I built a 2.8 cu ft sealed box to use with my HT system and it doesn't sound right. Not very loud. Amp is a Behringer 2500. So its getting plenty of power. The xover is a behringer ultradrive 2496. I have no clue on what size to make the new box. This box for sure isn't right because the sub doesn't get loud, or sound good. Sub isn't blown and works fine just doesn't get deep etc like a 13" w7 does. Please help Thanks.