bass is a whole lot more than 100 hz and down. Listen to some well recorded solo acoustic stand up bass and you will see low fundamentals and then harmonics well, well above that. Quality is more than fixing frequency response issues caused by small rooms. Swarm is an approach to frequency response averaging with constructive and destructive interference- BUT a cheap resonant cabinet that is out of phase to the input signal is hardly what I would call high quality. A poorly damped cabinet will ring far above the fundamentals. so SWARM or any other sub done right is way more than just buying lots of them....
IF you have an RTA ( there is that pesky Fourier transformation again, perhaps a revisit w Keith is in order ) i suggest listening to well recorded acoustic bass....Pretty sure there is a screenshot in my virtual system pics.
Also, most audiophiles actually dig SLAM, which is about 80-160 hz.
enjoy the music, all of it.