Add a subwoofer?

Thanks to all who offered their thoughts on this. I went with one SVS SB 1000. Easy to tinker with settings through the app. Huge positive change in my system. I can see where 2 would be peachy, but down the road maybe. Don’t think I could go back from this. Kind of magic . Box disappears but music gets bigger.

YES! Exactly!!! This is what a good sub(s) can do. It offers SO MUCH more than just more bass. Add another sub and you’ll be equally amazed at what it can do. Subs add ambiance and have presence we can’t know until we get a good one and properly set up it up. Turn the sub off and the music and soundstage just shrinks. It’s amazing. Those who don’t try will never know the difference. Goodonya!!!

You obviously are not familiar with Cornwalls which are capable of prodigious output. They will swamp two 12" drivers. I many systems subwoofers do more harm than good. If the OP is a critical listener and continues along the path he is on he will be very disappointed.

@mijostyn First, the OP has already said he’s not satisfied with the bass he’s getting and is looking for improvement, so clearly their bass output is not all that prodigious in his room. Second, there’s no way a pair of 12” subs that go down to 20Hz -3dB will not add meaningful information that the Cornwalls are simply not physically capable of — that the subs’ drivers are not 15” is determinative of nothing.  And third, he can try the SVS subs with absolutely no risk, and I’d bet big $$$ he would not be disappointed and would not return them.  There are precious few speakers (if any) that wouldn’t get at least some benefit from adding two good 12” subs just to better manage in-room bass issues if nothing else, and the Cornwalls are not “magic speakers” that somehow defy physics and logic.

To improve the sound quality you would need to add two 15” subs and a two way crossover.

I disagree with this completely.  You don’t need 15” subs as even 12” subs will be more than adequate in your situation, and using the adjustments on a good sub and proper setup will be more than fine without an external 2-way crossover.  Could it possibly be better with bigger subs and an external crossover?  Yeah, but at much higher cost but you’ll still get very significant performance improvements without those things and to say otherwise is really just silly talk IMHO.  Try the SVS subs risk free as I suggested above and you’ll see just how much benefit you can get for relatively not much $$$.

I was told that the Cornwall has huge bass and I’d need a very large sub to notice a difference.

You were told wrong — the Cornwalls only go down to the mid 30Hz range, which is why you feel like you do about their bass capabilities. Especially for music you’re much better off with two subs, and as @damusicguy mentioned subs not only fill out the bass but also contribute substantially to producing a more voluminous soundstage with better imaging. Once you listen with good subs properly set up you’ll never go back — it’s that significant. I’d recommend these SVS subs as they’re very good performers, are only about 13” square yet go down to an honest 20Hz, include software to facilitate better/easier setup, and they offer a 45-day trial period including shipping both ways so absolutely no risk to try them. Plus you can get a pair of them for as little as $1149 (depending on finish), which is simply a no brainer to me to at least try. I’d bet big bucks you would not be returning them. Hope this helps, and best of luck.

https://www.svsound.com/products/sb-1000-pro-subwoofer