I suspect surrounds on midrange cones and woofers become more supple as they are used. Though that could vary widely depending on the surround material. Usually showing gains in lower frequency response and probably dynamics too. I was also told by a very prominent speaker designer that the caps in the crossover will "sweeten up" with several hundred hours of use. I guess he means the caps become more linear over time and thus differences could be audible and measurable. I would agree that if the speaker in question were to sound bad right out of the box, other problems might exist.
Can speakers sound worse during break-in period?
I purchased a NOS pr of speakers ( I’m not disclosing their name. Not interested in hearing from their haters) and was really liking them before I started to seriously break them in. It seems like after 24 hours they seem to have changed and sound worse, or not as good as they did. Are they just going through changes with some drivers opening up faster than the others? I know there are many components involved in this process and some might be a head of the others. I’m assuming that’s the case and when everything comes together they will sing.