To Doug Schneider,
Thank you for your generous response to my question. You continue to be one of the elite audio reviewers and, it would seem, a genuinely good guy to boot.
Is it possible to ask KEF’s Johan Coorg about the Uni-Q drivers used in KEF's various models? Apart from the color and surrounds, it's possible there are some differences in construction quality or materials or tolerances such that the best efforts are reserved for the Blade and perhaps the LS50, which they clearly consider a statement product at some level. Of course, the cabinets are also very different between the LS50 and the R-series speakers, and the parts quality of the crossovers may be another area of difference. The specified Uni-Q mid-frequency to high-frequency crossover point varies across these models as well: 2.2kHz for the LS50, 2.8kHz for the R500, etc.
I defer to your much greater experience when considering your assessment of the voicing of the LS50, but so far (I've had mine for a couple of weeks), my reaction to them is that they are indeed quite neutral. Regardless, I think my sense of their "magic" is more related to the Uni-Q than to the voicing, though I may be wrong about this. The speaker has a remarkable continuousness and seamlessness about it, particularly noticeable in reproduction of piano. I've owned single-driver and similar designs before but don't recall quite this level of success. I'll have to listen to some of the R-series models to see if the addition of bass drivers "disturbs the force."
You make good points in this, but I can't address them because I don't have the technical insight into the designs. So I did as you suggested and sent your questions to KEF's Johan Coorg and this is what he said:
It may be of use to go into a little more depth about our Uni-Q development:
The drivers from the Q series, R series and LS50 all share a common lineage. The Q-series speakers were the first to be developed around 2010 as a concerted effort to get some of the features of the Concept Blade drivers into "affordable" loudspeakers. Over the years following the launch of the current Q range, we have refined and tweaked the drivers, resulting in those used in the R-series and LS50 drivers.
A quick summary: There are 5.25”, 6.5”, and 8” Uni-Q driver arrays in the Q range. The driver in the two-way R100 is based on the Q100 driver, but has a different cone (which you can identify the driver by from the font) and some tweaks to the tweeter and midrange magnet systems to reduce the distortion (addition of shorting rings and a copper cap).
The LS50 driver is a special edition of the R100 driver with a different voice-coil spec (to give a slightly different bass response in the system). The surround is also different and gives a slightly tidier upper mid-frequency response. We slightly adjusted the geometry around the tweeter-magnet outside diameter, also to improve the mid-frequency response.
The R-series Uni-Q as used in R300, R500, R700, and R900 is better than the LS50 one. The tweeter is the same as the LS50 tweeter. The small surround on the R-series mid-frequency driver greatly improves the response of the midrange and also improves the tweeter response as it presents smaller "disturbance" in the waveguide.
As ever with loudspeakers, people have different tastes -- we have come across many who love the LS50 (79Hz, +/-3dB), but require more bass and scale. They often choose the R300 (50Hz, +/-3dB) or R500 (46Hz, +/-3dB). Some others, albeit fewer people, go for combining the LS50 with a subwoofer. But most appreciate the raison d'être of the LS50 as a purist point-source monitor, and, given the right acoustics and positioning and driven by quality electronics, are more than happy with the bass extension.
KEF's fundamental approach is to try to offer differing designs with engineering trickled down as far as possible from the very best, to suit varying tastes, but trying also to maintain a "family sound."