A ported speaker box produces a sound directly related to its design.
Ported subwoofer boxes have a design that is distinctly different from the bandpass or sealed boxes. The port of a subwoofer allows the sound coming from the rear of the speaker cone to exit the box at a desired frequency and volume. The size of the port determines the result of the sound. The overall box size is about twice that of sealed enclosures because the needed air space for a ported box is larger.
Top, Bottom, Back and Sides
1. Put the 16-by-12 1/4-by-3/4-inch MDF on the worktable. Make several marks 3/8-inch from three of the edges. Place the framing square on the marks and connect them with a line.
2. Drill pilot holes on the lines with a 1/16-inch drill bit 1 inch from the end of the lines and then 4 inches apart. Drill 3/8-inch-deep countersink holes on the pilot holes. These are the sides to the subwoofer box.
3. Place the two pieces of 16-by-14 1/2-by-3/4-inch MDF on the worktable. These are the top and bottom of the subwoofer box. Measure from one 16-inch edge and make marks at 1 3/4 and 2 1/2-inches. Place the framing square on the marks and draw 12 3/4-inch lines.
4. Position the framing square so you can draw perpendicular lines from the ends of the 12 3/4-inch lines. Make these lines 5 3/4 inches long. Drill pilot holes between the lines. Turn the pieces over and drill 3/8-inch-deep countersink holes on the pilot holes.
5. Make several marks 3/8-inch from one 10 3/4-inch edge of the 10 3/4-by-5 3/4-by-3/4-inch MDF. Connect the marks as before and drill pilot holes followed by countersink holes.
6. Apply glue to one 10 3/4-inch edge of the 12 3/4-by-10 3/4-by-3/4-inch MDF. Secure the 5 3/4-inch piece to it through the pilot holes with the drywall screws. Glue the L-shaped edges and secure them between the top and bottom pieces as before.
7. Run a bead of glue on the 16-inch edges of the top and bottom pieces and secure them to the sides of the box through the pilot holes with the drywall screws. Next, brush glue on the four edges of the 14 1/2-by-10 3/4-by-3/4-inch MDF with a small paintbrush. Secure it between the top, bottom and sides through the pilot holes with the drywall screws.
The Front, the Port and the Speaker Hole
8. Lay the 16-by-12 1/4-by-3/4-inch MDF on the worktable. Make several marks 3/8-inch from the edges. Connect the marks as before and drill pilot holes followed by countersink holes.
9. Measure from one of the 12 1/4-inch edges and make marks at 1 and 2 1/2 inches. Place the framing square on the marks and draw lines across the material. Make marks on the lines 1 inch from the 16-inch edges. Connect the marks to create a rectangle and cut it out with the jigsaw.
10. Measure from the opposite 12 1/4-inch edge and make a mark at 6 3/4 inches. Make a mark on that mark 6 1/8 inches from a 16-inch edge.
11. Set the compass on 4 5/8-inches. Stick the point on the intersecting marks and draw a circle. Cut it out with the jigsaw. Apply glue to the front edges of the box and secure the front to it with the drywall screws.