What does Constrained Layers Mean?
In a constrained layer damping system, a damping material exists along side of one or (usually) two other stiffer materials. This method provides resistance to lateral movements.
For example, Sorbathane (tm) is wonderful as a damping material underneath equipment, if the equipment can only move up and down, which isn't the case. Try it. If you simply nudge it, you'll see that equipment oscillates like it's sitting on Jello(tm), Damping materials need constraints.
Constraints can be aluminum layers to make a composite.
Constrained layers are a version of composite layering. For example, people pour sand into speaker stands, then metal pieces, etc. to limit sound transmission, because different materials transmit different frequencies with different efficiencies. Of course, a small amount of sound moves up and down the outer legs of stands.
Les Davis Audio and Butcher Block Acoustics offer products that stifle vibration at reasonable costs.