What is wrong with a sub?

I bought a smaller REL i7.  I was thinking maybe I should go bigger. 
Assuming the same total $pend...
Seems several think having several smaller might be better than one bigger.  I expect bigger can go lower Hz.  If this was for a home theater, maybe I'd get the earth quake / bombs better with a single bigger sub, but for music, which is what I want, that little i7 REL is low enough - I think, then I don't have the bigger ones.

Thoughts on more smaller vs one bigger?

The simplistic statement by, once again, our eric squires, says it all. Purchasing the " correct " ones, and the " set up ", is the key. Subs ( Wawa, makes excellent Hoagies, and this is what they are referred to ) are needed in almost every situation, ime, but getting them to " match and blend " with the main speakers, and the room, is the ticket. I tried running my Lascalas, with a crossover, but based on my listening, I prefer them to run full range, and allow them to taper, naturally, on their own, and bring my built pair of subs in, at that point, where it is the most seamless, to me. I do not hear the subs as a separate entity. Took a lot of time, and work. Test tones with spl measurements can be a wonderful tool, as well as selecting a recording or two, that you feel, is truly wonderful, at that " transitional " point, between the mains, and subs. There are subs, that only excel with home theater, and subs, that only excel with music. Of course, there are subs, that excel at both. Anyone who simply plops down a sub or two, might find it great, but believe me, adjusting, and readjusting, tweaking and some more tweaking, can truly get you phenomenal results. Enjoy ! MrD.

I feel that adding a good Sub to a system can take it where no amount of cable or tweak $$ can bring you. I have Scansonic MB6’s and adding a JLA Fathom 113 v2 took me to a whole other level....it is incredible (to me) to say the least!!! (Now I need to save for a the CR1 crossover and I think, (based on what I have read) I will be satisfied forever.....unless I hit the mega millions, then a pair of M Q7’s will be ordered!!!

Idk, I spend a fortune on a pair of full range speakers and that’s what I expect. I had the salon 2’s and couldn’t get smooth bass from them below 60 he as common in this room, I get the dolly and bring my bipolar sub out of the ht and within a half hour I had flat response to 20 hz... I found nothing musical about what I was hearing, too much mechanical excitement with that much power. Personally I like it speaker that can play reasonably flat to 40hz and roll off after that for music .

Using my brain, not my ears, seems that the lower freq are just fine located in different locations.  I would not buy a full range speaker until I had this figured out.  If the speaker is just more cone speakers of different size and the bottom one is big - why not have it located someplace else?
 
In live music the instruments are in different spots.  Bi-symmetrical (stereo) may be because we are bi-symmetrical with two ears.  However lows are both felt and heard.  I feel a sub which is why for me speakers sound better than headphones.  I'd rather move the sub around.