Something like LLP is technically a double wall barrier. As I'm sure you understand, the foam is there to keep the barrier from becoming resonant by decoupling it from the surface. Not sure what Don is doing in his test rig, but in our car the substrate the barrier's sitting over might be resonant. In this case, you can get better overall STC numbers by damping it first (outside of "mass loading" the surface.)
What that graph shows is the importance of decoupling the barrier (ie making a double wall barrier) and damping the substrate to push the RF down as low as possible. If it's 80 hz then you'll see that coincidence drop and then the TL go way up (theoretically at 18 db/oct). Below 80 hz (the RF of the barrier system) a double wall is no better than a single wall (ex just some MLV thrown down on the floor) but above it you see what happens.
Not sure if any of that made sense. :surprised:
Also, LLP isn't straight up 1 lb/sqft. It's more like 1.3#. The PVC foam used is pretty dense and heavy as far as foam is concerned. It's no Ensoheavy, but it's aaaite (inside joke).
