I don't know what you'd call it actually.
Two things inspired me. The back pack vibrating box thingy you stick on your strap, and the board you sit your chair on which is a big flat vibrating bass speaker thingy.
I baulked at the price of either but got to thinking.
The result of my cogitation?
This is a 100w 4ohm audio exciter or transducer or something like that.
Cost about 14 quid delivered. Screwed it to the underside of my seat. Hooked it up to an amp. Sent a line out to my headphone amp (Zoom B1on). Stuck on my headphones... and there was a small explosion 💥
Not really. It actually worked. One of my inventions is actually brilliant.
I live with an elderly relative who sometimes dislikes it when the peas dance off her dinner plate if I'm rehearsing. So silent practice is the norm. This takes it to another level. It's extraordinary. The bass becomes complete. Mids and tops in the cans everything else everywhere else at once, and barely audible in the room.
It's wonderful. You can have any setting you want, from mild buttock shake to full personal violation. I'm off for another go.