Martin Colloms review first appeared in Hi-Fi News, 1984
Panel Power II
Quad's original electrostatic now approaches its thirtieth birthday, It is still available and Martin Colloms takes a long hard look to assess its quality by the standards of today's more exotic panel speakers. He discovers it is something of a bargain, particularly second hand and if certain simple modifications are carried out.
Whilst musing on the subject of high quality mid-priced speakers recently, we were reminded that Quad's original Electrostatic Loudspeaker is still in production, some 30 years after its first appearance on the market demand is obviously fairly low today, but upwards of some 60,000 pairs have been sold since 1955. Many are still in use, but there has been a steady stream of second-hand models on the UK market at least, especially since ESL-63 appeared selling for £250-£450 per pair depending on age, condition and recent service history. Quad naturally continue to recondition the model.
Brand new from the production line they retail for about £700, little more than half the price of the ESL-63, which first became available some four years ago.
To tie in with our recent coverage of large panel design speakers, we felt it would be interesting to re-evaluate the original Quad design and see how it compares with more up-to-date designs.
Its appearance is pure 1950’s, with the curved bronze expanded metal panel mounted on short stubby feet and framed with teak sides. Quad also supply a black grille as an alternative, inevitable visual comparisons are drawn with a popular electric convector heater of the time!
However, despite changing tastes, the sound quality of this speaker has stood the test of time well, as many satisfied owners will testify, Indeed some maintain that the new model has not surpassed it.
Mains-energized high voltage is supplied as a constant charge to the diaphragm, which has a high, defined surface resistance. Perforated metal plates as electrodes are mounted on either side of the 2.5 um thin film diaphragms, which operate in push-pull. The drive is achieved by a stepped-up high voltage derived from a crucial matching transformer, fed from a power amplifier in the normal way This has never been an easy loudspeaker to drive, however, and even now some power amplifiers prefer to be connected with an additional series resistor of an ohm or so.
lnternally the speaker has some unusual design features, A central panel 15 cm wide covers the mid and treble frequency ranges, and is flanked by two low frequency panels 30 cm wide, The overall panel width is almost 90cm, while the height is a mere (?) 78.5cm A flat mid/treble panel of this height would have very poor directional properties in the vertical plane. (it is for this reason that many recent panel speaker designs have become so tall in their effort to control the vertical distribution by creating a sort of 'line source' effect.
The unique feature of the electrostatic is the convex curvature of its panels, which has the effect of widening the critical central radiation lobe in the vertical plane. The comparatively narrow panel width of the mid/treble driver naturally gives reasonable distribution in the horizontal plane,
Speaker stands were virtually unknown in 1955 The Ouad, originally intended for mono use, was fitted with short screw-on wooden feet, arranged to tilt the speaker back and so beam the central axis at the listener, Such a position, only inches from the floor does encourage floor reflection, so experiments with the modern- by now virtually mandatory - speaker stand seemed a good idea,
Open panel speaker designers have long been worried by the effects of the rear sound radiation, which is equal to that from the front, and have often tried to absorb some of the rear contribution, to reduce the effects of wall reflections. The electrostatic uses a kind of hessian cloth over the bass areas, and layers of thick felt for the mid/treble, but a major problem with these absorbers is that they also produce some reflections, giving audible coloration plus a loss of subjective transparency. Peter Walker himself stressed this aspect when describing the design of his newer electrostatic, the ESL-63, so we have tried to establish the influence of the rear absorbers when revisiting the old Electrostatic.
Sound quality
Used as originally designed, with considerable care taken over positioning, this loudspeaker was found to perform surprisingly well. All the traditional virtues were there in full measure, A smooth character was allied to a lively but unexaggerated transient response, which was kind to spurious noises and record clicks.
The midrange was exceptional, possessing an essentially natural balance and offering fine detail. The treble was rather critical of listener position and showed some unevenness, the bass had a 'fluffy' nature, lacking impact and real definition, though tuneful in a harmonic sense, The lower mid was coloured by the obvious and inevitable floor cancellation, and some loss of transparency was evident.
The stereo image tended to fill the centre stage rather strongly, so the loudspeakers benefitted from overwide spacing, stereo focus was quite good, particularly in the midrange, though depth perspectives sounded compressed.
At this stage the verdict was 'promising but not yet fully convincing', A pair of Quadropod II stands designed to accept the Electrostatic were obtained, and we decided to give the taller 30 cm high column option a try, in fact any length can be obtained to order, and tests using a different sand filled conventional stand suggests that 42cm elevation also works very well However, this certainly alters the appearence of the speaker: 'Flying high', the Electrostatic looks rather more 'sculptural' and shakes off its 'heater' image.
Once mounted on the stands, there was a considerable change in the sound. This now emanated from a more natural height, and was judged more even, open and articulate. The bass was significantly clearer, and stereo focusing was also improved.
At risk of offending PJW, the rear grilles were then removed (power off and allow at least an hour to elapse for the high voltage to dissipate. If in doubt, consult your dealer), and the rear absorption stripped out. This is, in fact easier than it sounds, since the felt pads can be prised gently away complete with their batten attachments.
A further major improvement in sound quality was the result. The image was no longer concentrated in the plane of the panels, and now developed better depth perspective. The speaker sounded more 'open' and transparent and the bass register in particular improved to a satisfactory level of clarity, now blending well with the high standards set by the remainder of the frequency range.
A most satisfying overall result was obtained with a low enough level of coloration to put a large number of box systems to shame. Clearly the Electrostatic can provide upmarket audiophile electrostatic quality at a relatively realistic price. Presentable sound levels were possible but arcing occured with heavy bass input above 50W peak program. This therefore remains a model for those who are less demanding of high maximum sound levels.
Measurements
Quad specify a measuring distance of 3m to allow for proper integration of the panel outputs, so the approximate semi-anechoic graph illustrated must be regarded as no more than a 'close-up snapshot'. Given experimental errors, the speaker might scrape +/- 5 dB limits from 45Hz to 20kHz. The trend is not atypical of previously published data: the midband is smooth but a little prominent; the treble slopes away gently before peaking in the 16kHz region; the bass is prominent at 50 Hz with a suckout evident at 200Hz. While the lateral off-axis response was not too bad, the vertical plane distribution was rather poorer (not shown).
Stand mounted in the room, the computer averaged response gave a tidier result. Perhaps the extreme treble should roll-off a little more, but otherwise the output was reasonably well balanced. The 200Hz dip had moved and reduced, suggesting that a boundary effect rather than the loudspeaker's own output had been responsible. The bass extended only down to about 40Hz in a room and sounded that way. The main mid register remained somewhat prominent.
As acknowledged in the literature the speaker overloads electrically (arcs) on more than 50W peaks- less than that if driven too heavily in the bass. Sensitivity was around 86dB/W, so an in-room maximum sound level of 97dBA is indicated. The impedance curve remains shocking. Measuring 4.5ohms at 20Hz, it rises to 30 ohms between 100 and 200 Hz, falling thereafter to a low of 1.8 ohms at 20kHz, which is fortunately a point where the acoustic output of most program has fallen considerably. Over most of the main program power range, the impedance averages 16 ohms, the original specification.
Conclusions
Stand mounted but unmodified, the Electrostatic has many great qualities which will continue to endear it to many faithful users. Modified by removal of the rear damping material, stereo depth and transparency improve to such a level that comparison with models at two to three times the price becomes possible.
In my view its musical performance continues to qualify this as a great loudspeaker. It is a bargain at second-hand prices, and well worth considering new- It even takes on the new '63 in some areas and wins. notably in the mid-treble transparency and depth. Conversely It loses out to the '63 on stereo focus, sensitivity, power handling (only just), and uniformity of on- and off-axis response. It is just as low in coloration as the new model, though it is definitely less just 'even' in perceived and measured frequency response.
If you are prepared to position this speaker carefully, space it wide and at least 1.5m from the rear wall, and then stand mount it at what at first sight appears to be an excessive height you will be rewarded with a fine sound. It should be loud enough, particularly on classical program. but will not go REALLY loud, so have a care. The Electrostatic can win on subtlety, but not by brute force.
HI-FI NEWS & RECORD REVIEW JUNE 1984
