Stereophile: Quad ESL-63 loudspeaker

Quad ESL-63 loudspeaker
J. Gordon Holt & Various, September, 1983

Warning to Purists: Despite certain qualities about the ESL-63 speakers which you will probably like, Quad equipment is not designed primarily for audiophiles, but for serious-music (call that "classical") listeners who play records more for musical enjoyment than for the sound. Quad's loudspeakers do not reproduce very deep bass and will not play at aurally traumatizing volume levels, and Quad's preamplifier is compromised through the addition of tone controls and filters, all for the purpose of making old, mediocre, and/or worn recordings sound as listenable as possible.
The Acoustical Manufacturing Company, better known as Quad, is one of the few remaining in the world which still view high fidelity as a service to serious music rather than an end in itself. Their products are designed to meet the needs of classical-record collectors who frequently play old, technically primitive (or inept) recordings for the music or the performance rather than for the sound.
Despite all the improvements in recorded quality that we have witnessed in recent years (with even RCA and CBS getting in on the act), audiophile-quality recordings are still very rare. The variety of fare represented on good recordings is exceedingly small, and the performances themselves range from good to ho-hum. To quote one observer, "Good sound and inspired performance seem mutually exclusive." Amen! Dedicated audiophiles would rather listen to silence than bad sound; record collectors will put up with awful sound if the music is worth listening to.
Quad's view is that a system should be able to reproduce everything of value that is on a recording, while minimizing the irritations of the average (call that "mediocre") recording. Quad's components reflect that philosophy.
Because these were designed as the components of an all-Quad system, I elected to review them as a complete system as well as individually. The units were substituted, one by one, in a system consisting of a pair of Acoustat Fours, an Acoustat 200 power amp, and a Berning preamp. Program sources were from l5ips 2-track tape, CDs from a Sony CD-P101 player, and several of our high-rated cartridges in a modified Rabco arm. The same signal sources were used to audition the entire Quad system.
The ESL-63
This full-range electrostatic speaker uses a unique radiating system. The diaphragm surface is divided into concentric circular areas fed by delay lines. An impulse fed to the speaker goes first to the center of the circle, then in turn to each larger ring until it reaches the periphery. This produces a close approximation to a spherical wavefront, similar to that radiated by an actual sound source of finite size. In practical terms, the result is a system that is (1) almost perfectly phase-coherent, and (2) free from treble beaming through a very wide included angle spanning the listening area. (There was a more detailed description of the ESL-63 in Stereophile, Vol.4 No.10, starting on p.13.)
Unlike the original Quad Electrostatic, which had a tendency to break down if overloaded for an instant, the '63 has a sophisticated protection device designed to short out the input signal if its level approaches an amplitude that could do speaker damage. Shutdown is claimed to occur rapidly enough to provide full protection to the speaker, but some power amplifiers will not tolerate output shorting and may blow fuses or sustain serious damage. Tubed amplifiers won't be harmed by this, but some solid-state amplifiers could be. If in doubt about your amplifier, check with its manufacturer or, to be safer still, use the speakers with Quad's own amplifier.
On first listen, two things hit me right between the ears. First of all, these speakers have inner detail like nothing I have ever heard! And secondly, of all the electrostatics I have tested through the years, these were the easiest to set up for proper imaging. The speaker reproduces depth and spatial locations like gangbusters, almost regardless of where one places them relative to the listening area. Like all large-panel dipole systems, though, their overall balance as well as the amount and smoothness of their bass are profoundly affected by where you locate them in the room. The best bass is obtained with them toward (but not in) the room corners, but distant (from the listening area) placement tends to obscure detail because of multiple wall reflections in most rooms.
The '63s have a gorgeously, sumptuously smooth and open high end without a trace of hardness. I do not agree with those who have complained about these speakers not having enough high end. As a matter of fact, it isn't even high end that these people are talking about, it is brightness, which is a function of the circa 7kHz range. These do, in fact, have less brightness than most systems, but the result is better reproduction of many instruments—violins in particular than one is accustomed to hearing anywhere. The real high end, which contributes (among other things) the gutty sheen of strings, is there in abundance.
Sheffield's Los Angeles Philharmonic recordings, which tend toward steeliness through most speakers, sound as well-balanced through the Quads as I have ever heard them sound before. Strings have that combination of bite and velvety sheen rarely heard outside of a live performance, but the sheen seemed a bit exaggerated and the system sounded oddly powder-dry, like the texture of chalk. This was the case with the Acoustat TNT-200 and with Quad's own 405-2 power amp, and the dryness persisted even when there was no preamp in-circuit. What I heard sounded like something that might be completely cured by the proper choice of electronics, but I haven't found the magical combination as of yet.
Surface-noise clicks occurring at the same pitch indicated some upper-midrange ringing, and there were instances where one speaker's protective circuits seemed to be shutting down at levels well below where they ought to, which would suggest a defect (footnote 1). Since this shutdown level was still reasonably high, it did not prevent completion of the listening tests, but it did make it impossible to check out the validity of some complaints I've heard about the '63's inability to reproduce high volume levels. Quad rates the speakers' maximum output level in a cryptic form that I couldn't decipher, but if we extrapolate from their figures for sensitivity and input-power capability (footnote 2), we arrive at a figure of 106 dB, which is very loud.

Footnote 1: That speaker subsequently started arcing, which would suggest that the problem may originally have been in one of the elements rather than the protection device. A replacement speaker is on its way to us.—J. Gordon Holt
Footnote 2: If the specified efficiency is 86dB at 1 watt in, and the maximum input is 100 watts, then the maximum output would be 86dB plus 20dB (100 watts is 20dB more than 1 watt), or 106dB. Not all loudspeakers show a linear increase in output with respect to input, however, so this calculation of ours could be off by as much as 3dB.—J. Gordon Holt

Incidentally, Quad's instruction booklet for the 34 preamplifier makes a very good point about listening level, asserting that for a given recording there is only one correct volume setting. I agree generally, but with qualifications. The "correct" setting is where the perceived volume of the instruments "agrees" with their apparent distance from the listener, which makes perfect sense when the recording was done with "purist" microphone technique—two, or at most three, microphones for pickup of the entire group.
But many multimiked recordings produce an ambiguous perspective, where instruments sound very close yet far away (London is a past master of this so-called near-far sound), and for these the "correct" volume setting is far less preordained. In either case, proper volume adjustment requires a certain familiarity with the sound of the real thing, which is something audiophiles as a group cannot always bring to a listening session. Some recordings, such as the ones Harry James has done for Sheffield Lab, demand very high playback levels in order to sound realistic; for these kinds of recordings, the Quad '63s are simply not appropriate.
Many audiophiles like to play all recordings at very high level, sometimes because the loudspeakers are "slow" and seem to prevent the sound form escaping from them, sometimes simply out of a wild and crazy desire to feel the music (footnote 3). And hard-rock enthusiasts are notorious for playing their systems at ear-shattering levels for no better reason than Because.
The Quads are not designed for that kind of abuse, and although they may not be damaged by it (unless continued for some time), they just won't deliver that much SPL. They are designed primarily for the classical-music listener who intends to listen at volumes one would encounter in a typical (perhaps even distant) concert-hall seat.
Those readers who are familiar with the startling aliveness of the original Quad Electrostatics are going to be very surprised by the '63s, and not necessarily in a pleasant way. They are far smoother and more extended at the high end, but while the originals were somewhat bright and forward-sounding, the '63s are by comparison warm, withdrawn and almost overly rich.
The '63's low end extends to just a bit below 40Hz (see fig.1) and the quality of that bass is superb. It is tight, detailed, as solid as oak, and (with the right room location) excellently balanced against the upper part of the range. There is a problem, however. As we listened to a number of dynamic recordings in an attempt to locate just where the '63s would shut down, or sound threatened, it was always on low-frequency notes such as bass drum or kickdrum that problems were encountered.
For this reason we recommend subwoofers for those who listen to music with a lot of impactive low frequencies, or for those who wish to listen to wide range symphonic music at true concert-hall levels. Unfortunately we do not know of a subwoofer that is as psychoacoustically "fast" as the Quad's low end and would thus blend with it. (It would be almost impossible for a dynamic woofer of any size to be literally as fast as the Quad diaphragms.)
One recommendation could be made from the Chicago CES, with the reservation that we have not spent time with the product: the RH Labs subwoofer, made in Portland, Oregon. A pair of these were teamed up with the Quads in the Electrocompaniet room and the result was dynamically more satisfying than the Quads by themselves.
In short, I was impressed with some of the things I heard from the 63s, but less impressed with their accuracy. Their persistent dryness and slight top-end tizz led me to suspect that they might sound exceedingly good with the right tubed amplifier. At the time of this writing the only such amplifier which has worked well is the EAR 509 reviewed in Vol.6 No.3. Catch 22: I was able to spend only two hours with that combination before the amplifier had to be shipped back to the distributor. We have the promise of a further loan and will report on the results of that and any other successful combinations as soon as we've spent enough time with them.
Addendum to the Foregoing: After this review was written, the second speaker of the first pair of ESL-63s I received started arcing over on loud passages. Now, one failure out of two speakers can be bad luck. But two breakdowns out of two is rather pushing the laws of chance, and would seem to indicate a real problem.
Our first suspicion was quality control at Acoustical Manufacturing, but Quad USA was surprised to hear of our having any problem, and in fact we have not heard of problems from consumers—which we would have if the failure rate was 50%! Sure enough, when we talked to our friend Alan Hill of Plasmatronics about our experience, he confirmed that the low atmospheric, pressure, low air density, and extreme lack of humidity present at 7000 feet (remember we're doing this testing in Santa Fe, New Mexico) could bring about significant problems with arcing.
Our second sample pair hasn't had the arcing problem but we've also been fairly cautious in our playing of them—it doesn't help our reputation with manufacturers when two pairs of speakers in a row fail, regardless of the reason.
Unfortunately, we still do not have a satisfactory explanation of the low SPL availability of the 63s. In repeated tests we get maximum levels in the 88dB range, which simply isn't enough. This has been true with both high and low powered amplifiers, tubed and solid-state—and of very high quality. Another as yet unsolved mystery, on which we will be sure to report in the future. In the meantime we recommend a careful audition of the Quads prior to purchase. If they meet your loudness requirements, that's all that really matters.

Footnote 3: JGH himself is not totally immune to this temptation—Larry Archibald

Follow-Up from November 1983 (Vol.6 No.5):
Our full report on the Quad ESL-63 electrostatic loudspeaker last month was inconclusive because (1) our first two samples of it broke down and started arcing, protection circuit or not, and (2) 1 had the feeling that there must be amplifiers which would them sound better than I had them sound to date.
Since then, we obtained two more of the speakers; here's what we found:
On most program material, the '63s would play cleanly at levels up to 98dB SPL, measured at 1 meter on-axis. Above that, one speaker's protection started closing down; the other's did not. This was the same condition we had experienced with the first pair, followed by the diaphragm breakdown of the "ailing" speaker, and shortly thereafter by breakdown of the non-ailing one.
On material with deep, heavy bass, which included many Compact Discs, that same speaker's protection circuitry shut down at levels measured at around 86dB, which isn't exactly soft but it won't blow you out of the room either. With Telarc's CD of the Firebird, shutdown in that speaker occurred on deep bass at the same measured level, but because that recording has much more dynamic range and bass on it than anything else we have on CD, the 86dB figure put the rest of the program at a level lower than most people are going to want to listen at.
Our conclusion: Regardless of the sonic merits it may possess, this system simply does not have the power-handling capability needed to cope with some of the program material available now on both CD and the better analog discs, let alone what tomorrow may bring. And our experience indicated that the protection circuits cannot always be relied on to protect the speakers from permanent damage due to momentary overload. Crossing over to an external subwoofer would improve the '63s' ability to handle high signal levels, but not by much more than 4 to 6dB. Without a subwoofer, we can recommend this system only to those people who listen to symphonic music at significantly lower than live-music levels, or to people whose tastes run to chamber or small-group music. With a subwoofer, the speakers do significantly better, but still will not reproduce an orchestra at close to a live-music level.
In the light of the foregoing, our experience with '63s and the EAR amplifiers may seem irrelevant, but we'll relate them anyway.
Because the EAR amplifiers had to be returned to the manufacturer (who needed them for CES) at the very time we set up our second pair of '63s, we were not able to audition this combination for more than a couple of hours. This was, however, long enough to confirm my suspicions that the "right" amplifier would make these speakers take off and fly! The sound was simply superb, in every respect. Which is all the more frustrating in view of our findings about the speaker's maximum-output limitations.
Damn! I had such high hopes for the '63s.—J. Gordon Holt

Anthony H. Cordesman wrote about the Quad ESL-63 in December 1984 (Vol.7 No.7):
Calling these Quad ESL-63s "Improved" may be a bit misleading. The only significant change in the latest Quad is a pad built into the dust cover to damp vibration in the diaphragm and control a 60Hz resonance. This change begins with serial number 13,041, and is not retrofittable.
However, there have been enough significant changes in the ESL-63 since its introduction for us to view current production as a different product, thus justifying the appellation "Improved." These changes have been: the development of a new and far more rigid frame (ca serial #200); more improvements to the panel structure after serial #11,601; and new protection circuitry after serial #11,825. (Please note, I did not have this serial number when I wrote the "Quad Mods" article in Vol.7 No.2). You can easily tell whether your unit has the new protection circuitry by checking the serial number).
Let me stress that these changes should not lead you to believe your older '63 is obsolete. The improvements do not change the speaker as much as improve it by small increments, while some have had no effect on the sound at all. The changes in the frame, for example, simplified the manufacturing and acted to reduce a 28Hz resonance in the original frame. Since that frequency is below the speaker's working range, it had little effect on the sound. While the new Quads are better than the old, only the protection board change is really critical, and it can be retrofitted. (The two boards you will require are available from Quad USA for $52.52 each. You will probably also need a service manual and considerable skill with a soldering iron.)
The new protection board is essential to ensure that the Quads will not eventually distort while using the wideband amplifiers common in the US. It still does not allow you to ignore Quad's 100W power-limit specification. Buy the best 100Wpc amplifier you can get; more power is not only a waste of money, but it can break down even the new protection circuits.
Sonically, the latest Quad ESL-63s are enough improved over the original version to warrant an updated review, as well as a critical comparison with the Stax ESL-F81 and Acoustat 1+1. The ESL-63 is almost a sonic midpoint between the Stax and the Acoustat. It is more dynamic than the Stax, but less so than the Acoustat. It can play at a sustained 95dB versus about 90 for the Stax and 98+ for the Acoustats. It is flatter and cleaner in the upper four octaves than the Acoustats, but less so than the Stax. It has good midbass and some low bass, and solidly outperforms the Stax in bass extension and lower-midrange linearity, but it has less bass than the Acoustats. It has more overall depth than the Stax, but less than the Acoustats.
The Quad ESL-63s outperform both the Stax and the Acoustats in several important respects. They provide a more natural (if less exciting) image than either of the two other speakers, they provide the most natural sound stage of the three speakers, they can be heard to advantage from a fairly broad (2.7689 person) listening area, and they are almost completely free from the Vertical Venetian Blind effect. They are easier to place in a room for flat response, and they will work quite well with amplifiers rated at only 50Wpc.
The Improved Quads have less of the dryness that was a drawback of previous versions. I don't know whether to credit this to the damping pad or other minor production improvements, but the units with serial numbers in the mid 13,000s and up do seem to give a more coherent and balanced sound. They still have relatively, narrow upper-octave dispersion, but for some reason this does not result in the etched sound and imaging of the Stax, nor in the apparent rolloff of the Acoustats.
However, I should note that the transient resolution of the Improved Acoustats and the Stax is slightly superior to that of the new ESL-63. I doubt if this will matter to most listeners, but it is apparent with the faster top-ranked moving-coil cartridges and better preamps. It is also apparent using the Stax Lambda Professional Earspeaker system, which provides an excellent way of finding out what electrostatics can do when they are free of room effects.
This loss of resolution is slightly greater if you don't bypass the coupling capacitor of the ESL-63s (footnote 1), and is even more apparent if you do not remove the grille cloth or change to a material that is sheer enough to clearly see the diaphragm through the fabric.
Shunting the 220µF coupling capacitor at the input leads will lead to slight frequency irregularities between 500 and 1000Hz, but will make the speaker sound slightly cleaner. Prolonged tests of the newest versions with bypass capacitors show you can get virtually all of the benefits of shunting with none of the drawbacks by paralleling the 220µF electrolytic with a 1µF or higher Wondercap or other polypropylene-dielectric capacitor. I can't recommend a brand name for a new grille cloth and the Quad cloth is far better than most but many fabric stores have open-weave stretch fabrics that will give you at least vestigial cosmetics and a more open sound. Alternatively, you can remove the grille cloth, entirely, although the look of a naked ESL-63 is an awkward cross between a 1950 electric heater and something out of Star Wars.
The regular Quad stand has recently been improved, and now comes with small pointed feet that couple it solidly to the floor. I have not yet found a dealer for. the "Pod" base in the US, but would definitely recommend you try it instead of the Stand-and-Deliver base imported by Quad, which is available from most dealers. Alternatively, you can try making your own stand, fitting Pod feet to the Stand and Deliver frame, or making a frame that will fit the entire Quad speaker and raise it from the floor.
As for speaker connectors, Quad is now putting in banana jacks, which should finally provide a decent connection. If you have an earlier model, fitting banana jacks to it takes only about two hours work. The Quad benefits strikingly from a really good speaker wire and solid connection. The Monster Cable Powerline II and Straightwire speaker cables seem to work particularly well with the ESL-63s.
Even without any tweaking, the Improved Quads are among the most musically natural speakers around. If you can accept halfway reasonable limits to your bass and dynamics, and something less than the ultimate top octave, you can listen to the ESL-63s for hours without being aware of their limitations. I use them as one of my reference speakers without a qualm about my inability to audition cannons, heavy metal, and large-scale organ fundamentals (technically known as "Falwell Organasms" (footnote 2) ).—Anthony H. Cordesman

Footnote 1: See AHC's article on the Quads in Vol.7 No.2.—Larry Archibald
Footnote 2: No, no, Tony, those are Organ Fundamentalists.—Larry Archibald

Sam Tellig wrote about the Quad ESL-63 in July 1985 (Vol.8 No.3):
"You sold your Quads!!!"
My son had just returned home from college.
I wondered myself whether I had done the right thing. Probably I'd done it as an audiophile version of the three-year itch more than anything else—always trying something new. (That's why I became a reviewer: to save myself from personal bankruptcy!)
Or did I have good reason to sell the Quads? I still don't know for certain, but my time without them has convinced me that, as superb as they are, the ESL-63s are still not perfect.
For instance, I always had trouble placing them in my listening room—center fill was never quite right. And I detected a certain fuzziness, a lack of definition in the treble region. This was something that went unexplained until I read Richard Heyser's review of the ESL-63s in the June 1985 Audio. (Heyser found that early reflections within the speaker assembly were interfering with the direct sound at certain frequencies.)
Then there were the Quad mods. While I concede that certain mods are beneficial, I hate the idea of mods in general. When I find a mod that works I get mad at the manufacturer for not having thought of it first—optional metal armboards for the AR turntable (available from Audio Advisor in Grand Rapids, MI), for example. Also, the problem with mods is that once you start you can't stop.
On the Quads I was more than willing to go along with updated protection boards, which after all was an update rather than a mod—and made them more practical, to boot (that's not the case with all mods). Ditto for the Mod Squad capacitor bypass. But there was so much more: spike the stands; remove the grille cloths, they veil the sound (which indeed they do, but they also prevent the speakers from looking like industrial monstrosities); replace the chintzy spring-clip cable connectors with five-way binding post, either heavy-duty or standard; and a complete rebuild of the speaker's structure. (Some people insist that is the only way to the ultimate Quad Sound!) Oh yes, one more thing: you need a subwoofer—except that there aren't any that work. Catch 22.
Moreover, the ESL-63s are very fussy about amplifier and, to a lesser extent, preamplifier. The best sound I got from the Quads came out of the little Quicksilver mono amps I wrote up in the last issue. Also good were the NYAL Moscode 600 (though the 150 should do just as well), the B&K ST-140, and the Hitachi HMA-8500. In other words, Quads like tubes best, and MOSFETS nearly as much.
Quads can be a pain in the keester (thank you, Ronald Reagan) to own. They can be difficult to position, each speaker has to be plugged into an AC outlet (unsightly cords on the floor, not to mention the speaker cables), they're easy to tip over—particularly if you have small kids—and they protect themselves by shorting out your amplifier! That is, until the resistors which absorb the current from your amp until it shuts down sizzle a little.
But...the Quads do have tonal neutrality, exceptional spaciousness, and astonishing transient response. These are qualities that make it difficult to find speakers you can be satisfied with after living with Quads for any period of time.—Sam Tellig
Sam Tellig also wrote about the Quad ESL-63 in January 1987 (Vol.10 No.1):
Owning a pair of Quad ESL-63 speakers is like marriage to a difficult woman you love—hard to live without, sometimes hard to live with.
The $2950/pair ESL-63s are among the very few speakers I could live with for any length of time. They are as free of coloration as any speaker I know. Like other electrostatics (and ribbons), they are fast: transients are quick, and there's no sound trapped in the box because there is no box.
Weaknesses of the Quads are well known by now, and sometimes overstated. They do not play particularly loud. This can be a disadvantage not only with rock music, but also with large-scale orchestral works—Mahler becomes moderated, Bruckner bridled. Haydn and Mozart do fine, though, as does chamber music of all kinds. Known as a classical-music lover's speaker (kids into rock can't afford them anyway), the Quads are also terrific for jazz. Listen to a tenor sax on the Quads—driven by tubes all the way—and you know you're listening to the truth. The tenor sax is, for me, the most difficult of all instruments to reproduce.
Philips engineers use Quad speakers (and amplifiers) for monitoring their recordings. Philips recording artists like Bernard Haitink, Alfred Brendel, and Jessye Norman have purchased Quads for home listening (though Sir Neville Marriner uses Magneplanars).
I have yet to hear speakers I like better, though I have yet to hear the Sound Lab A-3s reviewed by JGH in Vol.9 No.6. Still, the Quads aren't perfect. I am not bothered so much by the fact that they don't play loud or that the bass doesn't go particularly low (although it goes lower than you think with an amp like the PS Audio 200C). What bothers me most about the Quads is a certain fuzziness in the treble, which I first heard identified by Richard Heyser two years ago in an Audio review. Along with this fuzziness goes a certain lack of precision in imaging. This might seem surprising, considering the sense of spaciousness and depth the speakers produce. I'm talking about two different things, however: spaciousness is not imaging.
I was surprised to see Alvin Gold savage the ESL-63s (in the September 1986 issue of Hi-Fi Answers) while reviewing the MartinLogan CLS speakers. True, the MLs do things the Quads don't: they have exceptional transparency through the treble, and image as well as any speakers I have heard. In fact, I was so taken by the MLs after hearing them at CES in the summer of '85 that I had a pair on order. Dick Olsher had problems with his pair, though, and I put the order on hold.
The first indication that there might be something wrong with the MLs—based not on home audition but on several listens elsewhere—came at last winter's Vegas CES. The speakers sounded thin, peaky, and deficient in the bass. And the bass bottomed out, just like the Quads, when cranked up on certain killer Telarcs.
For a while I entertained the idea of a pair of Apogee Calipers; they certainly made a favorable impression on everyone at last summer's CES. Subsequent auditions, though, revealed problems with those speakers as well. Yes, they may be more transparent through the treble than the Quads—a lot of speakers are, including the Celestion SL-600s—but they also struck me as bass-heavy.
So, at least for the moment, I am sticking with the Quads—my second pair, acquired earlier this year. If Bernie, Al, and Jess can live with them, I suppose I can, too. And, they are quite good for reviewing. One of the surprising things is that the Quads, without having much deep bass, reveal those amps which produce deep, tight bass. That's one of the first things I notice when I switch amps—a change in the bass. (The Quads reveal that the British Fidelity P-170 has deeper bass than the B&K ST-140, for instance; otherwise, these two MOSFET amps sound virtually alike. I can recommend both for use with the Quads.)

Martin Colloms added some comments in January 1987 (Vol.10 No.1):
The Quad ESL-63 uses an 0.00137" diaphragm, with 0.001" plastic film for the dust-cover membranes. (The ESL-63's diaphragm weighs just 0.003gm, or 3 milligrams, not too far removed from the tip mass of a pickup cartridge!) The diaphragm diameter is subdivided no less than eight times, providing a controlled reduction of element size with frequency, and thus maintaining a good radiation angle.
Electrostatics generally have a finite sound-level limit, due to considerations of peak voltage and electrical flashover, or saturation limiting in the cores of the step-up transformer. Other problems include aging—changes in the diaphragm tension—and dust build-up due to electrostatic attraction. The Quad ESL-63, however, is dust-proofed.
For the record, the Quad ESL-63, while not able to play rock bass to the same level as the MartinLogan CLS, Apogee Duetta,or the Magneplanar MG3.5 speakers, was, in fact, the best as regards tonal balance and low-frequency uniformity. It was also consistently neutral to a wide range of sources.—Martin Colloms

Larry Greenhill reviewed the Quad ESL-63 US Monitor in February 1989 (Vol.12 No.2):
Electrostatic loudspeakers (ESLs) have always held a fascination for audiophiles. The Jantszen, Beveridge, KLH, Acoustat, Stax ESL-F81s, and Servo-Static models in the late 1960s and '70s, as well as the MartinLogans and Sound Labs of today, all promise faster transient response, low distortion, and a higher order of "transparency." Why? The driver, instead of being a cone with a mass of several ounces, is an extremely thin sheet weighing mere grams, often made of Mylar, and suspended between two charged plates. The musical signal, applied to the plates, causes the diaphragm to move. Many of the designs operate full-range, without complex crossovers and their attendant problems.
Like all exotic systems, there is a price to pay. Electrostatics, particularly the early models, are planar systems and have beaming problems. The bipolar dispersion pattern of the sound makes them very sensitive to placement. Although the low-mass membrane can move very quickly, it can not move far; deep-bass response is limited unless huge panels are used. Electrostatics require power supplies and transformers, and the impedance and phase angle of the interface can vary tremendously depending on frequency. Many solid-state amplifiers have had problems driving such complex loads. Charging the plates requires expensive, high-voltage power supplies, often mounted in the speaker's base.
Unreliability plagued many of the early models, arcing of the diaphragms giving a wonderful blue glow in the dark but giving the owner a sinking feeling—an expensive repair was in the offing. This unreliability added insult to injury, as the price of these systems can be quite high. Although we are now jaded with the thought that a full-range, "all-out" speaker system can cost in excess of $10,000, the early members of the electrostatic club in the late '60s clearly were buying then the most expensive speaker systems, at costs of several thousand dollars. All this was justified, for the dedicated hobbyist (and eventually neurotic, worried owner!) who could tolerate the expense, breakdowns, and cumbersome speaker enclosures, for these speakers offered low-distortion, non-fatiguing sound with superb imaging and detail.
Why review the Quad ESL-63 again, now presenting itself in the United States as the US Monitor? Because the Quad, now in its third version, is the longest-surviving consumer-grade electrostatic speaker on the market, if one counts the first version made in 1957. Only 11 full-range electrostatic systems are listed among the 1376 loudspeakers in Audio's 1988 Annual Equipment Directory, and these are manufactured by only four out of 257 speaker companies in the audio industry. Sound Lab makes three full-range ESLs and four ESL subwoofers; Acoustat offers six models; MartinLogan has only one "pure" ESL system; and there is the Quad US Monitor. (In addition, Stax still offers the ESL-F81, 'F83, and the ESTA-4U.) Stereophile's "Recommended Components" for April 1988 (Vol.11 No.4) lists only the Sound Lab A-3 and Quad ESL-63 in Class B. For many, the US Monitor will be a serious contender for the "best" ESL: accurate, superb imaging, no crossovers, with great sonic coherency, practical size, and high reliability.
The Early Quad
The first Quad electrostatic, which remained in production for 25 years, had all the electrostat's virtues and vices. As with all of Peter Walker's products, some new principle was applied—the first Quad employed the "constant-charge" technique, which insures an even distribution of charge across the entire diaphragm. The speaker was a curved rectangular panel, with the longer sides horizontal, a look that was copied by Jon Dahlquist for his DQ-10. These relatively small panels imaged beautifully and, for me, gave the ultimate in midrange accuracy, speed, transparency, and imaging. On the other hand, it could not play loud, had very limited bass response, and less than optimal dispersion patterns for stereo imaging. It would arc instantly (blue flame and hole in the Mylar) if you were rash enough to overload it even for a second using an amplifier that put out an instantaneous voltage exceeding 27V.
Finding the right amplifier was another part of the electrostatic owner's lifestyle. The amplifier had to be right sonically, of course, but also had to have exactly the correct voltage peak or it would literally "consume" the loudspeaker. The Acoustical Manufacturing company made a small solid-state amplifier, the 303, which was safe to use with their electrostat. In the early 1970s, John Curl and Marc Levinson designed another amp for the Quad panel, the ML-2. This product fit the exotic, hyper-expensive world of electrostats to a T. Sporting huge cooling fins, the ML-2 was a 65lb, monophonic, full-duty cycle, class-A amplifier than ran as hot as a space heater, putting 25W into the speaker and 150W of heat into the room. It cost then about $4000/pair (current special-order versions of the ML-2 are still available today from Madrigal at $9600/pair!).
The sonics of this speaker-amplifier combination were highly touted, and have since been regarded as one of the few "classic" pairs of audio components. This original Quad, for its extreme midrange transparency, did not offer as much at either frequency extreme, and required total dedication on the part of the owner. Some high-end dealers supposedly even taught their customers to repair the diaphragms themselves, using Mylar and a hair dryer!
The Quad ESL-63: the first 7 years
Peter Walker began to redesign the Quad in the early 1960s (the "63" in the ESL-63's name supposedly designates the year of the design). The new version was released at the CES of 1981, and seemed smaller because the long side of the speaker's rectangular frame was now vertical. Many exciting and clever technical inventions were incorporated into the '63 (detailed in an excellent article by Reg Williamson in Speaker Builder, Vol.3 No.1, pp.10-18, February 1982).
The first involved a new protection circuit, offering a technically sophisticated triac clamping circuit to prevent arcing. The circuit operated by limiting the input, and when that failed, by short-circuiting the input with a "crowbar" technique (the amplifier needed to have adequate protection against the speaker!). This crowbar circuit was actuated by an RF "sniffer" that was set to sense the high-frequency noise that accompanies the ionization of air that occurs when the speaker arcs.
The second innovation was the speaker's unique radiating element, which used driver plates that employed a printed circuit board of annular rings, like the ripples formed when a stone is dropped into a lake. These rings were fed by delay lines (employing some 11 miles of wire!) which allowed the flat diaphragm to radiate the sound first at the center and last at the periphery, as if it were a radiating sphere—the ideal shape for approximating sound emanating from a point source with an apparent location 12" behind the panels. The single element in the new Quad also meant the elimination of a venetian-blind, treble-beaming effect found in speakers with multiple panels. This design meant near-perfect phase coherency, as shown by Quad's show-stopper demos in which two squarewaves, out of phase with each other, are fed to two Quad speakers. A microphone placed between the speakers shows that the two signals cancel out completely, suggesting very low distortion in the speakers.
Many of this magazine's major reviewers have made excellent and critical statements about the '63's strengths and weaknesses. Bill Sommerwerck opened with a very technical description following the speaker's first CES showing in 1981, praising "FRED" (Peter Walker's technical name for the ESL-63, which stands for Full Range Electrostatic Driver) for its natural-sounding, pristinely focused, unstrained ability to capture the acoustical space in a recording.
JGH had a mixed opinion, praising the '63 for its imaging, but faulting it in other areas. He found the sound to be "warm, withdrawn, and overly rich . . . [with a] persistent dryness and slight top-end tizz" (Vol.6 No.4). The new Quads quickly shut down during orchestral climaxes, which led him to withhold his recommendation, "regardless of the sonic merits it possesses." The loudspeaker "simply did not have the power-handling capability" for program material then becoming available on CD (Vol.6 No.4).

This inability to play loud turned out to be related to an altitude effect, the speaker being unable to play any louder than 97dB at the 7000' Santa Fe elevation (still, the original '63s were no rock loudspeaker, even at sea level). Stands (Arcicis, sand-filled to reduce vibration and increase stability), subwoofers (perhaps Celestion System 6000 dual-mono subwoofers), and tube amps (Futtermans) were recommended associated components for the owner willing to go the full route.
Then came the next period in the life of the Quad ESL-63—modifications and improvements. Some were done by Quad itself. AHC carefully documented the improvements Quad made to the protection circuitry (ca 1983) to tolerate higher levels (fixing the clamping level and increasing the shutdown time to 4 seconds); modifying the louvers to reduce resonances (above serial #11601, new louvers are white); and the pad built into the dust cover to damp a 60Hz resonance, beginning at serial #13,041 (Vol.7 No.7). From 1987 on, most Quad ESL-63s were less dry-sounding, as noted in the speakers' description in this magazine's listing of "Recommended Components" (Class B, October 1988, Vol.11 No.10).
Other mods were installed by audiophiles. The Arcici stands were substituted for the "Stand and Deliver" units offered by Quad. AHC detailed many of the other mods in a separate article (Vol.7 No.2), including capacitor bypasses, replacing the snap-in speaker-cord terminals, replacing the grille cloth, and rewiring some of the connector wire with heavier cable. Some audiophiles actually removed the metal grilles. During one CES, the highly modified '63s of Damien Martin (Spectral) had no grilles or grille cloth at all!
All in all, the Quad ESL-63 maintained a firm hold on its Class B listing in "Recommended Components." I purchased a pair, finding that the '63 was a big improvement sonically over the original Quads, particularly in lateral image width and front-to-back depth.
1988: Enter the US Monitor
Now the US Monitor has made its appearance and will be the only version sold here in the States. Ross Walker, President of Quad, and son of Peter Walker, the '63's designer, explained that the US Monitor evolved from a special "pro" version that had been developed for Philips' European recording division. They had requested "ruggedized" '63s that could take on-location recording, with all the moving, hoisting into trucks, and other non-audiophile types of abuse. Quad obliged Philips by replacing the '63's aluminum frame with steel, putting handles on the sides, and rubber kick-pleats at the base. Philips was delighted, and soon other studios were requesting the "pro" version.
Ross felt that the speaker was much more durable and rugged, and the combination of the steel frame and metal grilles truly reduced speaker resonances in the audible range. Even though its weight had gone up by 30%, it was best suited for shipment and moving about. It was decided that this model, perhaps because of its superior mechanical ruggedness, was optimal for export. Thus the US Monitor was as much a product of necessity as sonics.
The issue concerning "visible and obvious" external changes was answered directly by Ross and by Ed Gardner, Vice-President of Quad sales for the American distribution company, Tovil Distributors. I want to list the visible changes first.
Turning on the AC power switch is followed by a soft click, suggesting that a relay has been added. The grille cloth is more sheer, more acoustically open. Moving the wooden top piece to the side and pulling down the grille sock reveals more differences. The metal protective grille is now flat, with large, 8mm² open spaces, in contrast to the original '63's downward-angled needle-thin slots. Like the earlier '63, the US Monitor has four horizontal panels stacked in the frame, their leads soldered together. The electrostatic sections are a bit more efficient, with reduced thickness in the printed circuit on the plates themselves to reduce the plate gap. The US Monitor's circuit boards (in the speaker's base), including the protection circuit, audio transformer, delay lines, and high-voltage transformer, look identical to those in a late-model ESL-63. With the steel frame, all these changes make it impractical for the manufacturer to offer upgrades. Alas, those of us with original '63s will have to buy the US Monitor outright to "move up"; no factory-supported upgrades can make a '63 into a US Monitor.
Quad made no audiophile-inspired changes. Walker stated that any mods would only be added if measurable improvements could be shown, and, to date, the company has yet to find a user-generated mod that helped directly. So American "tweaks" of signal-cable wiring, capacitor bypasses, and metal-screen-ectomies have been ignored by the manufacturer. Although Ross did admit that the '63s sounded a "bit more accurate" without the metal screens, he quickly added that the company needed those screens to protect customers from the speaker's high voltages. In addition, he noted that all '63s without their protective screens become mechanically unstable and begin to vibrate at low frequencies. So those metal screens not only protect the owners from nasty 10kV shocks, but also make the speaker much more rigid and reduce those ugly, unwanted resonances which could muddy the sound.
In reviewing the US Monitor, I had several questions in mind. Besides the increase in reliability and durability, did the speaker sound different from my stock Quad ESL-63s (serial #9010)? Could the speaker stand up to some heavyweight, high-power solid-state amps? I would hope so, for opening up the gain on my 100Wpc Threshold Stasis III (which clips at 125Wpc) quickly shuts down my early-model '63s, and the '63's "crowbar action" neatly takes out the Threshold's rail fuses in the bargain.
Setup & Listening Tests
No doubt about it, the US Monitor is more rugged in dealing with American amps. It tolerated full-tilt +3dB peaks on the Threshold (200Wpc peaks) and handled all the Levinson ML-9 could dish out (close to 700Wpc peaks, or 75V peaks!). I found that the speaker smoothly clamped the ML-9, for the sound levels did not increase (actually diminished a bit) as I advanced the ML-9 to its full output.
The listening sessions were carried out in two locations (after all, Ross, these monitors are meant to be schlepped about, are they not?). Most of my listening was carried out in my rectangular, 5400ft³ living room which sports a 12' semi-cathedral ceiling. The room's 25' length has allowed my own ESL-63s to develop impressive deep-bass levels. The speakers were placed about 5' from the back wall and 5' from either side wall. The sound in this room has always been zippy and fast, with a small peak in the 7kHz region.

The US Monitor stayed very close to the sound of the my early '63s for most vinyl recordings and CDs. The new speakers played louder than my originals, and there was an enhanced openness, particularly in the upper midrange. In addition, the amplifiers continued playing as I cranked up the volume control (my older Quads would shut down just as the amplifier's protection circuits or fuses acted). By comparison, my older ESL-63s had a "dark" tonality. In many respects, the "intact" US Monitor (with its metal screens on) sounded like the older Quad with the screens off (footnote 1). As a result, I heard more inner detailing, depth, and a better sense of spatial location in the new US Monitor. The US Monitor appeared to have more upper midrange and less bass than my old ESL-63s. This may represent some lack of rigidity in the older Quads that adds an added "whumph" in the midbass area, a byproduct of the less rigid speaker frame's vibration.
Image width excelled, with rock-stable specificity and needle-sharp focus in the far lateral field. Dispersion in the US Monitor was generous—it became possible to move around without losing the stereo image (no pinpoint "sweet spot"!). Two people (who no longer need to be Siamese Twins) sitting side-by-side could easily experience the speaker's superb imaging. The US Monitor has quickly become my hands-down favorite over all other speakers in reproducing the female voice. Grain is gone, and I felt I could "blow-up" (figuratively!) any aspect of the musical texture and find more detail. I find the image height is less restricted than that of the original ESL-63s. Although the Quad-supplied "Stand and Deliver" metal stands diminish the bass extension, the speakers become more accurate in the midbass when so elevated.
The US Monitor reproduced live recordings with a sense of immediacy and coherency that added greatly to their energy and realism. Billy Joel's Toys in the Attic was wonderful, and listenable with an immediacy I had not found before with dynamic systems. Glenn Gould's Goldberg Variations had transient speed and transparency, both on vinyl and CD, that had just not been apparent to me with other systems. The other element I must comment on: coherency. There was a sense that the soundfield emanated from a point, both bass and highs, so that I was not aware of separate transducers (which was accurate, for there is only one radiating element per loudspeaker).
Location Two
The second location was picked to allow for comparisons between the US Monitor and Sound Lab A-3s. The listening took place in Glenn Hart's (footnote 2) rectangular 15' by 24' living room, heavily carpeted and furnished with two overstuffed couches. The Sound Lab speakers were placed at one end of the room, 3' from back wall and side wall and on either side of French doors that opened onto a porch. The 6' Sound Lab A-3s sat immediately behind the Quads for listening comparisons.
Just to test the Quad's ruggedness, we used a pair of Moscode 600 amplifiers, rated at 300Wpc. The A-3s, by the way, were set up by toeing them in at 25 degrees across the door opening. A large number of vinyl records were auditioned, using an Oracle turntable and a Koetsu Black cartridge. This was followed by a highly revealing California Audio Labs Tempest II CD player and some favorite CDs. A noncontrolled format was used, listening to each selection fully, then switching to the other speaker.
First, a caveat: The listening situation in room 2 was not optimal for the Quads. We chose to leave the Sound Lab A-3s in place because of the limited time for setup and listening. The Quads' frequency balance and imaging can be affected by placement because of the bipolar sound-radiating pattern. In many ways, it may have favored the Sound Lab A-3s, which kept the "favorable" position in the room. Even so, the Quads and Sound Labs both sounded eminently natural and smooth. The Quad imaged beautifully, producing a three-dimensionality rarely exceeded by the Sound Labs.
Vocals proved very revealing. The Quads excelled on a Philips LP of soprano Fredericka von Stade, whose voice was less shrill and strained than on the A-3s. Lou Reed's Walk on the Wild Side on CD showed impressive front-to-back depth on both systems. The Tempest II CD player did pinpoint a possible frequency-balance shift in the Quads, perhaps due to their location in that room. On one CD of female vocals (Radka Toneff, Fairy Tales; Odin, BB, Oslo-Norway Records, Tottesgate), the voice took on a chestiness over the Quads that seemed to shift her entire range down. A pop vocalist, Basia, showed no changes in vocals, but the bass synthesizer took on a midbass emphasis. Using the wonderful Vanguard recording of the Weavers' 1962 Carnegie Hall Reunion ("Guantanamera"), the voice of Pete Seeger seemed more natural and less nasal on the Sound Lab A-3s; in addition, the soundstage on the A-3s was wider, and Seeger's voice was positioned further to the right.
Orchestral music showed a similar effect, with the string sound on the Quad having a very smooth, non-fatiguing quality. The A-3s, if anything, were more analytical, emphasizing inner detail. On the Pulcinella Suite, I heard what sounded like a pizzicato on violins over the Quads; the A-3s resolved this sound into a clear low-frequency drumbeat. In all fairness, the Sound Labs' ability to yield this type of low-end detail would be expected from its much larger panel system.
Clearly, the US Monitor had a very "civilized" character, and sounded smoother and less bright on some recordings than did the Sound Labs. We even noticed that vinyl record noise was less apparent on the Quads. (Perhaps this is in agreement with JGH's observation, in his original review. He found that the Quads were free of a 7kHz brightness often found in other "exotic" loudspeakers.) The comparison with the A-3s may be unjust, not just because the positioning favored the Sound Labs, but because the Sound Lab is a full-height, 6' curved panel speaker which costs 50% more than the Quads. Still, the A-3 is something of a standard at this magazine.
It is a great credit to the US Monitor that it was a serious contender with this much bigger, more expensive ESL. Both speakers proved highly detailed, natural sounding, and clean. The Quad excelled in a pinpoint three-dimensionality that gave the imaging solidity, while the A-3s created a very wide soundstage. On some recordings, we admired the A-3s' speed, snap, and open high end; it seemed more "correct." On others, it was amazing how the Quads, in a disadvantaged position, could generate a palpable, solid sonic image that we felt we could reach out and touch. The comparison should be repeated in other settings, however, if you decide to narrow your speaker selection to these two units. It is quite possible that moving the Sound Labs into a different position would have enhanced their ability to create a solid, three-dimensional image. Similarly, the openness and "correct" balance of midrange and midbass I heard from the US Monitors in my own living room could have been captured in Hart's room with different placement. Many ESLs are sensitive to room positioning.
Conclusions
As a current owner of the older Quad ESL-63, would I pay for a factory-sponsored upgrade to the level of the new US Monitors, if such a deal existed? Definitely! But since this is not possible (sigh!), I will have to struggle with the decision facing many Quad ESL-63 owners—should I buy a new pair of $3990 US Monitors and sell the ESL-63s? After all, I now have a suitable amplifier that won't break down (either amp or speaker) with ESL-63s. Tighter bass and a more open upper midrange make the new US Monitor a clear winner over older Quad ESL-63s. The US Monitor is much more open (perhaps because of those new metal screens), faster-sounding, with tighter bass, and slightly less blurred highs than on my ca 1983 ESL-63s.
The big news here is the Quad's increased ruggedness and reliability; it also displays slight to moderate improvements in sonics. I was impressed that the Quad (to my ears) bettered the "top-seed" A-3 system in solidity of imaging and on some recordings of high soprano voice. The speaker can't be damaged by any signal level that I threw at it (those of you who know the ML-9 will respect its punch!). It now is an acceptable speaker for pop and rock; what it loses in bass sock it more than makes up in naturalness and imaging. It is rugged, sturdy, can be moved around by one person, and is easy to place in a living room, having a good WAF (Wife Acceptance Factor, footnote 3). It can even be shipped for repairs or grille-cloth changes by UPS (the Sound Labs A-3 is platenized and shipped directly by a special trucking service). Sonically, the Quad remains one of my all-time favorite loudspeakers in terms of imaging, focus, low distortion, and low listening fatigue.
For those who are first-time buyers, the US Monitor is a godsend. If you must have an electrostatic, you will appreciate the speaker's long and honorable origins, development, and well-developed protection circuit. Its price point is set well below the most expensive Sound Labs, Apogees, Duntechs, and IRS Betas. They may excel in the deepest bass range, have more dynamics and greater soundstage width, but the US Monitor will hold its own in naturalness of sound, pinpoint three-dimensional imaging, and signal coherency over the frequency range (sounds emanating from a single source).

Footnote 1: I gave up the "barefoot" ESL approach—no metal screens—when my cat began to use the old Quads as a scratching post!—Larry Greenhill
Footnote 2: Glenn Hart, an audio writer in his own right and the Sysop of the CEFORUM on Compuserve, kindly donated time, his living room, and his Sound Lab A-3s for these tests. He also contributed valuable opinions.—Larry Greenhill
Footnote 3 Thanks again to Glenn Hart, who did not coin this term—it was Lewis Lipnick—but from whom I heard it for the first time!—Larry Greenhill

Sam Tellig's final comments on the Quad ESL-63 appeared in June 1989 (Vol.12 No.6):
Remember Fred?
Not Fred Yando, of Quad USA. But FRED as in Full-Range Electrostatic Dipole—the now venerable Quad ESL-63, available in its new US Monitor version.
This is my third pair of ESL-63s—a very early pair, followed by a later pair, and now the new ESL-63 US Monitor. I guess I am a creature of habit. I've been married to these speakers now for seven years. And married to Mrs. Audio Anarchist now for 25.
"You're getting another pair of Quads," shrieked one of the Thursday night 'philes at Definitive Hi-Fi. "That's not progress."
AHC said as much several years ago, when he talked about the ESL-63 being a good speaker "in its day," implying that its day had passed.
Well, newer speakers have come (and gone). But you still have to go some to better the Quads. And now, having welcomed them back, I cannot name you a speaker I would more prefer to own. (My friend Lars says I have been suffering from metal-dome tweeteritis.)
Oh, yes, some speakers are more extended on top. Some are subjectively more transparent. There are definitely speakers which play louder and go lower. And yet...well, welcoming back the Quads was like climbing into bed with an old girlfriend after a long absence (in this case, the absence was 18 months). Not that I would know about such things. But I do love these speakers!
They are so neutral—so free of coloration. There is no discontinuity from bass to midrange to treble—it's all so natural. Transient response is excellent. There are no boxy colorations because there are no boxes. So what if they cost $3990/pair. I can put another 20,000 miles at least on the VW Jetta (it has 86,000 already—good car, cheap to run). To hell with the money.
When I first asked Ross Walker, of Quad, whether I should sell my old pair of Quads and buy the new US Monitors, he told me not to bother. (I suspected then, and still suspect, that Quad was trying to get rid of me as a customer.)
I asked Ross why Quad was introducing them.
Marketing considerations played a role, according to Ross. They were going to have to raise the price of the ESL-63 anyway because of the fallen dollar. So they decided to improve the product and put up the price a few hundred more.
Ross pointed out that Quad was already building a heftier version of the speaker—this for recording studios. Stronger, more rigid frame. Some other things, too—forget what. So the US would get a premium version, and the rest of the world, presumably more price-sensitive, would get the ordinary Quads, which are still to this day sold outside North America. I'm not sure what Canada gets.
Maybe Quad had another motive. Because of a price disparity between the UK and the US, some audiophiles were importing Quads directly from the UK. Quad dealers in the US were not so happy about that. If you try to import a pair of Quads from abroad now, you will be able to purchase only the ordinary ESL-63s, and only in 220/240V, although an overseas dealer should be able to change over the voltage.
It would be pointless to import a pair of "ordinary" ESL-63s from the UK, however, because you can readily find used ESL-63s on the market here in the US, and at reasonable prices—as low as $1000/pair for early-production ESL-63s, up to about $1500/pair for later production.
That's quite a disparity. $1500 for a pair of used, regular ESL-63s, $3990 for a pair of new ESL-63 US Monitors. I think I'd opt for a used pair. At the same time, I have to say that the new US Monitor version represents a significant improvement on the older ESL-63, which Quad still deems good enough for the rest of the world.
How has the speaker been improved? First, the bass. It's more extended. It's more defined, possibly because resonances in the frame are better controlled. (I use my Quads in sand-filled Arcici stands, and the bass is good enough that I wouldn't dream of adding a subwoofer.) Next, the treble—it's less confused, crisper, better defined, not slightly fuzzy the way it used to be. The speaker is more transparent. At the same time, the treble still does not "go over the top," the way so many other audiophile speakers do.
The word I keep coming back to is "listenable." The Quad ESL-63 US Monitor is the most listenable speaker I know—and for this reason (and also because I hate the notion of mods), I decline to have my speaker modified by Crosby, as touted by The Absolute Sound. With the Quads, I can forget the speaker, and forget the recording quality, for that matter. The Quads do not make poor recordings sound worse. Most of today's audiophile speakers do.
I have also noticed that I can enjoy listening to CDs with the Quads—I don't feel the urge to shut off my CD player and turn to my 'table. Lately, having returned several CD players to their respective manufacturers, I have gone back to an old 14-bit, Philips-based Marantz CD65 player. The soundstaging is so natural. Many very expensive, very sophisticated current players don't do nearly so well, including, I'm afraid, some offerings from Magnavox/Philips.
Incidentally, I found that the Quads take a while to break in. (Or were the speakers ready out of the box and I had to take time to break in? I don't know.) I felt that the speakers were smoother, cleaner, clearer after about a week to ten days. After my first day back with the Quads, I was reasonably happy, but not overwhelmed. After ten days with the Quads, I was in ecstasy because I felt I was listening to music rather than to audiophile sound.
While the Quads sound okay with such inexpensive amps as the Adcom GFP-535 or the B&K ST-140, they can use power. They like current. They like to be driven—they sound cleaner, the bass becomes tighter. An amp like the B&K ST-140 reveals all its strengths (tube-like midrange) and weaknesses (flabby bass, rolled-off highs, lack of ultimate transparency) when used with the Quads.
[A version of the speaker, called the 988, is still being manufactured in 2001. You can read Sam Tellig's thoughts on the 988 in "Sam's Space," November 2001.—Ed.]

Sidebar 1: Specifications
Description: Full-range electrostatic speaker system. Power capacity: 100W, 10V rms, 40V peak maximum signal input. Nominal impedance: 8 ohms (6.2 ohms minimum). Sensitivity: 86dB SPL for 2.83V rms at 1 meter.
Dimensions: 36" H by 26" W by 6" D (base 10" D).
Serial numbers of review samples: 13,955 & 13,956, 1984.
Price: $2850/pair, 1983-1985; $3990/pair, 1989. Approximate number of dealers: 50.
Manufacturer (2001): Quad Electroacoustics Ltd., IAG House, Sovereign Court, Ermine Business Park, Huntingdon, Cambs PE29 6XU, England. Tel: (44) (0)845-458-0011. Fax: (44) (0)1480-431767. Web: www.quad-hi-fi.co.uk.
US Distributor (1983): Quad USA, 425 Sherman Avenue, Suite 130, Palo Alto, CA 94306.
US Distributor (1984): Quad USA, 695 Oak Grove Avenue, Menlo Park, CA 94025.
US Distributor: (1989): Tovil Distributors, 14120-K Sullyfield Circle, Chantilly, VA 22021. Tel: (703) 631-8810.
US Distributor: (2001): IAG America, 180 Kerry Place, Norwood, MA 02062. Tel: (877) 440-0888 or (781) 440-0888. Fax: (781) 440-0333. Web: www.quad-hifi.com.

Sidebar 2: Measurements (from June 1989, Vol.12 No.6)
As I had dragged my motley collection of test equipment (footnote 1) over to Larry Archibald's listening room to carry out a set of measurements on the Mirage M1 loudspeaker he has reviewed elsewhere in this issue, I thought it might be a good idea to quickly take a look at the measured performances of the latest, "US Monitor" version of the $3995/pair Quad ESL-63, which had so impressed Larry Greenhill in February (Vol.12 No.2). Sam Tellig also writes about the Quad in this month's "Audio Anarchist" column, and the particular sample measured has been serving as Dick Olsher's primary reference for the last six months or so.
The Quads were held clear of the floor with Arcici's excellent dedicated stands and had their cloth "socks" rolled down. Fig.1 shows the speaker's modulus of impedance, measured with an average 10mV drive level. Dropping below 6 ohms below 50Hz and between 5kHz and 18kHz, with minima of 3.5 ohms at 10Hz and 13.85kHz, this represents a reasonably demanding load for an amplifier to handle. Tube amplifiers would be best used from their 4-ohm tap (if they have one), though any solid-state amplifier that more or less doubles its power output into 4 ohms compared with 8 ohms would have no problems driving the Quad.

Fig.1 Quad ESL-63, electrical impedance magnitude (2 ohms/vertical div.).

Unusually, the position and height of the impedance peak in the bass is level-dependent. I am not sure to what cause the resonant peak at 22.4kHz can be attributed; perhaps it is the Helmholtz resonance of the airspaces in the plastic grid used to resistively load the diaphragm. As it will only be audible to dogs and very young children, however, neither of whom have sufficient disposable income to be able to afford the Quads, it is presumably benign (though the two small impedance peaks at 8.3kHz and 12kHz do tie in with audible amplitude-response peaks).
Turning to the spatially averaged 1/3-octave response at a 3m listening position (fig.2) (footnote 2), this is one of the smoothest through the midrange that I have ever measured. With the exception of the slight dip in the 250Hz region due to interference between the direct sound and the reflection from the floor between the speaker and the measuring microphone, ±1dB limits cover the deviation from a flat in-room response between 160Hz and 5kHz. The top two octaves appear to be somewhat depressed on the spatially averaged response, though the region between 12.5kHz and 16kHz can be seen to be a little lively, but this is more a function of the speaker's very limited dispersion in this region than of a true lack of on-axis energy. The individual measurements used to derive fig.2 show that in the vertical plane, the top two octaves drop by 6dB when the listener is level with the top of the speaker, while below the central axis, there is a 3dB drop in the treble. The same applies to off-axis lateral listening.

Fig.2 Quad ESL-63, spatially averaged, 1/3-octave, in-room response in Larry Archibald listening room.

The Quad US Monitor must be listened to on its optimum axis level with the speaker's center, therefore, if the treble is not to be excessively dulled, which means that only two listeners, at best, will be able to get full HF measure. For a normal listening position, it will therefore be essential to use stands; as implied above, the Arcicis, which are excellent value at $175/pair, are the best we have experienced. Exacerbating this sweet-spot characteristic is the fact that the speaker's limited treble dispersion and dipole nature will rob the room's reverberant field of HF, which will make the Quad sound a little lifeless, particularly in overdamped rooms. On the bright side, however, the dipole nature means that bass room resonances will be less easily excited.
Note, for example, that neither the 31.5Hz or 63Hz peaks that appear on the Mirage or Infinity response measurements, due to the two major resonant modes in Larry's room, appear in fig.2. Of course, to be honest, the lower resonance is hardly likely to be excited anyway by a speaker that starts to roll off below 55Hz. In-room, the low-frequency response was 6dB down at 40Hz, though in the nearfield, the response didn't reach -6dB until 32Hz.
The design of the Quad, with its concentric diaphragm regions driven with signals featuring successively increased time delay, is intended to synthesize the acoustic equivalent of a point source positioned some 12" behind the diaphragm's midpoint. Its impulse response should therefore be excellent. Fig.3 shows the 55µs-long unidirectional rectangular pulse that I use as an analytical test signal; fig.4 shows the output of the Quad US Monitor over a 5ms window with the measuring microphone on the optimum axis at a distance of 1m. Pretty damn good, I'm sure you will agree; in fact, it is the best impulse response I have ever seen from a speaker, with a clearly defined, single main spike, with then a small negative undershoot on its return. The slight ringing overlaying the tail of the pulse has a period of just under 1ms, equivalent to a frequency of approximately 12kHz. This resonance is probably due to the dust cover. Fig.5 shows the step response calculated from this impulse response. It has an excellent, time-coherent, right-triangle shape, with a lazy overshoot resulting from the bass alignment.

Fig.3 55µs test pulse (5ms time window).

Fig.4 Quad ESL-63, impulse response on listening axis at 1m (5ms time window, 12kHz bandwidth).

Fig.5 Quad ESL-63, step response on listening axis at 1m (5ms time window, 12kHz bandwidth).

Time-coherent impulse and step responses imply an inherently good squarewave response. Fig.6 shows the Quad reproducing a 1kHz squarewave with the microphone 1m away, a hair above the optimum listening axis. Again, this is superb performance, the wave having beautifully defined leading and trailing edges, with the tops broken up by ringing at the same frequency featured in the impulse response, approximately 12kHz. The slope of the top of the squarewave is dependent on microphone position. Moving the mike down a little flattens the top at the expense of increasing the initial overshoot. The waveshape in fig.5 implies a slight low-bass exaggeration on this particular axis, which correlates with the relatively severe treble beaming found earlier in the vertical plane, while the increased overshoot on the optimum axis confirms the steady-state implication that there are slight resonant peaks in the top octave.

Fig.6 Quad ESL-63, 1kHz squarewave response on listening axis at 1m (5ms time window).

Looking at the Discrete Fourier Transform of the US Monitor impulse response (fig.7), this time taken over a 10ms time window and plotted up to 10kHz, reveals a reasonably flat amplitude characteristic, broken up with what I would imagine are mainly interference peaks and dips. It would have been best to take the impulse response at a 2m distance, where the sound from the individual driver sections would have integrated better, but the measurement would then have been rendered invalid by early room reflections of the pulse emitted by the speaker. The low treble seems dominated by two distinct regions, one between 2 and 5kHz and the other centered on 8kHz. Above 10kHz but not shown on this figure, the on-axis response features a slight peak in the 12-14kHz region.

Fig.7 Quad ESL-63, anechoic response on tweeter axis at 1m.

To conclude, the Quad US Monitor features excellent time- and frequency-domain performance, which will render its sound neutral and unexaggerated throughout the midband and low treble, coupled with a freedom from transient smearing. Above that range, some listeners may be bothered by a slight degree of liveliness in the high treble due to the small resonant peaks, but to put these in perspective, they are considerably lower in degree than with almost any dynamic speaker you can name. Low frequencies are adequate at reasonable levels, but the Quad will never be a loudspeaker for bass-drum freaks or Telarc fanciers (footnote 3).
To get the best balance between mids and highs, the Quad's dispersion pattern indicates that it should be listened to on its optimum axis, which will effectively rule out its use for more than two listeners. Those more than a little off-axis will hear a sound significantly depressed in the top two audio octaves. This sensitivity to listening axis will also make it mandatory to raise the Quad off the floor on suitable stands. (With it on the floor, I find the quality of the Quad's upper bass to become, for want of a better word, "puddingy.")—John Atkinson

Footnote 1: Audio Control Industrial SA-3050A 1/3-octave spectrum analyzer with calibrated microphone and integral pink-noise source; Heath/Zenith PC-controlled 8-bit storage 'scope; Fluke 87 true-RMS multimeter; homebrewed computer-controlled sinewave, squarewave, and pulse generators.—John Atkinson
Footnote 2: Individual 1/3-octave response curves are taken for both left and right loudspeakers at 14 positions covering an approximately 8' by 3' spatial "window" centered on the listening position. The curve shown in the figure is the average of these responses, weighted toward the actual listening position. I have found it to give a benchmark response that eliminates the effects of LF room resonances to a large degree, and includes enough of the room sound with that heard direct from the loudspeaker for it to correlate very well with a loudspeaker's subjectively perceived tonal balance. It is not intended to be accurate in absolute terms, but as a consistent basis for comparison with other loudspeakers reviewed in Stereophile, it has proved very reliable.—John Atkinson
Footnote 3: Does anyone else get irritated with Telarc's editorializing when it comes to bass drums? Take the opening of their Maazel Tchaikovsky Symphony 4, when an unscored bass-drum thwack is added to the opening in measure 13, presumably on the grounds that one is present at the analogous moment in the fourth movement, and that any bass drum is a good bass drum.—John Atkinson

Sidebar 3: The Arcici Quad Stands (from January 1987, Vol.10 No.1)
The Arcici stands came at the right time in my life—just as I decided to forget about the Martin-Logan CLS and Apogee Caliper to stay with ESL-63s. I had been offered a pair of the Chicago Speaker Stand Quad stands for audition, but wasn't impressed by what I saw (I didn't have much chance to hear them). Most important, the Chicago stands don't significantly add anything to make the speakers' frames more rigid, which is what ESL-63s really need. Moreover, filling the CSS stands with sand or lead shot—as recommended—makes them weight two or three hundred pounds! You can hardly move them around, a big disadvantage for a reviewer (though perhaps not for you).
The Arcici stands seemed much more promising. For one thing, they raise the Quads over 16" off the floor, while the old Stand and Deliver stands raise the Quads just over 8". I thought the extra height might be beneficial, raising the soundstage along with the speakers. Also, the Arcicis reinforce the frames, holding the speakers at the base and clamping to each side with setscrews top and bottom.
You get other benefits, too. With the Arcici stands, the Quads become very stable. It would be hard to tip them over, which is otherwise a real hazard with the Quads, especially if mounted on the S&D stands with little kids or large dogs running around the house.
The Arcici stands change the appearance of the Quads rather dramatically. The speakers look more 1986 and less 1963. (If you are buying a pair of Quads at the same time you buy the stands, you might choose black for the wood finish; it will blend better with the Arcici's black wrought iron.) The sound is affected, but not dramatically; it is, however, a definite improvement. Raising the speakers does raise the soundstage, and helps the Quads fill the room with music. The Quads can use all the help they can get in this regard, since they don't play particularly loud. Bass is tighter (the stands are spiked), and the overall sound has a little more clarity and definition. An altogether worthwhile improvement for $175/pair.
The stands are a good value, too; that will become obvious when you see how well they are made. A lot of careful thought went into the design, and they can't be cheap to make. I'm surprised they cost so little. (Don't raise the price, Ray, the way John Iverson raised prices when we called his Eagle 2 a bargain.) You must fill the stands with sand or lead shot (or a mixture of both), however. Otherwise, they ring; besides, the added weight in the base increases stability. And you must install them carefully, to avoid damaging the speakers. If the setscrews are not firmly secured, you could have a disastrous crash; with the setscrews firmly in place, stand and speaker become one, each supporting the other. Be prepared, too, to touch up the stands with semi-gloss black spray paint; UPS can really rattle these around. (Actually, they should be wrapped in bubble pack for shipment so you don't have to worry about paint.)
I don't regard stands for the Quads as optional, and the Arcicis are far and away superior to those from Stand and Deliver. With the speakers selling for such a premium over the UK price, it's nice that the Arcici stands are made in America. They are worth every penny and every Quad owner should immediately order a pair. (It's also nice to see us get a leg up—no pun intended—on the British, standwise. Bravo, Arcici!) If you have difficulty in finding Arcici, they can be located on (212) 724-6021.—Sam Tellig