I had this sub in my car and thought I had everything ok but I blew it. So I got it repaired by JL and in the meantime I had a Rockford Punch HX2 which wasnt hitting as hard but it sounded great. I got my JL sub back and popped it into the box with the same amp settings my rockford had and the JL sub has this hollow sounds sometimes, similar to right before it blew. I have a 1.3 cubic foot sealed box. Can anyone help !!! I'm not sure how the amp should be setup.