Cut a hole, 6-inches in diameter, in the center of each of the two 2-by-2-foot sheets of plywood.
Create a rectangular enclosure with the two of the 2-by-3-foot plywood sheets and the 2-by- 2-foot sheets. Drill screws into the joints to secure the enclosure.
Drill another 2-by-3-inch sheet of plywood to one of the exposed sides to create the bottom of the enclosure.
Lay the remaining sheet of 2-by-3-foot plywood on a flat surface and secure four hooks in a line down the center of the board. Secure four hooks to the bottom of the reverb enclosure in the same pattern.
Screw two hinges to one side of the enclosure's open end. Secure the remaining 2-by-3 foot sheet of plywood to the hinges to create a door for the reverb box.
Loop the springs around the hooks on the bottom of the enclosure and the door.
Place an amplifier in front of a hole on one end of the box and place a microphone in the hole on the other end to capture the reverb.