In reply to:
The reason is that there are a lot of things we don't know how to measure. Like soundstaging and resolution. Graphs of horizontal dispersion and noise floors do not prove anything, though they are useful.
Specifically with regard to the speaker break-in, we should not diffuse out or mystify the role of physical measurements. There are only a very limited number of visco-elastic moving parts on the speaker drivers that
could exhibit the use-dependent physical changes, namely, the spiders, surrounds, and the cones/domes themselves. I cannot think of anything else that could possibly change permanently. In other words, these changes, if they are indeed physical, must manifest as obvious changes in the driver's T/S parameters that are readily measurable (i.e., resonance frequency, quality factors, equivalent air compliance, etc.). There is little room here for unmeasurable, mystic alterations.
I do agree that the currently available measurement techniques do not completely cover what we may perceive as a change the sound quality. But specifically in the case of speaker break-in, the actual change in sound quality must be the direct consequence of these
measurable physical changes in the driver parts.
