Setting a post in a viola that had just come into the shop, I saw this through the endpin hole. I wasn’t sure what was going on, so I took the top off, and this is what I found:
No, it wasn’t working all that well. I’ve never seen another like it, but it appeared to be very recent. This was a very expensive viola–too expensive to be doing this kind of experiment on–and it’s not in there any longer. With a normal bar the instrument sounded fine, so I really don’t understand what justified putting this mess inside.