Just took a look at this thread; the title didn't obviously say "read me" so it took me a while to check it out.
Lowpass drivers lag behind highpass drivers in both time and phase, and a sloped baffle can introduce a limited amount of compensation for that, along with a tilting of the driver axes (which may be desirable in some cases). In and of itself, it's not enough compensation to make much difference, but could be part of a full-scale time-coherent effort such as Roy Johnson's magnificent speakers.
"Phase coherence" and other phase-based terms have been used loosely and don't necessarily mean what we think they mean. For instance, the woofer can lag the tweeter by 360 degrees at the crossover point, yet the system could be called "phase coherent".
Roy's designs are truly "time coherent", and that puts them in a different league; they're the real thing. His designs do everything we might have optimistically hoped for, such as waveform preservation, when we first came across the term "phase coherent".
As for how small manufacturers can do decent design work without access to an anechoic chamber, one answer is time-gating. That's a measurement technique wherein the microphone is turned on briefly to catch the direct sound from the speaker, and then turned off before the first reflection arrives. Time-gating has limitations relative to what can be done with a true anechoic chamber, but it sure costs a lot less.
Roy, I'd be very interested in reading any clarifications you care to post, and have zero problems with your making specific references to your products. The inherent rapid rolloff at the bottom end of the horns I use prevents me from ever doing what you do without totally changing directions (and going back to college), but that doesn't lessen my admiration for your work.
Duke
dealer/manufacturer
