I have had this cab a while and like it a lot. I have a situation I wonder if anyone can explain to me though. At low or medium volumes, I can play down to the low Bb (I have a 5-string and detune a half step) I know the cabinet isn't really rated quite that low but it works. It claims -6dB @ 35 Hz, which is C#. Bb is 29Hz. At loud volumes, everything still works fine, except the really low notes. If I play those, the speaker cones start to move A LOT and it sounds very bad. My amp is a GK 400RB-III, 240 watts. The cabinet is rated for 175-350 watts. The amp has a clipping light, which never goes on. The tweeter in this cab absorbs extra energy and sends it to a lightbulb, but that doesn't apply here. My questions are 1) is the speaker cabinet now broken? 2) if I persist in the above behavior, will it become broken? 3) any suggestions besides, "Don't send such a loud low signal through that cabinet?"