Curvi BMR Mk2 loudspeaker
It takes quite a lot of courage to adopt a relatively new technology in a market where the norms are already well established, but that’s exactly what Curvi founder Dr Chris Liauw (a materials scientist) has done. It’s almost on a par with the development of the electrostatic transducer in the days when conventional’ coil and cone based drivers were the norm.
Not only that, but with an interesting set of what might be termed limitations’ which in reality turns out to be simply’ the maximum practicable size of the drive unit – around the 6-inch mark – they perform way beyond what first sight might suggest. In many other respects the speakers (aside from their visually stunning design) could be mistaken for any one of a number of other similar offerings. However, let me assure you from the outset: they’re absolutely not.
I’m not going to go into the technical reasons why these speakers are different. That’s not the point of this review, and the technical stuff is referenced at the foot of the review for those who need to know. My sole purpose is to attempt to convey to you how these speakers perform in the context of my own rooms and systems.
First thing to say is that visually they have a slim profile, finished in solid natural plywood. The choice of material is particularly important due to its resonant characteristics, and the fact that due to the constantly changing cross-grain effect of the ply’s laminations it’s both a consistent but also very inert material.
As you can tell the Curvi is very distinctive, this was most definitely the effect Chris Liauw wanted – something which wasn’t overtly speaker-like. In fact, so very gentle though this shape is, it does mean that the speaker becomes a part of the listening experience rather than simply being the source of the sound. Connection is by 4mm banana sockets, just the one pair, located at the rear of the plinth. Being a single-driver design there’s no crossover, so no need to bi-wire. The integral heavyweight plinth is supported on large sharp adjustable spikes which discretely anchor the speaker to the floor. The plinth itself has quite a large profile (footprint) so there’s very little danger of toppling the speaker once in situ.
The view from the front displays the single driver, but at that point there’s a substantial diversion from conventional design. Originally these speakers were designed with a single Jordan JX92S Controflex driver; in the opinion of the designer this was the best full range drive unit available when the cabinet design was registered in 2006. The design, and the length, shaping and configuration of the transmission line was therefore tailored to suit. But this and other full range drive units have their idiosyncrasies which, no matter how hard you try, are difficult to totally design out. The only other feature (apart from the rather lovely grain of the ply) is the beautifully scalloped transmission mouth vent port at the bottom of the speaker.
Research originally culminating in the NXT drive unit produced the Balanced Mode Radiator (BMR), offering a rather different way of making sounds from what appears initially to be very similar to a normal cone-driver. However, as its name implies, it is a rather different beast and full details of the design can be found here.
Chris Liauw felt that the BMR offered rather more potential than the Jordan and pursued development with this driver. A number of different sizes were explored, but the best compromise between performance and size was found to be in the version used here. Fortunately the line length, shape and taper suited the BMR to the extent that the cabinet could have been made for this drive unit. The line damping though required total revision; Herdwick sheeps wool plays an effective role here.
Visually, the only real difference is that the front of the driver is flat (not unlike some of the Wharfedale drivers of yesteryear) but that’s where the similarities end. The story of the development of the speakers’ is quite well documented on the Curvi’s website if you’d like to know more. Sensitivity is a low-ish 84dB but the impedance curve is relatively benign, Chris recommends amplifiers with 30 or more Watts, but it will need to be rather more in particularly large rooms. That having been said, I did also experiment with my humble 2A3SE single ended triode amplifier with interesting results.
Balanced mode radiator
As I said from the outset, the way in which this speaker presents music is as different as the difference between electrostatics and conventional driver designs. The polar response of the BMR is quite different from a conventional driver which results in a much wider range of listening positions – you could say it’s rather more sociable than some designs. Its impedance curve is not ruler-flat but certainly benign enough that unless an amplifier has a predisposition to instability it won’t adversely affect either the amp or the speakers’ performance.
As far as room positioning is concerned, again the Curvi is remarkably tolerant. Siting reasonably close to a back wall might help lift the bass response in some instances, but in free space they also perform well. There’s no lack of bass, but conversely there’s no bass emphasis. The extended upper regions – normally the province of a tweeter or even super tweeter have much more shape and texture than I’ve heard before, particularly from what is a full range design. The more common shouty elements of a lot of full range units are simply not present – or rather, if they’re there they’re not obvious.
The one criticism which afflicts many full range designs is a resonant peak at a certain narrow frequency band; Lowthers of old exhibited it, and other designs less so. The challenge of designing a truly full-range driver is to make it seamless top-to-bottom. The reality is that the BMR’s frequency response is so very even that any peak or trough really is quite minimal, and relatively easily compensated for by judicious cabinet (and computer modelling) design.
How do Curvi BMRs sound?
As I said initially, they do challenge expectations. While they are of relatively modest sensitivity they are not undynamic, and can be driven very hard without distress. Even using a 100W amplifier I failed to elicit anything untoward. However, their ability to conjure up the recording space is really quite marvellous.
An initial disc on the turntable was Elgar Sacred Works on Argo. A disc from 1959, it is exceptionally well recorded, with the recording perspective as if one were sitting half-way down the nave of St John’s College chapel. You are immediately aware of the enormity yet cosiness of the building, and aware of the presence of the choir in the distance even though you can’t hear them. The Curvis manage to convey that stuff of the sixth sense which alerts you to something being there.
Perhaps the biggest test of this disc is the title track where the solo treble is pitted against the very low organ pedal notes. At no time did the speakers lose their composure. The image of the chapel remained resolutely in focus, and Alastair Roberts’ voice remained a model of clarity. The organ pedal notes simply failed to upset anything, and even when raising the volume rather higher than normal, the poise and clarity of the recording remained firm.
Moving to something a little more modern, again on Argo (ZRG575), the recording of Stravinsky’s Pulcinella and Apollon Musagete is an absolute model of clarity and transparency. The rasp of the brass is wonderfully immediate, the rumbling waddle of the double basses starkly laid bare in all their fervour, and the flute and piccolo glorious in their differences. This was a recording from 1968, with Neville Marriner and the St Martins band who are obviously revelling in the almost bawdy element to the music. However, don’t let that fool you. There’s also a tendresse to a lot of their playing in the quieter sections and here the Curvis’ ability to convey subtle nuances remains high on the praise list.
What was interesting is that when I was sitting in the traditional hot seat (i.e. right in front of and between the speakers) the image was rock steady, and gave great depth and perspective to what I was hearing. However, when I sat off-axis, although the aural picture did change, it was only because I had moved and was hearing the players from another point in space. The image of them playing was far more holographic off-axis than I’d experienced with any other speaker designs (even those claiming to be omnidirectional). This may have a lot to do with the BMR’s almost 180-degree dispersion capability.
Similarly, while listening with the driver at head height gave an amazing insight into recordings moving up or down did not appear to have much effect on the core mid- and upper frequencies. The bass may have changed a little due to the altered reflection angles from the floor but otherwise the presentation was remarkably benign (that sounds like a criticism – it’s not. It’s most definitely a superb trait.)
And while we’re on the subject of bass, yes, it’s most definitely there. Being purely pragmatic it’s not a speaker for producing prodigious uber-bass with chest/wall bending effects. However, it is very like the bass you get from a good truly full-range electrostatic. The Curvis have an uncanny ability to move not only a lot of air (needed to good bass reproduction) but also do it with control, appropriate weight, and in balance with the rest of the aural spectrum. The deep organ was reproduced with rather disarming realism, the bass drum with uncannily lifelike slam and the footfall in Private Investigations (Dire Straits) with such realism that the cat looked up to see who it was.
There are those who also adore heavier material though. Physical Graffiti is a Led Zeppelin tour de force. Covering a plethora of musical styles (blues in In my time of Dying’, acoustic forays in Bron-Y-Aur’) but Page’s mainstay is his love of distortion as a musical colouring pen. Time and again he pushes the boundaries, and as with a lot of hard- and heavy-rock music it simply cries out to be played loud.
Worryingly (for my neighbours at any rate) the Curvis really do go very loud. Refreshingly the frequency extremes don’t suffer when at full bore either. Quite often as volume increases you get the feeling that a speaker is beginning to lose a little of its poise either at the bottom end, or becoming rather shrill or strident at the top. Not so here. They remained utterly composed, whatever Page riff you threw at them, they reproduced it calmly, but still conveyed the passion, the effort, the sweat dripping off his nose. As an emotional journey through Led Zep’s music they didn’t hold anything back, it was a totally immersive experience.
I guess the other test of a pair of speakers is their ability to reproduce those utterly exposed elements – especially solo voice or solo instrument. Well, I dabbled with some female vocal, ranging from Beverly Craven, Suzanne Vega, Kiri Te Kanawa, through to Suzi Quatro and Mary Black. As they say, perhaps unkindly, nothing to see here. It was as I’d anticipated – vocal reproduction was remarkably free from any semblance of cabinet colouration, no undue sibilance, nothing muted; in fact the most amazing thing about these ‘smaller’ recordings was that you really could shut your eyes and almost persuade yourself they were singing for just you. Quite uncanny.
But as I’ve said in the past a solo instrument is quite something to get right. It’s probably one of the few things which could conceivably fit into your own listening room and be played. So I dug out an ancient recording of Mario Parodi playing solo acoustic guitar on a very budget label Music For Pleasure (MFP2094) – a label turning out some of EMI’s older recordings.
Mesmerising. Absolutely mesmerising. No other description fits. A lot of the pieces on this LP were transcriptions of classical favourites rewritten or arranged for solo guitar. The beauty of a disc like this is that it was relatively close-miked. The pressing was exceptionally good (so there’s very little background noise or hiss) and the recording has managed to capture not only the sound of Parodi’s fingers moving on the strings but also when he shifts his weight while playing, the slightest creak of his chair or stool. When played at a realistic volume in your own room it’s uncannily, and I mean uncannily lifelike. This rendition, through the Curvis blew me away. Absolutely.
Was there a mismatch between the driver and its rear-loading / transmission line? Not that I could hear. The presentation was seamless from top to bottom. Was there any deficiency in anything I heard? – No. Absolutely not. Was there anything I thought the Curvis could improve upon? Well, from a personal perspective, only their efficiency
The Curvis’ efficiency is quoted as 84dB, for most people with good amplification that’s absolutely fine. However I have a love of flea-powered valve amps and high efficiency loudspeakers. So, being inquisitive I coupled up my 2.5 Watt 2A3 amp to the Curvis and sat back. Utter gorgeousness aurally. It really was a sublime experience. However, as you might conclude, the 2A3’s ability to drive the Curvies’ BMR driver to its fullest capability was compromised quite severely. The sound quality really was quite something, and the top and bottom were just wonderful but despite the amp’s ability to cope with transients into a 95db+ driver, the Curvis weren’t quite so willing to respond. That’s not a criticism; simply physics, the amp is just not quite powerful enough. Now an 845 or 211-based amp might be a different matter.
Is the Curvi BMR a great speaker?
Would I recommend the Curvis to anyone? Yes, everyone who reveres good music reproduced exceptionally well and in an emotionally connective way. Overall, the conclusion has to be that Chris Liauw has done an amazing job of creating an unusual-looking but superbly performing loudspeaker which, because of its looks, should find domestic acceptance in most homes. While it most certainly isn’t inexpensive it represents such good value for money and delivers so much in a remarkably small footprint that it cries out for the top end recommendation. I really will rue the day when this pair has to be returned, and sadly that will be all too soon.