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Kii Audio Three BXT

Bass Extension System By Phil Ward
Published February 2020

Kii's BXT module is hard to miss. It is 80cm tall and incorporates a total of eight 17cm bass drivers — four facing forwards and two on each side panel — and once a Kii Three is in position on top (as shown above), the combination makes for a 1.2-metre tall and decidedly imposing sight.Kii's BXT module is hard to miss. It is 80cm tall and incorporates a total of eight 17cm bass drivers — four facing forwards and two on each side panel — and once a Kii Three is in position on top (as shown above), the combination makes for a 1.2-metre tall and decidedly imposing sight.

Few monitors have impressed us as much as Kii's cardioid-radiating Three speakers. With the launch of their matching bass extension unit, have Kii made the best even better?

Readers with good memories may recall my enthusiasm for the Kii Three monitor in SOS January 2017. I wrote at the time, and I've had no reason to change my opinion since, that the Kii Three produced the best sound I'd ever heard in my own studio room. So it was quite a significant product. We at Sound On Sound were pretty early to the party with our review of the Kii Three and it's since gone on to attract numerous high–profile users all around the world: Jacob Collier, Max Richter, and Nigel Godrich, to name but three.

Along with providing such a rewarding reviewing experience, the Kii Three also went a long way towards rehabilitating for me the whole concept of high-power DSP (digital signal processing) within monitors. You see, up until the Kii Three came along, it often seemed to me that the genuine benefits of DSP within monitors were somewhat nebulous and that their extra cost and complexity tended to pull resources, both intellectual and commercial, away from the more fundamentally important electro-acoustics. But the Kii Three demonstrated without doubt that if there's a genuine and worthwhile role for DSP within a monitor, something that can't be done by traditional means, then it could truly change the game.

One Direction

The game that changed as a result of the Kii Three's DSP is directivity control. Almost all monitors, be they passive or active, are naturally omnidirectional at low and mid frequencies. Omnidirectional radiation continues up the audio band until frequencies are reached where the wavelength begins to approach the monitor's physical dimensions. From that point upward, the acoustic directivity will tend towards a cardioid character. As far as I'm aware, in the pro monitoring arena, there's just the Geithain range and the Dutch & Dutch 8C that display low–frequency directivity characteristics that are not fundamentally defined by their driver and enclosure dimensions alone. The cleverness of the Kii Three was to employ side– and rear–facing drivers, managed via complex DSP–based algorithms, to impose cardioid characteristics right down to 54Hz.

The reason this is so significant is that with low– and mid–frequency cardioid directivity, the acoustics of the listening room begin to become less significant. It's no coincidence that most room acoustic issues occur at low and mid frequencies, because that's where traditional monitors radiate just as much acoustic energy backwards, sideways, upwards and downwards as they do forwards towards the listening position. Since our 2017 Kii Three review, Kii have launched two new products, the second of which, the BXT bass extension module, is the focus of this review. The first product that wasn't around when we originally looked at the Kii Three is the Kii Control, and I've given that its moment of fame in the side bar (see 'Kii Control' box).

On Location

As with my review of the Genelec S360 last April, the size and weight of the Kii Three and BXT combo meant that it was impractical to consider my home studio room for the review, so I decamped to Echo Zoo studios in Eastbourne, who had generously donated one of their rooms for the day to enable me to get eyes and, more importantly, ears on the system. Eyes first, however, because in contrast to the relatively understated and compact nature of the Kii Three, the BXT module is hard to miss. It's 80cm tall and incorporates a total of eight 17cm bass drivers — four facing forwards and two on each side panel — and once a Kii Three is in position on top, the combination makes for a 1.2–metre tall and decidedly imposing sight. The BXT closed–box enclosure is constructed in a similar manner to the Kii Three: from two moulded polyurethane structural foam halves glued together, with the join line covered by anodised aluminium trim and heatsink components. A combined BXT and Kii Three weighs a not insignificant 51kg.

Within each BXT, powering its eight drivers are eight channels of custom–designed Ncore Class–D amplification, each amp rated at 250 Watts, so the BXT is not short of power. At the base of the module is an anodised aluminium foot component that raises the unit slightly off the floor and incorporates four adjustable feet. Around the back of the BXT, tucked out of the way near the floor, is a connection panel that offers just a mains input, an XLR socket that's switchable between analogue and AES3 digital inputs, and a pair of RJ45 sockets that enable connection to the 'Kiilink' control infrastructure. Kiilink enables the BXT and Kii Three to communicate and integrates their electro-acoustics, but it also ties in the Kii Control unit.

Working Together

While the role of the BXT may appear at first sight 'just' to be providing enhanced low–frequency bandwidth and increased maximum level, it actually also plays a significant role in directivity control. Used alone, the Kii Three's low– to mid–frequency cardioid directivity can suppress reflections from the rear and the side walls; however, cardioid directivity does less to reduce ceiling and floor reflections between the monitors and listening position. With the addition of the BXT that all changes, because the four line–source bass drivers effectively manage the vertical directivity of the whole system. This provides suppression of floor and ceiling reflections that the Kii Three alone can't achieve. The significance of the directivity function of the BXT module is perhaps reinforced by the relatively modest nature of its contribution to low–frequency bandwidth. Used alone, the Kii Three reaches -3dB at 25Hz, which itself approaches subwoofer territory, but the BXT module extends the bandwidth by only another 5Hz. The BXT module is as much about enhanced directivity control as it is about bass extension and power handling.

Along with obvious integration in terms of visual appearance, the Kii Three and BXT module are integrated both mechanically and electronically when used together. The profiled bottom panel of the Kii Three simply slides into slot features set into the top surface of the BXT module, and a mains output socket on the top of the BXT is then used with a short IEC jumper cable to pass mains to the Kii Three. Similarly, RJ45 and XLR jumpers connect the Kiilink control infrastructure and analogue input signal from the BXT module to the Kii Three.

The tonal balance of the system is just about as flat as is technically possible, its extraordinarily analytical nature over a hugely wide bandwidth is unmatched, and its insensitivity to room issues is unavailable from, as far as I'm aware, any other monitor.

Upright Bass

The Kii Three and BXT system is clearly right up there with the most technologically advanced monitors money can buy, but as before when I used the Kii Three in my own space, and even in the unfamiliar surroundings of Echo Zoo Studios, any thought of advanced technology is forgotten as soon as the music begins to play. While the sense of endless low–frequency bandwidth, apparently unlimited volume, unquestionably natural tonal balance, apparent lack of any traditional 'speaker coloration' and completely transparent clarity are incredibly impressive, it's still the 'party trick' of cardioid directivity down to 54Hz that dominates for me (it's fascinating to walk behind a pair of working Kii Threes and hear the volume fall away). Reducing the effect of the room, even a well–controlled, benign control room such as at Echo Zoo seems to change fundamentally the way the illusion of stereo is set up in psycho-acoustic terms. It's hard to put the experience into words, but the Kii Three and BXT combination somehow combines the explicit, analytical clarity of really good headphones with the sense of real-life scale that only seriously high–performance, wide–bandwidth speakers can provide. The Kii Three and BXT also somehow sound as if they are closer than their physical distance to the listening position. Perhaps this effect is to be expected, because in driving the room less hard off axis, the boundary between the acoustic nearfield (where direct sound energy dominates) and reverberant field (where direct and reflected sound energy are of nominally equal intensity) will occur further from the monitors. Even rationalised like that, however, it still requires a degree of re-familiarisation to the whole experience of stereo.

But back in the real world of pro audio, however capable and impressive is the Kii Three and BXT system, where exactly is the niche for a floor–standing monitoring system that will leave no change from such a very significant pile of cash? A pile of cash that could buy, for example, a whole cupboard full of very fine microphones? It seems to me that for mix monitoring, certainly in nearfield and into mid-field installations, a pair of Kii Three speakers alone is all that's likely to be needed. And for main monitors, in traditional studios that might have the financial clout available, the Kii Three and BXT floor-stand format may well be difficult to accommodate in the same space as a large–format mixing desk. There is a niche though that the Kii Three and BXT seem to me to be pretty much perfectly configured for, and that's high-end mastering studios. If any stage in the music production workflow fundamentally requires what's on offer from the Kii Three and BXT, it's mastering. The tonal balance of the system is just about as flat as is technically possible, its extraordinarily analytical nature over a hugely wide bandwidth is unmatched, and its insensitivity to room issues is unavailable from, as far as I'm aware, any other monitor.

From my perspective, listening to a whole bunch of familiar material at Echo Zoo, I don't think there's really much doubt that the Kii Three and BXT combo is unique, or that it's easily one of the finest monitoring systems available today. I'm pretty sure I could have listened to my entire CD collection and heard on every disc something I'd not appreciated before. The same would be true on all my old Pro Tools mix sessions (actually I listened to a couple and cringed at the new mistakes I heard) and that, I guess, is the acid test. The Kii Three and BXT is a truly remarkably monitoring system.


In terms of directivity control, there are no alternatives to the Kii Three and BXT, but if I had the sort of sum to spend on monitoring that they command, I'd think I'd owe it to myself to hear perhaps the ATC SCM150 ASL Pro, the Barefoot MiniMain 12, the HEDD Tower Main and the PMC IB2 XBDS, for a start.

Kii Control

Kii Audio Three BXTOne of the very few issues I had with the Kii Three back in 2017 was that control, in terms of adjusting the EQ or the directivity, for example, required reaching around the back of the monitor and squinting at some tiny knobs and legends. The same snag arose when switching between low–latency to phase–compensated modes. That all changed with the arrival of the Kii Control unit a few months later.

The Kii Control is a compact, wired desktop unit that offers volume control, input selection and a full range of setup menus. It also offers three additional digital audio inputs — S/PDIF, optical TOSlink and USB — for the downstream Kii system. The paint–finished Kii Control top panel carries a large volume knob surrounded by capacitive touch buttons that select inputs, setup presets (up to six can be stored) and functional modes. A small colour OLED display beneath the volume knob provides visual indication of volume and, in setup mode, the necessary configuration menus.

Around the back of the Kii Control, the three audio input sockets are accompanied by an RJ45 Kiilink socket that enables connection to one of the Kii monitors, from where the other monitors, be they stand-alone Kii Threes or a Three–plus–BXT system, are daisy-chained. Connection to a monitor via the Kiilink also provides power for the Kii Control. A cool little feature of the Kii Control is that it incorporates an infrared receiver that enables volume and mute to be adjusted via a conventional RC5 format or Apple remote handset. The Kii Three and BXT can be operated without a Kii Control, but it brings so much more convenience to the whole experience that I'd say it's pretty much obligatory.


  • Incredibly analytical monitoring across a huge bandwidth.
  • Significantly reduced room effects.


  • None, apart from the cost.


The BXT module adds bandwidth and level to the Kii Three, but more than that it adds another element to directivity control. It's the Kii Three, just much more so.


Kii Three BXT system (two Kii Three speakers, two BXT units & Kii Control) €25,500 excluding VAT.

Kii Audio +49 (0)2202 2356289

Kii Three BXT system (two Kii Three speakers, two BXT units & Kii Control) $36,965.