> I imagine it could play a pure 7Hz tone if you turn it up.
You're misunderstanding the numbers here. Going from 12 to 7 Hz is most of an octave, nearly doubling wavelengths.
Also SVS's numbers are gonna be the usual marketing stuff, so they're assuming a fat room gain curve, and just looking at their website they have a disclaimer on their graphs that it doesn't represent actual total output capability. Which is a way of hiding that if you actually try to drive it that hard that low with ~3kw electrical in those voice coils are going to torch.
The non lying way to prove that claim is to show large signal Kipple results including the heat soak. They ain't doin' that here.
Basically stuff going this low is really exotic and more in the realm of servos that simulate earthquakes than traditional transducers.
Tom Danley is the world expert on this sort of thing. He used to build stuff like ultrasonic levitation ovens and full scale sonic boom simulators for JPL/NASA.
In the audio world he was first famous as the tech lead behind ServoDrive. This now defunct company made special effects subwoofers using DC rotary servo motors to drive the diaphragm. They were used as special effects subs in that era by big acts like Garth Brooks. But they didn't catch on outside that niche because very little music has significant content below 40 hz as it just turns into a muddy rumble that harms sound quality as a whole. So to use these sorts of things you have to mix for it specifically. Cinema goes lower with the rumbles down to 15hz, but that's basically it.
Getting anything that's like a clean tone at 7hz is not gonna happen without a purpose built device.
FWIW Tom Danley started his own company[1] after Servo Drive failed on the business side, where he focuses on large scale horn speakers using novel topologies. They're among the best in the business at what they. Again, they don't have anything that even remotely tries to go down to 7hz.
[1]: https://www.danleysoundlabs.com/
Tom's a nice guy, I've traded emails with him a few times over the years. He used to be pretty active on the DIY speaker building mailing lists sharing his very in depth knowledge freely.
