Just an idea to expand the space inside the box with out having to really build an extension. My idea is to use the empty space between the left rear panel and connect the already made subwoofer box to the empty space with 2 ports. I will then fill the space with some fiber-fill like the subwoofer box. In theory this should increase the volume of air the subwoofer has to work with and produce a better sound. Idk of this concept will work so I will need some expert advice from any subwoofer box builders.