useful posts by Brian Ravnaas at http://www.avforums.com/forums/home-cinema-building-diy/284503-diy-sound-proofing.html
Ok ok, i think i get it...
stiffer materials resonate at higher frequencies, limpid materials at lower ones. In terms of soundproofing construction, the goal is to make the resonance as low as possible, because above the resonance, decoupling allows walls to vibrate seperately; at the resonance, sound is perfectly reproduced from one wall to the other; below the resonance, individual wave lengths are more than long enough to pass through the full thickness of the wall, such that both wall sections behave as one (a single solid mass). Stiffer materials may resonate at a higher frequency, but because below that frequency they act as a solid mass not decoupled, they kind of suck a blocking most frequencies we need them to. If a material were to be made limp enough that the resonance is low enough to be inaudible, it's individual constituents act more independently, regardless of whether or not it is incorporated into a decoupled wall system.
So then, in the case of the containers of water, i would hypothesize that what waves are being more easily reproduced through the barrier would depend on how the masses of different rocks (larger ones creating larger wave lengths and smaller ones creating smaller wave lengths), interact with different stiffnesses of barrier; that is, if we assume these barriers are made of similar materials, putting aside other variables. For example, comparing a much softer plastic to a much stiffer one at similar densities and thicknesses. That might be an interesting test.
Look at my @$$ up in here; i make the questions and anwser them too
with research baby (which almost entirely involves believing what people i dont even know tell me)