Quad ESL Article


This information was graciously provided to me by:

Massimo de Majo
Copenhagen
Denmark
Massimo_de_Majo@mermaid.dk

Sound Practices - Fall 1994

The Quad Electrostatic Loudspeaker

by Haden Boardman / Mellotone Acoustics


A good electrostatic has something special, a magic spell that weaves itself over you. Critics (of which there are few) moan on ~bout "won't play rock" or "only for string quartets". Ask these plaintiffs what system they have, or what kind of speakers, and the usual response is some old west coast monster.

Electrostatic speakers generally consist of four main parts: a power supply, to provide the necessary electrostatic charge; a rigid plate (or plates) to hold the charge; a flexible plate to act as diaphragm (only 2.5m thick in the QUADs) which makes the music, driven by a step up transformer to multiply the voltage output from your amplifier to a level high enough to move the flexible plate.

It's a difficult thing. The fixed plate has to Iet the sound pass through it, and so is usually perforated. The flexible plate has to have near zero mass to be moved by the output from the amplifier. It's amazing the whole thing works at all.

It's funny that while in studios condenser microphones are the bees knees, the electrostatic loudspeaker has never enjoyed a similar level of "professional" attention, and therefore suffered a relative lack of development.

Although electrostatic speakers have been known to exist from the nineteenth century, the first commercially made speakers were fitted to a few picture houses in Chicago in the late 1920s. Nothing is known about these early devices, if anyone has any information about these I would be delighted to know.

Peter Walker was the first in 1956 to offer to the public a High Fidelity electrostatic loudspeaker. Others have followed: Acoustats, Audiostatics, Dayton Wrights, Martin Logans, etc. But QUAD were fust. QUAD still manufacture an electrostatic, of course. 1980 saw the introduction of the ESL 63, so called because that was the year that Walker & Co. started work on a replacement for the original. In a lot of people's perspectives, mine included, the new design did not quite match the earlier speakers' performance in some areas, for others the new model was a revelation.

The original's cookie '50s look amuses me something rotten. The expanded metal grille, the stubby little feet are all pure 1950's Britain. Most were fitted with "bronze" grilles and with classic teak end caps. Later production had severe (and very boring) black grilles along with rosewood end caps. There were variations-I recently picked up a pair of late 1959 items with black end caps and baby sick green grilles. I will be parading these things about next year at shows, be warned'

There are few, if any loudspeakers that raise as many passions as the QUAD electrostatics. Like the DECCA cartridges, Linn LPI 2, Tim de Paravicini, LS3/5a and other quirky Brits a relationship with a pair of QUADs is either pure love or pure hate relationship.

Let's get the hate bit out of the way right noe If you head bang, please turn to The Gallo's article (in SP #6) right now, waste no more time, do not pass go, do not collect $200. Maximum SPLs are about lOOdB for a pair, in an average British living room, less I would imagine at your average Texan ranch. Stacking a pair can of course give you far more headroom, if less house room, but more on that later. Subwoofers and other low life can also add a few extra SPLs thanks to the reducing burden on the ESL. But basically ESLs will never make your ears bleed.

The biggest total hate (on my part) is the directivity of the thing. These speakers are so directional it hurts. For those inexperienced in the ways of the ESL, these things make a pair of ALTEC 604s sound like an omnidirectional design.

Forget using ESLs if using some super amplifier or super budget amplifler. Powerwise, pair of ESLs need 15 watts per channel, a stacked pair double. Any more and you risk of destructive lightning within your speakers' panels. Due to the varying impedance (1.8 ohm at 20 kHz, to over 60 ohm at 150 Hz.) and highly capacitive load, ESLs are not suitable for any amp that is not totally stable into any load.

I once saw the remains of a little Rotel RA 820BX that some bafoon wired up to a pair of ESLs, the innards resembled a scaled down model of downtown Hiroshima, circa 1946. Craters where transistors once sat, melted resistors and capacitors everywhere. Single ended triodes are fine, in fact more than fine, they're great with the ESL, as long as you do not mind mushy bass.

Final fly in the ointment is the build quality. QUAD has a reputation for making the best built kit here in Blighty, and I do not want to chink the armour but it has to be said some of the production techniques used to assemble the originals is a bit dire, if limited by fifties technology. This manifests itself mainly in dust cover rattles. Yes folks, ESLs can rattle, pop, buzz and fart.

Enough of this negative vibe, what about the plus side? Well, thankfully to say it is a much longer list. For spec. freaks, these babies are a dream.

Frequency response? 40 Hz to well past 20 kHz. Distortion? Compared to any moving coil unit, it's non existent. Impulse test? Quicker than the measuring microphone. Fine, but how does this mumbo jumbo manifest itself in the sound quality?

I do not want to mislead subjectives into hating this speaker on the "measure flne, must sound like dog shit" knee jerk reaction - although they would be right with some QUAD crap like the 405 family. This speaker was extremely well regarded from the outset. It earned the nickname of "Walker's Wonder" very quickly. Both Harold Leak and Gilbert Briggs went into blind panic on first audition in the '50s. Leak quickly set to work on his own ESL (although nothing other than a couple of Wireless World articles ever came of it). Briggs answered with the not totally unsuccessful Wharfdale sand filled baffle three. Logic being if you can do it with static 'lectric you can bloody well do it with big magnet speakers. Even Goodmans (Mr. E. Jordan, one of my heroes) developed one.

A pair of electrostatics can sing. They add no spice to the sound. They play it as the electrical signal on their input terminals tell them. They add nothing and take very little away. The truth, the whole truth and nothing but the truth. If your system is bogus, on the end of a pair of ESLs it will sound "line me up and shoot me" bad. If your system really sings, and does not need speaker coloration to give it bass, check out a pair or, even better, a stacked pair.

The most common criticism against them is the lack of bass. This is total bullshit. Yes, the bass will not play loud enough to annoy the neighbours. Yes, it's free from the usual boxy boom most makers engineer into their crappy little box speakers. What bass there is, is clean fast and unbelievably cool. I get totally pissed off with all these "boom" box subwoofers. Most of them have resonances about 30 Hz, adds a Technicolor bass bloom. Christ, even QUAD themselves are at it now. When is a dipole subwoofer not a dipole subwoofer, when it's a Gradient of course! As for these over amplified boom boxed which seem to have gathered street cred in the last couple of years, most of 'em are ripoffs of Audio Pro. QUADs have bass, and anyone who wants to argue the toss is either a wimp or tone deaf, so there.

At the other frequency extreme it's just as delightful. So clean and free of sibilance. No spit. No sizzle. Nothing added, very little taken away. Some do complain the ESL rolls the top off, and I suppose it does a bit, but then so do half of the single ended amps on the market at the moment. The bit inbetween also rates as "jolly". The midrange is ever so natural and unrushed. You could never accuse the ESL of forcing the sound onto you. You walk "into it" rather than it walking over you. I can think of no other speaker that handles the midrange as well as the original ESL, period.

By now, you either want a pair or have already turned over to a different article. Two very important words to remember when chasing QUADs: caveat emptor or if you skipped on Latin lessons at school, let the buyer beware. And boy, does the buyer have a lot to watch.

Budget on at least $500 minimum for a pair when refurbished, if it costs you any less, you have been very lucky. If buying condition unknown, never pay more than 100 for a pair. Serious. In time everything can and will go wrong with an Electrostatic speaker. Budget on a complete set of new panels, (there are three in each speaker, two bass and a treble panel) plus a new EHT unit. These items cover 99% of Electrostatic ailments.

The treble panel is usually the first to have problems. Solid state amps tend to clip quite hard into an electrostatic speaker (due to the difficult load and falling impedance at higher frequencies). This tends to cause arcing, which burns holes right through the centre diaphragm and removes the electroconductive paint off the fixed plates. This reduces the efficiency and power handling as well as causing strange popping noises from the panel. Bass panels suffer similar problems, over excursion causing a similar effect, although the symptoms can be more tricky to spot, it usually manifests as lower efficiency.

EHT units tend to die with age. Either no output or so low you cannot hear it are the fault. The rest of the electronics are pretty reliable. I have seen both audio transformers and mains transformers dead, and they are most certainly not cheap to source. QUAD automatically flt a protection circuit ("clamp") on the ESL these days, which does its best against abuse. It's not 100% perfect, so watch yourselves.

Anyone thinking about doing DIY work on QUAD ESLs should plan to be extremely careful. Disconnect the mains, leave for a minimum of six hours and disconnect the amplifier. This last bit is very important. The audio transformer steps up the AC signal (sound) to a very high level, if by accident music is playing into an unenergized QUAD and you happen to touch the wrong wire, YOU ARE DEAD. It's far more potent than the ESLs' power supply, due to the low source impedance of the audio transformer.

Servicing the ESLs is fairly easy. Unscrew the back panel, the wooden end cheeks. Carefully tease out the staples from the metal grill and remove them. If you have no cats, dogs, or rug rats, and don't object to staring at naked QUADs, use 'em like this. The expanded metal grille does a big fat zero for the sound quality, if everything for the looks.

Carefully unsolder the connections from the back of the panels (make a sketch to show where each wire came from). There are 5 wires on the treble panel and 3 on the bass panels. Be very careful when moving the units. They have a thin "cling film" protective dust cover over the entire frame. Watch for dropping "solder blobs" which will drop straight through the panel. Inspect yours closely. Any tears, riips or holes should be rectified with some new dustcovers.

Most covers sag periodically, the cure being a heat gun or hair dryer. On the lowest motor speed setting and maximum heat, carefully move around the diaphragm with the heat, and most of the wrinkles will disappear. Sonically, loose grilles equal buzzes, rattles and farts. It is impossible to completely mitigate, you will always have a bit of a buzz. Dust covers are always replaced when replacing a faulty panel.

Damp is the biggest threat to the longevity of the panels. If you put your ear close to the speaker and detect a slight rustling noise, trapped humidity is eating away the conductive paint on your panels. This is the main reason why the panels lose efficiency for no apparent reason. I suppose this is going to be a bigger problem to me than most reading Sound Practices. Manchester does have a bit of a reputation as far as damp is concerned.

All of the electronics are screwed to the base of the cabinet. Audio transformer with crossover components soldered underneath to the left, EHT power supply (6000 volts for the bass and 1500 volts for the treble) and mains transformer to the right. On the whole, these are fairly robust. As earlier mentioned, the older EHT units have just about run out of steam, making necessary their replacement. I have seen unserviceable audio transformers, but not many. Their failure is usually due to the speaker being connected to some 4000 watt monster of an amplifier that did not like the difficult load and decided it would eat it instead.

Tweaks and mods are all now pretty well established. For the unacquainted, here's the HTB guide to QUAD tuning:

l) If using a single, use a rigid stand, ideally about 18" to two feet (45-60 cm) I have seen several different stands for these beasties now, some of which clamp the sides, some of which screw into the sides where the wooden end cheeks are. Most seem pretty competent. Best solution was by a good friend of mine, who built a mini brick wall underneath them.

2) Positioning. Never put an ESL flat against the wall, or running parallel with a wall. Don't forget, as much energy comes out of the rear as comes out of the front. It's wrong to say ESLs are only for large rooms, I've found they wQrk better in small rooms. The most ridiculous was an 7 x 8 foot ( 2,13 x 2,45 m) room. They sounded really great. If you are lucky, and have a bloody big room, best idea is as much space behind them as in front. Keep the beasts a minimum of a metre away from the side walls. On 18 inch (45 cm) stands like this, they really sing.

3) Lurking behind the panels are a couple of furry devices designed to stop the sound reflecting back from the wall behind the speaker. With the aforementioned positioning, all our furry little friends do is make the speaker sound dirty. Remove 'em. The items over the bass units resemble sack cloth!

4) Grille removal. Dodgey one this. Not only does it expose the naked panels to the outside world, risking the film dust cover's life, it exposes 4000V to your room, risking some bugger else's life. Like everything else in audio they sound really good naked, but it ain't for the party man or the family man. Tread carefully. Easy to do, see above.

5) New frame. The original frame has slightly contoured shape. When the pane are securely mounted, they take on the slightly bananas profile. Although this aids dispersion, it does not help the rattles. new, more rigid frame helps quite a lot. I have built several now, and have taken t opportunity to position the electronics at the bottom in a plinth, with the frame and panel up in the air. Drive units flat.

6) Which leads us nicely to the ultimat QUAD mod, STACKING. Extra efficiency higher SPLs and deeper bass. Twice the height also equals twice the W.A.F. (sorry Joyce). If you just want to stack an origina framed pair, it's quite easy. If you want t be a real smart ass, build complete new frames for both, so you can locate the panels as close as you can together, awesome. Most just stick to the original QUAD recommendations.

7) For those who like to hang upside down, only like the dark, and get miffed if there is not much output past 20KHz, DECCA ribbons have been used to complement the higher registers. A buddy of mine has horn bass (under the house!) electrostatic mid and ribbon tops, all home made, being driven via single ended transistor. Anyone who thinks this can't work, should think again- it does, really well.

For my ears, the ultimate QUAD setup is a stacked pair in solid frame. One of the best sets I've heard belongs to "Mr. Hard-wired" himself, Glen Croft. Lover of OTLs, No. 1 fan of Julius Futterman (I think Glen has a Futterman shrine buried somewhere in his Erdington workshop), Glen has produced the best sound I have heard out of a quartet of QUADs.

Running without the film dust covers is a very silly idea, this screws the beasts up in a matter of months. Even if it does sound cool.

No, the first commercially produced ESL has a lot going for it. Just watch the reliability. When they were discontinued around 1985, after a production run spanning back to 1956 over 60,000 pairs have been made. The price then was 700 a pair, roughly 60% the cost of the inferior ESL63. Today's price for the '63 is near enough 3000. A rough calculation makes an original ESL worth around 1800. Second-hand, you get laughed at if you ask any more than about 600 for a mint pair. I reckon they are worth triple that.