KEF Blade Two loudspeaker

The story’s been often told: 30 years ago, British speaker manufacturer KEF was asked to design a small, spherical loudspeaker that could be used in a European project to research room acoustics. The speaker had to have wide, even dispersion, so KEF’s solution was to mount the tweeter coaxially, on what would have been the woofer’s dustcap. That “point source” drive-unit, called the Uni-Q, began appearing in KEF’s commercial speaker models in 1989, starting with the Reference 105/3—but it wasn’t until the appearance of KEF’s 50th-anniversary loudspeaker, the LS50, which I reviewed in December 2012, that I felt that the Uni-Q drive-unit had fully fulfilled its promise, at least in a speaker I had auditioned in my own room.

Designed by a team led by engineer Jack Oclee-Brown, the LS50 is a superb performer. As I wrote in a Follow-Up review last January, “The KEF LS50 gave a sound that was evenly balanced from the upper bass through the high treble, with superbly defined imaging.” But the LS50, a minimonitor costing $1500/pair, is necessarily limited in both loudness capability and low-frequency extension.

The LS50’s driver was derived from the Uni-Q model used in KEF’s full-range flagship, the Blade ($30,000/pair). Though I had listened to the Blade at shows, at 62″ tall, it was probably going to be too large to work optimally in my room. But when I heard, at last October’s New York Show, that KEF was about to introduce a slightly smaller version, the Blade Two ($25,000/pair), I asked for review samples to be delivered as soon as they became available in the US.

The Second Blade
An examination of the Blade Two gives an overall impression of elegant and effective audio engineering.

At 57.5″ tall, the Blade Two is only slightly shorter than the original Blade and shares its form factor: an idiosyncratically shaped, parabolically curved enclosure designed by Eric Chan, of New York-based ECCO Design. This is formed from high-density polyurethane that, with a stretch of the imagination, resembles a knife blade, hence the name. The elegant cabinet is no wider than it needs to be, and is shallower and narrower at the base than higher up. It is therefore supported on a wide plinth. The plinth has a spirit level at its rear, and can be fitted with carpet-piercing spikes.

The Two’s complement of drive-units is similar to the Blade’s: an advanced development of KEF’s Uni-Q driver is mounted in a shallow recess on the front of the speaker. Whereas the LS50’s Uni-Q has to operate full-range, and the 5″ cone therefore must be able to undergo significant excursion, the Blade Two’s Uni-Q is crossed over at 320Hz. This means that a different surround, optimized for high-frequency operation, can be used, but other than that, the Blade Two’s midrange cone looks similar to the LS50’s: both are formed from an aluminum-magnesium alloy, but the Blade’s has a ribbed skeleton attached to the rear of the cone and a 3″ voice-coil, which pushes break-up modes as high in frequency as possible. The die-cast basket of the drive-unit’s chassis is profiled to present the smallest degree of acoustic obstruction behind the cone.

The 1″ aluminum-dome tweeter, vented to its rear, is mounted at the exact acoustic center of the midrange cone. It takes over above 2.4kHz and has a dual-profile dome, elliptical at the base for maximal stiffness—which pushes the primary dome resonance up to around 40kHz—but with a spherical cap to optimize dispersion. KEF’s patented “tangerine” waveguide is mounted in front of the dome; this and the profiles of the midrange cone surrounding the tweeter, the drive-unit’s surround, and the its recessed, flared mounting plate, plus the profile of the enclosure, all contribute to optimal control of the Blade Two’s high-frequency dispersion.

Low frequencies are covered by two pairs of woofers, mounted on opposite sides of the enclosure and with their chassis coupled together to cancel reaction forces that would otherwise excite enclosure resonances. However, whereas the Blade’s low-frequency drivers are each 9″ in diameter, the Blade Two’s are 6.5″. The woofer cones, formed from aluminum, have a shallow concave profile, and each opposed pair of bass drivers is mounted in a discrete, ported chamber separated from the other pair by an internal partition, this construction said to increase the frequency of any internal standing waves beyond the crossover point. Two large-diameter ports vent to the enclosure’s rear.

The Blade Two’s crossover filters are said be “simple, low-order” types using “the best components available, carefully selected by a rigorous auditioning process.” Rather than being mounted on a conventional circuit board, these crossover components are hardwired. Electrical connection is via two pairs of WBT binding posts, to allow biwiring or biamping. For single wiring, which was how I used the Blade Twos, patented linking plugs are screwed in between the WBT terminals.

Setup & Listening
I began with the KEF Blade Twos in the same positions as the DALI Rubicon 8s ($7995/pair), which had preceded them in my room. Though dual-mono pink noise sounded smooth and evenly balanced, with no frequency regions either being too prominent or splashing to the sides, the low frequencies sounded too loose. I moved each speaker from side to side and forward and back, a half-inch at a time, until I achieved the most even transition between the midbass and upper-bass regions; only then did I insert the spikes in the bases. With the spikes, the Blade Two’s tweeter is 39″ from the floor, which is a couple of inches above my ears when I sit in my listening chair. However, the character of pink noise changed very little as I moved my head up and down. Its Uni-Q drive-unit gives the Blade Two wide, even vertical dispersion.

The first recording I played through the KEFs after optimizing their positions was a charming disc of Romantic waltzes Kal Rubinson had given me, with the Orchestra de la Suisse Romande conducted by Kazuki Yamada (SACD/CD, Pentatone PTC 5185 518). The orchestral balance of the SACD layer was rich and full, if sounding undoubtedly more mellow than through the DALIs. But the stereo imaging was superbly precise and stable. In oboe-and-violin duet in the waltzes from Richard Strauss’s opera Der Rosenkavalier, the image of each instrument was appropriately small compared with the orchestral backdrop, yet not obscured in any way.

The same impression held when I played “The Mooche,” from the Jerome Harris Quintet’s Rendezvous (16-bit/44.1kHz ALAC file from CD, Stereophile STPH013-2). The sound was mellower than it had been through the DALIs, especially with the polite-sounding Bricasti amplifiers, which made differentiating Bill Drummond’s swishing cymbals in the first verse from the air escaping from alto-sax player Marty Ehrlich’s embouchure a little more difficult. But again, the stereo imaging was superbly stable. I had recorded Steve Nelson’s vibes in stereo and panned them in the mix from audience left to just left of center stage. Through the KEF Blade Twos, every mallet stroke was precisely positioned in space.

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GP Acoustics (UK) Ltd.

US distributor: GP Acoustics (US) Inc.

10 Timber Lane

Marlboro, NJ 07746

(732) 683-2356

www.kef.com

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