Set all eight pieces of the 1-by-4-by-30-inch lumber on a worktable. Starting from one end, mark the lumber at ¾, 9¾, 10½, 19½, 20¼ and 29¼ inches. Put the framing square on the marks and draw lines across the width of the lumber.
Apply glue to the long edge of four of the pieces of 1-by-4-by-30-inch lumber. Place the other pieces on top of the glue. Be certain the lines connect to each other. Secure the pieces with 4-penny finish nails. Clean up excess glue immediately with a damp cloth. These are the legs of the audio shelf.
Run a bead of glue about 2 inches from the corners of the four pieces of 23 1/2-by-23 1/2-by-3/4-inch plywood. Secure them between the lines drawn on the legs with 4-penny finish nails. Clean up the excess glue immediately with a damp cloth.
Lay the audio shelf on one of its sides. Measure the space between the legs. Cut the decorative flat mold with a hacksaw to fit on the edges of the shelves, then apply glue to the backside of each piece.
Place the decorative flat mold on the shelf edges and secure it with 1-inch brads. Clean up the excess glue with a damp cloth. Sand the entire audio shelf.