Depends on the subwoofer as well. Rubber surrounds tend to become more rigid than foam. I just went through a -30 and -40 winter and nothing went haywire. Never went from -40 to full blast though.
A little frost on the amps and dust caps, but nothing too bad. When it hit -40 my normal idle voltage of 14.4 ended up at 15.2 haha. Oh, Canada...
Just use common sense and you should be fine.