diduknowthat
formerly liuliuboy
because they are big and also because they are ran by a lot of power; they can "vibrate" quickly.
another thing is that all the air they are pushing is exiting through small holes.
if you were to build a box with a hole in it, them put a plunger in the back, you'd be able to push the same amount of air as a sub does in one stroke.
Well a subwoofer doesn't exactly vibrate "quickly". Good ones go down to 15-20hz, as compared to tweeters which vibrates REALLY quickly.