Auralex - 4 Inch Studiofoam Metro - Brown
The differing height protrusions on the 4" Studiofoam Metro-24 panel serve to spread sonic energy out in the time domain, as well as each absorbing a slightly different slice of the frequency spectrum. Since it takes slightly different amounts of time for sound waves to travel through the different sections of the panel, strike the mounting surface and travel back through the panel into the room, the wave-fronts are in effect softened rather than just being absorbed.
A 4" Studiofoam Metro-24 treated room will retain a bit more "feel" than a room that's treated with a stronger acoustic absorber like 3" or 4" Studiofoam Wedges or Pyramids. A well-controlled, natural-sounding acoustic space will result when coupled with a judicious amount of MetroFusors.
The panel displays slightly more absorption than a 2" Studiofoam Metro-24.