December 2010

rclogosm_noyear201012_kef1Since its inception, KEF has earned a reputation for being one of the most innovative and technologically advanced speaker companies. In fact, it wasn’t long after Raymond Cooke founded the company, in 1961, that KEF transformed the loudspeaker industry by being one of the first to design and build their own drive-units and associated surrounds entirely of synthetic materials. This innovation opened the door to countless new applications, ranging from ultrasmall portable radios to drive-units flexible enough to be installed in homemade cabinets and even in walls. In the late 1960s, Cooke reestablished his affiliation with the BBC, and signed an agreement allowing KEF to manufacture the BBC-designed LS5/1A minimonitor. Production of the LS5/1A and several of its successors continued into the mid-1970s; it eventually evolved into the LS3/5 and then into the LS3/5A -- a completely re-engineered minimonitor designed specifically around the drivers used in KEF’s then-popular Coda model.

KEF kept the ball rolling in the early 1970s by becoming the first speaker maker in the world to use computer-assisted design techniques, which they called “total system design.” In 1973, the Model 104 not only exploited KEF’s total system design, but became the company’s first Reference Series model. The next four years saw many improvements in this design, and then, in 1977, the world-renowned Model 105 was launched. Two years later, the Model 105 was joined by an entire family of Reference speakers: the 105/2, 105/4, 103/2, and 101.

The 1980s marked the introduction of KEF to this side of the pond, in the form of KEF Electronics of America. It proved to be a dynamic time for the company; they not only continued their success with their Reference line, but broke into car audio with their Universal Bass Equalizer (KUBE), and released their first in-wall speakers, derived from drivers designed and built in the ’60s. Most notably, however, in 1988, KEF introduced the revolutionary Uni-Q system. The Uni-Q technology continued to evolve throughout the 1990s -- as did KEF, releasing several new speaker lines, home-theater products, and numerous new driver technologies. Today, almost every speaker made by KEF, including the model reviewed here, employs Uni-Q technology.

Peeling back the veneer

KEF’s XQ line consists of two bookshelf models, two towers, a center-channel, and a subwoofer, the three-way XQ40 tower ($4500 USD per pair) being the top dog. Once I’d unpacked them, I removed the sturdy grilles, which cleverly attach with magnets flush-mounted in their frames. The magnets adhere to the speaker’s faceplate of brushed metal, while the entire grille is precisely positioned via rubber dimples that fit into the shallow sockets of the countersunk faceplate screws.

Immediately, my eye was drawn to the titanium-finished Uni-Q driver array. At the center of the midrange cone, where you’d normally find a dustcap or phase plug, is a 0.75” elliptical aluminum-dome tweeter capable, KEF claims, of singing all the way up to 55kHz. Protecting the tweeter is something that KEF calls its “tangerine” waveguide. This is said to not only protect the tweeter, but also to aid in providing a smoother, more even dispersion of high-frequency energy, to yield a more natural sound.

Another key factor of the Uni-Q technology is driver placement. Using aerospace technology originally designed by NASA, the tweeter is mounted at the precise acoustic center of the midrange cone, which essentially time-aligns the two drivers. The advantage of this is twofold: First, a narrow listening “sweet spot” is all but eliminated, as the dispersion of sound is performed far more evenly across the room than is typically possible with more traditional multi-driver designs, thus vastly improving soundstaging and depth of field. Second, the speaker positions become less critical. The performance advantages offered by this technology are applicable to both two- and multichannel systems.

201012_kef2Taking over from the tweeter at 2.5kHz is the other half of this coaxial Uni-Q driver: a 6.5” midrange cone made of a layer of polypropylene between two titanium skins. This is responsible for handling frequencies down to 400Hz, at which point two independently loaded, 6.5”, “ultra-low-distortion” bass drivers handle the low end, from 400 to 45Hz, ±3dB. To achieve this excellent response from such small drivers, KEF increased the excursion of the bass drivers’ pistons by redesigning their coils to be of low mass and to use edge-wound aluminum wire coated in copper. In addition, these bass drivers’ dynamic range was increased by way of Faraday rings, which coincidentally help reduce overall harmonic distortion. Managing all of these frequencies are fourth-order crossovers derived from KEF’s Reference Series and said to use audiophile-grade components. The crossover boards are decoupled from the cabinets in an effort to isolate them from unwanted vibrations and internal acoustic pressures.

Encompassing all of this technology is one of the most elegant, luxuriously finished cabinets I have seen on a speaker costing up to twice the XQ40’s price (save Monitor Audio’s Platinum series). Standing 40”H, just under 1’D, just over 9”W, and weighing 53.5 pounds, the XQ40 leans back slightly -- the look is distinctively high-end. The XQ40 is available in high-gloss Khaya Mahogany, Birdseye Maple, or Piano Black. Under the classy veneer is an extensively braced cabinet built entirely of 0.5”-thick MDF, with separate enclosures for each bass driver and another for the Uni-Q assembly. The side, top, and bottom panels are bowed and taper toward the back, in an effort to eliminate internal standing waves.

The XQ40 is a bass-reflex design in which each bass driver has a dedicated, forward-firing port. At the base of the rear panel are four high-quality binding posts to permit biwiring or biamping, spaced far enough apart to easily accommodate large cables, regardless of termination. My only quibble is that the XQ40’s support spikes and feet offer little in the way of lateral stability.

Power, timing, finesse

While reviewing the XQ40, I was surprised to find that despite its three-way, four-driver architecture, nominal impedance of 8 ohms, and efficiency of 90dB, the speaker was surprisingly easy to drive. When I dug a bit deeper into the supplied specs, however, I learned that the XQ40 can drop into the low 3-ohms region when pushed hard with bass-heavy material. This is nothing to be concerned about; for most intents and purposes, the XQ40 can be driven by any decent-quality receiver. However, I’d wager that anyone willing to buy speakers of this caliber will be driving them with amplifiers of equal or greater caliber. As luck would have it, I happened to have three such amplifiers on hand.

I broke in the KEFs with my tried-and-true 200Wpc reference amp, Rotel’s RMB-1095. I’m very familiar with the Rotel’s sound, and knew it would have no problem driving the KEFs to their full potential. During the break-in period, most of the changes I heard in the XQ40s’ sound occurred quite quickly -- the speakers took less than 50 hours to fully settle in.

I began my serious listening with some lighter fare: The Very Best of Diana Krall (CD, Verve 0251741595). The double-bass solo at the beginning of “All or Nothing at All” was the first surprise the KEFs had in store for me, rendering it with incredible focus and depth and placing the instrument dead center and low on the stage. Each note was clearly articulated from start to finish, allowing me to follow the bassist’s fingers as he plucked each string, and appreciate the natural decay of each note. When Krall began to sing, her voice, too, was dead center -- but slightly higher, as if she were sitting on a stool. The Uni-Q drivers really strutted their stuff here, offering excellent timing and tightly focused images. This made it easy for me to paint in my head a picture of where everyone and everything was on the soundstage. What’s more, the XQ40s did this while I was sitting about 15 degrees off axis.

Wanting to hear what the KEFs could do with something a bit more lively, I cued up “Come As You Are,” from Nirvana’s self-titled album (CD, Geffen 06949350720). The kick drum at the beginning of this track was delivered with real punch, and the visceral nature of Kurt Cobain’s voice was immediately apparent. Unfortunately also apparent was a slight emphasis in the mid- to upper midrange. Some call this part of the audioband the presence region, and with almost all the music I listened to through the KEFs, I found this region slightly more pronounced than I’m used to. At times this was welcome, as it made subtle details more obvious and could add a bit of life and vibrancy to an otherwise dull recording. But with already vibrant recordings, or compressed music played at higher levels, it could induce a bit of listening fatigue over time. Having noticed this with several different recordings, I decided it might be a good time to try a different amplifier and see if this characteristic persisted.

In addition to the Rotel, whose sound is fairly neutral, I had on hand two distinctly different amplifiers just itching to put the KEFs through their paces. Rated at 150W for each of its nine channels, Integra’s DTA-70.1 home-theater amp has a unique architecture that lets it crank out over 180Wpc into a two-channel rig. The other power pusher on hand was Bel Canto’s REF150, rated at 75Wpc and based on Bang & Olufsen’s ICEpower technology (review coming soon). These three amps use very different design approaches, and each has its own sonic signature. Although the KEF XQ40s were easily powered by any of them, it was the surprisingly warm and natural sound offered by the . . . well, I won’t spoil the surprise.

With the Rotel RMB-1095 the sound was consistently clean, articulate, full-bodied, and controlled. With all that power on tap, the KEFs could dig convincingly deep when told to, delivering swift dynamic swings and offering meticulously imaged instruments and voices in their respective places. By contrast, the somewhat analytical nature of the Integra DTA-70.1 tended to emphasize that upper-midrange bump, favoring detail over musicality. Such audible differences effected by simply changing amplifiers showed that the XQ40 is a very revealing speaker, and that care should be taken when selecting associated equipment.

But within minutes of inserting the Bel Canto REF150 in my system, it was clear that this would be the last amplifier swap I would be performing for this review. The Bel Canto’s smooth, faintly warm sound proved to be the best companion for the KEFs. The soundstaging scale was on a par with the Rotel’s, but images on that soundstage now had tighter focus, voices had less grain, and the timing was superior -- all of which contributed to a more relaxed and believable sound. Piano notes, in particular, lingered in the air with dimension and left with wonderful decay. The midrange bump that had reared its head from time to time with the Rotel, and especially with the Integra, was now a thing of the past.

I cued up “Wicked Game,” from Chris Isaak’s Best of compilation (CD, Warner Music Canada CDW 49418). Rowland Salley’s bass line had just enough impact and weight to be convincing through the Bel Canto, but simply thumped when driven by the Rotel. The KEFs did a credible job of portraying the dynamic range of Isaak’s singing, too; I couldn’t help but appreciate the emotional intent of his performance, as supplemented by the seductive bass line. The XQ40s presented the lead electric guitar of James Calvin Wilsey in a rich, melodic manner, complemented by Kenney Dale Johnson’s subtle taps of his cymbals and his brushed snare.

“Brothers in Arms,” from Mark Knopfler’s Private Investigations (CD, Mercury 0249874051), sounded massive through the XQ40s. The rolling thunder at the beginning of this track extended well beyond the speakers in a soundstage as wide as it was deep -- and this was with the speakers not more than a foot from the front wall. Later on in this track, Knopfler’s electric guitar was portrayed with an earthy texture, his voice had a particularly raw yet natural character, and the percussion instruments were reproduced with subtle dynamic shades all across the soundstage.


I’ve listened to countless speakers over the years, and it wasn’t too long ago that I was very happily using a pair of B&W 804S speakers ($4000/pr. when available) as my references. During my time with them, I valued their lovely top-end detail and palpable if somewhat colored midrange. Their build quality was simply outstanding, and, driven by properly matched ancillaries, their musicality proved tough to beat. What I grew increasingly disappointed with, however, was the B&Ws’ bass performance, the time required to position them properly, and how much space they demanded -- in all directions around them, and between them and me -- to sound their best.

The KEF XQ40 was expert in all of these areas. It’s one of the easiest speakers to set up I’ve had the pleasure of working with, due to that lack of a locked-in sweet spot; its bass performance was impressive for a tower of such modest size; and its midrange was decidedly neutral. Using so neutral a speaker can be risky -- it will showcase any weak links in a system and recordings -- but I take it as an opportunity to improve my system, not to keep me from listening. Overall, the XQ40’s build quality is on a par with the B&W’s, but the KEF’s cabinet -- with its curved top and bottom plates, raked stance, and high-gloss finish -- is, to me, a classier, more stylish statement. The one thing for which I still prefer the B&W 804S is its articulate top end. The KEF was wonderfully detailed and superbly timed, but it just couldn’t match the B&W’s rendering of texture.

Summing up

In my years as a reviewer and audio enthusiast, I have auditioned several speakers that have impressed me in one way or another: some with their appearance, others with their sound, and some for how they went about the business of reproducing sound. But a speaker that does more than one of these things, let alone all three, is a rarity, especially for only $4500/pair.

The KEF XQ40 is one of those rarities. From top to bottom, KEF’s XQ flagship is an exceedingly well built, classically styled tower that sounds as good as it looks. It may not be the last word in neutrality across the entire audioband, and it might require some close attention in being paired with other audio gear, but the best things in life are never easy, and I have yet to hear a speaker in this price range that can match its low-end prowess. Equally impressive was the ability of a pair of XQ40s to present a rock-solid image without my having to first endlessly fuss with positioning them, and then make sure I never moved from a narrow sweet spot.

If you’re in the market for a speaker that performs well above its price and looks as if it costs twice that, I highly recommend an audition of the KEF XQ40. I immensely enjoyed my time with them -- so much that I’ve decided to retire my B&W 804Ses and buy the XQ40s. They’ll be my new reference speakers.

. . . Aron Garrecht

Associated Equipment 

  • Preamplifier -- Integra DHC-80.1
  • Amplifiers -- Rotel RMB-1095, Integra DTA-70.1, Bel Canto REF150, Rotel RMB-1075
  • Sources -- Rotel RCD-1055 CD player, Oppo BDP-83 Blu-ray player
  • Power conditioner -- Rotel RLC-1040
  • Speaker cables -- River Cable Flexygy 8
  • Interconnects -- Analysis Plus Copper Oval-In

KEF XQ40 Loudspeakers
Price: $4500 USD per pair.
Warranty: Five years parts and labor.

KEF Audio
Eccleston Road, Tovil
Maidstone, Kent ME15 6QP
England, UK
Phone: +44 (0)1622-672261
Fax: +44 (0)1622-750653


KEF America
10 Timber Lane
Marlboro, NJ 07746
Phone: (732) 683-2356
Fax: (732) 683-2358