This is a device that I eyeballed from description and some pictures of a similar thing. It was made as a gift for a friend who plays base. I have no idea how it supposed to work but I only assumed that it need to resonate to some frequency which is dependent on weight and springs. So I made this extremely adjustable. Put any wire through holes and put as much weight in the box and adjust the distance with a threaded bolt through the middle.

I never got a feedback on this. So if you try and make it work let us know.