Originally Posted by Steve Goff
But my question is about intermodulation distortion. Have you performed any tests showing that the intermodulation distortion on the current crop of KEF speakers (or earlier ones with similar drivers and crossover regions) is audible to such an extent that it compromises the accuracy of the speakers? Most of these speakers cross over between the woofer and midrange at about 400 Hz. I understand and agree with your conclusion that the spinorama measurements correlate well with listening tests. Have you performed listening tests that show a similar relationship between listener preference and intermodulation distortion?
IMO there's some weird but apparently long-standing institutional bias going on at Harman against concentric drivers. I speculate, but maybe this unwarranted bias stems from ALTEC having the niche as the American coaxial speaker company with their (not very good) 604 coax, or because the Urei “monitors” Harman finally killed off genuinely sounded bad?
At all but one of Andrew Jones' stops - KEF, Pioneer/TAD, ELAC - he introduced new and innovative concentric drivers. Two very different ones (IRIS and CST) at Pioneer/TAD. The one exception: Infinity!
It's their one blind spot, and an unfortunate one because it slightly undermines the wonderful and beneficial work they’ve done and shared.
The "air" stuff is also a little disingenuous, because air in the treble depends on the dispersion of the waveguide, which to large extent boils down to the depth of the waveguide. That waveguide can be a midrange cone or a fixed piece. Some concentric drivers, such as the TAD units, have quite shallow midrange cones. Also, as Dr. Toole points out in his excellent book, different listeners have different preferences as to directivity. Dr. Earl Geddes asserts that some of it is based on program preferences: wider dispersion for people who judge speakers based on orchestral or chamber music, narrower for studio work. I do not know of support for that theory in the literature though.
IMD - sure, I guess, in a small coax asked to play too low too loudly. Here is a great article with demo recordings comparing a JBL cinema setup with little KEF LS50s, with and without subwoofers on the LS50s.
I've personally tried to listen for it in speakers based on concentrics from KEF, Tannoy, TAD, Elac, and Pioneer. I’ve never really managed to hear it.