KEF KC62 — An applied review and guide for setting up an audiophile desktop setup (Part XXX)

Now we quickly recall the subwoofer history before we start:

• Velodyne MicroVee: that was indeed the first and a remarkable subwoofer for its size; i think now there is a renewed version of it, offering acrylic transparent glass such one sees the inner tech–a marvellous piece of engineering. Somehow the levels below 40hz seemed to falloff very quickly. Now that is true, but i also know the room response much better now and thus know that to some extent the room was camouflaging the low output: not so bad after all.
• Then the idea was to get a KEF KC62 (which indeed was a very interesting piece of technology with lots of aggressive DSP correction in the lower ends), which was somewhat similar sized but promised much deeper end, up to 10Hz (!) which is weird if you see the size of it. The integration was quite smooth, i remember the Adam D3V speakers with it resulting in quite a pleasant signature, airy, lightweight etc.
  Back then, i was still quite illiterate when it comes to deep understanding of phase and timing, but still pleased by the sound of the system. At some point, of course, the impact in the deep end was not sufficient so i got an
• SVS SB-3000, which was a good support for a while, very impressive deep end capabilities, but ultimately a bit too much group delay by again aggressive DSP below 40Hz. But during that time, i learned how to time and phase align the devices.
• Before switching to the Velodyne SPL-X 10, i did lots of research on subwoofer construction types, which is summarized in some of the recent articles. There is a little detail i need to correct i think, and that is that the servo mechanism in the new velodyne model is only partially analogue, which makes it a little less rigid, but also more musical and linear in the group delay response. This means that it does not have a physical sensor any more. It means the Velodyne people somehow learned from the elegance of PSI Audio or Abacus in the sense that the membrane is not touched any more. In earlier versions, the membrane was literally measured for deviations, and that is quite a unique and fascinating concept which immediately resonates with audiophile fundamentalists: one measures the last line of defense between the ear and the device, the membrane. Not the current, not the coil, not the housing response, but the membrane, which hosts all errors (leaving tiny air motion and temperature entropy in front of the membane aside). This will lead to Velodyne DD+ models probably even gaining value now that they are not produced any more.
  There is both a fascination, but also some sort of conceptual overdrive in physically measuring the deviations membranewise: intuitively, one would not like to touch the membrane in any way, on the other hand, that is the most precise way to do it.
  So in the new SPL-X models, it works a little bit different:
  – no physical sensor, the feedback is voltage and current based and follows a modelling, like others do it somehow as well. It seems as if the basic concept is quite close to the PSI audio model, adding a modelling layer. In that sense, it is a continuation of the PSI audio concept
  – the membrane is thus not physically corrected, but current and voltage are

This is a bit different still from the dolifet concept, which is doing its thing at the output of the amplifier, correcting deviations between the target current and the measured current. Completely no knowledge about the system. Why does that work at all? It works because 80–90% of distortions emerge from the power amplifier non-linearity, changing impedance of the speakers and voltage limiters through protection circuits.

So where does the system stand now?

I am currently working on a handbook encapsulating all learnings, theory and practice that is needed for setting up a reference grade system. This also goes hand in hand with more higher-order tuning parameters, which means that the linearization of the system is to some extent finalized, but that does not mean it sounds perfect yet: balance between deep and high frequencies, total energy of deep frequencies in symphonic recordings etc. will finally be markers to arrive at a well balanced, musical but very precise signature.

That marks the current state.