I reviewed KEF’s original 207 model back in Issue 26, along with the PSW5000 subwoofer, a combination that delivered a scale, transparency and musical sophistication that belied their relatively modest asking price (considering the material content of the complete system). Of course, getting a pair of large, visually imposing loudspeakers into the average domestic environment can represent something of a challenge: adding a substantial sub-woofer too could just be the straw to break the matrimonial back. Well, in a world where less is so seldom more, the good news is that KEF’s 207/2 manages to shed a drive unit compared to its predecessor, dispense with the sub-woofer and still advance its overall sound quality. They’ve also dramatically improved the finish along the way, the boat-backed cabinets now coming in a range of deeply polished lacquer or wood veneers.
Clearly, given the sonic improvements, the changes are more than just skin-deep, and they start with the new ‘Austin’ Uni-Q array contained in the speaker’s head unit. This driver was developed as part of the Project Austin development programme, widely reported on after the 2006 Munich High-End show. The experimental mules seen there were to evolve into KEFs recently launched flagship, the Muon (including their innovative bass loading), but their midrange driver, together with its centrally mounted tweeter has also become the key element in the new Reference series.
Primary design goals for the latest generation Uni-Q were improved dispersion and off axis response, creating a more natural overall tonality and balance. As the midrange cone also acts as a waveguide for the tweeter, its profile is critical to the high-frequency performance and the even transition from midrange to tweeter that characterizes the Uni-Q’s sound. Improving dispersion called for a shallower cone, which under normal circumstances would compromise the stiffness and thus the structural behaviour as a result the midrange output of the unit, losing on the swings what you were gaining on the roundabouts. But advances in computer measurement and modelling of cone behaviour have allowed the designers to optimise cone thickness and material properties to circumvent the problem. At the same time, adding a shallow roll to the previously flat surround has extended the useable output at low frequencies, allowing a lower crossover point of 350Hz and an even smoother transition to the 10” lower midrange driver.
The other obvious change in the 207/2 is the absence of the hyper-tweeter that graced the previous version. This has been made possible by advances in the design of the tweeter itself, which have extended its range (and quality) significantly. One of the challenges in designing the high-frequency element of the Uni-Q array is presented by the space limitations imposed by the need to mount it within the midrange driver’s voice-coil. Whilst KEF have always wanted to vent the tweeter assembly, with the gains in low colouration and dynamic performance that go with the approach, reducing the volume of available magnetic material imposed too high a performance price in terms of linearity and sensitivity. But, in this latest version, they’ve finally cracked it by the clever use of three separate neodymium magnets. Combined with a new composite dome assembly in which a shallower titanium diaphragm is driven by a 25mm voice coil, the former of which also curves in to brace the dome structure nearer to its centre. Together, these changes have resulted in a significant improvement in performance at both ends of the spectrum, including pushing the first break-up mode out beyond 30kHz, thus rendering the hyper-tweeter redundant.
Naturally, such fundamental changes across the speaker’s upper ranges have necessitated revisions lower down. Although the lower mid unit has remained the same, the greater range of the Uni-Q has eased its working bandwidth. Meanwhile the bass drivers have had their output extended by some 5Hz, but more significantly it has also been re-voiced, the more natural balance achieved by the ‘Austin’ Uni-Q allowing a fuller, more authoritative bottom-end than the impressively agile but slightly dry low-frequencies generated by the original.
Other features that remain the same are the integral spirit level, triwirable crossover and Uni-balance adjustments for high-frequency level (from +0.75dB to –1.5dB in four discrete steps) and bass contour, allowing the user to compensate for placement near walls or in smaller rooms. One word of warning – the three sets of terminals on the back are there to be used. This speaker definitely benefits from bi- or tri-wiring. The bridging wires supplied are there to get you going, but if required I’d strongly recommend replacing them with eithr high-quality links made from the same wire as your speaker cables, or even better, a set of the Vertex AQ Mini Moncayo speaker links, which were spectacularly successful. Indeed, before installing them I was wondering whether KEF might have been a little hasty disposing of the hyper-tweeter. I needn’t have worried, as installing the Vertex links revealed the new HF unit in all its considerable glory.