Probably best suited to smaller rooms, it nevertheless provides a persuasive argument in favour of standmounts over floorstanders
Improved Uni-Q driver
Excellent openness and neutrality
Lean output through upper bass and lower mid-range
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This pretty, compact but unquestionably muscular - and decidedly expensive - standmount is the first model in KEF's new Reference Series to escape from captivity.
The anticipation has been growing for months: an AES paper supplied important clues last October; the press release went out in January; the products were there to stroke and admire at the Bristol show in February.
But KEF wasn't going to rush things, and finding a company in Britain able to supply sufficiently exceptional cabinetwork and finish took time.
Over the last 30-odd years, KEF's Reference Series has become something of a British hi-fi institution, and the history is worth retelling.
Back in the early 1960s, a young Yorkshireman named Raymond Cooke left his job as chief engineer at Gilbert Briggs's Wharfedale just outside Bradford and set up shop in a Nissen hut on the premises of a metalworking operation called Kent Engineering & Foundry in Tovil, a suburb of Maidstone.
His plan was to create loudspeaker designs based on firm scientific and engineering principles, making use of the new materials and test techniques that were becoming available.
Advanced cone materials soon made KEF a major player on the hi-fi scene, and Cooke set about assembling a engineering team which went on to create some of the most interesting hi-fi speakers on the market over the subsequent decades.
The BBC's Research Department had highlighted sample consistency as a major problem in loudspeaker production during the 1960s. The introduction of synthetic diaphragm materials such as plastics was a major step in reducing sample variations, and also in eliminating hygroscopy (paper cones tend to change over time, especially in humid countries, as they absorb water from the atmosphere).
In the mid 1970s KEF introduced its first Reference Series models, which were guaranteed to hold within exceptionally close production tolerances, with each sample of a stereo pair consistent with the other and with the design prototype.
These close production tolerances, introduced with the radical R104 and more conventional R103, remain a cornerstone of the Reference Series models to this day. However, 1988 saw an important innovation in the form of KEF's proprietary Uni-Q drive unit.
Taking advantage of the development of ultra-compact and powerful rare-earth magnets, the Uni-Q driver is a variation on the coaxial theme, placing a tiny tweeter on the end of the pole piece in the centre of the bass/mid cone, so that it's actually positioned at the latter's effective acoustic centre.
As usual, there are positive and negative aspects to this. On the positive side, the Uni-Q makes crossover integration between midrange and tweeter relatively simple from an acoustic point of view, and also ensures that output is entirely consistent and symmetrical at any given measurement axis (that is to say, it's 'axisymmetric').
It's therefore also free from the vertical axis 'lobing' that's invariably created in the crossover region where the two sources are spaced apart, as in conventional two-way systems. At the same time, it can be argued that placing a tweeter so that it's recessed within a cone isn't an ideal way to create wide dispersion, and surrounding it with a cone that is itself moving might also be best avoided.
However, KEF has been steadily refining its Uni-Q design for 20-odd years, and many of the constraints it originally had to contend with no longer apply. For example, developing rare-earth magnet technology means that limited tweeter sensitivity is no longer an issue. The latest versions of the tweeter are also the first to have drilled pole pieces, thus avoiding the back pressure created with a sealed-back unit.
In addition, the shape of the bass/mid cone and its surround has recently undergone a major change. This was first described by Mark Dodd, head of research at KEF's parent company GP Acoustics, in a paper entitled Optimum Diaphragm and Waveguide Geometry for Coincident Source Drive Units, which he presented to an Audio Engineering Society convention last October.
In it he describes how the cone and surround of a coaxial/coincident Uni-Q driver act as a 'waveguide' to the tweeter output.
A tweeter tries to radiate its sound omnidirectionally, like a continuously expanding sphere, but with the Uni-Q design, this expanding sphere is constrained by the cone. If the sound is reflected from the cone, these reflections will cause phase interference with the direct sound and perturb the on and off-axis responses.
The solution is to ensure that these reflections don't take place, and the way this is accomplished is elegantly simple.
The trick is to arrange the shapes of both the tweeter diaphragm and the bass/mid cone and surround in such a way that the edge of the propagating tweeter wavefront is always kept perpendicular (at right angles, basically) to the cone profile at the point of contact.
As long as this perpendicularity remains constant, the wavefront will continue to propagate without generating unwanted reflections, and consequently a clean, undisturbed tweeter output will be maintained. As a result of KEF re-engineering its two-part 25mm titanium dome tweeter, the additional 'Hypertweeter' of the previous Reference Series models is no longer needed or fitted.
Naturally, the Model 201/2 we're looking at features this new design; its 165mm Uni-Q driver has a flared 125mm plastic cone with an unusually flat surround. While this key component does most of the work, it's only used as a mid/treble unit here.
By creating an enclosure with an attractively domed/tapered top surface, KEF has also managed to squeeze a separate 165mm bass driver with a 120mm paper cone into the compact cabinet, and this is loaded by a port that exits through the rear of the top surface.
Aided by its modest dimensions, curved sides and top, and internal braces, the whole speaker feels exceptionally solid, and it weighs a hefty 12.3kg. Samples are available in a rather lovely high-quality deep-gloss piano black, lacquered-cherry, American-walnut and a very fine satin-sycamore, done of which disappoint.
The rear terminal block features three pairs of (non-locking but good-quality) terminals, enabling you to employ any combination of bi-/tri- wiring and amping. An interesting extra feature uses captive grub screws to provide a range of adjustments to the relative tweeter level (+0.75dB, 0, -0.75dB, -1.5dB), and also a -2dB bass cut to improve bass alignment if the speaker is placed close to a wall.
KEF was rather keen that we should use the model's matching stand, which actually bolts to the base of the speaker. It has substantial pressed-steel top and base plates, separated by a lozenge-shaped, 62cm extruded-alloy column that's stiffened by a bracing web.
Classy chrome-finished spikes and chunky nuts add a touch of style, but the hefty £400 price tag reflects the low production volume that's inevitable with a model-dedicated stand. Some mass loading is recommended, and adding some Atabites certainly improves the physical stability - without it, the assemblage does seem rather top-heavy.
The specifications state that the 201/2 has a modest enough 86dB sensitivity, but even this seems a trifle optimistic, as our assessment based on in-room far-field conditions is 84-85dB.
That's a low figure by any standards, but neither unacceptably nor unexpectedly so in view of the small dimensions and decent bass extension (-6dB is down at a surprisingly low 28Hz under in-room far-field conditions), as well as a relatively benign amplifier load, which dips only momentarily below six ohms around 140Hz and above 10kHz.
Our initial attempts to measure the frequency response revealed a minor problem to do with the treble-level adjustment. The speaker was obviously too bright when first delivered, but ruler-flat once the two treble-adjustment screw caps had been removed.
Further measurement work showed that the calibration was faulty; KEF engineers were advised, and a potential short circuit was discovered in time for it to be dealt with before production got properly under way.
Certainly the extreme change originally encountered has now been eliminated, but after modification, the insertion or removal of the little screw-cap adjusters doesn't seem to make all that much difference to either the impedance or the response.
Not that this matters, though, as the 201/2 delivers a beautifully flat and smooth in-room response from 400Hz upwards through the midrange and treble. Things are less smooth below 400Hz, but that's largely due to the effects of room modes. Output is a little lean through the upper bass and lower midband, but healthy output from a port tuned to 42Hz gives realistic bass extension down to 30Hz under far-field in-room conditions.
The success of KEF's latest Uni-Q driver is very evident in the listening experience. The first thing one notices about the 201/2 is its exceptional neutrality, helped by the seamless integration between midrange and tweeter. Another key strength is the fine consistency of sound as one moves around an unusually wide listening zone.
Being a compact standmount, it's inevitable that the model will lack some muscle and weight at the bass end of things, but there's compensation in the freedom from boxiness and pinpoint imaging that such a small enclosure, positioned well clear of the ground, brings to the proceedings.
This speaker has a lightness of touch rarely found in floorstanders, especially through the midband and in imaging terms, presumably because the space left beneath the speaker helps prevent early reflections from affecting the direct output from the bass and midrange drivers.
At the same time, the 201/2's tonal balance is attractively open, making voices impressively intelligible, even when the system is playing fairly quietly. However, the sound is in no way aggressive, and the upper range is essentially sweet. Midband coloration is generally low and stereo image location is excellent, though focus and ultimate coherence might have been slightly sharper, and dynamic expression seems a tad restrained.
The 201/2 might be a little bit lacking in warmth and weight, especially when situated in large rooms. However, it also proves a high-quality standmount can have real and positive advantages over the floorstander.
And most importantly, it demonstrates unequivocally that the Uni-Q driver has come of age, as the latest version used here delivers outstanding smoothness and integration through the vital midrange, presence band and treble.
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