Factory Subwoofer?

[deicustoms1]

I didn't find anything on this....so

There isn't a subwoofer with the standard system right? But there is one with the monsoon system. Where does that subwoofer go, and would I be able to add my own sub to that space?

I'm trying to add some bass to my system, but don't want it to be visible/take up space. Any ideas? thanks