I think the bit where you tune it to share around a big mass around it may be the non-obvious part.

Because frankly, I played with and disassembled many speakers of various sizes too when I was young, and one thing I internalized then is that speakers are piss poor at shaking anything except their own membrane. You can't just make things vibrate with a small speaker glued to a random thing. That's why as a kid I was not surprised to discover vibrators are spinning some unbalanced weight around - obviously that would shake things (as experienced by anyone who saw a washing machine decide to take a walk).