What is wrong with a sub?

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. 

Never had much success integrating a sub in a 2 channel system.
Always found it reduced upper frequencies transparency even when set up right.

Guess the benefit of being old and new (to audiofile stuff ) is I have not had that issue, which was the reason behind the OP.

Integration not always easy