Stand the speaker upright on one of the "Top / Bottom" sheets of plywood, and draw around the base. Lay it down on its side on one of the "Side" pieces, and draw around that. Lay the speaker on its back, and draw around it on the "Front / Back" sheet. Create a different template for front and back if they are different sizes for a speaker with tapered sides.
Cut around the drawn lines with a saw. Create six sheets of plywood that form the outer panels of the cabinet. Remove the corner protectors from the existing cabinet, and remove any screws or fasteners with a claw-hammer or pry bar. Use caution when separating the panels because there are wires and electronics inside that may be anchored to different panels. Pulling the sides apart abruptly could break wires or soldered connections.
Unscrew the speaker cones from the inside of the front panel. Disconnect the wires leading to them, if they are "Push/Pull" spade connectors. If they are hard-soldered, leave them in place. Unscrew the cable sockets and the crossover unit, if present, and lift everything from the cabinet. Write down the positions of all the electronic hardware inside the previous cabinet.
Draw around the speaker cones on the front panel of the new cabinet, cut the hole, and secure the speaker in place with the mounting screws. Trace and cut the hole for the cable sockets on the rear panel, but do not screw them into place. Assemble the sides of the cabinet, and screw them together, leaving the back panel off. Secure the crossover unit to the inside of the cabinet with the mounting screws. Test the speaker by connecting it to an amplifier, ensuring no exposed metal or wires are in contact with anything.
Pass the cable connectors through the hole in the rear panel, and screw them to the rear panel. Fit the rear panel to the other five sides, and screw it into place. Use the hot glue gun to cover the cabinet with the speaker carpet, and screw the grille and corner protectors into place.