I recently heard from our local AH Geologist that Graphite is a precursor to Diamond. IOW, Graphite ain't so bad.
I think there's a lot of materials fetishization in audio, mostly driven by the need for various firms' marketing arms to differentiate their product I suspect.
I stopped caring about what stuff was made out of when I heard the Tannoy D700 in the late 1990s. If a 10"
poly midrange (playing up to 1.5kHz or so!) with a fairly standard metal dome could sound that spectacular, then clearly design plays more of a role than materials.
I don't know if it is true, but one reviewer said the S-4EX actually measured flatter than the S-2EX, which in turn measured flatter than the S-1EX, although I'm confident all the TAD designs measure very well.
Probably true as to that reviewer, but I'm sure we're talking margin of error/measurement setup differences rather than "real" differences.
While I've not heard them in the same room, I can't say from memory that the treble from the Be dome one struck me as any better up top than the CG one. (Bass I can't compare, because different rooms.)
IMO, the choice between those three comes down to looks, cone area, and price sensitivity. The translam cabinets of the higher end Elite EX speakers are clearly more expensive to produce than the more conventional cabinets of the diffusion-line ones, and I expect the teak veneer on the higher end ones is more expensive than the wenge/beech on the diffusion line ones. I think the woofers on the higher end line are a bit bigger. Obviously, the diffusion line is cheaper, though currently (given the idiocy with which Pioneer marketed these speakers, and the fact that they came out just before the Bush crash) the price difference may be less if one can find the speakers.
I recently took some in-room measurements (crudely, just using the Quick Measure function on my Anthem MRX) of the three Pioneer Elite EX S-iw691L's* I'm considering using or parting out for my front three speakers, to see if I could just run them open baffle in the midbass (~120-500Hz) to delay the transition to omnipolar radiation a bit. (The concentric is in a separate closed box.) Turns out I can't (drop like a rock from 300Hz down) but the response was the best I've seen in this room from about 500Hz up (smoothly declining sound power), and they sounded just so focused and coherent. And that's with in-wall bezels just propped up on stands!
Andrew Jones designed some winners with this line. Pity so few have been able to hear them.
*In-walls that use the same part number (per Pioneer's parts website) magnesium+graphite concentric driver as the S-3EX, along with sandwich-cone woofers that have a presumably a little less motor (eyeballed average of my three, taken with a Dayton WT3 in windows xp running in Parallels on my MacBook, is Qes=0.85, Fs=55Hz) than the S-4EX's woofers.