Cut the wood needed for your passive monitor. A good monitor will include a woofer for mid and low frequencies and a tweeter for high frequencies. Cut two pieces of MDF or maple to 17 inches by 18 inches, one to accommodate a 15 inch woofer and tweeter and the other serve as the back of the monitor.
Cut two pieces of the material to 12 inches by 18 to serve as the sides of the cabinet and two pieces to 12 inches by 18 to serve as the top and bottom of the cabinet. The overall cabinet will be 17inches wide, 18 high and 12 inches deep after it has been completed.
Assemble the frame of the monitor by attaching the 12 inch by 17 inch and 12 inch by 18 inch pieces to form an open box. Glue them together first, making sure that there are 90 degree angles where the four pieces meet. Nail the corners after the glue has dried to add extra stability.
Rout the front piece of material to be able to add the woofer and tweeter. Use the 15-inch speaker template to draw the outline for the speaker on the wood. Place it two inches from the top of the monitor and leave one inch on each side. This will allow you to have enough room to add the tweeter to the top in the center or on one of the sides. Drill a hole within the outline and use the router to finish the job, staying inside the line to assure that there is enough wood to screw the speaker into place.
Rout the hole for the tweeter using the same method as described in Step 4. The tweeter will usually be round or square. Be careful to stay within the line to leave enough wood to screw the tweeter into place. Rout the back piece of wood for the speaker jack by tracing the outside of the speaker jack onto the wood. Drill and rout the hole as you did with both the woofer and tweeter.
Glue and nail the front piece of wood into place on the open frame you assembled in Step 3 and screw the woofer and tweeter into their respective holes after the glue has dried. Attach the back piece of wood to the monitor and wire the woofer and tweeter to the speaker jack. Screw the speaker jack into place on the back of the completed monitor. Plug in a sound source and make sure that both the woofer and tweeter are working.