Quad ESL-989

Quad’s Peter Walker was absolutely right to seek a better way to make a loudspeaker. He was inspired by the failings of his flagship loudspeaker – the Quad CR Corner Ribbon – which was a bold hybrid design that used a ribbon tweeter and a conventional bass driver in a wood cabinet. One of the most advanced products of its time, it was still not quite what Walker wanted. Years of development work, allied to great innovation and huge ingenuity lead to the launch of the ESL-57 electrostatic in 1957. It was a landmark event, and legend has it that many rival loudspeaker manufacturers went away from the first demonstration of the Quad electrostatic with their heads in their hands…

Whereas the Corner Ribbon melded a ribbon tweeter and moving coil bass driver, the new ESL-57 used ingenious new push-pull electrostatic panels to cover bass, mid and treble in a seamless way. With the help of mathematician Peter Baxendall, Walker pulled off something remarkable in the great scheme of hi-fi things – it gave full-range sound with none of the cabinet colorations or drive unit issues of a conventional speaker. Using plastic film in its drive units, vibrating between two charged plates to produce sound waves, there was literally nothing else like it – the Quad Electrostatic sounded clean and detailed and open and smooth like no other of its day.

Understandably then, Quad had a real problem replacing it and the speaker stayed on sale for nearly two and a half decades. Finally in 1981, the ESL-63 appeared – the number reputedly being the year in which its development started. It was a significant progression from the ’57, being the first Quad electrostatic designed for the stereo age. The previous model had been made from the start as a mono product, designed to fire into a room from the corner, and fill it with sound from a single place. The ’63 by contrast was of course a full stereo design from scratch, and was used differently, placed in pairs in a listening room. For this reason, Walker spent a lot of time working on how to improve its dispersion characteristics, and came up with redesigned panels with two sets of concentric annular electrodes fed through sequential delay lines.

“That was a complete rethink, he went back to basics to produce a true point source,” says Comeau. “Peter Walker came up with lots of ideas, and even at one stage thought about putting a loudspeaker in a wall but realised that it just wouldn’t do for most people’s homes! So then as he often did, he went back to the mathematics, and thought through the idea of a delay line – a loudspeaker where as you move up through the frequency range, the elements of the signal gradually get more delayed, so you end up with a spherical waveform emitted from the loudspeaker, a true point source. That gave him the annular rings that you see in the panels of the ESL-63 and all its successors. In the middle you’ve got a pair of panels which couple together to form annular rings, with high frequencies in the middle gradually moving out to midrange, then right at the outside you’ve got the two bass panels top and bottom. The method of panel manufacture was much more robust too, it was a real step change.”

The ESL-63 was a great loudspeaker in its day, and a real improvement on the ’57 in a number of ways – although arguments still rage even today about which is the better. One criticism of both was the lack of deep bass, and their inability to drive large listening rooms to high levels. During the ESL-57 days, there was a fashion for stacking them on top of one another, effectively driving four speakers as two. It produced great results, and so for Quad’s replacement for the ’63, this idea was developed. When the ESL-988 came out in 2,000, it was a subtle revision and update of the ’63, but Quad also offered the ESL-989, which was an altogether larger electrostatic loudspeaker that promised the magic of those early stacked ESL-57s but in one piece. The ‘989 featured an extra pair of bass panels, but they didn’t increase the bass performance simply because of the extra panel area – the considerable height increase came into effect too, acting as a force multiplier…

“The taller speaker is getting closer to being a line source in the bass,” explains Peter Comeau. “This is in addition to the speaker being a point source in the midband, and it makes for an interesting combination. People stacked ‘57s in the mistaken belief that what they were doing was increasing panel area and sensitivity, but in fact it was far more than that. The sum of the combination was far greater than what they were trying to do – what they ended up with was something approaching a line source in the room. If you look at professional audio, where you’re trying to drive power over a distance, you do that with a line source – usually with a series parallel combination of bass/midrange drivers which add up to an acoustic source bigger than the sum of its parts. In a room things are different because you haven’t got a big open space to fill, so you’re trying to power the room. The great thing about a line source is that it doesn’t obey the inverse square law of power versus distance, once you get a reasonable distance away from it. Power drops off markedly with distance with a point source, but with a line source you reach a point where it stays the same, which can be useful, especially in terms of bass response.”

The ESL-988/989 was the first attempt by Quad to produce its electrostatic speaker using modern methods. Now owned by International Audio Group, the smaller ‘988 was essentially a modernised ESL-63, while the larger ‘989 was the reinvention of the ‘stacked Quad’ idea. The ‘988 got a much-needed, more rigid cabinet with improved electronic components. The wiring in the delay lines was upgraded, and the concentration of copper in the electrodes was increased. At the same time, the speaker was tilted slightly backwards. The £4,000 ESL-989 benefitted from all the aforementioned tweaks, but thanks to its new panels had fifty percent more radiating area than the old ’63 and was 40cm taller. It weighs much less than you’d expect at around 25kg, and this is partially explained by the fact that its 1,335x670x315mm cabinet has plenty of air inside. Bass is said to go down to 30Hz (-6dB), against the ‘988’s 35Hz, with better power handling than its baby brother. Quoted sensitivity is 86dB/1w/1m and nominal impedance is said to be 8 ohms. Recommended amplifier power is 50 to 150W, although in truth at least 100W is best.

Properly placed, the Quad ESL-989 sounds like nothing else around. It sports an evenness and coherence of sound that few other loudspeakers at any price can better, and it able to drive the listening room in a way that makes most conventional speakers – again at any price – sound unconvincing. However, don’t expect fireworks – this isn’t a showy or a flashy sound. There’s no artificial bass peak around 90Hz to give it extra bounce, and the treble isn’t zingy and tinselly either. Some will find that their particular musical favourites sound slightly underwhelming, despite this great loudspeaker’s many fine attributes…

The ‘989’s neutrality and balance is highly desirable for classical music, as is its speed. There’s so little overhang to transients, so everything sounds clearly delineated and spacious. There’s oodles of low level detail too, and it displays wonderful subtlety in the way it handles the harmonics of brass instruments for example; massed strings are also a delight with orchestral music. Then there’s the superlative stereo imaging and soundstaging; the ‘989 takes to you a vast space where there’s music all around. Inside of this, instruments are placed with laser-like precision. This big electrostatic is also great with electronic music, sounding wonderfully clean and precise, with superb dispersion of sound all around the room and excellent rhythmic ability thanks to the panels’ ability to stop and start so fast.

Some will find rock music is a little less visceral than they might like however – the treble lacks sparkle and the bass lacks slam. Electrostatic bass is great; it switches on an off like an LED, but it doesn’t have the physical heft that some rockers will crave. Indeed, the ESL-989 also begins to show its own structural weakness here; its cabinet is simply not rigid enough to really convey the full dynamic impact of densely recorded rock music. You can see why the ESL-2905 that followed five years later had a substantially upgraded frame and rear bracing bar. It’s not perfect then, but no loudspeaker ever is – and the ESL-989 does some things way better than its contemporary price rivals.

Like all its electrostatic predecessors, the ESL-989 is a dipole, meaning that it radiates as much sound from behind as it does in front. This means positioning is critical; each speaker needs to be a good distance away from the boundary wall, but can stand fairly close to the side wall if need be, for additional room reinforcement. The ‘989 is of course a floorstander and so uses the floor to give additional bass extension. “However,” notes Peter Comeau, “the taller electrostatics are closer to the ceiling and you start to bring this into play, giving far more bass power and extension than it ought to have for the panel size. If people only paid attention to putting the big ESLs in a room correctly, they wouldn’t need to mess around with subwoofers – because they’ll go down to 30Hz with no problem…” Correctly placed, the new ESL-989 was the first ever production Quad electrostatic that was able to pull off this feat, offering all the advantages of electrostatic operation plus a deep, strong bass that gave way little to a box loudspeaker, providing it is properly positioned.

A fascinating large loudspeaker, the Quad ESL-989 was one of the great audiophile bargains of its day – when properly placed it was well able to better many moving coil speakers at several times its price. These days it’s an excellent secondhand bargain – especially if you’re a classical music fan – and prices start from £2,000. Go for a good condition pair that ideally has recently been serviced, you will be amazed.

quad-esl-989

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