sdecker - I am not fluent enough in the art to answer much about the nuances of Thiel's phase coherence. I will point out that your "completely time and phase coherent" is not something that Thiel claimed. The applicable term of art is "minimum phase transducer", which has a complex set of definitions revolving around the least phase error possible given the particulars of the design parameters. To a prior question of whether this is marketing-speak, I say it is not. Jim was extremely careful to not claim anything beyond the real, hard facts. I must demure to more knowledgeable folks regarding bass reflex phase error. Please let us know what you learn from your studies, The Asylum, etc.
Here is something I do know. If the bass extends below the program limit, much of the phase shift problem evaporates. All Thiel models push that lower limit quite deep. Note also that Thiel's bass tunings typically produce low and controlled impedance peaks with phase plot following closely and well, indicating significant attention paid to coherence at all frequencies.
As you know, I am a fan of sealed bass, and I have shared here how disappointed Jim was that his equalized bass solution did not meet better market acceptance. I speculate that a more purist EQ execution, along with true balanced design, and today's better interconnects - that an equalized sealed-box bass might be viable.
Just for fun, you all might enjoy reading about Thiel's first product the 01. It is an equalized 10" 2-way with bass to 30Hz with third order slopes which are phase correct in many ways, excluding polar dispersion, in a 1.2 cubic foot enclosure at 94dB efficiency. That product got us to Germany by 1978 and via Europe got the attention of advante-garde American dealers. I have seen no evidence of audiophile interest in the 01, but it most clearly represents Jim's initial design impulses and orientation.
