Once you have your measurements for the box, its time to put it together. Cut the sides,top (with open face to allow for the speaker ring to fit through for contouring of the face), back, and bottom to prepare to assemble. Next, put all your sides together, making sure to leave the back non-permanent. Apply wood glue to all the permanent pieces. Reinforce with staples on all edges.
Use the router to make a speaker ring for the size subwoofer you will be using for your project. Cut a 2x4 piece of wood to desired length for the contour and face of subwoofer box. Mount the 2x4 to the back of the box and mount ring to opposite side of 2x4. Set the box up to show the subwoofer ring.