@microstrip ”This subject was clearly explained in Stereophile Wilson Audio reviews by John Atkinson in the measurements section. The reviews are available at their site”
Hmmm…. I checked two of his Wilson reviews and didn’t see anything on this. This is a quote from Fremer’s review of the XVX:
The heart of the speaker, though, is a version of the micrometer-based aluminum-and–stainless steel gantry system developed for the WAMM, which allows precise time alignment of the mid- and upper-frequency drivers relative to each other and the drivers below. In a
conversation with Jason Victor Serinus, the late Dave Wilson described the goal of the system as achieving "synchronicity of the alignment of the leading edge of the transient."
While flat–front-baffle speakers fixed at 90° from vertical can have an error of hundreds of microseconds, Wilson explained to young Jason, the WAMM's micrometer/gantry system allows for adjustments down to about 2µs. "It's nice if you have phase coherence, but it is not necessary," Wilson said in his chat with JVS. "What I'm interested in is the synchronicity of the leading edge of each note."
Someone earlier asked about the point of time alignment if it can be changed: the point is to time align at the listening position. So you align the mid and high drivers to align in time at the listening position.