I think you've got something there, SpockT!
The discussion has mostly centered around mechanical break-in, but I rather like your observation about humidity. Even though the aluminum in the cones would be unaffected by changes in humidity, the entire speaker system (including all of its components made of other materials) could, conceivably, maybe be impacted by acclimating to the temperature and humidity of a new environment. Whether it's enough to hear or not, I don't know or care. But I had not considered the impact of temperature and humidity. Of course, if those are the agents of change, then "break in" of the speaker (rather than your ears) could be accomplished without playing music; just let the things sit and get used to their new space.
