsion and attraction to accomplish the same thing. Minimally, this entails having a stationary plate called a stator and a moving plate called a diaphragm, both of which are electrically conductive but which are insulated from one another. If you apply a constant voltage to bath but superimpose an AC signal over just one of these two elements. the constantly varying signal will result in constantly varying degrees of electrostatic repulsion and attraction. and whichever of the two parts is free to will move back and forth in synch with the signal. If the AC is in fact amplified music - well, there you go.

Early designs for an electrostatic speaker appeared as early as the late 1910s, and some prototype models were available in the 1920s - but for the most part materials technology prevented any great strides forward. The first electrostatic devices were made in 1881 when Dolbear first showed a telephone system at the Paris Electrical Exhibition. These designs were later refined between about 1975 and the early 1930s, when a number of different speaker and microphone designs appeared, for the most part in Germany.

Many such early devices used a crude punched aluminium sheet (for the stationary part, or "stator") and a waxed and corrugated, metallised paper element (the moving pan, or diaphragm). The movement of the diaphragm was restrained by a form of long-haired wool, which prevented the paper from moving too far, but still allowed enough movement for audio purposes. This "wool suspension" (all natural!) meant that the active displacement was in one direction only, the wool returning it to its original position. It seemed to perform very well at higher frequencies, but as it was in many respects only a "half-wave" transducer, and so diaphragm excursion was limited ?its effectiveness at lower frequencies was strictly limited. [Note that before the common application of a sufficiently high polarising voltage to the two halves of a "half wave" transducer? which will 'bias" the device, just like a tube ?,such a speaker would tend to double the frequency of any signal fed to it because it would interpret the positive? arid negative?going halves of a single wave as two waves. In other words, you'd have frequency doubling, and that doesn't do much for the cause of low frequency reproduction?ed.]

The next set of developments for the electrostatic principle were almost entirely in the realm of microphones, and nothing more of real note in the speaker field arose until 1954, when F.V. Hunt's book titled Electroacoustics appeared.

His pioneering work in analyzing mathematically the "problems" with the electrostatic principle did much to pave the way for Peter Walker's development of the original Quad design. In particular. Hunt demonstrated that in order for an electrostatic speaker to function correctly. its diaphragm must have a constant charge rather than merely a constant voltage. Hunt also suggested that two plates with a central diaphragm - a "push-pull" transducer - would offer far better operating conditions than a single-plate design.

Well, as they say. if you want something done, ask a busy man. Peter Walker of the Acoustical Manufacturing Company certainly qualified for that given his engineering and commercial success in the field of amplification. Walker set to work and by 1955 had produced two working prototypes, which he presented in exhibition later that year. One was a true dipole with open back and front. the other used a closed box design.

The open type was later refined further and was developed into the ESL that we know today.

It has to be said that Hunt's work on the constant charge principle was one of the real keys to Walker's success: Regardless of the signal applied or the location of the diaphragm (as a result of excursion), as long as the diaphragm is between the plates, the constant charge maintains a linear motion as a function of the applied signal.

The other key: Development of a material which could be used for that electrically conductive diaphragm. which had been the real hurdle faced by earlier attempts. Then in 1949 DuPont came up with a little number called Mylar ? and that changed everything.

That points to the greatest of all ESL advantages: Since its diaphragm is essentially mass less (consider the weight of a meter-square sheet of Saran Wrap) it couples with the air very, very well, and as it is also driven over id whole surface area, it has a huge advantage over essentially high mass conventional drivers.

Its notable sonic benefits are increased transparency, better transient response, and a complete absence of "motor effect" (the effect where a conventional cone is trying, courtesy of its Suspension, to return to its "no signal" position, and the motion effectively creates a signal which drives the amplifier output backwards).

Developing a working prototype, of a constant charge ESL speaker was no mean feat. The primary problem was how to create a diaphragm which would retain and "hold" that constant charge ESL speaker was no mean feat. The primary problem was how to create a diaphragm which would retain and "hold" that constant charge without either leakage, inductance, or the charge varying or constantly changing on the surface of the diaphragm itself.

The solution was to develop a special polymer paint which was applied to a benign .sheet and which produced the necessary attributes required.

This, sadly, is no longer available, and for a while new or replacement panels have not been available. There is good news at hand. however, since an appropriate new coating has been sourced from the United States rind new production of ESL panels and perhaps even completed ESL loudspeakers has been setup in Koblenz, Germany (see page 38). In order for a constant?charge, push?pull electrostatic loudspeaker to work property the voltages must necessarily be kept high. Both insulation and materials (generally) must be of the highest quality.

In the ESL, the power supply to the plates is a very simple 50 Hz ladder?type step?up circuit which delivers some 7kV (peak) at a few micro amps ? not that user?friendly, but certainly not lethal. The other "main" item of hardware is the matching transformer which raises the audio input to very high voltages indeed. This pail was perhaps the most challenging to design, and constitutes a large proportion of the overall weight of the speaker.

The perforated stator plates are themselves very thick in order to minimise secondary audio emissions at very low frequencies, and are protected from the atmosphere by Saran-Wrap-type covers. (As any budding schoolboy physicist will know, rubbing a plastic biro on a suitable furry jumper or jacket will soon produce a dust?gathering static charge; an electrostatic speaker is no different!)

Electrically the speaker can be difficult to drive. Its nominal sensitivity is around the 84 or 85 dB/Watt mark. but subjectively iris a lot more efficient than that. It also has a falling frequency/impedance curve which is also highly capacitive, making amplifier stability a desirable attribute. For those who wish to know, impedances are approximately 1.8 Ohms at 20 kHz but 60 Ohms at 150 Hz. This means that lovers of single?ended valve amplifiers will be able to enjoy that topology ants best, and where the amplifiers' bottom?end performance might otherwise be a weak link the ESL's own bass characteristics will complement superbly welt. The venerable Quad II is an ideal partner, and in reality any valve amplifier which is well designed and built should perform very well. The exception here is the range of OTL designs, which seem motto many too well to this particular speaker.

Solid State amplifiers are, by and large, much more difficult to match well. Ironically, the original Naim Nait amplifier is a real peach match, as is the Quad 33/303 (assuming it's in top notch condition) but here the key to success is a conservative, simple design. The Quad is very revealing of flaws in partnering equipment.

The Subjective Bit (Or, 57 Reasons To Buy A Pair...) For those unused to hearing anything other than a box loudspeaker, the ESL will be a totally new listening experience. The most common concerns might be, "Where's the bass!" or "DO they play rock!"

The answer is that they do have bass, and they will play rock, though as you will shortly read there is a caveat to that statement.

Unlike many, if not all, cone loudspeakers, almost the whole of the frontal area of a Quad ESL is the sound reproducing bit. Its nearly-meter-wide, half-meter-tall profile will make siting it in some homes something of a problem. However, because it couples with the air so well. there are two benefits. The first is that you don't have to play it loudly to move a lot of air: Because the whole area radiates sound it is remarkably good at projecting the sounds it makes with ease. The second point, almost a function of the first, is that its apparent loudness does not fail away as rapidly as a cone driver's loudness as you move away from it.

You can sit further back and still enjoy good dynamics, great sound-staging and engaging presentation.

Bass is often thought to have gone missing, but only by those who don't know the speaker. Please be assured that if you use the ESLs on their original, 3 inch legs, there is precious little bass to enjoy. But equally, please also be assured that if you mount the speakers firmly oil a high?mass stand some 14 inches tall, you will be able to enjoy huge (and deep) amounts of bass. But be warned. Quad ESL bass is unlike -no, totally unlike - box speaker bass. It goes deep. it has weight, it is articulate, and it is clean. And if you've never heard a pair, it's that last one that'll cause the problems.

What many don't realize is that loudspeaker designers (of the box variety) use the cabinets which house the drivers to supplement the lower end output. Most loudspeaker drivers have a limited output at lower frequencies. You can usually see how low they'll go if you check the drive?unit manufacturers specs: The resonant frequency is a good guide to how low the unit will produce a useful output. If you see the same unit in a box with a much lower quoted spec, you can bet your bottom dollar the box is doing most of the work.

Now consider that drive unit manufacturers spend a lot of time getting the cone profile and angles right to produce a good clean output, and then ask yourself how good a rectangular multi-composite box will be at complementing that output, and you can begin to see the problems growing exponentially.

With the Quad there is no cabinet resonance to worry about. All the output is purely from the panels. (Well, given the age of some of the units in service, that may not be quite the case: overtime some of the panel retaining clips may have become a little less secure, but they can easily be tightened again.) The result is a very clean. distortion-less output from 45 Hz up to well past 20 kHz.

There are some ironies, too: In its impulse test (even at low frequencies) the ESL is quicker than most measuring microphones, and it is also totally without phase anomalies. But, as noted above, it's not a wholly kind load on amplifiers.


Getting the best out

The ESL is an experience. Once connected to suitable amplification with a high quality front end and mounted on high?mass stands, the original Quads are still perhaps the hardest hi-fi - no - make that music?playing ? act to beat. They will play any sort of music, and will convey exactly what's on the software to your ears. However, their presentation may not be Quite what you're used to. Remember what I said about box loudspeakers. Well, the Quads will play rock. and play it loudly. But do be aware that in rock music there's precious little below the bottom note of a bass guitar. Classical organs, double basses, and other instruments will go an octave lower and beyond. and the ESLs will do them all justice. You just have to forget about the box support for the driver and enjoy perhaps for the first time, a really clean low?end presentation.

It's not an up-front-and-in-yer-face rendition Of music, but more of a "walk-in-and-enjoy" revelation. There's no fuss or fluster, nor is there any hint of strain (until you try and overdrive it). and the naturalness and realism is something which most other speakers will only aspire to.

There arc limitations to rising the ESL. Small towns are not really appropriate (though I have heard them working superbly in a 7 by 9 foot condo box room!), but an "average" room, providing you can site the speakers away from the "back" wall, will do fine. Placing them right up against a side wall is no problem at all.

They will play rock, but there are dynamic and ultimate loudness limitations which must be home it mind, otherwise damage to the speaker will result. If you drive them so hard that you hear distortion, or see fireworks behind the grille, back off the volume and get them checked out.

That having been said, you can drive them with an amp of any size provided you don't overdrive them. I have used Lumley 120 Walt monoblocks very successfully as well as a single 2A3 design. The most important thing to bear in mind is that the amp will cope with the speaker.


Listening tests. They sound great.

Once you're used to the uncoloured (but not sterile. dead, or boring) sound of a Quad ESL, you will find it hard to go back to a conventional speaker system. Some say the imaging is a bit critical, but in my experience that's more a function of room placement and "geography" than it is solely the speaker.

Driven with a variety of equipment, and sited on proper stands, the Quads give of their best every time.

We've sat through nights and nights and nights of good music, and with every change of disc the perspective and ambiance of the recording changes. Beware for startling revelations too: things which you never knew were on your records. Also beware the sudden revelations of recordings which are not up to scratch and of badly executed multi-miked productions. You'll find drat because the speaker is phase?accurate it is much more revealing of this sort of recording aberration than other speaker types; you'll also easily hear image?shifts when dubbing or editing is not so good.

Apart from that. this is a speaker which does indeed let the music breathe. It has a poise and refinement which is enviable even by modern standards, and it has the uncanny knack of being able to recreate musical performance in your own home with a beguiling. engaging quality which is unsurpassed.

Although its successor, the ESL 63, has a high power handling capacity, and is perhaps a little more hi-fi and pin-sharp, the ESL is still, to my ears, the more musical performer and the one which I continue to use as a "reference." Overall, it gives me the greatest musical satisfaction long?term on a hugely wide variety of program material.


Caveat emptor

If you want a pair, they're all second-hand now (unless and until the new ones stall rolling off the assembly line in Koblenz). Don't skimp on the price. because they're not things you can fix with a soldering iron and a bit of insulating taps. Save until you can pay for a pedigree pair in first class condition. Although they're simple in principle. there are potentially a lot of little things which could go wrong which you, Joe Public, won't be able to fix. l guess that a good premium pair should set you back about $1000. But remember, when I wrote this in November, replacement panels weren't available, nor the wooden frames. Most of the electrical parts can. be obtained direct from Quad, though the HT and audio transformers are not cheap items.

But I guarantee: Get a good pair, drive them properly and set them up right and you'll never sell them.

Mike Trei comments: I bought my first Old Quads on a whim about eight years ago. Old wizened people f trusted told me they were special, so I took a chance and bought a fairly beat pair from a guy in Baltimore for $400. When I got them home. I hooked them up to a funny pair of German amps called Omtecs, and knew I had found the speaker for me. Later I bought a minty fresh pair from a friend in Canada, and I use them to this day.

The original Quad is for me the best loudspeaker ever made. They have a sense of "rightness" that no other speaker I have owned or installed?and that's a whole lot of speakers? ever came close to. They are supremely transparent. fast, and coherent.

Many of the criticisms levelled at them arc the result of incorrect use. When used properly, there is no roll-off in tire top end, the bass becomes extended and tight, and they can rock and roll. Getting the best from them is not difficult if your living situation is amenable to the following conditions:

These are antisocial speakers. Only one person can get the whole hog. A second person will get, at best, 75 percent, and this is achieved by sitting one behind the other, jet fighter style. This is not the best setup for a romantic evening with your significant other. The speakers need to be well out into the room (mine are eight feet out, spread wide apart). and you need to sit fairly close (f sit seven feet away). The speakers should be used on stands like the Arcicis ($295).

Before playing anything through them, make sure they are fully charged up. Playing an uncharged speaker can cause permanent (expensive) damage. I recommend charging Quads for at least 24 hours before first using them. Positioning by tape measure is the name of the game. Make sure your chair is where you want it, then enlist a friend to help with placement. Put the speaker as high as it will go in the Arcici stand, and adjust the angle and tilt so a tape measurement from each ear to all four corners of each speaker gives the same reading. Now play a CD with white or pink noise on it, or use a tuner's inter?station noise, and listen to one speaker at a time. Refine the tilt and angle of the speakers by moving your head up and down and side to side. so that maximum high frequencies are heard in your normal position. (Yes, Quads are that directional.)

Put on some real music and prepare to enter the gates to musical nirvana.

Some other thoughts: I like to use them as they come with no mods other than stands. Resist the temptation to remove the covers, add tweeters, add woofers, stack two pairs. or install any number of modifications. All sully the purity of the original, and most who try them eventually get bored with them.

Use friendly amplifiers. Low powered tubes work great, but this is a weird load so you have to try it and see. Panel meltdown is a distinct possibility if you use an overpowered amp. l play everything including hip-hop on mine, and have never damaged a panel, but abuse can lead to heartache.