Thank you! I like this answer. My new F228Be have about 50 hours on them and whether they required break in or not (doesn’t seem like it) they sounds great.That would be me...
All mechanical devises are designed & manufactured within the boundaries of their pre-determined specifications. Those specifications are either achieved at the time of manufacture, or after a breakin period. Years ago, for a combustion engine to be at spec, it required a breakin period, but nowadays engines are manufactured at spec on the production line, so they no longer require breaking-in.
A speaker is no different. Depending on what materials were used & whether it was manufactured at spec or not, determines whether a speaker needs to be broken in or not. Also, like all other mechanical devises, a speaker will slowly wear out & lose spec over time which can obviously be measured. Also, a speaker cone made of paper is going to be in & out of spec at completely different times & for different lengths of time to a speaker cone made of aluminum.
So what does this all mean? In the pro-audio world, everything "mechanical" is broken in because it just makes sense to do so, but that doesn't necessarily mean that everything mechanical needs to be broken in or that it can be measured or heard (when new), but because there is no blanket answer that covers all possibilities, breaking in has just become the logical thing to do. At the other end of the scale, all speakers will eventually wear out, lose spec & sound completely different which can also be measured...
Btw, did you see that the new Corvette C8 limits revs until the engine is broken in?