Dual vs single sub

What’s your purpose in uograding, SPL, bass extension, or sound quality? 
 
Also, I know SVS has an upgrade program, but their higher end loses bang for buck due to the digital screen, remote mobile app control, room correction, etc. I mean, if you want those things, it’s great, but from raw performance, a Rythmik F18 smokes the SVS SB-16 Ultra. 
 
Dual subs give a more even response, better seat-to-seat consistency, and lowers localizability.

@don_c55  
 
You almost never get stereo bass unless your room is very dead and you crossover high. I have a single sub crossed at 80Hz that’s decently far from my speakers, and in my wooden-floor open floorplan with no treatment other than a rug, I almost never hear where it’s coming from.  
  
@bryantdrew  
 
I would say dual Rythmik F15HP, dual bundle brings it to <$2400, they are very “musical” and are +/-3dB down to 10Hz! I mean, if you have money to blow there is also their F18 :).