Don't know if this is a real concern just thought I would pass on an observation. I had a SA-WM40 Sony subwoofer that I returned. I did the Polyfill tweak and yes it did tighten the bass quite a bit as well as got a few more Hz at the low end. great subwoofer for the money just did not seem to have enough power fro my large room. I now have a PB12 and along the way it was recommended that this too might want to be polyfilled. I find that the PB12 at least for me is very quick, goes low enough and is tight so I am not planning to polyfill. Here is my concern don't know if it is a real issue just passing my thoughts on. This may be true for any subwoofer of similar construction. I am worried about potential overheating (or reduced life) of the amplifier in the PB12. The SA-WM40 has its amplifier vented with louvers on the back of the unit so polyfill would have little or no efect on the ability of the amplifier to cool itself. The PB12 has the amplifier totally inside the case and it appears to me that this design uses the heat dissipation to the inside of the unit to cool itself and the rear port just helps the cooling. If this design was polyfilled it might cause the amplifier to run too hot[/b} Just an unsubstantialed but possible concern I wanted to pass on.