I'm looking for some assistance here from some knowledgable cabinet people. I just took delivery of a USED Epifani UL2-410 today. I plugged my new head in (a Markbass F1), and it sounded a little empty in the low end to my ears. I noted some damage to the rear of the cab where the plastic housing for the horn attenuator and inputs are. I also took the grill off to inspect the speakers. Speakers are all intact. Both 1/4" / speakon inputs work on the back of the cab. OK, here's where I need help. When I hit a low note, there is speaker excursion from all four speakers. However, there appears to only be SOUND coming from two of the four. If you're looking at the front of the cab, the top left and bottom left are the ones with an audible tone. The top right and bottom right do not appear to actually produce an audible sound. Anyone have any experience with this sort of thing? I am an electrical novice so I'm not sure I would know how to test anything. I can not take it to the place I bought it because it was an online retailer in the US (I'm in Canada). I will be able to send it back, but I'm trying to determine with certainty if there is something wrong with the cabinet first. Is it also possible that there is something wrong with the Markbass F1? You guys seem to know your stuff, I'm hoping someone can help. Thanks!