equipment

review
Ken Kantor (Acoustic Research, NHT, International Jensen, Vergence), whos been designing speakers for longer than anyone would like to remember anyoneincluding himprofesses to be an avowed fan of electrostatic loudspeakers I confess to getting a little bit light-headed when listening to really good panel speakers he wrote in the August, 1987 issue of the now-defunct US magazine Audio. Flat speakers share some important general characteristics [that] lend themselves to some of the best sound many of us have had the pleasure of hearing. Hes in good company of course. I doubt theres a speaker designeror hi-fi reviewer anywhere in the world who doesnt either own or have a soft spot for electrostatics. And when it comes to electrostatics, the most famous electrostatic loudspeaker in the world is the Quad ESL. Founded by Peter Walker in 1932 and kept in family hands up until only

oudspeakers

ESL-988 Electrostatic Loudspeakers
ten or so years ago, Quad has recently changed hands several times, being owned first by Wharfedale and then by Verity before ending up with the present owner, International Audio Group. Since purchasing Quad, IAG has been busy updating the Quad ESL-63. However, for all this so-called updating, the final product (now known as the ESL-988) is basically just Peter Walkers original ESL-63 design with a new base and an upgraded power supply and transformer. IAG says that 95% of the components have been upgraded, which is true, because the old components in the circuits have all been replaced with the most modern (and superior) equivalents. The larger ESL-989 is a different story. Although its based on the ESL-63, and is essentially just an ESL-988 with two additional bass panels, its notstrictlyspeakinga Peter Walker design.

I | AUSTRALIANH -

[*A cursory search of the Internet will reveal that at least 88 companies have in the past tried to make electrostatic loudspeakers, including some very big names in the speaker business.Very few lasted the distance however, and of those that did, fewer than ten ever produced more than a thousand ES speakers. Some, such as Braun, in Germany, merely licensed Quads technology.]

AUSTRALIANH - I IF

Electrostatic loudspeakers are the Ferraris of the audio world. For starters, its very difficult to build electrostatic loudspeakersso difficult that over the past eighty years, only a handful of manufacturers have been able to produce them in commercial quantities*. I should qualify that by saying that its difficult to build them to a consistent standard, and in volume. Peter Walker was once asked whether he thought could improve the ESL-63 and said that he could easily do so as a one-off project, but that he could not do so in a production line situation. Because the construction of an electrostatic loudspeaker does not lend itself to automated assembly, Quad ESL-988s are still built in England, and almost completely by hand. The speakers I received for review (Serial Numbers 901280 and 901281) were assembled by Guy, tested by Ivan and packed by Lee and Ivan at Quad Electroacoustics Limited, in Huntingdon, Cambs. Because of their rarity, its very possible that many readers might not be familiar with the operation of electrostatic speakers, so a brief explanation might be in order. Whereas conventional speakers depend on the interaction between a fixed magnetic field (created by the speaker magnet) and an alternating magnetic field (created by the current passing through the voice coil) to produce sound waves, electrostatic speakers depend on the interaction between different electric charges to produce sound.

The sound in an electrostatic speaker is produced by an almost massless sheet of mylar film thats only a few microns thick. Unwrap a roll of ordinary plastic food wrap to the height of a loudspeaker and youll have a fair idea of what the mylar film looks like, and how much it weighs. The mylar is then stretched taut and suspended between two perforated metal plates, one carrying a high-voltage positive charge and the other a negative charge. When an audio signal is applied (via a stepup transformer), the mylar moves back and forth, creating sound waves. Because the mylar film has virtually no inertia and moves only a tiny distance, it adds almost no distortion to the audio signal (less than 0.1%) whereas conventional magnetic drivers add up to 3.0% distortion under normal drive conditions, and up to 10% distortion when driven hard. Perhaps more importantly, the tonal quality of an electrostatic speaker does not change with frequency because the same film produces both high and low frequency sounds, whereas in a conventional multi-driver system, the audio band is split between a woofer, a midrange driver and a tweeter, each of which stamps its own particular tone on the part of the spectrum its reproducing. This means that the sound of an instrument would be different depending on whether that instrument is making a low note (being reproduced by a woofer) or a high note (which would be reproduced by the tweeter). There are also spatial considerations that arise when different frequencies are produced by different drivers. If a violin-
ist plays a low note, the source of the note will appear to come from the bottom of the speaker. If the violinist then plays a very high note, the source will appear to come from the top of the speaker. If the two speakers are further away than the size of a violin, the acoustic image will be incorrect. Most loudspeaker designers locate drivers as close together as possible on the front baffle to get around this problem, but it must still exist in any multi-driver speaker system. With an electrostatic speaker, because the same film that produces the low frequencies also produces the high frequencies, the sonic image must be cohesive. (In electrostatic designs that use different panels for different frequencies, the two panels are always adjacent, and the panel areas are very large, so the problem still does not arise.) That said, not all electrostatic speakers are equal. One design feature that sets the ESL-988 apart from all other electrostatic loudspeakers is that the electrical signal is delayed depending on where on the panel the sound will be reproduced. There are six concentric circles of electrode rings on the ESL-988, and between each theres a circuit that causes a 20microsecond delay. The effect of this is that the soundwaves produced are delivered with a spherical wave pattern that mimics a perfect point source. Brand: Quad Model: ESL 988 Category: Loudspeakers Suggested Price: $13,900.00 Warranty Period: Five Years Distributor: International Audio Group Australia (IAG) Pty Ltd Address: 18/58 Box Road Taren Point NSW 2229 Tel: (02) Fax: (02) E-mail: iagaus@bigpond.com Web: www.wharfedale-speakers.com For additional information, turn to page 114 and circle 0281 on our Reader Information Service Card.

Electrostatic speakers may create difficulties for manufacturers, but they also create difficulties for end users. One immediate problem is that theyre highly inefficient, so you need a fairly high-power amplifier to produce reasonable sound levels. These days, obtaining such high power amplifiers is easy, except that theres another problem presenting electrostatic speakers, which is that their maximum output level is also relatively low, because it is limited by the breakdown voltage of the air itself. At sea level, this voltage (the dielectric strength of air) is nominally 29kV per centimetre, but can be affected by humidity and atmospheric contaminants (pollution, salt spray, etc). If the voltage is exceeded, the speaker arcs, discharging the diaphragm and possibly damaging it and/or the electrode. The Quad ESL988s have protection circuitry built in that prevents them from being overdriven, by simply shutting down the panel when the voltage gets too high. Its because of this protection circuitry that you must exercise a
degree of care when selecting an amplifier to drive the Quad ESLs. The reason being that when the inbuilt protection circuit triggers (and I say when rather than if because the circuit will certainly trigger from time to time) the speakers will effectively present as a short-circuit to the amplifier. If the amplifier does not have its own internal short-circuit protection, it is highly likely to be damaged. Therefore, you should not use any amplifier that does not have fast and effective short-circuit protection. Note that when I say shortcircuit protection, I do not mean a fuse! Apart from the fact that transistors often fail before the fuses that are designed to protect them, output stage fuses are normally located inside an amplifier, where they cant be replaced by the owner. In terms of power output, the amplifier should be rated between 50-watts and 120-watts continuous per channel (into 8 ohms). The reason for the lower limit is simply that the ESLs are so inefficient that you wont get appropriately loud volume levels with anything less. The reason for the upper limit is that the Quads will just turn themselves off if the input voltage exceeds 30 volts, and a 120-watt amplifier is all you need to deliver 30 volts. It is also important that the amplifier is happy driving highly capacitative loads, because the ESL-988 will look like a big capacitor to the amplifiers output stage.

Listening Sessions

Its quite a long time since I heard a pair of ESL-63s, but the memory of those sessions is burned into my brain, and I can say unequivocally that the new ESL-988s are noticeably improved over the original 63. The most obvious improvement is in sound pressure levelthe ESL-988s simply play much louder than the older 63s. Theyre so loud that Id guess than in most ordinary-sized living rooms, it will be possible to attain concert-hall volume levels fairly easily. However, if you have a very large living room, or an openplan design home you will find the highest volume level you can achieve may not be loud enough for
you. And if your idea of musical heaven is house music at 100dBSPL, you and the Quad ESL-988s will certainly not be a match made in heaven. The best part of this is that its very easy to ascertain whether the Quads will play loudly enough to suit you before you buy a pair. Its simply a matter of putting the speakers in a showroom the same size as your listening room and asking the dealer to crank up the volume whilst playing back your usual music. If you throw in the towel before the speakers, you will have your answer within a few seconds. One word of caution, though: the distortion levels of the ESL-988 are so amazingly low (or, if you prefer, the sound is so beautifully clean) that unless you monitor the sound level with some type of external reference (such as constantly checking to see if you can hear yourself speak over the music) you will probably find that you are listening at far higher levels than you would normally listen. If youre going to try this test, take the time beforehand (that is before you blast your ears) to listen to the ESL-988s at very low, almost background levels, so you can be stunned by the effortlessly detailed performance at these levels. Given that its likely youll do more listening at low to medium levels than louder levels, the superior performance of the ESL-988 at low levels cannot be overemphasised. I suspect this is just a trait of electrostatics, which by virtue of their operating principle respond instantaneously and have very low mass. A conventional speaker, on the other hand, has to deal with hysteresis problems and the fact that the mass of the speakerand the compliance of the surroundare more significant at low voltage drive levels than they are at high ones. My second surprise with the ESL-988 was the strong, powerful bass delivered by the panels, which was more extended than I remember being delivered by the ESL-63s. This may have been partly due to the room and/or the room placement (the room I listened to the ESL-63s is no longer available to me) but it
may also be due to the stiffer frame (something Quad says its paid particular attention to) and the stronger, heavier base. Whatever the reason, the proof is in the pudding, and the bass is particularly good. Bass freaks will feel the need to add a subwoofer, but then theyd feel the need to add a subwoofer to any speaker system! That said, bass response is not one of the ESL-988s strengths, which I guess is the reason for the development of the ESL-989 with its extra bass panelsthered otherwise be no reason at all for its existence! To prove the ESL-988 was full of surprises, the upper treble response was also slightly improved. What wasnt a surprise was that you need to be really, really careful placing the speakers in the room and in aiming them very accurately at your listening position. There is most certainly a sweet spot for the extreme highs with the ESL-988s and if you dont sit in it, youll miss out on the best highs. In most situations, you will have to tilt the speakers backward to get the treble aimed at your ears when youre sitting down. You certainly wont get the right sound when standing up, so dont even try a quick showroom audition in this position. My favourite listening position quickly became a low seat about three metres from the speakers. As for the Quad ESL-988s midrange, what can I say? Its perfect. Its perfectly flat, perfectly linear, perfectly neutral, perfectly open, and perfectly detailed. Yes, thats a rave and I know it sounds a bit over the top, but its a very accurate description of the sound across the midrange. I ABed back and forth between the Quads and a variety of very expensive, highly credentialled conventional (dynamic) loudspeakers and although they could equal (and sometimes better) the Quad ESL-988s in the bass and also the treble, not one of them could hold a candle to the Quads across the midrange. Switching back to any one of them from the Quad was like someone was drawing a curtain across the stage. One of the review discs I use in my evaluations is A Feather on the breath

of God which consists of sequences and hymns by the abbess Hildegard of Bergen (Hyperion CDA66039) and while I was listening to it, I felt the title of the CD also perfectly described the midrange sound of the ESL-988s. It too, truly is like a feather on the breath of God. In many ways, I think I am doing the sound of the ESL-988s a disservice by dividing it into bass, midrange and treble and discussing each in turn in this review, because the ESL-988s greatest strength is that when youre listening, you are not conscious of the distinction, in fact its enormously hard to hear when the bass stops and the midrange begins, and the same for the mid/treble transition. For all practical purposes, these transitions dont exist in the ESL-988s sound. Instead, the whole audio spectrum seems to just appear in the room, as a musical event, rather than a recreation of an electrical signal. The sound is gloriously detailed, and the music reproduced so transparently it is really as if there are musicians in the room, instead of just a pair of speakers. This impression is reinforced by the fact that when a crescendo comes along, the tonal quality of all the instruments involved remains exactly the same: all you hear is an increase in volume. This isnt what happens when listening to conventional loudspeakers. With dynamic loudspeakers, distortion always increases with increasing level, so music sounds a little harder during crescendos. With the Quad ESL-988s, distortion is not only lower to start with; it stays low irrespective of volume.

greg borrowman

Readers interested in a full technical appraisal of the performance of the tinue on and read the LABORATORY REPORT published on the following pages. All readers should note that the ed in performance charts and/or disshould be construed as applying only to the specific sample tested.
Quad ESL-988 loudspeakers should con-
results mentioned in the report, tabulatplayed using graphs and/or photographs

Test Results

The frequency response of Quads ESL-988s was very good, as you can see in Figure 1, but not outstandingly so. Across the all-important midrange, the response was within 1 dB from 300Hz to 8kHz. The slight bump in the response at around 100Hz is most likely a measurement/room artefact, and if its included in the tabulated figures, it limits the overall 3 dB response to 45Hz in the bass and 8.5kHz in the treble. However, if you accept that the bump is an artefact and ignore it, the lower limit is pushed down to 30Hz and the higher limit out to 14kHz. Overall, thats 30Hz14kHz3 dB, for those not paying attention. The high-frequency roll-off graphed is not unexpected from this design, but the steepness of the slope indicates the measuring microphone may not have been exactly aligned with the panel and, with a panel electrostatic, if the alignment is not perfect, the high frequencies will certainly disappear. The second graph, of impedance, shows the resistive part of the ESL988 is quite benign, dipping below 4-ohms only between 10Hz and 18Hz and again at 10kHz and otherwise averaging around 7-ohms over most of the audio band. The sensitivity of the Quad ESL988s was measured at 82 dBSPL for a 2.83V input, using Australian HI-FI Test Laboratories standard test conditions and procedures. This is inefficient by any standard, so even though in his review, Greg Borrowman recommends an amplifier with a 50-watt minimum power output, I would per-

Conclusion

Quads ESLs (whatever their model number or vintage) have always been ugly ducklings and I dont think the ESL-988s have progressed one iota in the appearance stakes. And unfortunately, unlike the ugly ducking, they dont get more beautiful with age. But it really doesnt matter, because once youve heard them, the beauty of their AHF sound will blind you forever to their appearance.

lab report

sonally recommend an amplifier rated at at least 100-watts continuous per channel. The panels shut down quite quickly when tested with continuous sine waves or with high-level pink or white noise (which showed that
Quads protection circuitry works) but it was more reluctant to shut down when driven by high voltage music signals, which is as it should be. Nonetheless, I would not recommend trying to burn-in the speak-
ers with test or burn-in CDs. With electrostatics, burn-in is completely unnecessary, any way. All you have to do is leave the speakers switched HF on all the time.A(Dont try to play the speakers when the panels are not
Figure 1: Frequency response @ 1 watt @ 1 metre
Figure 2: Impedance vs Frequency

ESLmanual Feb02

11/02/04

9:14 AM

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ESL-988 & ESL-989 Electrostatic Loudspeakers Instruction Manual

CONTENTS

IMPORTANT NOTES. 2 INTRODUCTION. 3 PACKING LIST AND UNPACKING THE EQUIPMENT. 3 GUARANTEE AND PRODUCT REGISTRATION. 4 SERVICE ARRANGEMENTS. 4 ACCESSORIES. 4 INSTALLATION. 5 CARE AND MAINTENANCE. 8 CONNECTION PANEL. 8 SPECIFICATIONS. 9

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IMPORTANT NOTES European Union Directives
Quad equipment is designed to comply with the legal provisions of EU Directives 89/336/EC and 72/23/EEC. The standards which have been applied were those in force at the time of the introduction of the product.
The product bears the CE mark:
Compliance cannot guarantee perfect performance. In the very rare circumstance that you experience problems you should first try to locate and remedy the origin of any disturbance. A further option is to relocate the Quad equipment in order to reduce the interference. Your dealer should be able to provide assistance if the problem persists.

FCC Rule 15 Class B

This equipment has been tested and complies with the limits for a Class B device, pursuant to Part 15 of the FCC Rules. These limits are designed to provide reasonable protection against harmful interference in a residential installation. This equipment generates, uses and can radiate radio frequency energy and, if not installed and used in accordance with the instructions, may cause harmful interference to radio communications. However, there is no guarantee that interference will not occur in a particular installation. If this equipment does cause interference to radio or television reception, which can be determined by turning the equipment off and on, the user is encouraged to try to correct the interference by one or more of the following measures: Re-orient or relocate the receiving antenna Increase the separation between the equipment and the receiver Connect the equipment into an outlet on a mains circuit different to that to which the receiver is attached Consult the dealer or an experienced radio/TV technician for help This Class B apparatus meets all the requirements of the Canadian Interference Causing Equipment Regulations.

Information to the user

Alteration or modifications carried out without appropriate authorisation may invalidate the users right to operate the equipment. It is always good practice to switch off equipment before connecting or disconnecting signal leads. This will prevent unpleasant and loud noises coming from the loudspeakers and avoid the risk of damage to equipment. This equipment is double insulated and does not need a safety earth. It is important, though, that any equipment connected to it is earthed according to the manufacturers instructions. This becomes more important as the number of units which are connected together increases.

Noise Pollution

Please be aware that very high sound pressure levels can cause permanent damage to your hearing and also severe annoyance to neighbours.

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INTRODUCTION
The Quad ESL loudspeaker is a full range electrostatic loudspeaker doublet. It consists of a very light electrically polarised diaphragm suspended between two sets of concentric annular electrodes. Signal is fed to the electrodes via sequential delay lines causing the diaphragm to move and 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. WARNING: The Quad ESL loudspeaker has very high internal voltages. No attempt should be made to remove the protective grilles or the baseplate. Amplifiers which are not short circuit protected may be damaged by the protection circuits in this loudspeaker and should not be used with the Quad ESL.
PACKING LIST AND UNPACKING THE EQUIPMENT
The packaging contains the following items: The Quad ESL loudspeaker AC power lead 3m with 13A 3 pin plug (3A fuse), QUKES23 (UK only) Instruction Manual Warranty Registration Form One set of packing materials comprising: One set of packing pieces One cardboard carton One polythene protective bag Consult the dealer from whom you purchased the equipment if any of these items is not present. The Quad ESL loudspeaker is completely assembled. To remove it from the packing, spread out the flaps from the open end of the cardboard carton and then invert the complete pack on to the floor, taking care not to let the contents slide out. Lift off the cardboard carton. Please retain the packing materials for future use or return them to your dealer. If you decide not to keep the packing, please dispose of it sensibly. The paper and plastics components are recoverable and may be taken to an appropriate recovery service. Please retain the user manual and the information concerning the date and place of purchase of this equipment for future reference.

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GUARANTEE AND PRODUCT REGISTRATION
Your Quad equipment is guaranteed against any defect in material and workmanship for one year from the date of purchase (proof of purchase required). We ask you to complete and return the enclosed Warranty Registration Form (UK). This will also enable us to keep you informed of future Quad products. Within the guarantee period, Quad will undertake replacement of defective parts free of charge provided that the failure was not caused by misuse, accident or negligence. Your statutory rights within the territory in which you purchased the equipment are not affected by this guarantee. Quad carries out a regular review of its products and reserves the right to adjust the specifications and performance from time to time. There are no user replaceable or serviceable parts inside this equipment. Unauthorised attempts to service or modify this product will invalidate the warranty.

SERVICE ARRANGEMENTS

If your Quad equipment requires servicing you should return it to the dealer from whom the equipment was purchased. If you are abroad and there is no suitable dealer in your area, please contact the distributor for the country in which it was purchased or Quad Electroacoustics Ltd. Equipment returned for service should use the original packing. You should enclose a brief note with your name and address and the reason for returning the equipment.

ACCESSORIES

Quad accessories are designed to match Quad equipment and to provide the best possible performance. Please contact your dealer or Quad direct for further information.
Item AC power lead 3m with Euro/13A 3 pin plug (3A fuse) AC power input connector Euro/straight

Order No QUKES23 PSR0413

Note: We do not supply loudspeaker cables terminated with 4mm plugs nor the 4mm plugs themselves.

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INSTALLATION
The ESL loudspeaker requires an energising voltage for operation and therefore needs to be connected to an AC power supply.
Checking the AC power supply
The ESL loudspeaker is designed to operate on one range of AC power supply only, 50/60 Hz. Either 200-240V or 100/120V. The correct operating voltage is clearly marked on the base. It may be changed from 220V to 110V operation or vice versa by a suitably qualified technician. Before connecting to the AC power supply check that the voltage range marked on the base corresponds with that of the supply.

Connecting to the AC Power Supply (UK only)
The ESL is supplied with an AC power lead with a moulded 13A 3 pin plug with 3A fuse. Do not cut off this plug or use it with its fuse cover removed. If however for any reason the plug has to be removed then it must be disposed of and under no circumstances plugged into a 13A socket outlet. A suitable plug can be fitted, as explained below: IMPORTANT: Fitting a mains plug. The wires in the mains lead are coloured: Brown = Live Blue = Neutral
The Brown wire must be connected to the terminal marked L or coloured Red. The Blue wire must be connected to the terminal marked N or coloured Black. If the lead also has a Green/Yellow wire than this must be connected to the terminal marked E or coloured Green or Green/Yellow.
Note: When a fused 13A plug is used a 5A fuse (ASTA approved to BS1362) will be adequate for a typical Quad system. For other types of plug, then fit a 5A fuse either in the plug, or adaptor, or at the distribution board. If in doubt consult a qualified electrician.
Connecting to the AC Power Supply (other markets)
The ESL should be supplied with a power lead terminated with the correct plug to match your local regulations. If the plug is an incorrect type or if you experience any problems with installation you should consult your dealer or local Quad distributor.
Connection to the Amplifier
Audio input is via binding posts. For runs up to 10m a cable with a rating of 6A (24/0.2mm) should be adequate. Longer runs may require heavier cable. The basic rule is that the total resistance of the cable should not exceed 5% of the loudspeaker impedance, ie 0.4 Ohms. Inductance should not exceed 1mH per metre and capacity can be ignored.

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Each loudspeaker should be connected to its appropriate amplifier output so that the two pairs of wires are connected in the same way, to ensure that the speakers operate in phase.

Switching On and Off

The on/off switch has a rocker action; press the bottom to switch the ESL on and the top to switch it off. A red LED next to the on/off switch indicates that the speaker is on.

Amplifier Requirements

The ESL loudspeaker should be used with an amplifier of output capability between 20V and 30V rms (40-100W into 8 Ohms). The impedance characteristic is essentially resistive and presents no problems to the amplifier. The ESL protection circuits limit the maximum input voltage to 40V and there is no volume benefit from using an amplifier with an output greater than 30V rms (100W into 8 Ohms). Amplifiers with an output capability in excess of 35V rms (150W into 8 Ohms approx) may be used but with caution see Loudspeaker Protection. If the Quad 405/2 power amplifier is used, the amplifier voltage limiters should not be fitted.

Loudspeaker Protection

The ESL loudspeaker is fitted with a protection circuit, incorporating a special device called a multifuse, which prevents damage from excessive programme input signals. Should the loudspeaker be severely overdriven, for any length of time, the circuit will operate and effectively reduce the drive to the loudspeaker, causing a reduction in the volume level with some loss of quality. If this occurs, then the volume control of the amplifier should be turned down. After a delay of a few seconds to allow the circuit to reset, the volume can be increased, but only to a point below which the protection circuit initially functioned, otherwise the circuit may operate again. Persistently overdriving the loudspeaker will cause the multifuse to completely fail, necessitating its replacement by a qualified engineer. The above conditions are unlikely to occur in normal use or with amplifiers with a power output rating of less then 100W. Steady state signals in excess of 10V rms should not be fed to the loudspeaker. When the AC power to the loudspeaker is switched off or disconnected, the signal input protection circuit operates to prevent excessive signals being fed to the loudspeaker elements though care should be taken to ensure that the loudspeakers are not driven for long periods (minutes) with no AC power applied.
Positioning the Loudspeakers
However good the loudspeaker, the final results will depend very largely on the acoustic characteristics of the listening room and the position of the loudspeakers in it. Do not be afraid to experiment with both position and orientation and make a point of trying some of the less obvious as well as the more obvious positions. The benefits obtained from the time spent doing this can be very rewarding. The subject of room acoustics is complex and beyond the scope of this manual. It is assumed that the loudspeakers will be used in a room with moderate reverberation, neither too bright nor over damped. Furnishings can alter the acoustic characteristics of the listening room, and here common sense is the best guide. The loudspeakers have constant directivity over a wide angle in both horizontal and vertical planes, so the response does not vary with the height of the listeners ears from the floor.

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When experimenting, it is preferable to use good recordings or works with which you are familiar in the concert hall or good quality speech. The ESL loudspeaker, being a dipole source, has considerable advantages over conventional loudspeakers in terms of room placement. No energy is radiated in the plane of the diaphragm and as a consequence, the respective axial room modes are discriminated against. Normally the loudspeaker is placed at an angle to both horizontal room axes and will excite both sets of horizontal axial modes, 3 dB less than with a conventional source and discriminate entirely against the vertical axial modes. The loudspeakers should be placed at least 60cm (2 ft) from the rear wall of the listening room and angled towards the listener and never in corners or alcoves or behind furniture. Because the ESL is a totally homogeneous sound source it will be found that they can be placed considerably further apart than normal, broadening the stereo sound stage. Close proximity to the side walls is not detrimental to performance. Simple geometry will show that if the ESL loudspeaker is placed at an angle to the side wall, there will be no audible reflection at the listening position. The ESLs are provided with optional floor spikes which screw into the four threaded holes in the baseplate. The heights of the individual spikes can be adjusted to ensure that the loudspeaker sits securely level on the floor. Take care to avoid the tips of the spikes which are quite sharp.
ESL BASE AND SPIKES Programme Material A small note of caution. We believe that a pair of Quad ESL loudspeakers give a more realistic picture of an acoustic event than has been possible before, but only if the best source material is used. They are very revealing of faults in recording techniques and ownership of these loudspeakers will cause you to re-assess the virtues of your collection of recordings.

Loudspeaker Phasing

If there is any doubt about the way the loudspeakers are connected, their phasing can easily be checked by playing a mono source when the sound should appear to emanate from a point midway between the two loudspeakers. If this is indefinite, then the connections to one of the loudspeakers should be reversed. When correctly connected, the loudspeakers will give a definite centre sound source with more full bodied tenor and bass registers.

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CARE AND MAINTENANCE
The grille cloth may be cleaned with a soft brush or a hand held vacuum cleaner. They are protected against the ingress of dust etc. Periodic servicing at two year intervals is recommended to keep your speakers in pristine condition. Great care has gone into the selection of materials to ensure long term stability under a wide range of temperatures and humidity. In countries where the relative humidity regularly exceeds 90% it is recommended that the listening room be air conditioned for optimum performance.

CONNECTION PANEL

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ESL-988 SPECIFICATIONS

All measurements made with a 230V AC supply.
Maximum output Sensitivity Impedance Maximum
N/m at 2m on axis 1.5m bar per volt referred to 1m. (86 dB/2.83V rms) 8 Ohms nominal Continuous input voltage (rms): 10V Programme peak for undistorted output: 40V Permitted peak input: 55V 125 Hz 500 Hz 1 kHz 8 kHz 5.0 dB 6.4 dB 7.2 dB 10.6 dB

Directivity Index

Axis band limits (low level) AC Input (double insulated) Power fuse
-6 dB at 35 Hz 3rd order -6 dB >20 kHz 220-240V or 110-120V See rating details on base of unit 63 mA anti-surge, 200-240V 100 mA anti-surge, 100-120V 6W Height 94cm (including 10cm base) , width 67cm, depth 31.5cm (including terminals)approx. Net 20.5 kg approx. Gross 23 kg approx.
Power consumption Dimensions

Weight

The right is reserved to alter performance and specification as required. This equipment complies with the radio interference requirements as laid down in EEC (European Economic Community) regulations.

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ESL-989 SPECIFICATIONS
N/m at 2m on axis 1.5m bar per volt referred to 1m. (86 dB/2.83V rms) 8 Ohms nominal Continuous input voltage (rms): 10V Programme peak for undistorted output: 40V Permitted peak input: 55V
125 Hz 500 Hz 1 kHz 8 kHz
5.0 dB 6.4 dB 7.2 dB 10.6 dB
-6 dB at 30 Hz 3rd order -6 dB >20 kHz 220-240V or 110-120V See rating details on base of unit 63 mA anti-surge, 200-240V 100 mA anti-surge, 100-120V 6W Height 133.5cm excluding feet (including 10cm base), width 67cm, depth 31.5cm including terminals approx. Net 25.3 kg approx. Gross 28 kg approx.
IAG House Sovereign Court Ermine Business Park Huntingdon Cambs PE29 6XU England Telephone: +44 (0) Facsimile: +44 (0) email: info@quad-hifi.co.uk website: www.quad-hifi.co.uk
Instruction Manual for Electrostatic Loudspeakers ESL 988 and ESL 989