Interesting. They also have flight simulation among the applications, which made me recall an old family friend who was a passenger airline pilot during the 70s and 80s. He also played a bit with older Flight Simulator versions, and one time he commented "yeah, it's very accurate but it can't be the real thing: you don't just pilot with the instruments, you also need to feel the airplane with your ass".

That's not just vibration but also (and maybe more significantly) G forces.

Need a butt swinger for that: https://www.youtube.com/watch?v=KW-ONbO5NYU

They're pretty common in more expensive sim-racing rigs too. I wish I could add some to mine, but I've read online that it will be perceptible to the downstairs neighbors without a lot of floor damping.

Child’s play. Let me introduce you to the BOSS platform:

https://www.avsforum.com/threads/the-hideaway-theater.299152...

HT enthusiasts are crazy about this stuff:

https://www.avsforum.com/threads/the-tactile-response-thread...

Eight 18” subwoofers in the demo video at the start of this thread, and that’s one of the smaller setups.

https://www.avsforum.com/threads/show-us-your-tactile-bass-c...

Here’s what 6 hz looks like from a video from that thread.

https://www.youtube.com/watch?v=agSaMJ_H7VE

There was this DIY design I came across decades ago that I've been trying to re-find for years. It had 4 12-15" cheap paper cone woofers mounted 2 sets of face to face with both sets axially loaded and wired so that all 4 cones move together. The whole thing was put in a big loaf of bread shaped box and then some kind of bandpass something and vents to the outside. It was reportedly very good for this low low base stuff, not so good for higher end responsive bass stuff. Anyone have any pointers for where to look?

Maybe you’re referring to an infinite baffle setup like this:

https://jonathanfoulkes.com/ibsub

https://ibsubwoofers.proboards.com/board/13/builders-gallery