breaking in a sub

whats the correct way to break in a sub?

Car audio subwoofers and other speakers are built for extreme changes in climate and tough conditions.  Therefore they need less TLC when they're new than, say, audiophile-quality home speakers.  If a woofer needs a specific break-in session (and I don't know of any specific ones that do), the manufacturer will say so in bold print in the manual .  If nothing is mentioned, then just play the sub at moderate levels for the first 5 hours or so, and let the sub loosen up.  Then you can recheck/reset amp gain and crossover settings.

But if you want to watch your sub excurt to its fullest with very little power applied...which is cool to watch, BTW...there is a way to do this.  You need:  a test tone CD with a frequency recorded that matches your sub's resonant freq (fs).  You can do this at the car location, and the sub is not installed yet (free air).  Play the frequency at low volume, just turning the volume up enough to get close to maximum excursion from the sub.  10 minutes of this is a break-in session.  Your sub is now ready to be mounted and amp settings made at this time will be good.