For me, stone dust (Home Depot) is the most dense, heavy-as-hell filler.
Imagine a 3' by 2' bag of sand. I would estimate the equivalent size in stone dust to be roughly twice as heavy, at least that's what it feels like. This stuff is so dense, it feels like you are lifting a frigging stone of the same size.
For me, stability is my main concern. I then put a Husky neoprene-like tool-drawer-bottom liner between the top plate and the speaker bottom for protection and grip. The whole thing is pretty tight and solid...
Imagine a 3' by 2' bag of sand. I would estimate the equivalent size in stone dust to be roughly twice as heavy, at least that's what it feels like. This stuff is so dense, it feels like you are lifting a frigging stone of the same size.
For me, stability is my main concern. I then put a Husky neoprene-like tool-drawer-bottom liner between the top plate and the speaker bottom for protection and grip. The whole thing is pretty tight and solid...