can subwoofers make things worse?

Thank you all for the replies. 

To answer some questions asked of me. It would be used for both, but primarily music - to add the bottom octave my speakers don't reach (48hz - 23khz). 

 The speakers are 2 feet from walls, and 6 feet apart and i sit 5 feet from them, dead center. The speakers "disappear" and fill the whole space in front of me. 

I live in a rented studio apt with no one underneath me. No issue with adjacent neighbors - only the guy who lives above me. He's been pretty cool so far. I wouldn't play the sub loud - just subtle addition of that low bass. 

I barely have room for a tiny single sub. A pair is not possible. 

Ive read recommendations for all 3, but the SVS micro may be the best combination of size, cost, and being able to set it from my listening position. 

Of course - last night i listened to James Taylor and Billy Joel and didnt feel like i needed a sub. Sounded great to me. But the common thought is, as soon as i add a sub ill hear what i was missing. I was told Best Buy Magnolia has SVS and KEF subwoofers. I can try to see them there.

In a heart beat 

The tools you need are DSP EQ and measurements.  Additionally, high pass filters and plugging ports in the main speakers, along with bass traps can also highly improve the integration and benefits of a sub, but the EQ and measurements alone are the minimum required to ensure any sub can go in without turning the room into a horrible sounding mess.

I picked up on this linkj reading  Audiogon.   His argument is that subwoofers are inherently out of phase alignment with the speakers.     Its worth checking out.

https://soundoctor.com/whitepapers/subs.htm

His argument is that subwoofers are inherently out of phase alignment with the speakers.

That’s why subs have phase adjustment.  Duh.