Subwoofer breakin

honestly I dont believe in "Breaking in" subs but the only difference I could ever see is that they will be flexed out and ready to move massive amounts of air but to tell you the truth brand new they should be ready

If you really want to do it, you should hang the speaker (no enclosure) up in the center of a room and feed it a test tone at the frequency of its fs.  If the fs is 22Hz, send a 22Hz tone to it for about a 10 minute period, wait awhile, then do it again a few times.

The point being that the speaker's impedence is at a very high point at fs, and the speaker will flex to its maximum without getting overheated.

I've done this once, just to try it out.  But I think that just playing a wide variety of music at normal listening levels after the installation will do the same thing.  Do this for a few days with the head unit at half and the amp gains at one-third, to be on the safe side of clipping.  Then, after the speaker has flexed for this amount of time, go ahead and set the gains properly, which requires that the system gets max'd to its extremes.

Car audio speakers do not generally need the same sort of break-in that professional drivers or home theatre drivers do need.  Car equipment is designed to be tougher and to handle temperature extremes and tends to have more flexible components.  That being said though, ANY speaker benefits from break-in and will last much longer if you allow a break-in period. 

I usually recomend listening to your normal musical taste material at moderate volme (no more than 1/2 the equipment's capability) for at least 5 hours total time (not necessarily all at once) before you turn the volume up for the first time.  And then when you do turn it up, do so slowly.  Hitting a brand new sub with 100% of its rated power right off the bat can pop the voice coil right off the former (cone doesn't move.)  I have seen it happen.