In many speaker and amplifier reviews I have read, there is a mention of "break-in" period. For example "initially the speakers sounded harsh, but after 100 hours of break-in period, they sounded great", etc.

Questions:

From the viewpoint of the speakers, why is this break-in period needed for them to sound better? I would like to understand it from an electrical/physical charateristic and something that is measurable. For example, maybe the crossover capacitors not fully-formed, the woofer spider suspension is not sufficiently pliable, etc.

I am sure that wood for cabinets, the copper or aluminium wires for voice coils and the speaker magnets themselves should not change their properties in 100 hours to make the speakre sound better.