I have been going crazy over this and there is no accurate explanation on the thx website, and no one seems to have posted results of BGC on vs off to make a conclusion myself. I do not have an SPL and i really would like to know if my system could benefit from this setting. It helps get rid of most of my subs passive radiator noise (passive radiator vibrates at high volumes mkaing noise), but the rattling also goes away from deactivating audyssey eq (it is not bottoming out, it is what could be called the port distortion of a PR sub, I have an earthquake supernova MKV 10" btw. I believe BGC rolls off some frequencies at the lower end, wich audyssey boosts after room correction. Does anyone know exactly what BGC (boundary gain compensation) actually does? If someone could post some results (BGC on with audyssey eq on and viceversa) it would be a lot of help. Thanks guys!