Kii Seven

Kii’s impressive new cardioid monitors prove there’s still room for innovation in loudspeaker design.

It was back in the January 2017 issue that we reviewed the the`n‑new and remarkable Kii Three active cardioid monitor. For a significant number of professional engineers and consumer audiophiles, the Kii Three set the benchmark for what is possible from a pair of loudspeakers. And now, after a somewhat extended gestation period, Kii have launched a smaller sibling: the Kii Seven.

I mentioned both the professional and consumer markets, and that’s because Kii have been unusually successful in both sectors with the Three. Kii are one of very few speaker manufacturers who have pulled off that trick. Dynaudio and PMC, for example, have successful consumer audio product lines alongside their professional monitors, but not with the same speakers. A Kii Three sold as a studio monitor is the same as a Kii Three sold as a consumer hi‑fi speaker. Now, this not only demonstrates, as I’ve always believed, that a good loudspeaker is a good loudspeaker however it’s used, it has also impacted on the design of the Kii Seven. Because, while this review is going to concentrate on its performance and suitability for nearfield monitoring, there’s a lot about the Seven that is aimed at consumer applications. For a start, it is to be sold in singles, for use as a mono, stand‑alone audio player. It’s an expensive way of playing Spotify from your kitchen table, but that’s never hampered Bang & Olufsen, for example. It’s perhaps fortunate that this review will primarily concern professional applications, because at the time of writing some of the consumer streaming features of the Seven aren’t fully implemented. The reasons for this, I suspect, are not so much technical as commercial, because navigating the licence demands required to implement multiple streaming services on the same product is far from trivial. However, Kii say that by the time these words are published, Spotify and Tidal streaming will very likely be available or imminently so, and that Apple Airplay, Qobuz and ROON Ready will follow as soon as the third‑party certification processes are complete.

Going Pro

A cutaway render of the tweeter waveguide and lens. The lens broadens the tweeter’s directivity at the top end of its frequency range, while the waveguide narrows it at the lower end.

Let’s leave all that consumer streaming malarky behind and concentrate on the Kii Seven in a studio environment. If you’re familiar with the appearance and design of the Kii Three, the look of the Seven won’t come as a great surprise. It sports a very similar aesthetic and is the same width as the Three, but it’s significantly less tall and less deep. It’s dimensionally better suited to compact studio spaces than the Kii Three – especially in its reduced depth. The Seven’s enclosure construction is of the same foamed structural polyurethane as the Three, with the same black‑finished aluminium trim panels. It comes in either white or dark grey finishes, and Kii say that the custom colour options of the Kii Three will not be available for the Seven.

Like the Three, the Seven has bass drivers located in each side panel, but it does without the Three’s additional two rear‑panel bass drivers. This perhaps makes for easier installation because, where the Three demands at least 8cm of free space to the rear, the Seven can be used with its rear panel hard up against the wall. In fact, Kii recommend that if a pair of Sevens is to be used in close proximity to a rear wall, they are best located right up against it. The Seven does come with one positioning constraint, though, and that concerns space either side to allow the side‑mounted bass driver room to ‘breathe’. Kii Designer Bruno Putzeys put it to me this way: “An obstacle should be further away than the size of the Kii Seven or the obstacle, whichever is greatest.” This of course means that you might need to avoid additional monitors sharing a shelf with Kii Sevens, but without wishing to spill the beans before getting to the end of the review, considering the presence of other monitors if you have a pair of Kii Sevens might be a moot point.

Beam Me Up

The side‑panel drivers are nominally 140mm‑diameter, aluminium‑diaphragm units — the same as those employed in the Kii Three. And while they nominally work in parallel up to around 125Hz, where they hand over to the midrange driver, things aren’t quite that simple, because the secondary job of the side‑mounted bass drivers is to help create the Seven’s cardioid characteristics, by overlapping with output from the midrange driver to modify its directionality. This overlap works all the way up to around 900Hz, where the cardioid character that results from the Kii Seven’s enclosure dimensions begins to take effect. In blithely writing that the LF and MF driver outputs “overlap” to yield a cardioid radiation pattern, I’ve simplified something that’s actually been achieved through the combination of deep electro‑acoustic understanding and some complex DSP. Kii describe the technique as “beam‑forming”, and it involves a beam‑forming filter fed from the output of the midrange driver’s band‑pass filter. The filter’s output is then routed to the bass driver feed after the output of its low‑pass filter. The bass drivers are consequently employed in the overlap region, in parallel with their low‑frequency duties, to manipulate the summed mid and bass driver output to create the cardioid radiation pattern. The schematic of Diagram 1 illustrates the general arrangement of the Kii Seven signal flow and filtering.

Diagram 1: A signal flow diagram of the crossover network and beam‑forming filter. Note that the beam‑forming signal is derived from the mid band, but sent to the LF drivers.

In their conventional role, the bass drivers work with closed‑box loading up to a fourth‑order (24dB/octave) low‑pass roll‑off at 125Hz. In contrast to the Kii Three, where cardioid radiation extends all the way down to 50Hz thanks to the combination of both rear‑ and side‑firing bass drivers, the Kii Seven displays cardioid radiation...