Small or large sub for music

"It’s nice to use subwoofers for theatre systems. The best option is to buy speakers for your audio system that do NOT need subs."

Why? The best speaker placement for imaging and bass are generally mutually exclusive!!!!! Are you willing to place 4 main speakers around your room at the optimal positions to minimize standing waves (ala a swarm setup)?  Show me a full range speaker system that can go flat below 20hz that costs less than $10,000 a pair and is optimized for placement in the bass where the imaging is the best. The system in my office (a used set of Totem Mites and a Rythmik L12 for a total cost of $900) does that comfortably (when I say comfortably, it starts to roll off at 23 hz is and 1 db down at 20hz).

Even with "full" range speakers, good subwoofers with proper setup make a great difference. The problem is most people want to plop them down, spend no time setting them up, and then turn them up too loud resulting in a bloated, slow, plodding sound.

It takes time to get a sub properly setup and integrated. In my office, it took over 100 sweeps with REW with the sub in 3 different places to get a really good integration where it disappears. It can take a lot of playing with phasing, crossover and placement to get it right, but once you do, you can enjoy truly full range sound that lets you hear things you never knew existed.

I have a “full” range speakers supported by 2 JL212 subs. The subs Integrated with the main speakers so well that now I cannot listen to the system without the subs. The quality of the subs is very critical. 

When I first purchased my Wilson Max II’s and was talking about adding a new sub, someone on this forum laughed asking why I would even want a sub, using the Wilsons.  I purchased one JL Fathom 113 and it was great.  I then added a second one, placed in the opposite corner diagonally facing each other and it really smoothed out the response.  I use a DBX subharmonic sythesizer, along with a Sony  TA-E2000ESD, as a separate remote volume control.  The Sony has a parametric eq that I filter down the 50-60 hz frequencies and turn my crossover point on the subs, as low as it will go. I come out of my line stage’s tape monitor output, so I can isolate the bass.  Because the Sony has a motorized dial volume, I can pretty much tell, where to set it on the clock dial.  When I turn my main speakers off, just to hear the bass level, most of the time the bass is at a fairly low level and is not overpowering.  I get an almost seamless contribution from my subs.  I can also turn my subs off, to hear what it sounds like, without the subs.  The difference is almost always very subtle, but can hear a definite improvement with the subs.  I built some hefty stands, 18” tall with metal castors, so I can easily roll them around the room, to establish the best position. I think the trick, is to set your sub volume, as to not make them shake the room.  They’re like a quartet, each contributing, but none overpowering the other. They definitely have their place in my system.  

Since you have both why not just try them both and use the one you like the best?

There are no speakers currently manufactured that " need " subs. If a person wants to add a little more foundation to the music they may choose to add a sub or two or one might suppose a swarm of subs.