I just posted this in response to a question on another thread but thought it would be useful here to assemble links to
Axiom's position on break-in (they recommend two hours for the speakers). Here's
another post by Ian on break-in. And
one more by Alan Lofft.
FWIW, as part of my speaker auditions I "broke in" three sets of speakers over the last two months (Athena AS-F2, M22ti, and M60ti) because Athena recommended it in their owner's manual. (I ultimately kept the M60s). I did not notice any change in sound quality in any of the speakers following the break-in period. I wish I had because my wife and kids thought I had gone nuts.
