its not as bad as the literature makes it out to be. 1 good sub placed right does a great job of the bass. there may be a couple of frequencies which may need to be cancelled out with 2 so 2 is better but not double better
The problem is getting that right place to place it and then dial in the right cutoff, volume and bass . it took me months.
IN between one of my subs has a problem with a driver so had only one and it die maybe 75% of the job a stereo sub did..at least that is my experience. the %age is not exact but i believe representative.

IN between one of my subs has a problem with a driver so had only one and it die maybe 75% of the job a stereo sub did..at least that is my experience. the %age is not exact but i believe representative.