The membrane absorbers in Control Room A and Alcatraz are large surface-area panels that completely encircle the room. They are different from traditional "bass traps" in that they work by reducing the power of the sound waves rather than the velocity of the pressure front.
Sound energy strikes membrane, membrane flexes, dissipating energy as heat.
The membrane panels are lap-jointed on flat walls, and coupled with resilient straps at the corners, making the entire surface area of the absorbers effective, rather than the individual panels.
The membranes are made of oriented-strand board (OXB), and are suspended from the structural ceiling members. The membrane panels are hidden from view by the interior fabric panels.