If you haven't read this quite detailed article on Audioholics, you should:
Speaker Break In: Fact of FictionFor those in a hurry, here's the conclusion at the end of page 2:
Conclusion
In an electrodynamic driver featuring the usual surround-diaphragm-spider construction, driver suspension mechanical compliance plays a key roll in determining the measured value of various driver parameters. All of these parameters will shift as the mechanical compliance of the driver's suspension shifts in value. The bulk of a driver's compliance shift will occur at the time of initial burn in.
Subsequent shifts in compliance are largely temporary in nature. An example of one such mechanism contributing to such temporary shifts is that which arise from the elastic deformation of butadiene-styrene surrounds. Given sufficient time to recover, these changes tend to reverse themselves and the driver returns to its pre-stimulus state.
As the enclosure compliance in both totally enclosed boxes and vented cabinets dominates that of the driver for most practical implementations of either type enclosure currently in production, any potential changes in system amplitude response attributable to changes in driver suspension mechanical compliance tend to be minimized. Normal production unit-to-unit driver spec variances can affect final amplitude response of a system to a larger degree than that expected from normal pre- post-burn in driver suspension compliance changes.
