Quad ESL-63 loudspeaker Anthony H. Cordesman
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Let me stress that these changes should not lead you to believe your older '63 is obsolete.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