A sub-woofer is a great way to give your sound system a bit more "oomph". I'm a great believer in having a sound like the house is falling down if the movie shows a house falling down. Ditto cars, rockets etc etc.
Today I discovered something about sub-woofers which I thought I'd pass on. On the back of the sub-woofer you frequently find a tiny little switch labelled "phase". This is changes whether the speaker moves in or out when the sub-woofer makes a noise. It's important. If the sub-woofer is moving in when all the other speakers in the room are moving out the noise it makes will tend to subtract from the sound rather than add to it.
So, you might think that you just leave the phase switch in the standard setting and never touch it. However, there's a bit more to it than just speaker cones pulling and pushing. Different positions of the sub-woofer will introduce different phase distortions as the various sounds all bounce around the room. So it might be that flicking the switch will make the bass sound better. It did when I flicked the switch on mine, and it's certainly worth a try.