Do you adjust your subwoofer

I have a Hsu Research STF-2 which has worked fine for me with the Vandersteen 2ci. I have tune the sub where is seamlessly with the 2ci to a point where is like a house curve response. This usually a boost in the bass region and a downward slope to the high end region where usually around -3 to -6 db below reference. So to answer your question,  you would need to do it once after you figure out the right placement. Find a well recorded music with a full spectrum response.

I use one sub in my room and it has worked fine for me. But again I use acoustic software that has RTA, phase , and coherence. If you are listening in one spot only, one should not do much adjustment unless you trying to fill an area that requires more area to fill like for HT where their is more then one person in the room then I can see your point in using an array configuration.

@liquidsound 

I also have a small listening room. I have my sub is also in between my speakers but I have it slightly off center. This give me the the best of both worlds with seamless and tight bass. My Vandersteen 2ci has the adequate bass for the room but I want to be able to reproduce better subbass frequency that I am able to control.