In order to ensure that the cabinet walls are sturdy enough, we have used 22 mm boards. The walls and the internal reinforcing frame are glued together. If you are going for the active variant with the Proteus SW 2.5, you will need to install the angled partition which will protect the amplifier from alternating pressures inside the cabinet. This angled arrangement reduces the internal size of the cabinet by the minimum amount. If a different module is used, the dimensions of the opening and the arrangement of the partition will need adapting to suit.
Finally, there is the double baffle that the driver is mounted in.