You can make a high quality speaker box with medium density fiberboard. This project requires careful calculations and takes about two days. Each variation in volume, the amount of polyfil and the density of the wood will change how you speaker sounds. For each of these elements, you should be as close to the manufacture's directions as possible.
Step One: Calculations and First Cuts
The first thing you will need to do is calculate the volume of your box. The speaker driver's manual should include the optimum volume for the box. You should take braces into account when you begin calculations. Once you know the size of your box, use the router to cut 6 pieces of equal size. Use the manual to calculate how big the holes should be for the driver. Trace the holes onto one piece of fiberboard. Carefully cut out the holes. You will also need to cut out a hole in the back panel for wiring.
Step Two: Frame
Once you have cut the board to size and cut out the patterns it is time to build the frame. Place all of the pieces together to form a cube. Leave out the front panel. Use wood glue to adhere all of the pieces together. The box should stay together without the screws. Allow the glue to dry. Next you will need to screw all of the corners together. Make sure the screws have an unthreaded top.
Step Three: Braces
The braces need to be carefully cut into triangles. These triangles should be placed in each corner, from left to right, spanning from one side to another. Screw them in securely, but don't allow the screws to come into contact with previous screws.
Step Four: Silicon
Once your frame is assembled you need to seal it. Apply silicon to each edge following manufacture's instructions. As the fumes may harm the speaker equipment, allow the silicon to dry for at least 24 hours before moving on to the next step.
Step Five: Polyfill
After the silicon has dried it is time to add the poly fill fiberglass. Again, this need to be applied according to manufactures instructions. Leave room for the speaker driver and the cables.
Step Six: Speaker Driver
Place the speaker driver over the correct holes on the front panel. Screw it into place. Each hole should already be clearly marked by the manufacturer. Once the driver is secure, thread the wiring through the box and secure the front panel to the rest of the box using screws.
Step Seven: Speaker Cloth
You may choose to cover the front of your speaker with speaker cloth. This cloth should be glued or stapled to the front of the speaker once it is assembled.
Your speaker is now complete. You simply need to wire it up to your sound system and enjoy the sound.