The difficulties of T/P are substantial and the prevailing wisdom from Canadian Research Council, Harmon, etc. is that the ear-brain doesn't care. We here lean toward the opposing opinion. And I am personally convinced that T/P as executed with first order slopes is worth its considerable effort.
Andy pointed out that the coincident driver eliminates the upper frequency lobing, plus Jim managed that inherent dispersion problem quite well via very low cross points. A seated listener at 8' or more distance gets a properly integrated wavefront, although the summed energy into the room has some potential unevenness. But I suspect that Thiel's polar patterns would hold their own against Von Schweikert and others who manage T/P via high order slopes.
I can't decipher whether Magico and other high-rollers are really dealing with T/P. It seems that such measurements aren't often included in reviews, or such products don't submit to reviews which do consider T/P. Lots of folks are using 4th (24db/octave) slopes to produce zero phase, non time-aligned hand offs. Zero phase means 360° (one cycle) revolution, so the signal harmonics are separated from the fundamental, but not completely scrambled. 4th order, whether active, DSP or passive does introduce pre-and post ringing and time smear at the XO point. Minimum phase is a term of art to describe phase and time in natural alignment considering deviations from flat amplitude response, as in crossover slopes. The lead and lag components add and cancel, producing no ringing or time smear, producing an added output with flat amplitude and phase with no ringing - allowing time alignment via physical offset.
Vandersteen and Thiel were chasing the same goal. Meadowlark seemed similarly aligned, but the only product review I saw was an early model, which didn't quite do what it claimed. Does anyone here know whether Avalon or other highly regarded speakers worked in the T/P domain?
