Quad ESL-989 electrostatic loudspeaker:
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The speaker's structural rigidity was increased for the launch of the ESL-63 USA Monitor in 1988. This evolved from a special "pro" version used by Philips' European recording division for location recording. Quad replaced the '63's aluminum frame with steel, and put handles on the sides and rubber kick pleats at the base. Philips was delighted, and soon other studios requested the "pro" version. Quad decided that the improved structural rigidity made it the best version for export, even though it increased the speaker's weight by 30%.

The ESL-63 maintained a firm hold on its Grade B ranking in "Recommended Components" from 1987 through 1996. Why? The '63 produced a sense that one could "reach out and touch the musicians," as John Atkinson noted in the December 1992 article naming the ESL-63 his "Editor's Choice" component in Stereophile's Product of the Year listings for 1992. JA also enthused over the speaker's precise imaging and lack of coloration. I also felt the ESL-63s had formidable imaging, specifically its front-to-back depth and horizontal dispersion—it was possible to move around and keep the stereo image (no pinpoint "sweet spot"!). On the other hand, the '63's midrange lacked the ESL-57's transparency, its image height was restricted, and its bass response remained limited, requiring a subwoofer. The Finnish Gradient subwoofer, designed for the ESL-63, made an extremely smooth acoustic and visual match, but the Velodyne HGS-18 sub went far deeper.

John Atkinson's choice of the Quad ESL-63 USA Monitor as his "Editor's Choice" for Stereophile's 1992 Product of the Year listings summed up the yin-yang experience of many audiophiles: "...as good as the '63 is, it could be better. It doesn't go loud. It doesn't go deep. It needs to be used on stands to get the cleanest upper bass. (The recommended Arcicis clamp the speaker in a loving embrace, stiffening the rather torsion-prone frame.) The limited lateral dispersion in the top two octaves renders the sound rather dull for those who sit more than 10' away in well-damped rooms. There is a slight fizzle in the mid-treble that annoys some listeners more than others. But in the areas where it excels, it still outperforms almost every other speaker."

Enter the ESL-989
In 1995, Quad Acoustics was sold to the Verity Group, which at that time owned Mission Loudspeakers. In 1998, International Audio Group (IAG) purchased Quad, and set out to remanufacture the classic ESL-63 using modern methods. They first produced the ESL-988, a direct replacement for the ESL-63 that retains all of its original features. The rigidity of the speaker's frame was improved, and 95% of the components were upgraded. IAG improved the quality of wiring in the delay lines, and increased the concentration of copper in the electrodes. All new Quad ESL models were given a 5 degrees backtilt.

They also produced a new model, the ESL-989, which had 50% more radiating area than the '63, weighed about 11 lbs more, was nearly 16" taller, and had two additional bass panels for improved low-frequency performance (-6dB at 30Hz vs the '988's 35Hz rating). The '989's power handling was also increased, particularly in the deepest bass range. Quad's Julian Maddock stated, "The '989's protection circuitry is all but identical to that found in the ESL-63, albeit with higher-quality components. However, the upper voltage limit for the ESL-989's protection circuit has been increased, due to the greater power handling and low-frequency performance of the larger diaphragm. We can let more through. Similarly, the power supply is a bit beefier too."

IAG expanded Quad's manufacturing facilities and production staff, and facilities were built in China that adhered to the strictest quality control Quad engineers could devise. Each plant features a large, air-conditioned anti-static room (with double doors, etc.). Quality control was also improved by testing each speaker for 72 hours before release.

The protective metal screens just under the grillecloth were heavily modified. No longer is the screen made up of downward-firing slots. Rather, it uses "straight-through" circular perforations. More important, Quad increased the rigidity of the chassis to which the screen attaches. The effect of this change was similar to taking a moving-coil speaker off a shelf and putting it on a good rigid stand.

But in order to preserve Peter Walker's vision, IAG changed little else. Like their predecessors, the '988 and '989 operate as electrostatic doublets or dipoles, radiating as much sound behind as in front. As IAG's website and instruction manual state, the Quad uses "a very light, electrically polarized diaphragm suspended between two sets of concentric annular electrodes. By using a series of concentric anodes, rather than just two plates, the Quads are able to produce a spherical sound-pressure pattern. A series of electrode rings are fed with delay lines, so each ring responds to the change in current a split second after the previous ring, creating movement in the diaphragm identical to a 'ripple in the pond.' The motion of the diaphragm produces a sound-pressure pattern which is an exact replica of that from an ideal source placed some 30cm behind the plane of the loudspeaker diaphragm."