I would solve the >30hz range first with the local PA woofers (21's etc)
Power it with a nx3000d or 6kD
Because 90% of bass is 30hz and above.
It's where all the explosions and dance/pop/rock/country/metal/dubstep/rap music is at.
<30hz is for earthquakes, pipe organs, BassILoveU, and other such extreme basshead music.
It's much more rare to find 1-19hz content, and much more infrequent when it occurs. For 3 hour movie, you might not get any, or it might be only once or twice etc etc.
It also takes a lot of power, cone-area, box space, and amplification/breakers. Every octave deeper gets 4x more expensive.
1hz is 4x more expensive than 2hz
2hz is 4x more expensive than 4hz
4hz is 4x more expensive than 8hz
8hz is 4x more expensive than 16hz
16hz is 4x more expensive than 32hz.
Then save up for a pair of sealed SI-24's and a FP14k + miniDSP to solve the infrasonics (or not really solve it but... vastly improve it.)
I would not bother with subwoofers smaller than 18's, unless there is an extreme space or budget constraint; they just don't have enough displacement.
I can barely hear the 6 UM-15's in my fronts, even when powered with 12kW
they simply can't keep up with the other 23 18's/21's/24's in my system (powered with even-more watts)
You wanna hear a GoPro compressing and struggling to comprehend the bass it is being subjected to? Here ya go!
Like 20hz, at full dynamic range. LOL!
Heck, more like full swings of 10-300hz or whatever...
My average playback is roughly ~15db above THX (with peaks into whatever...)
No audible clipping or distortion in-person.
The amps are still at 5-10% output here. The cone excursion is about the same.
Barely even idling, yet still scalping your face. (As it should be!
Heck, even this vid, which is 1hz. That's only 0-25% excursion still. (It goes louder...