I just set up my 20-39cs and Samson S700 last night and the difference from my old Energy ES-10 is amazing. My wife had to send my son down to tell me to turn it down as I was "shaking the whole house". Other equipment is a Denon 3802 and the room is about 1,300 cf. I hooked everything up according to the manual that came with it with the amp cranked all the way up and calibrated using the Denon's internal test tones and the Ratshack spl meter. The only factor that I can change is that I did have the door to the adjoining equipment room open while I was doing the calibrating, and I'm not sure if that affected the spl levels. The problem I am having is that on the really heavy bass scenes, like when the ground opens up under Buzz at the beggining of Toy Story 2 or some parts of the pod race in TPM, the sub started making this awful clacking sound, which i am assuming is the driver bottoming out. I originally calibrated the sub a little "hot" at about 5db over the rest of the speakers whcih was +1db on my Denon 3802. This produced lots of clacking, so I brought the sub down to 75db like the rest of the speakers, which is about (-3db) on my Denon. When I replayed the scenes at 0 master volume (reference level) there was still an occasional clack at the really low bass parts. So I turned the master volume on the receiver down to -3 and that seems to have pretty much stopped the clack. Does this meen that I need to calibrate the sub to less than 75db if I am going to do any listening at reference levels? I know it is rare for movies to have this much low bass and I picked two very demanding scenes for my test, but if I calibrate so the sub won't bottom on these scenes, will I be missing some of the bass on less demanding stuff? Thanks for any advice, that "clack" sound is awful and I don't want to hurt the speaker.