Driver breakin period, what’s the science?

So have these new speakers and been told they need a hundred hours to be broken in, and then sound will improve.

What’s going on as break in occurs?  More important for tweet, mid or bass?  
My initial listening has simple vocals/music passages sounding very good, and more complex and very layered sections that may have potential to improve.  
I doubt there is very much to it. It is mostly your ears getting used to the new speaker. Yes, there may be some break in happening like anything else, but no where near as long as some suggest.
Are you using ported speakers? Is that how the spiders enter the enclosure? My cabinets are sealed enclosure.  HVAC
Relative output of your driver's did not change more than a fraction of a db after the first few hours. The crossover points may have changed a very small amount.
Back in the day, we broke in studio woofers with a Crown DC-300 input pad plugged into the wall. Played 60Hz for at least 24 hours before swapping. Never measured for any level difference, but sonically, un-buzzed woofers sounded flat and lifeless. Old woofers were sent back for reconing. Mid/Tweet drivers could be reconed on site. Techs used to hang shredded diaphragms on the wall marked with the band / musician who blew them.

Note that the above speakers were abused and suffered mechanical failure. 

To the long break-in crowd:
Do you log listening room parameters Temperature, Pressure, Humidity, Line Voltage? see  ieLogical WinterBlues
How accurate is your level control? [Have you ever verified it?]
Have you verified the amp is operating at EXACTLY the same BIAS point?

My 35 year old speakers break-in CONTINOUSLY due to the above. The CBLF is infallible and contributes not...
Psycho acoustics? After MC comments, this makes no sense.

Everything makes sense. You just have to look at it logically. A lot of people are psycho. Unable to distinguish fantasy from reality. Some of them hear sounds, don't know what they are. They are psycho-acoustic.
Years ago when I received my Shahinian Diapasons I remember them taking a long time for the sound to settle in. For the past year I have a pair of Bache Audio Tribeca speakers and they sounded great right from the start. If there was any change with these speakers it is unnoticeable. 
My experience tells me that the crossover plays the largest role with speaker break in. The Diapasons have a very complex crossover, while the Tribeca's use a cap on the tweeter and a coil on the woofers. The wide band is directly connected to the amp.