How does adding a second subwoofer improve your systems SQ?


The title pretty much covers my question. Thanks for any insights or comments.   
markj941
With two subs (or more), you often can get more even bass frequency response. You have to be willing to find the best spots for them.
Search DBA, distributed bass array, Geddes, and study posts of noble100, audiokinesis, and millercarbon. Geddes worked out the relevant science and acoustics that is the basic foundation for using multiple subs. Duke as the only current maker of these type systems has by far the greatest technical knowledge and experience. Tim was a fairly early adopter and has posted extensively on just how well the Swarm works. And I myself used their combined knowledge in building my own DBA. https://systems.audiogon.com/systems/8367 Which is how I know the more, the better.
@erik_squires Another great post! Really well done, and attractive to boot. I’m wondering if you can tell me what the sonic difference might be if I added a second subwoofer? 
The reason that I ask is that in my present set up, my single subwoofer provides enough bass and it is fairly clean and tight. I had to connect the subwoofer to the two mono blocks and that provided a speaker level input into the sub.

 Many people have said that I really need to have a second sub woofer but if I were to get another one what would I notice about the sound (assuming that I could place them correctly)?