KEF Q700 Surround Sound Speaker Package

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by AVForums Feb 7, 2012 at 12:00 AM

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    Highly Recommended
    KEF Q700 Surround Sound Speaker Package
    SRP: £3,450.00

    Introduction

    Although the name KEF needs no introduction, with a long and illustrious heritage, they had perhaps been one of the quieter big names in recent years. Quiet is a relative term, as they still offered a speaker for most pockets and applications, but KEF is one of the manufacturers that wrote the rule book. So quiet, in KEF terms, is with respect to technical innovation and most of the last decade was characterized by evolution, rather than revolution.

    Then, at the beginning of last year, the pregnant silence was broken. First came the showcase Blade, but then far more surprisingly, a number of new models at the budget end of the spectrum, utilizing a number of trickle down technologies, learned during the research for the flagship. The norm is for the tech to devolve down in range order, but who cares? The slightly tired Q Series, that occupies the ultra competitive £400 to £1200 (for a pair), was given an instant lease of new life, in it's most radical overhaul to date and that dear reader, is the subject of this review.

    We were given pretty much the pick of the range to choose from, but as regular readers of my efforts may have spotted, I tend to prefer speakers that are a natural match, both with each other and especially the room in which they will work. The system in question uses the Q700 floorstanders (£1000/pr), Q300 standmounts (£450/pr), Q600c centre speaker (£499) and finally, the Q400b subwoofer (£480), the only subwoofer currently in the range.

    Technical

    At the heart of most of KEF's ranges for the last two decades, has been the Uni-Q Array. This coincident source unit, depending upon application, is variously a treble/mid or treble/mid-bass unit. It's the latter that is mostly employed throughout the new Q Series. As mentioned, every part of this array is new, so lets have a look at what makes one up.

    Central to the ethos of (any) coincident source driver, is that all sounds are supposed to emanate from a single, coherent point in space and thus radiate in all directions, with an equal energy, at any given frequency. To do this, the tweeter must share the central axis of the surrounding mid/bass driver. It wasn't until rare earth magnets became commercially viable, that tweeter motors could be made small enough to allow the tweeter to sit on the pole piece of the main driver, rather than fire through it from behind. This meant that not only did the two drivers share an axis, they now shared the same plane and were thus, time aligned. The surrounding mid bass driver cone, also serves to act as a shallow horn and/or waveguide to the tweeter which has other advantages. One is that the flare of the mid-bass cone acoustically loads the tweeter more efficiently at the bottom end of it's range where distortion is worst. The other, is that the radiation pattern of the tweeter is constrained into a neater cone, thus preventing excess treble energy being sprayed toward the walls where it's reflections interfere with the sound that reaches the listeners ear direct from the speaker. This serves to make the sound less room dependent and therefore more consistent.

    KEF Q700 AV Technical

    Great, but there's no free lunch in engineering and placing one driver inside another solves a number of problems, but brings a new set into play. The first is that, as with any speaker, the two drivers overlap each others output, either side of the chosen crossover point. As the sound from the tweeter passes over the surface of the mid-bass driver, the vibrating air is, in turn, modulated at the same frequencies by the larger driver. Now, a crossover is a complex place, that by it's very nature suffers shifts in phase, so whilst the two drivers may be emitting the same frequency, they might not be doing it exactly in time with each other all of the time. This can result in the output of the two drivers interfering with each other, to a greater or lesser degree, at different frequencies and can result in a slightly ragged response.

    The next problem is diffraction. If you set a tweeter in an infinitely wide panel, it will act as a point source. However, where sound radiating along the face of that panel meets a corner or other discontinuity, it will create a point at which frequencies will diffract and re-radiate in different directions, thus giving the illusion of another tweeter, blurring the effect of the point source. The distance to this discontinuity is directly related to the dimensions of the most affected frequencies and the closer the discontinuity, the stronger the effect. In a coincident source driver, the first discontinuity is right at the edge of the tweeter, in the transition to the flare of the main cone and then there's another whopper, at the main driver's roll surround. This is obviously entirely contrary to the advantages a coincident source is meant to offer.

    It is precisely in these two areas, that the KEF's ministrations have been most tightly focused and the advantages over the preceding generations is most notable. The new 25mm, rear vented, tweeter, "tangerine" waveguide and the surround are much larger than the previous 19mm generations. This is a good thing, as a 25mm tweeter naturally shifts more air, a fact that in itself already delivers lower distortion at the bottom end of it's range. So with the entire tweeter assembly measuring nearly 50mm across - nearly double the previous size - the edge of the first discontinuity has been pushed outward. Progressing outward, we meet the new smooth aluminium cone of the mid bass driver. I'm a fan of metal drivers. Implemented correctly, they remain pistonic (read accurate) over more of their passband. The flip side to this, is that as you move beyond the end of their operating range, the pistonic behaviour starts to break down and they, quite literally, ring like a bell and it doesn't sound nice - worse than a paper or plastic which break up earlier, but do it in a more benign fashion.

    So the art is in controlling the cone resonance, which KEF have done in a number of ways. First is fairly standard in that the cone is flared, rather than conical, thus spreading the break up modes over a slightly larger range, but at a lower level. The second is that the large tweeter requires the mid-bass driver to have a 50mm voice coil, this reducing the width of the cone surface and so pushing the breakup frequencies higher out of the drivers pass band. The next is a clever use of a decoupling ring between the mid/bass cone and the voice coil former. At lower frequencies, the ring is effectively rigid, but as frequencies rise above the working range of the cone, it starts to become flexible, damping the inner cone edge and tuned to do so most effectively at the cones first breakup mode. Finally, the termination of the cone - the roll surround - is responsible for damping the outer edge of the cone. A large, traditional, roll surround might give high excursions in the bass reason, but is the complete opposite of what is required to damp high frequency energy at the cone edge. As noted, it's not much cop where diffraction of the tweeter's output is concerned either. In the Z-Flex surround, KEF has provided a virtually flat, short face to the surround in order to prevent diffraction of the tweeter's output. This, in concert with the ribbing, helps control midrange energy and the higher frequency breakup. The vertical outer face you can't see, is responsible for providing control of the higher excursions in the bass region.

    These larger excursions, require large power and therefore heat dissipation. The larger 50mm voice coil is wound on an aluminium former, which in concert with the aluminium cone is a very effective radiator of heat, reducing power compression. Further more, the massive ferite magnet motor has a large and flared vent through it's pole piece. And I use the word massive carefully. At launch, KEF were proudly handing round a sample of the new Uni-Q unit and I kid you not when I say the magnet is damn near the diametre of the cone. That's not unheard of in high end designs, but I can't think of a single speaker at £450/pair with anything like it. Not one. The Uni-Q driver is, top to bottom, a remarkable piece of engineering.

    With the exception of the two stand mounts in the range, which a are 'straight' reflex ported two ways, the rest of the range are 2.5 way, bass reflex, but use Auxiliary Bass Radiators (ABRs), instead of reflex ports. More on that in a minute. The dedicated bass drivers, of which there is only one in each of the floorstanders and centres, draws heavily in the Uni-Q driver's architecture, in terms of the motor and basket, but the cone is a smooth inverted dome of aluminium, braced to the rear and terminated in a traditional roll surround - There's no high frequency dispersion/diffraction to worry about, just big bass excursions and a roll surround still fits the bill in that regard. This driver rolls in just below the baffle step, to augment the Uni-Q driver's output as per a normal 2.5 way design.

    KEF Q700 AV Technical

    It's the way in which KEF have reflex loaded the enclosure to increase bass extension, that is less than normal and bears further comment. Actually, for KEF, the use of ABRs is pretty old hat. Those of us, at least old enough to have stayed in to watch the opening night of the UK's fourth TV channel, will dab a misty eye whilst remembering the 'race track' flat diaphragm drivers and ABRs employed by KEF in the sixties (okay, I don't remember that far back) 70s and into the 80s. So, what is an ABR? Well, it's an acoustic resonator, just like a reflex port, but rather than a mass of air, it uses a a dummy driver instead. Basically, you take the magnet and voice coil off a driver and replace them with a weight on the cone. The amount of weight determines how low the resonance and therefore tuning, of the combined cabinet and driver is set. But why use ABRs? Because they avoid port resonances, which are audible much higher in the frequency range, unless you use an inconveniently large port and also they don't 'leak' higher frequencies from the rear of the other drivers in the cabinet. Stick your ear against a reflex port whilst the speaker is playing (for god's sake, quietly!) and you'll be surprised how much you can hear of the midrange. So why don't we see more of them? Quite simply, because they're expensive.

    Think about a couple of cheap plastic moldings glued to the end of a tube that make a reflex port, against the cost of half a driver and it's obvious they cost more. Further more, you need two for every active bass unit, or at least one ABR of double the area. Because you are asking the ABR to cover deeper, higher excursion bass than the driver on which it is based can manage, you need to double them up to cope. There is one final point of note, that where as a bass reflex port rolls off 4th order (24dB/octave) an ABR rolls off sixth order (36dB/octave). So when you see an ABR equipped speakers -3dB bass extension quoted, it really does pretty much drop off like a stone below that point, even with the assistance of the gain of the room in which it is sitting. KEF quote a -3dB of 36Hz for the Q700, so please don't get the idea that this means ABRs lack bass extension compared to their reflex ported counterparts, because they don't.

    Those of us remembering the aforementioned speakers of the eighties, will get another case of déjà vu when looking at the cabinets all of this technical prowess is wrapped up in. The black, wood grain effect (it's not vinyl) could have dropped straight out of a time warp, so resolutely black and sharply square edged is the new Q Series, especially with the grills on. Personally, I quite like the look and with the grills off, the seriously modern looking array of metal drivers, lifts the look to a nicely understated techno minimalism. I also decided I liked the careful imitation of imitation black ash, popular decades hence and preferred it to the wood veneer alternative. No matter, the cabinets are seriously dense and have extensive horizontal bracing, the top one being solid to partition the Uni-Q array off from the rest of the cabinet in the Q700. At the bottom, plastic outriggers equipped with serious spikes make levelling a doddle because you can adjust them from above - hurrah! To the rear is a bi-wire/amp, speaker cable terminal plate that has basic, but nice and solid, gold plated binding posts. The bi-wire/amp split is between the bass driver and Uni-Q array, rather than the tweeter and the other drivers as is more the norm. Rather neatly, the splitting of the crossover is achieved by simply fully screwing out two thumbscrews, rather than by removing risable flat metal jumper plates, that you immediately loose. The grill is the only really disappointing feature, not because it's acoustically deletrious, because in that regard it's actually rather good. It's more that it never actually lies quite flat and flush, which you tend to notice if you walk in from the side of your room like I do. Further more, the locating pins are very small, which keeps the baffle looking clean, but they are very fragile. Be careful if you like to have your drivers on display on a regular basis.

    KEF Q700 AV Technical



    Setup


    The Q700s proved to be quite tolerant of positioning, mainly as a result of all bass radiators (the drivers and the ABRs) being on the front baffle. Had a port, or ABR, been positioned on the rear you would need to drag the speakers further out into the room for a bit more breathing space. As it is, I found the Q700s quite happy anywhere between 225-300mm from the front wall, in my reasonably large room. Likewise, with a metre to the nearest side wall, I found only a gentle toe in was required. The Q600c was happy sat at the front of my AV shelf with a similar clearance to the front wall. A bit of imagination was needed to tilt it up toward the listening position, as it doesn't come with tiltable base. Three large Focul Polipods at the front and two small ones at the rear sufficed and also decoupled it from the shelf, which is a good idea in any case. The Q300s on rear duties worked well just behind and either side of the settee, again about 225mm out from the wall. The Q300s were pointed at they're opposite number at the front, rather than toed in hard to face the listener. In my room, this gave the best blend of direct and reflected sound. Amplifiers used were my usual Audiolab/Cinepro combo and an Anthem MRX-700.


    Listening

    From my father's C55 of circa 1989, through my ownership of the original 'Eggs' and thence onto a Q5/Q9c/Q2ds system, I've dipped in and out of the Uni-Q drivers over most of my listening life, so I was looking forward to see what this latest iteration could do. In short, the new Q Series has built on the obvious strengths of the past, but at a single stroke, has basically removed the few issues that bugged me and added a dollop more of everything for good measure. I'm not sure that, certainly the latter generations, even bare mentioning in the same breath, so thoroughly improved is the new Uni-Q unit.

    The single biggest improvement to this reviewers ears is the newfound refinement and smoothness of the upper midrange through treble. It's a bit hard to point the finger at a single reason for the jump in performance, but the shift to a 25mm tweeter has definitely helped. I've yet to hear a 19mm dome (working in a two way) that didn't sound a bit stressed and edgy at the bottom end of it's pass band, especially when playing at high levels. The lack of surface area means it has to work harder and that results in things always sounding a bit busy and uncomfortable. With the new tweeter, working in concert with the tangerine waveguide and the attention to the smooth profile of the mid/bass cone and surround, the potential harshness has gone from the treble and been joined by a new found smoothness through the midrange, where the two drivers transition from one to the other. Potent midrange sounds, be they from a powerful female vocal, or from all hell breaking loose in a movie, are just clean and clear without sounding crowded. Best of all, the consistent and even dispersion characteristics of the co-axial driver, mean the people sitting around you get to enjoy the same presentation. That was always a Uni-Q strength and remains so.

    KEF Q700 AV Listening




    The other notable quality of the new driver is the brutal mid-range dynamics for a speaker of it's class. The alacrity of plucked guitar strings (Rodrigo y Gabriella, again!) is quite remarkable and is as much about the phase coherence of the drivers, as it is about the pistonic nature of the well controlled aluminium cone. This is sustained by a pleasingly weighted tone and body to the instrument that makes it sound entirely believable and quite distinct from the other guitar in the duo. It's all clever stuff, but it isn't at the expense of subtly and micro dynamics. The Q700s play the soft stuff just as happily, with quieter passages of an instrument like piano, still having a definite attack to a note, but without loosing the body of the sustain that follows.

    As mentioned, a wider than average selection of seats are served evenly. That means they all get to enjoy a nice wide and deep soundstage, with plenty of space and air around the performers on recordings from real acoustic venues. There is a slight 'but' and it's that image focus isn't quite as tight as I've heard. It's not like performers are bloated in scale, indeed they're all appropriately sized and well positioned relative to each other. There's just a slight defocusing, which if I had to take a guess, I'd pin on the razor square edges of the cabinets. It's a design feature that's in keeping with the style, but slightly at odds with the attention shown to to removing sharp discontinuities across the Uni-Q drivers surface. It's not a big issue. In fact, it's irrelevant in multichannel mode and certainly not one that spoiled my enjoyment of stereo, as my attention was continuously dragged back to the natural pace and drive of the music.

    Whilst it's easy to fixate on the Uni-Q driver, it's success can be completely undone if the all of the hardware providing the extra bass extension isn't up to the job. I'm a bit of a bass quality nut and I'm not about to be hoodwinked by a novel engineering solution that's clever for it's own sake. Fortunately, I found this ABR solution to be entirely convincing, as it has been tuned very sensibly. It's tempting to look at the impressive face of the Q700 and assume you're going to be met by an utter bass monster, but one must remember that you're only really looking at a 2.5 way loudspeaker (of admittedly generous size) and that half of the drivers are really just an alternative to a single reflex port. Just like a port, you can play a whole load of tuning tricks to make the bass initially

    mpressive, or over extend the tune to hit spec sheet impressive figures. KEF have resisted these urges and provided a nice flat, tight tune that once in a room, plays tunes and still reaches the low thirty something Hertz with authority. Bass texture was particularly noteworthy, with a nice fibrous quality that let you know how a string had been plucked and not just whether it had been. The double bass on Harry Connick Jr's 'A Nightingale Sang in Berkley Square' is a good test of bass texture. Most smaller speakers, lack the driver area to deliver the softer deeper notes with any real description, but the Q700s breezed through it. Even the deepest notes failed to soften and get fluffy and so the gentle swing of the track survived intact. This was impressive.

    For those with a smaller room, or less of an opportunity to cut loose in the antisocial sense, will find much of this character transfers to the smaller Q300, but obvioulsy withut anything like the bass extension. There's not quite the mid-range finesse of the larger speaker, as the main driver has to carry all of the bass duties and that's a far more arduous task in a straight two way loudspeaker. In the larger speaker, the extra bass driver rolls in below the baffle step to handle the extra bass, whereas the smaller speaker, handles this through increasing the driver's relative output in the low bass and that means greater excursion. It also obviously lacks the upper bass dynamics of the Q700 and it's near double driver area. At moderate levels, the impact is minimal though and this should be seen in the context that, it's exactly what happens in every other straight two way loudspeaker. Relative to it's peers, the Q300 is a cracking little speaker. It is exceptionally capable in terms of transparency and as good as anything in the class, in terms of bass tunes, to the depths it can plumb. KEF have again been sensible with the port tune, seeking to reinforce bass extension accurately.

    Like it's larger brother, the Q300 was quite happy relatively close to the wall, although I probably wouldn't make use of the wall hanging facility, unless you're using it for surround purposes. Positioned that close, you can plug the reflex port to reign in the lower bass, but there's not a lot you can do about the excess energy in the mid to upper bass. This does nothing for vocal or instrumental clarity with a somewhat chesty quality becoming apparent. This is not the Q300s fault - any free space speaker would suffer the same way. It's just a note that the wall bracket presents a compromise best suited to less critical surround duties.

    Whilst in stereo mode and with the Q300s up front, it made sense to introduce the Q400b into the mix. Whilst the greatest advantage of running a subwoofer is in true 2.1 mode, with the low bass being diverted from the speakers to the sub, many stereo systems lack the bass management necessary. So, the only option is to tune the sub to roll in, at the point where speakers naturally roll off. This obviously results in a lot more bass extension, the principle benefit of which is the increase in scale of the sound, but it's not much good if the subwoofer is a dull slug that can't hold a rhythm, play a note and keep up with the main speakers. It has to be said the success of such a pairing is as much about optimizing the subwoofers position in the room to avoid excessive bass through room interaction. The Q400b was a willing accomplice to the Q300s once this feat was managed. It certainly allowed the overall combination to plumb the depths of the Q700s and a bit more besides, and it did so in a respectably taught fashion. That a subwoofer was in operation wasn't obvious and it fairly rattled along with fast bass, subjectively matching the Q300s and their performance envelope very well.

    When trying the same trick with the Q700s, the effect wasn't quite so convincing. The upper roll off of the Q400b, can't quite be set low enough to avoid a fair bit of overlap with the increased extension of the floor standers, so you always end up with a bit too much energy in the 40-60Hz region. To be fair, some like the extra weight this gives and you do gain another 10Hz of extension, so suck it and see.

    In terms of the integration of all fivespeakers in surround mode, the integration is superb. Effects slide gracefully around the room, with no tonal discrepancies to mark out the transition from one speaker to the next. With the speakers so well matched in size, this blend is maintained even at high levels and believe me, the KEFs are happy at high levels, without any one speaker starting to crack prematurely under the strain. Big hits really punch hard, but without harshness and so frenetic action remains clear and well separated and easy to listen to over long periods.

    Conclusion

    8
    AVForumsSCORE
    OUT OF
    10

    The Good

    • Class leading sound
    • Happy at high, or low volumes
    • Easy room integration
    • Nicely screwed together
    • Look great with the grills off

    The Bad

    • Subwoofer weak
    • Looks are a bit '80s with the grills on
    • Grill fixing a little fragile
    You own this Total 0
    You want this Total 0
    You had this Total 0

    KEF Q700 Surround Sound Speaker Package

    So as a historical fan of Uni-Q drivers in general, the promise of a new, highly evolved generation that knocked the rough edges off was always going to interest me. However, the AV and hi-fi world is littered with evolutionary products that somehow throw the baby out with the bath water, failing to maintain the magic of the original in the quest for refinement. With the new Q Series, KEF have dexterously avoided that prat fall, although (and audio memory is a fickle beast) I feel the character is quite distinct from what has gone before. The calmer, more precise nature of the Q Series, particularly through the upper mid and low treble, coupled with a greater grip on the bass end, has delivered a range of speakers that sounds a little cooler and on first acquaintance, a little less attention gripping.

    That first impression would be wrong though and it's not unlike having existed on a diet of solid performing budget kit and then finally hearing something high end. Initially, you wonder what all the fuss is about, until it dawns, over extended listening, that it's the hash that's gone and what you're left hearing, is all you should have been hearing in the first place. Once that penny drops, you realize that the new Q Series, is a very natural sounding performer. Without an unnatural and harsh emphasis on leading edges to give a false impression of dynamics, nor a ramped up treble to throw 'detail' at you, or tricked up bass to fake depth and punch, the Q Series is a very satisfying, unfatiguing long term listen. It remains so at high volumes over long periods, but simultaneously manages not to close in on itself at low, late night, listening levels.

    The subwoofer is the weak link, but it's a bit of a side issue. You can sort that, without destroying the balance of the package as you would if you tried to change one of the main speakers. Because I have to test the package as supplied, it should be noted that the score for power handling and movie sound have been docked a point because of the sub. It should be seen in the context that if partnered with smaller speakers from the Q Series, their lower limits would expose the sub less as indeed does music listening. I need to make this clear, because I do not want those scores to detract from the speakers, which are excellent in every regard.
    Focusing on the speakers, because lets face it, that's why you are reading the review, then the answer is yes. Yes, they are almost a revolution, rather than evolution, compared to their forerunners. Yes, they are surprisingly easy to accommodate in terms of space required and yes, they are right up at the top of their class for sound quality. Finally, yes the new Q Series is a solid highly recommended, without caveat.


    Suggested retail price when reviewed: £3,450.00

    The Rundown

    Sound Quality

    8

    Build Quality

    8

    Value For Money

    8

    Verdict

    8

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