Hi DV,
I don't think this design would make a very good trap, but it would probably make a good sound isolator.
In order to effectively absorb acoustic energy, or any energy, you need to "match impedances" between the source and the absorber. In other words, the acoustic energy in the air needs to find a gradual path to the absorber. It's sort of like those deep plastic bumpers they put where the freeways split into two. If you make a bad move and your car goes crashing into the center divide, the bumper gradually slows you down. The energy of car is slowly dissipated into the bumper. On the other hand, if you hit into a concrete wall, very little energy is transferred. The energy stays in the car..... not a good thing!
So, heavy panels, whether they are wood, concrete, or sand filled, are not very effective at matching impedances with the air. They tend to reflect more energy than they dissipate.
If the sand had a softer interface, it could possibly work as a good bass absorber. For example, if you put a thick layer of sand on the floor and formed little "dunes" on the surface. This might work!
Thomas
