The Auralex SubDude(HD) is a 15" x 15" x 2.5" platform wrapped with ozite to fit any room setting. Its purpose is to prevent sound from transmitting through your subwoofer to surrounding surfaces.
Subwoofers create big vibrations (low frequencies) that you can feel in the floor and in objects placed nearby. When the source of the vibrations is coupled directly to the floor it causes these objects to vibrate or resonate – not only at the fundamental pitch the source is creating but also at harmonic frequencies that discolor the true sound from the source. Now you have two (or more) objects vibrating, which creates an acoustical problem called “secondary resonance”.
Note the graph of SubDude performance on a sample concrete floor, the most noticeable effect is on harmonic frequencies above 100 Hz. This is the harmonic range above the fundamental the sub is recreating, allowing you to hear a more true bass tone below 100 Hz by eliminating upper harmonic resonances. This translates to the listener as more accuracy in the low end, and a cleaner (less muddy) crossover between the sub and your full range LCR channels. The SubDude effectively reduces secondary resonance by decoupling your subwoofer from the floor so you hear your sub and not the vibration of the other objects in your listening environment.