Quad ESL-989 electrostatic loudspeaker Page 3

Like other electrostatic loudspeakers, the ESL-989 must be plugged into AC mains to charge the diaphragms. Operating them without plugging them in can damage them. A 6VA, 100mA fuse sits in the AC socket on the speaker's rear panel next to its On/Off switch and power-on LED. The step-up transformers also have fuses, to protect the speaker's internal power supply from extreme voltage surges. Replacing these fuses involves removing the cover of the power supply.

Each of my vintage ESL-63s has a sliding wood top and a base plinth of black plastic embossed with the company's name. The ESL-989 substitutes for this a plastic top cap engraved with "ESL." The frames and cloth grilles are available in black, blue, or silver.

Listening was carried out in my lightly damped, rectangular, 5400-cubic-feet living room, which has a 12' semi-cathedral ceiling. The listening room is only 30' above sea level, which is important—the ESL-989's peak SPL output becomes compromised at higher elevations. I placed the Quads 5' from the back wall and 5' from the side walls.

My room has a pair of Quad AC power cables permanently installed, which meant I could quickly switch between the '989s and my reference '63s for comparisons. Unlike my '63s, which need to be plugged into AC for 15 minutes before they have enough charge on their panels, the '989s could play music immediately.

Also unlike the old Quads, the ESL-989's speaker terminals have no provisions for banana plugs or biwiring. When the speaker lugs are unscrewed, they open up a tiny slot in the plastic, into which one can slide a wire. I slipped the point of a Pure Silver Cable's spade lug into this slot, but tightening the terminal's lug didn't secure the spade. However, a few minutes' work with a blade pops out plastic inserts in the center of the binding post, allowing a 4mm plug to be inserted. Quad might replace these posts in future production with heavier-duty connectors of their own design. According to Julian Maddock, "If we do go ahead, then the new terminal should be an easy retrofit for the customer or, more likely, the dealer. This cannot be confirmed at this time, but I'm 99% certain this will take place and be retrofittable."

Final adjustments before audition included comparative nearfield (9') and farfield (16') listening, phase checks, pink-noise listening, and finding the listening position that gave the best soundstaging and imaging. Setting the volume so that the 100Hz output registered 0dB on my RadioShack sound-level mete (C weighting, fast response), the '989's bass response was within ±2dB from 200Hz down to 50Hz. At 41.5Hz, the output rose to +4dB; at 31Hz, it was down by -4dB. By 25Hz, the signal had dropped to -10dB, with no doubling (second-harmonic distortion) apparent.

Playing Stereophile's Test CD 3 to check channels and phasing, I moved my listening chair into the speakers' nearfield until I could hear the in-phase pink-noise signal as a centrally focused patch. Soundstaging was optimized when speakers and listening chair described an isosceles triangle 9' on its longer sides, measured from the centers of the panels.

The '989's panel extends from 5" to 52" above the floor. This covered an area from below my seated ear height of 38" almost up to my standing ear height, which explains why the '989's tonal balance didn't change when I stood up while playing pink noise. In fact, I heard no major changes in pink-noise tonal balance until I stood beside a '989, in the null point of its figure-8 dispersion pattern.

During most of my listening I drove the '989s directly with a Bryston 14B-SST power amplifier. Later I used either Mark Levinson No.334 or Krell FPB 600C two-channel amplifiers. Alternatively, I routed the line-level signal directly to the internal electronic crossover of my Velodyne HGS-18 subwoofer, in which case all signals of 80Hz and higher were redirected to the Levinson No.334.

Paradoxically, the higher-powered amplifiers were less apt to trigger the ESL-989's protection circuit than the Mark Levinson No.334 (125Wpc into 8 ohms). Although the Levinson's power rating is within the 150W maximum specified in the '989's instruction manual, the speakers frequently shut down with some static when I played highly dynamic percussion music that exceeded peaks of 94dB, as measured at my listening chair, 9' away, with the RadioShack meter. (The RS meter under-reads peaks by 10-15dB; so more power is involved.) When overdriven, the '989's triac clamping circuit cuts in, short-circuiting the speaker terminals. This in turn would activate the Krell's protection system, indicated on its front panel by a single blue LED and, of course, no sound. After I switched the '989s off, the Krell's usual three LEDs came back on and music could be played.

Quad sent another set of '989s for me to check that the protection circuit of first pair hadn't been set to be too sensitive. However, the protection system in the second pair was activated at the same volume level with the same recordings. I concluded that moderate sound-level settings were necessary with highly dynamic music.

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