Your questions are so advanced that they probably triggered the Echelon in all five countries — hence no replies. Presuming others are dead and they already are tracing me:
$5 that nobody here tried GP yet.
I haven't had a chance to gut the Sony XBA series, but according to the people they are using acoustic only filters. If we ignore tubes length (as, to simplify, it just extends/condenses highs), or weird tube shapes, one can only play with dampers — i.e. only with low-passes.
Dampers (available to us) come in discrete steps, so you are usually limited to about 1-2 dampers choice or 2 × 1-3 two-damper combinations (a hair-range of freedom, but still). One, theoretically speaking, might also try own wool or other materials, or some other mechanical restrictor, like a grill (if have access to micro tools).
I guess they skipped the caps (if they did) because strictly (well, very strictly) speaking a cap — is hardly a crossover. The 1st order slope is so girly (unlike, say, 4th order ninja cuts) that they've probably decided they are better off combining driver properties (incl. sensitivity, power, etc) in a way that could do without it.
I don't think with 2 bores superimposing is an issue in general, and the XBA series is probably a good real-life example — if it really is what I think it is. But I doubt their motivation was THD, phase shifting or anything Bigfoot-related.
I'd speculate their approach is a result of the Japanese design culture, which is especially prominent in modern architecture — with its zen simplicity and shapes that create meaning with just few strokes. Speaking of strokes — I'd even say the sound was designed as a Shodo, but afraid you would be the only member that might agree.
The inside info on SONOVE and especially the Ferrofluids (which could be used to destroy the Earth by inserting a driver into a 1 m hole in the ground and playing «Friday Friday») was probably what triggered the Echelon and wiped out the members of this thread. But I'll tell you what I think since they can't tr
