Which structure is most effective against acoustic noise?
The most effective structure would be a room surrounded by a vacuum.
No air, no barometric pressure wave fluctuation.
Second would be a capsule with inner and outer wall and ceiling skins being composed of differing densities and thickness, laid up in an unlike schedule from inner to outer skin.
Filling the airspace between the inner and outer skins with glass wool fiber also soaks up energy very well.
The floor must be highly dense, decoupled from the surrounding media, and should ultimately be non resonant, which in practicallity means a resonant frequency well below operating parameters.