KEF R107 loudspeaker 1986 Measurements
I decided to measure the 107 before doing any serious listening (something I usually do not do) so I could sort out the KUBE options and optimize the 107's response for my favorite placement. With the bass cutoff set at 18Hz (the setting I used for my auditioning), the 107 puts out energy down to 20Hz, which is as low as I can measure. In fact, bass output is so extended that the 107 can readily overload a listening room. Standing-wave resonances were excited in my room like never before, including an especially nasty one at 60Hz. The contour control cannot cope with such narrow-band peaks or dips. It certainly works as advertised, shelving the response below 160Hz, but that only lowers and raises the peaks and dips without flattening them out. What is needed, in the absence of a digital time-domain equalizer, is a half- or third-octave equalizer that can work over narrow enough bandwidths. I was hoping to try Audio Control's "Richter Scale," but it did not arrive in time to meet my copy date.
The Q control does affect the prominence of the bass line, and is best adjusted for a given placement by ear (using, say, double bass pizzicato) until the proper heft and decay are achieved. Ultimately, the choice of proper Q is a matter of taste and room acoustics. In my room I preferred a Q of 0.7 for placements far removed from room boundaries and a Q of 0.5 for near-wall placements. From about 200Hz to 20kHz, the in-room response is exceptionally flat and easily meets specification. This sort of response smoothness is quite an accomplishment for a conventional speaker; only large-area electrostatics in the near field have measured better in this respect.—Dick Olsher