No, so-called break-in doesn't occur with loudspeakers. If if did, it could be measured, and the frequency response would change, and it's never been measured or documented. During my time testing loudspeakers at Canada's National Research Council, certain loudspeakers were kept around for many years to be used and measured in double-blind testing. The frequency response of those models never changed over many years, nor did the ratings applied to them by the listening panel.
Any "break-in" you are hearing is in your head, the result of your ear/brain accomodating the sound of new transducers.
The psychological effect with hearing and listening is huge -- if you imagine you're hearing more bass response, then you'll hear it! You may also find that changes in mood will affect the way you hear your speakers.
Regards,
Alan
