KEF R107 loudspeaker John Atkinson 1991 part 2

Apart from the new tweeter, other changes between the original 107 and the 107/2 involve a completely new crossover (although this still features KEF's Conjugate Load Matching, where additional circuit elements are used to make the unit's impedance fundamentally resistive and constant in nature), said to eliminate a slight thinness in the earlier model's lower midrange, and a new KUBE equalizer.

The 107/2 KUBE is less complex than the one supplied with the original version of the speaker, which offered control of both LF Q and extension. The new equalizer has just two rotary controls, marked "LF Contour" and "HF Contour," the former offering tailoring of the lows to best match the room acoustics and needs of the program material, the latter optimum voicing of the mid-treble to suit the "liveness" of the room. A button marked "Bypass" switches on an amber LED when pressed; the naïve audiophile (or reviewer) might think that it also removes the equalization. Actually, it only switches the unit's rotary controls out of circuit, allowing their effect to be quickly evaluated. It also led to minutes of fun as, not realizing this—I hadn't read the comprehensive handbook at this point—I switched this button out with the rotary controls at their center position and, perplexed, couldn't hear any difference at all!

The KUBE, which has a separate remote power supply, sports enough pairs of in/out RCA jacks that it can be used either between pre- and power amplifiers or in the preamp tape loop, where it replaces the preamp's tape monitor functions. It also offers a duplicate set of adjustable-level equalized outputs, to facilitate bi-amping of the 107/2s, and a set of fixed-level unequalized outputs so that the system can also drive a second, different amplifier/speaker combination in another room.

Internally, the KUBE's circuitry is neatly laid out on a single double-sided printed circuit board. Component quality is high, with a reasonably sized, regulated power supply and Signetics NE5532 dual op-amp chips used to implement the EQ and output drive. However, given the success aftermarket manufacturers have had in the US offering equalizers for the B&W 801—Denver dealer Listen Up's sonically superb MaughamBox comes to mind—I wonder how long it will be before KUBE substitutes appear for the R107/2.

The review sample bass bins were finished in a grain-matched walnut veneer, with electrical connection via two pairs of gold-plated Michell binding posts on their rears. (As supplied, these are joined by jumpers, easily removed for bi-wiring.) I've never been happy with these posts, finding that the knurled nuts tend to work loose over time with vibration. With the review 107s, fully tightening the nut actually started to rotate the entire post, but didn't affect the auditioning. These posts also accept 4mm banana plugs.

The Path to Power
Source components used during this review consisted of a Linn Sondek Lingo/Ekos/Troika setup sitting on an ArchiDee table to play LPs, a Revox PR99 to play 15ips master tapes, and either a Meridian 208 (Bitstream) CD player or the Stax DAC-X1t processor driven by the Meridian 602 transport to play the little silver devils. Line-level sources were fed straight into my Mod Squad Line Drive Deluxe (this recently updated to superb early-1991 standard, with solid-core internal wiring and Cardas jacks), which in turn fed the KEF KUBE equalizer via 1m of AudioQuest Lapis interconnect. Phono preamplification consisted of the Expressive Technologies transformer hooked into a Mod Squad Phono Drive EPS. Power amps used included a Mark Levinson No.23.5, an Audio Research Classic 60, and a pair of VTL 500W monoblocks, all connected to the preamplifier via 15' lengths of AudioQuest Lapis unbalanced interconnect. Speaker cable was 5' bi-wired lengths of AudioQuest Clear.

I use a mixture of nearfield, in-room, and quasi-anechoic FFT measurement techniques, using primarily DRA Labs' MLSSA system with a B&K 4006 microphone, but also an Audio Control Industrial SA-3050A 1/3-octave spectrum analyzer with its calibrated microphone.

Psychotic Reactions...
With the help of Sitting Duck Software's "Listening Room" program (footnote 3), I ended up with each speaker some 60" away from its sidewall and 37" from the front of the LPs that line the rear wall, giving a speaker-to-listener distance of almost 9'. The sidewalls of my dedicated listening room also have almost floor-to-ceiling bookshelves at the points where the speakers would otherwise produce strong reflections, and the room features 16"-diameter ASC Tube Traps sited at strategic points to even out its upper bass and lower midrange response. A recent addition to the room's acoustic treatment is a pair of RPG Abfusors behind the listening chair, which both improves the perceived depth of recorded image and ameliorates a slight tendency toward brightness with some loudspeakers. Having found the optimum positioning for the 107/2s, I removed the covers from the front spikes but placed two brass cones from German Acoustics under the rear feet of each speaker so that the reference axes were aimed at my ears—you should be able to look the name badges in the face.

First things first: I thought I would assess the optimum LF Contour setting with the bass warble tones on the Stereophile Test CD. Into the Meridian 602 went the CD. "Oh-oh, a rattle." The fix proved easy. The midrange unit and tweeter are covered by curved wire-mesh grids push-fitted into slots around the driver front-plates. It was one of these that was buzzing slightly; no problem to remove all the grids. (The tweeter remains protected from nosey fingertips by an additional fine-wire mesh.) The smoothest, most musically appropriate lows were obtained in my room with the LF contour all the way up for classical music, though I tended to back this off to the 3 o'clock setting for rock music, so that recorded kickdrum retained its transient snap. With the HF Contour at 12 o'clock, the tonal balance was a little reticent. Setting this control was a little tricky, the exact amount of boost depending on whatever record was playing. Ultimately, I decided on 2 o'clock, which added a suitable but subtle smidgin of "szing" to the mid-treble. (Without the Abfusors, a 10 o'clock setting was more appropriate.)

I decided to run the speakers in with pink noise overnight for two nights before proceeding with any serious listening. I couldn't help copping a listen, however. Now pink noise is a cruel test of a speaker's midrange smoothness. Yet the 107/2s offered a smooth, characterless presentation that boded well for the moment when I would actually play music through them. Leaving the pink noise playing and reaching for the stethoscope revealed the bass bin to emit very little of anything at all, the rear wall vibrating between 160Hz and 190Hz and at 270Hz and the side walls between 90Hz and 170Hz, but this was all to a very small degree. Promising. The head unit was more lively, a deep "aww" sound audible particularly from its rear panel through the stethoscope due to cabinet modes between 150 and 300Hz, but this was with the pink noise playing at a high level. It remained to be heard whether this would have an effect on music.

Footnote 3: Reviewed in December 1990 by Thomas J. Norton, this is an inexpensive ($29.95) program for IBM PCs and compatibles.—John Atkinson
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