I agree with @mijostyn - my experience is that adding a second sub resulted in significantly better sound compared to using a single sub. The designer of my speakers (Michael Kelly with Aerial) has commented about the benefit of multiple subs in the Aerial literature, in addition to saying more than two subs is even better. As full disclosure, at the time I added the second sub I also switched from larger, (almost) full-range, bass reflex floor standing speakers to moderate sized, acoustic suspension, stand-mounted speakers. The stand-mounted speakers are solid to about 40Hz and the subs roll in at that frequency. The result is a vastly superior ability to tune the bass to the room, lessening of nodes, absence of boominess, more power/drive in the low frequencies, and greater clarity up through the midrange. Both sets of main speakers utilize the same midrange and high frequency drivers so the only difference is in how they handle the bass. It is a bonus that the subs have their own remote control, making it easy to dial the bass volume up or down to sound best with specific musical content.
Single vs. Dual Subs
It's common wisdom that dual or multiple subs help smooth out bass response in different spots in the room, but what about for a dedicated listening room with a fixed single listening position? What do two subs add to the music presentation that a single dialed in sub is missing provided that single sub is dialed in perfectly for the listening position?
Caveat: not interested in the SWARM method or multiple subs at the moment, strictly comparing single to dual subs
Caveat: not interested in the SWARM method or multiple subs at the moment, strictly comparing single to dual subs