Although not mutually exclusive, time alignment, phase coherence, and generally "coherent sound" are not the same thing. I took the OP's question to be about how well a speaker "hides" it's crossover point, making it hard to discern where one driver rolls off, and the other comes in. I agree that. in general, speakers that do a good job of this are often designed with time & phase alignment as priorities, but not always. I think if the drivers are well matched, and the crossover points are just right, even a "conventional" 2 way can sound very much like a "one way"...even if doesn't use any "tricks" to delay the tweeter's sound getting to you, like sloped baffles, or complex crossovers. The Linn Kans that I mentioned are just such animals... as are a number of good box speakers like some from Advent, Celestion, or Rogers, to name some more.