Originally printed in the November 1996 issue of Gramophone.

In January 1995 I reviewed the 'entry level' model in KEF Audio's then new Reference Series. Three years had passed since I had looked at what was in effect its predecessor, the Model 103/4, a fine loudspeaker which cost in 1992 what the Model One now did in 1995 — 099. The 103/4 was in many respects the forbear of this new Reference range, bringing together as it did several of the features that KEF had developed in the preceding decade. First and most significant of these was the Uni-Q composite midrange/ tweeter. Second, the aptly named coupled-cavity bass loading. Third was conjugate load matching and fourth a complementary line-level electronics unit called KUBE (KEF Universal Bass Equalizer) which applied some 'correction' to the signal, increasing the low frequency output and offering a modicum of tonal adjustment to help match the loudspeaker to the characteristics of any given room.

The first two of these innovations were generally considered the most significant and therefore best suited to long-term development, and I'll come to them in a moment. With conjugate loading the basic crossover network is complemented by an array of additional components which mirror its impedance characteristic, the combination producing a constant, easy load for the amplifier. This is a clever arrangement but it was questioned in some quarters over the extent to which the audio signal was being compromised as a result of the complexity; the answer in all probability is not a lot, but in hi-fl less is generally more (or so it is widely perceived) and the benefit of presenting the amplifier with a very closely specified load which could therefore safely be of lower impedance (and so draw more current, making a small amplifier appear more capable) was comparatively small. Similarly the KUBE, though neat and well thought through, was never really accepted in practice and again there were questions over its transparency.

Uni-Q and coupled-cavity loading were outstanding developments, though, the former in particular gaining many plaudits. They were described at length in my January 1995 article but a repeat run-through of the essential parameters is appropriate.

Uni-Q is KEF's answer to the theoretical ideal of a point source loudspeaker. The tweeter assembly is mounted in the neck of the midrange cone where normally a dustcap would be sited, such that the two diaphragms are co-axial and co-planar; that is to say, their acoustic centres are coincident. Composite drivers of this kind have been tried before but were never feasible in this manner until the development of small, powerful magnets. (The famous and deservedly long-lived Tannoy dual-concentric drive unit similarly aims to realise a point source but in this a more conventionally sized tweeter is mounted behind the LF unit, its output ducted through the LF magnet assembly via a so-called Tulip waveguide.) Neodymium iron-boron was ideally suited to the job, having an energy product some ten times greater than conventional magnet materials of equivalent size. It found a perhaps more obvious application in high quality headphones where weight as well as size is a significant factor.

In the Uni-Q driver the carefully calculated profile of the midrange cone modifies the directivity factor (or "Q") of this ultra-compact tweeter such that integration in the critical crossover region (at and around 3kHz) is almost seamless. The name derives from this unification of Q. This composite drive unit has evolved into an extremely competent performer over the years and the fourth generation version used in the current Reference models is capable of producing an extraordinarily stable and accurate sound stage, as I discovered last year with the Model One and can confirm again here. Despite its complexity in manufacture, KEF has developed Uni-Q drivers for use in several of its much less costly models as well, so it is a Cutaway illustration of the cabinet showing the coupled-cavity system development which has clearly more than proved its worth.

The technique of coupled-cavity bass loading has also been proven and refined over a number of years. In Model One a simplified version was employed, using a single drive unit mounted within the cabinet. Model Three adopts the idealised form of a symmetrical, bellows-like configuration. Here the cabinet is formed into three compartments by two horizontal partitions. Two identical drive units are employed, one set in each partition, the two working back-to-back in opposition (hence the bellows allusion). Their rear housings are joined by a substantial aluminium rod which effectively cancels out unwanted movement which would otherwise find its way into the fabric of the cabinet. The loading of each driver is specified by an "interport" which vents into the central cavity. The final output into the room is via a single large port in the front baffle whose so-called air diaphragm has an area equivalent to the lower midrange cone. This, together with its location, provides a close match to the directional characteristics of the lower midrange driver so that once again the transition from the one source to the other can be made virtually seamless.

Model Three is a fairly tall (1137mm), quite slim floor-standing loudspeaker using five drive units in a four-way configuration. For the bass two 200mm pulp cone drivers are used as described. The lower-midrange and Uni-Q midrange cones are both 160mm in diameter and are made of polypropylene, while the Uni-Q tweeter has a 25mm fabric dome. These forward-facing drivers are mounted on a gently curved mineral-filled polymer baffle which incorporates the contoured port of the bass system. This baffle is compliantly mounted on the cabinet proper so as to minimize 'cabinet talk', which can cause smearing of the stereo image. The enclosure itself is made up of real-woodveneered Medite and particle board members, a combination of dissimilar panels which further helps suppress unwanted resonance. The two internal partitions also act as braces, breaking up the large panel areas and further reducing any tendency for the cabinet to radiate on its own account. All internal surfaces are lined with acoustically absorbent plastics foam.

The four-way crossover is assembled on a large printed circuit board which is mounted on the reverse of the plastics rear terminal housing. Eight inductors, 10 capacitors and two resistors are employed and the crossover points are set at 140Hz, 400Hz and 3kHz. Connections from this to the drive units are made with KEF's ownbrand heavy gauge OFC (oxygenfree copper) cable. Four gold-plated terminals are fitted which will accept 4mrrt plugs, bare wire ends or spade connectors and as supplied they are paralleled by links for use with a normal twowire feed. Bi-wiring from the amplifier (or indeed bi-amplification) separates the drive to the bass drivers from the remainder and, as with many other suitably configured loudspeakers, can enhance definition to a surprising degree. The use of good quality, lowimpedance connecting cable is always important, but more especially with loudspeakers which present a lowish nominal impedance — in this case 4 ohms.

The cabinets sit on shallow plastics plinths which incorporate simple but ingenious level adjustable feet made of goldplated brass. The threaded inserts of these can be reversed to expose spikes for use on carpeted floors. The plinths can be filled with lead shot for additional stability, although I imagine few will bother since despite the small footprint of these loudspeakers they are already heavy enough to stay pretty well anchored in place. Elegant finishing touches are the finely radiused cabinet edges, the veneer of black ash or rosetta burr (a sophisticated looking manmade grain comprising various real wood pieces which are united under colossal pressure), the subtle Reference logo on the plinth and the KEF company logo on the neat fabric-covered, open-frame plastics baffle cover.

Performance

With its high sensitivity of 91dB for 2.83V at lm and honest nominal load impedance of 4 ohms (I measured minimum values of 3.5 ohms or greater at 63Hz, 315Hz and 16kHz) this loudspeaker is suitable for amplifiers rated at 50W and above.

I have to confess that after living with Model One for a month or so for the January 1995 review I wondered what Model Three would offer in addition. I expected a similarly detailed presentation, greater low frequency extension and the ability to play louder (useful only in a much larger room than most of us have). The Threes had actually been with me for quite some time, waiting in the wings for my undivided attention. I wear several hats at Gramophone and with so much on the agenda at this time of year I had not rushed to hear them. Suddenly, however, a fault developed in one of my Quad ESL-63 loudspeakers so Model Three found itself not only on stage but taking the lead role at short notice. As I say, I had expected rather more 'oomph' but was little short of amazed at just how good this loudspeaker is in terms of detail, transparency and image definition, the three characteristics of the ESL-63 which in my experience eclipse just about all other contenders.

Such a cogent presentation is due primarily to the integration of the Uni-Q driver and the seamless quality of its marriage to the lowermidrange unit. So smooth is the offaxis dispersion that the usual 'roomfor-one' stereo spot is replaced by an image which will happily serve a three- or fourseat sofa; indeed a more than passable stereo impression is experienced listening well off to the side. Few loudspeakers achieve a focused spread of sound quite so impressively. Clearly related to this is its generally unfussy nature as regards positioning in the room, again something I found with the One. It really does play straight 'out or the box' and although some experimentation is of course worthwhile, the usual large fluctuations in perceived tonal balance for comparatively small changes in position are here much more subtle, more the concern of fine tuning.

Model Three has a remarkably neutral tonal balance, substantially free of the lower-midrange anomalies which colour the human voice (in particular) and which through a sort of 'collective absorption' over the years have come to give something of a false meaning to the term hi-fl. These are not 'hi-fl' loudspeakers, then, they are high fidelity loudspeakers of the first rank, capable of drawing the listener into a sound world which is truly believable, capable of generating the solidity of image which is what stereo actually means.

Listening late into the night as I write this paragraph, I am struck anew by the sheer beauty of Ian Bostridge's singing in his Gramophone Award winning recording of Schubert's Die SchOne Mullerin (with Graham Johnson, surely the perfect accompanist, on Hyperion (1) CDJ33025, 4/96). The final song "Des Baches Wiegenlied" (The Brook's Lullaby) will resonate long in my mind. It would have made such an Uni-Q drive unit impact in purely musical terms listening on any equipment, but I would not have been so transfixed had it not been conveyed with such clarity and focus (a pity, I think, that the recording couldn't have given the piano more equal billing).

Full orchestra and organ (real weight here down to around 35Hz) demonstrate the excellent dynamic behaviour, the good attack and minimal overhang. The dedicated fault-finder may discover some marginal thickening of texture in the upper bass, perhaps, the 20-20 vision just a fraction impaired in the cello's lower register, but if there is a blemish here it is tiny and is likely anyway to be significantly room-dependent.

Anyone seeking an elegantly crafted, aesthetically discreet, high quality monitor loudspeaker at or substantially above this price should be sure to give careful consideration to the Reference Model Three.

Specification 

Type: Four-way using five driver units Drive units 25mm soft dome tweeter/160mm midrange Uni-C) driver; 160mm lower midrange; two 200mm bass in coupled-cavity configuration Frequency range 40Hz-20kHz ±3dB (-6dB at 36Hz) measured at 2m on axis Sensitivity 91dB for 2.83V at lm Maximum output level 115dB at 1m for 1.83V pink noise input at lm Crossover frequencies 140Hz, 400Hz, 3kHz Nominal impedance 4 ohms Recommended amplifier rating 50-300W per channel Dimensions (H x W x D) 1137 x 275 x 340mm Weight 35kg Manufacturer KEF Audio (UK) Limited, Eccleston Road, Maidstone, Kent ME15 60P. Telephone 01622 672261. Fax 01622 750653 UK retail price £1,999 in black ask; £2,299 in rosetta burr.

Ivor Humphreys