Quad ESL-63 loudspeaker Larry Greenhill part 2

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.

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