| It's just a matter of Mass, if you will. Mass will isolate sound. The denser the mass (heavier) the more it'll isolate in the low frequency range. So basically, by adding a sheet of plastic (not too much mass) you'll isolate higher frequencies a bit from the absorbing material. Adding more mass will isolate it better and even lower in frequency. The energy gets reflected back into the room. Low frequency, as you should know by know, is harder to "isolate", so plastic will do squad in that case; resulting in a bass-only-absorber (well, sorta) |