I think some people don't have an alternative option. It is either the speaker's fault or it is nothing- the issue is never with the listener. This is why this thread drags on. People can't rule themselves out.
Yes, the alternative option seems to be the denominator. Black or white. Never gray.
Either 'break-in' is present in all units or not at all.
Unknown factors is a stick in the wheel when navigating a subject, even though this subject might have an importance as transient as a flick of a switch. But eventually one might pick a side to escape the discomfort of not knowing. Hint: One will usually pick the side that offers the least resistance.
ELAC's Andrew Jones explains in a video that before measuring a woofer driver, they feed it a signal below Fs for a few minutes, presumably at xmax, and later on mentions an example where Fs goes from 50Hz to 40Hz. Then he goes on to explain that the difference is not audible in a closed box because of the box pressure.
Now correct me if I'm wrong: If he believes that it takes 5 minutes below Fs at xmax, let's say 30Hz, to get the driver to spec, then that's 9000 full excursions. Let's say less than half of that, 4000, is significantly audible. Is it possible i takes more than a few secs or minutes to go to non detectable at normal listening levels playing music with 70-120 bpm?
To me, it's seems plausible it would be audible in a vented box, especially low tuned, if the spider, or even but less likely the surround is particularly stiff and complies rather slowly. You would probably also have to follow the speaker manufacturers' recommendation of a slow 'break-in' period .
From post #330 Neumann Speakers:
Concluding, burning-in loudspeakers came from the past when poorly-designed passive systems were
common. Today we have well-designed active solutions that can be used straight out of the box. To
take an analogy from the automotive industry: cars used to require a running-in period of 500 miles
(800 km), these days it is not required.
So at least at Neumann the myth was real in the past.