The Great GRAMMA Sound Isolation Riser (Gig & Recording Amplifier & Monitor Modulation Attenuator) is an incredibly effective device that's used to decouple a large loudspeaker from the floor, yielding nearly total acoustic sound isolation.
The result in purity of tone is significant. An additional benefit is that the sound source, particularly a subwoofer, will no longer resonate through the floor to any space below. While it may still be heard, the sound will be significantly diminished.
The Great GRAMMA comes complete with a carrying handle, road-ready carpet, Studiofoam Wedges (underneath) and PlatFoam (underneath.) One to two GRAMMAs will support 4 x 12", 15" or 18" speaker cabinets.