KEF R700 AV 5.1 Speaker Package Review
The best real-world application of Uni-Q to date
Recent releases from KEF can all claim a trickle down of some of the technology from the concept-come-reality that is Project Blade. The R Series is the line that lays the best claim to calling itself ‘Son Of Blade’, as it can actually boast components lifted straight from that technical tour de force. Understandably, this doesn’t include the individually hand made composite cabinets from a boat builder, but it can boast the self same tweeter and like their bigger brother, these are true three-way designs, the base model R100 excepted.
With this being a 5.1 surround sound package, I opted for a system with matched drive unit sizes and topologies. That’s right - for once, I resisted the urge to ‘send me the bigguns!’ The setup comprises the three-way, four driver R700 floor stander at £1999/pair, the three-way, three driver R300 stand-mount at £999/pair, the matching three-way four driver R600c centre channel at £899/ea and finally, the twin opposed driver R400b subwoofer at £999/ea.
I don't know what's in the water in Kent these days, but KEF certainly seem to be in a rich vein of form in recent times. In terms of the R Series package tested here, I'm struggling to think of anything that can really be called a weakness.
The R Series are rather bass proficient, which some may find makes them a little bass heavy, if their room doesn't allow the speakers full reign in terms of positioning. The dual mode bungs are a big help, but even so, you won't get away with cramming the Rs in a corner. Likewise, the Rs thrive on Watts and an amplifier capable of applying some grip. Don't drop the Rs on the end of a single ended triode amplifier or a 50 watter integrated and expect them to be held in check. Take the time and care to position, match them with appropriate amplification and the you'll be rewarded with class leading bass quality. Don't and you will suffer, but that's not the speakers fault.
The cabinets are somewhat less than swoopy and curvy, which does make the R Series quite an imposing visual proposition along side some of their peers. That said, the cabinets do exactly what a cabinet should do (ie, add nothing) and the proportions are quite handsome. Their stark simplicity, is further enhanced with the grills off to reveal the super clean lines of the drivers - the metal trim rings and that amazing Uni-Q unit helping to break up the expanse of black. These same stylistic cues, when applied to the R400b subwoofer, deliver what is, to my eyes, one of the best looking subwoofers ever, the central silver band being a stroke of design brilliance.
However, style is for nought if it's not backed up with performance and the R Series poses the world a number of problems, in a good way. The R Series Uni-Q mid/treble array is the ultimate development of an idea born in the 1980s and in this implementation, scales previously unheralded heights. It's clarity and stunning dynamics are now matched with a smooth maturity, that is found in the seamless integration of all aspects of it's performance. The Uni-Q concept always delivered good imaging, but in the R Series, KEF have really turned the screw. Performers hang in the space of a cavenous soundstage, rock solid in their positioning and totally free from the cabinets. They are not presented as disproportionately large, nor too far forward of the speaker's plane and if your musical tastes are more real world than studio, you are in for a rare treat.
This innate refinement doesn't mean the R Series can't rock, or kick ass with a movie soundtrack. They dig deep, stay firm and controlled and propel music along with the same conviction. They can also crack out a gun shot and they manage to do so without ever grating on your ears. So, the problem as it stands, is mostly for their opposition. There are a number of good speakers by the time you reach these price points, but the KEFs match, or better, the best out there in all regards and then apply an added homogenity, I can't recall hearing at anything like this at the price before. That's the definition of a class leader and it's also one that runs KEFs own Reference Series very close. In some areas of the mid and treble, the Rs are better, which means it's going to be very interesting to see what comes out of the Kent Engineering Foundary next.
Packed in solid boxes, with ample clamshells of polystyrene, all of the packaged R Series are satisfyingly dense to heft around. I even resorted to a sack barrow for the R700s, which isn't something I normally have to do unless it's a subwoofer with 'Made in USA' stamped on the box!
R Series R700
Starting with the R700s, the first job is to attach the outrigger feet, which attach individually in the same manner as the items on the Q700s reviewed previously. The difference is that rather than a composite molding, this time you are greeted with slabs of nicely machined aluminium. The spikes are long and project up through the outrigger, to accept a large round locking wheel. There is a soft rubber plug in the centre of this wheel, the removal of which allows you to insert an allen key into the top of the spike. Thus, all levelling is performed from above with a single tool, that can't fall off or slip around a locknut. Further more, the outriggers project both forward and backward, as well as sideways, which improves stability in all directions. It is the work of moments to get the R700s set level and the spikes don't loosen through vibration over extended use. This is first class execution of a feature that is too often over engineered and under effective.
With the R700s the right way up, we are greeted with a slightly taller than average, although slender, cabinet, immaculately finished in gloss black. Much of the speaker's weight comes from the 20mm MDF used, plus the multiple internal braces, the positioning of which were determined through finite element analysis of the cabinets vibrations and resonant modes. In practice, you feel very, very little vibration in the cabinets, even when playing loud. To the rear are a pair of well flaired reflex ports, one for each half of the cabinet - with each bass driver operating within it's own volume of air. The molding of the bottom port, extends to incorporate the the bi-wire/amp speaker cable terminals. Rather than use easily misplaced jumper plates between the terminals, KEF use a clever solution that utilises a pair of thumbscrews between each pair of terminals, but a word of caution is needed.
Whilst it makes no difference if you're bi-wiring, you need to be SURE that you have disconnected the two halves of the crossover when bi-amping. One advantage of the old plates/links, is that there is an immediate visual confirmation of their presence, or not, but the thumbscrews are less clear in this regard. Connecting two channels of amplification with the crossovers internally connected, will at best trip your amplifiers protection and at worst, let the smoke out of both channels, which is serious. Connect one amp channel to a speaker, confirm that sound is only comming from either the bass drivers, or mid/treble units and then connect the second amplifer channel. You have been warned! The eagle eyed will have spotted that I said bi and not tri-wire/amp, even though this is a three way loudpseaker. That does seem odd to me too, but given that the vast majority of improvement is derived by separating the bass amplification off from the mid/treble, then this is the way I would choose to do a two-way split of a three-way loudspeaker.
Turning to the front and the drivers look initially like those seen in the Q Series, but there are a number of significant differences. For starters, the central Uni-Q driver is a pure midrange unit, with a centrally mounted tweeter. With no bass duties what-so-ever, this brings a number of benefits. As midrange requires practically no driver travel, both the driver and the suspension can be a lot smaller and more focused on tighter control of driver resonance. The upper crossover in the R Series is 2.8-2.9kHz compared to the 1.8-2.5kHz of the 2.5 way Q Series, which moves the crossover to the treble unit further out of the all important vocal band. With the lower crossover to the bass drivers at 500Hz, the alu-magnesium mid driver is handling two and a half octaves, uninterupted, through this critical region. The tweeter (which in this case is lifted straight from The Blade) gets a boost in performance, as it is handling less of the upper mid-range and for much the same reasons as the mid driver benefits, the easier ride it's given, lowers distortion.
However, with the Uni-Q array, the relationship between the treble and mid range driver is interdependent to a higher degree than in a traditional two-way. The mid-range driver has the secondary task of acting as the wave guide, that controls the dispersion characteristics of the tweeter. The latest generation of the Uni-Q array delivered not only a larger 25mm aluminium dome with inherently lower distortion, but also a heavily revised and much larger Tangerine waveguide behind which it sits. The Tangerine waveguide, at nearly 50mm across, fills the twin roll of acoustically loading the tweeter with a constrained, stable volume of air, whilst also dispersing reflections at the throat of what is the mid-range driver. In a 'normal' loudspeaker, this role is filled by a dustcap, or phase plug, for which there is no room here. Further more, the Tangerine waveguide's profile is extended by the cone of the midrange driver that surrounds it. Unlike the waveguide, this is a moving structure and some of the frequencies at which it moves are shared by the bottom end of the tweeter, so care has to be taken in not only the phase alignment between the two drivers, but also the physical discontinuity where the two meet. This being a three way loudspeaker plays straight into the hands of these requirements. The mid cone is moving a lot less, so the join between the cone and Tangerine waveguide is far more consistent, plus the smaller suspension at the cone edge provides a near totally smooth transition out onto the front baffle, which aids imaging.
The bass drivers again show more Blade experience. The smooth parabola of the anodized aluminium diaphragm, fronts the composite construction of a cone behind, with the voice coil former being attached to both. This rigid structure is not only vented through the cone, but through the ferrite magnet structure of the motor too. In a departure from the Q Series, the surround to the cone is hidden behind a trim ring that all but touches the cone edge. This is interesting, because whilst a bass driver surround contributes a small amount of radiating area, it's often not very well damped at frequncies beyond those which it's designed to control. KEF have seeked to block it's output, so that only the highly pistonic driver cone is contributing. The pair of drivers are mounted above and below the Uni-Q driver D'Appolito style, the idea being that the acoustic centre of the pair is shared with that of the Uni-Q driver, to affect the ideal of a full range point source.
Of course, if the tweeter is to remain at ear level (which in this case is a slightly low 780mm), the top bass driver and therefore the cabinet, are necessarily taller to accomodate this demand. However, with it's slender façade, mounting screw and grill cup free baffle, plus understated trim to the drivers, it's a surprisingly unimposing speaker, even in gloss black. The grill, as I've mentioned, is a cloth covered piece of 10mm thick MDF that sits flush on the baffle. Each driver fires through a carefully chamfered, circular aperture, that matches the driver size. I will confess a marginal preference for the sound with the grills removed, but it's effects are minimal compared to the fabric over plastic mesh types used to make more interesting, but acoustically less benign shapes.
R Series R300 & R600c
The R300 is essentially the top two drivers of the R700 turned up side down in a stand mount package, although it's obviously more complex than that. Because bass, rather than mid or treble output, is the limiting factor, the maximum quoted output (parametres not stated) is 3dB down on the R700 and bass extension is up from 42 to 50Hz (+/-3dB). Perched on my heavily modded and mass loaded, 600mm Sound Organisation Z1 stands, the tweeter is a spot on (for my seating) 870mm off the deck, but the overall height is 130mm shorter than the R700s.
The R600c is, again for visualization purposes, the R700 lopped off at the knees and turned on it's side. Maximum output is quoted at the same 113dB as the R700s, although bass extension, due to the smaller internal volume is -3dB at 60Hz. Whilst I normally abhor symetrical driver layouts in centre speakers, it is another strength of the Uni-Q array in that it completely sidesteps the horizontal dispersion issues of two and two-point-five way speakers. As a true three way, you are below the 500Hz crossover frequency, before comb filtering effects start to create a ragged frequency response for off-axis listeners. Even then, the critical parts of the vocal range are unaffected, so it's output still remains clear.
With less budgetary constraints, more complex and exacting crossover design has allowed an extremely similar tonal match across all three speakers. Through the review period, I swapped the R300s and R700s between front and rear duties and each time I ran the setup test tones, I was struck by how similar the tones sounded around the room, bass end aside. It should be noted that the reduced extension of the R600c does not equate to being bass light and it enjoys a bit of free space to work in, definitely sounding best mounted on a stand in free space. Plonked on the shelf of my rack beneath the screen (where it is in the pictures) it suffered too much bass reinforcement up into the upper bass & lower mid. EQ hammered the response into shape, but less EQ is always better and I rigged a stand to get it free of boundaries and closer to the ideal ear level.
R Series R400b
We have yet to mention the all new R400b subwoofer. It seems to this reviewer, that most UK sourced, full sized surround sound speaker packages are generally under subwoofered. So it was with the Q Series, which sported a good little sub, the issue being it was about half the subwoofer the scale of the package needed. So, when I spotted the R400 subwoofer with a driver an inch smaller, albeit two of them, I was somewhat non-plussed. Then it turned up.
First off the weight, or rather the density, of the Q400b is most un-British, even if the 14" cube of space it occupies remains domestically friendly. The plate amplifier is Class D (which is light) and the cabinet isn't that big, so clearly, there's a serious pair of drivers in there. In essence, the drivers follow the model of the R Series' speaker bass driver, but beef it up somewhat to optimise it for low frequency operation. More roll surround, more travel and a lot more motor to motivate it all. The drivers act in opposition to each other, which results in force cancellation and to further enhance this, the motors are bolted to each other with a tie rod and the baffle to which each is mounted is double thickness. Each driver has it's own 250W (RMS) mono amplifier which is plenty, although I'm a little disappointed in the controls on offer.
The continuously variable gain and crossover (40-140Hz, no bypass) are fine, and I rather like the connection block for those requiring a high (speaker) level input, as it's a lot less faff than speaker binding posts. Line level inputs are courtessy of a pair of RCA Phono sockets, which is adequate, although XLR connections are becomming a common addition. What I dislike are the 0/180deg phase switch and the +6/+12dB boost switch.
The former seems a little parlous given the provision of high level inputs. I've set up a few subs for friends in resolutely stereo systems and I've yet to find one that integrated best at zero, or 180 degrees. In an AV system, which allows more control over delays and phase, I'll grant you, few would miss it, but this is a £1k sub and a proper phase control is not expensive.
The boost control simply has no place in a decent subwoofer. Essentially, it delivers a 6dB or 12dB boost centered on 40Hz to "compensate for room conditions or user preference". The only room condition requiring a 6-12dB compensation is likely to be modal and thus no amount of boost will help. The average room is far more likely to suffer huge modal peaks in this region, which require precisely the opposite of a boost to compensate. The other thing is, this little sub goes very deep and engaging the 40Hz boost, just masks the bottom end, which is counter productive. I feel KEF have missed a trick here as the same switch could just have easily provided a boundary gain compensation control, which is actually a very useful thing to have, for no fiscal penalty. Gripes over, because I don't want to detract from what the R400b does very well and that's loud, deep & well controlled bass from a small box.
It manages this, due to harnessing the laws of physics in it's favour, rather than through any technological slight of hand. You see, when you place two sub-bass drivers close to each other, the output doesn't double (ie, add 3dB) output, it quadruples it - That's 6dB. To put it another way - doubling the number of drivers doesn't just double the output, to the equivalent of one larger driver of equal area, which in this case would be 12.7". No, the mutual coupling delivers that, plus the equivalent of doubling the driver travel, or doubling the amplifier power. Unlike that single larger driver with it's more powerful amp, you gain the force cancellation advantage already mentioned, plus you also now have two voice coils over which to dissipate the heat generated. So, less heat equals less dynamic compression and less driver travel used for a given volume level equals lower distortion. Brilliant, simple and very effective. Of course, there is a quid pro quo and that is in two drivers costing more than one, so I don't expect to see decent twin driver subs turning up for £300 any time soon.
To wrap up the R400b description, It looks fantastic. It might be just me, but with the side mounted drivers and their trim rings mirroring the main speakers, plus the inset silver band bifurcating the cabinet to break up the expanse of shiny black, the R400b looks expensive way beyond it's price. It is easily the prettiest subwoofer I've had on the carpet.
An interesting thing happened during the course of the R Series tenure at Williams Towers. A representative of a third party visited to train me in the use of their room measurement and compensation system. The nature of a measurement microphone used to measure a sound field, rather than direct output, is that it is pointed at the ceiling. Thus a flat in-room power response, shows a 6dB/octave decrease from about 3kHz and up. The left hand R700 which enjoys virtually free space followed this curve +/-1dB all the way out to the 21kHz limit of the measurements. The right R700, which is a metre from a heavily curtained side wall, was basically the same, save for one additional peak which would push the limits out to +/-1.5dB. This is an exceptional in-room response and one that shows the remarkable room independence of the Uni-Q driver. It simultaneously delivers a wide sweet spot, whilst constraining spurious sideways radiation, delivering consistent results from one room to another. Okay, if you stuff one in a corner and another in free space, all bets are off, but that would be true of any other loudspeaker too.
Regardless, this makes the R Series very easy to setup. A gentle amount of toe-in so you can just see the inside panel of each speaker seems to deliver the best balance of image space and definition, leaving you to only worry about getting the bass right. In room, the R700s will deliver solid output down into the 30s of Hertz, so it's worth taking the time to get right. Generously, KEF have gone over and above in the provision of port bungs, each of which comes in two parts – an outer ring and inner core. Thus it is possible to not only try bunging different ports, but also partial bunging using the outer bung alone. This of course only affects the reflex port output in the low bass. The region above this (60-300Hz) requires the distance to the wall to be adjusted and for my room, the flattest response was achieved with 750mm between the rear baffle and wall. The very bottom end worked best with both ports plugged with the outer bung only. The full bung was slightly flatter in response, but also lost a touch of dynamic joie de vivre, which was the greater of two sins to my ears.
When used at the front, the R300s were a similar story, albeit they were happy with no bungs. When used as rears, the positioning constraints meant full bungs. The R600c, as mentioned, disliked mounting directly on my top rack shelf, enjoying a bit more room to breathe for optimal results, plus a partial bung. As ever, your mileage may vary and remember, this is me trying to optimise using positioning alone, before EQ of any sort is added into the mix. The R400b subwoofer worked best, just inside of the right speaker.
Amplification was generally my long suffering Audiolab 8000AP processor, in tandem with a Anti-Mode Dual Core on subwoofer EQ duties and a Cinepro 2k6 poweramp. At various points, a Datasat RS20i performed processor and EQ of all channels and a Marantz SR7007 interloped, at first as an AV Receiver and then as a processor with the Cinepro. Latterly, the R300s and Q400b were used with an Elipson Music Centre, using the the Anti-mode as EQ on the input below 300Hz. Cables were used.
If I were to encapsulate the R Series in a sentance, I'd have to throw adjectives such as unflappable grace, transparency with polish and boogy into the mix. One thing I will say straight off the bat is that I've seen a few people both in print and on-line say the R Series are a bit bright. Nonsense. As mentioned above, not only do they measure flat as the proverbial trouser cuff, they sound deliciously clear and incisive, without the least bit of spitty sibilance, crashy cymbals or 'demo friendly' over emphasis what-so-ever. This is not only the best tweeter I've yet heard in the Uni-Q array, it's a very nice tweeter full stop. That's not to say it will flatter harsh sounding separates, or poor source material, but it isn't provoked into making them sound worse. With a really good recordings, it's just a beautifully airy view through an open window, without glare or fuss.
Of course, this being a three way loudspeaker and one with a mid range driver that covers a good deal more than a small spot twixt the treble and bass, the fine treble is for nought if the mid driver isn't up to the same standards. Happily the mid-range, like the blend between it and the treble is more than up to scratch. It's simply superb. There is a coherence to vocal expression that is only really achieved with a single driver covering the larger part of it's range. The removal of time domain confusion, due to phase shifts inevitable in a crossover region, frees an extra level of emotion from the performance, elevating it from clear, to captivating.
I've listened to Hugh Masekela's 'Stimela (Coal Train) Live' off the Burmester 'Vorführungs Vol 3' sampler CD a number of times, not least because it's an awesome recording. It is a slow piece (and a long one at 10 minutes) that ebbs and flows with some superb dynamic shifts from both the instruments and vocals. The KEFs delivered the palpable sense of atmosphere of the venue in which it is played - the heat, the moisture, the low ceiling the unruly chatter from the audience, all pinpointed within a huge soundstage of great width and considerable depth. Few speakers I have heard convey the indignity, the sorrowful anger, the bitterness of Masekela at the forced economic migration of his countrymen in the way the R Series do and certainly none near the price.
In fact the speakers that have, have tended to be rather large and expensive multi-way dipoles, that tend to major on seethrough midband transparency due to lack of cabinet colouration, their sense of image depth being a slightly more artificial construct. Which leads me to the R Series colouration, or rather the lack of it. Initially, the lack of cabinet related bloom and warmth can lead you to thinking that the KEFs are a bit aloof, a bit cool, but when an oboe blows, a cello is bowed or an acoustic guitar picked, the natural warmth of the instrument is rendered clearly and distinctly from another of the same. The cabinet isn't chiming in to paint it's own tonal colour over that of the instument and the control of the mid driver isn't introducing any unwanted edge either. Violins, which send so many speakers into paroxysm, just soar without setting your teeth on edge. Powerful female vocals, that home in on cone break up modes, just crest with their natural power, rather than developing into a shout that the singer didn't deliver.
Up to now, I haven't distinguished the R700 from the R300, because all of the above holds true for both. As you drop down the frequency range, the bigger speaker obviously delves deeper and hits harder, which tends to give it a greater scale, but their bass character is very similar none the less. Both are very firm and well controlled down to their natural roll-off, with considerable authority. Tunes bounce along nicely, with well defined pitch and and unusually clean transient impacts. They let go of notes very swiftly, which ensures the natural rythmn and pace of the music, is unabated.
It's all in keeping with the upper reaches of the frequency range and when examined as a whole, the resulting impression is one of uncommon coherence. There's no sense that a nice tweeter has been found, mated to a nice mid, backed up with decent bass drivers and then tweaked to match with some crossover wizardry. It's deeper than that. It's more of a partnership of components that have been designed from the ground up, to be part of a complimentary whole. There's no impression of any one aspect standing out, nor another being slightly weaker, just a harmoious system at ease with itself and what it has to do. It's quite a trick to pull off at any price.
In multi-channel mode, the integrated nature of the individual speakers, transfers into a seemless surround music and movie experience. There's headroom aplenty and the R Series maintain their grace under pressure, sounds steering precisely and dialogue staying intelligible at high levels. The integrity of the sound field to the sides of the room is particularly worthy of note. During Kung Fu Panda, there was one sound effect that I always assumed sounded like it rolled off to one side of the room, but the front/rear cohesion of the R Series made it sound like it was rolling up the left of the room. The pinpoint placement of objects within the stereo sound stage, had delivered extra spacial definition to the nominally flatter, but curved, field of surround sound, in a very convincing manner. Indeed, the way sounds are allowed to detach themselves from the location of the speakers, makes for a very smooth transition all round and particularly across the front.
If the similarity between the R700s and R300s is commendable, then it's a mandatory requirement that the centre channel is a good match for the main front pair. And KEF have not sold us short. Tonally and in terms of capability, the R600c is a fine match for the R700. There were occasions when I had to check whether I was operating in stereo, or Dolby Pro Logic off 2.0 PCM television transmissions, because there is no appreciable shift in the presentation when switching between the two deliberately. The centre channel kept dialogue locked to the screen and even shifting the listening position off to one side, failed to collapse the front sound stage. Further more, because the Uni-Q array suffers little in the way of of axis lobing, compared to a discrete driver array, any changes that do happen are minimal and entirely consistent across all of the speakers, so they remain integrated. I recall the same quality during the Q Series review, but the advantages of a three way, ratchet this quality a notch or two further up the scale.
At the point of shifting to multi-channel fayre, the R400b subwoofer was allowed to join the party and it's a pretty thunderous little addition at that. KEF have traded a touch of extension (it's clearly rolled off below 25Hz) for output and that's sensible enough. After all, there's no point in a subwoofer slogging it's guts out, to reproduce frequencies that are inaudible. However, within it's pass-band, it's quite a hooligan, with real clout and a vice like grip that belies it's diminutive stature. In the scene where Tai Lun escapes from prison, there is a series of heart beats toward the end of the passage. The last is an enormous room bending pulse and the KEF only just stopped short of conveying the full weight of what is an epic bass effect. Up to that point, the axe heads hitting stone, slow-mo bass drops and all manner of crunching LFE effects, were delivered with profound conviction. The hackneyed phrase of 'punching above it's weight', is entirely justified, but lets not ignore the R400b's manifest other qualities.
For starters it stays remarkably clean when asked to cross over higher than the 80Hz norm. I ran the R300s and the R400b in a 2.1 system and as is usual, the phenomenon of floor bounce sucks up a little of the 100-150Hz upper bass power, so I run a crossover in the 100-110Hz region. This requires a subwoofer with a flat upper frequency response and further more, the sub has to sound clean when doing so, if it's not to sound obvious. The R400b was in it's element in this roll, blending seamlessly with the R300s, displaying superb subjective pace and a deft tonal touch. Slight quibbles about the feature count aside, this isn't just a good subwoofer for a package, it's a good subwoofer full stop and for once, I wasn't left wishing for another one when used with the larger speakers.
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5.1 Speaker Package
KEF R700 AV 5.1
Suggested price: £4,500
Reviewed 13th January, 2013 by Russell Williams
To get the best out of your TV or projector, consider getting it calibrated.