Use a tape measure to measure the height, width and depth of the speaker. The cabinet will be approximately 1/2 inch larger than the exact measurements, so the speakers will fit inside the enclosure. If vertically mounting more than one speaker inside the cabinet, multiply the height of the speaker times the number of speakers and also allow enough room in the height to place a 6- to 8-inch gap between the stacked speakers.
Have the side, top and bottom boards cut at a home improvement store to measurement. Also have the plywood backing cut to size.
Set the sides face up and slide the bottom board between them. Insert wood screws through the sides into the bottom board to hold it in place. Insert the screws with a screwdriver. Have the assistant hold the side boards while mounting the bottom board.
Place the top board between the top of the two sides and install it using the wood screws in the same manner in which the bottom was assembled.
Place the cut piece of plywood across the back of the top, bottom and side boards and fasten wood screws through the back to hold it to these pieces of the cabinet.
Drill holes into the back of the cabinet where speaker wires will run. The hole should be at least 1/2 inch in diameter.
Flip the cabinet onto its back and insert the speakers into the cabinet. Affix the speaker to the front of the cabinet by inserting screws through the speaker brackets and screwing them in with the screwdriver.
Connect the speaker wires to the back of the speakers and then feed the wires out through the drilled holes on the back of the cabinet.
Stuff the rest of the inside of the speaker cabinet with fiberglass insulation.
Snap the speaker cover on the front of the cabinet and insert and tighten the cabinet retaining screws or clamps.