- 1). Locate the speaker volume on the specifications for your speakers. This will be listed in cubic feet (i.e. 0.70 cf). This measurement tells you the enclosure size that the manufacturer recommends for the speaker to allow it to produce the clearest sound. The size of the speaker enclosure will hold a portion of the sound from the speaker and too large an enclosure can make speakers sound muffled; too small can cause a speaker to lose its low ranges. You want to build a compatible box to support this rating. For a three-speaker box you will need the specifications for each speaker, add them together to get the total cubic inches.
- 2). Measure the space where you want to put your three-hole speaker box so that you have a general idea of the size box you want to build. You will want to take measurements for the expected height, width and depth (in inches) of the box. Multiply these together with a calculator and then divide that number by 1728 (that is the base volume of a 12x12x12 enclosure). For example, a box that measures 6" x 18" x 12 " multiplied together and then divided by 1728 will give you a box that is capable of 0.75 cf of sound enclosure. If you have three speakers that add up to 1.25 cf, then you need to adjust your plans for the size of the box and placement until you are as close to equaling the speaker enclosure volume needs of your speakers with the volume of your three-hole speaker box. Once you have adjusted your measurements so they are as close as possible, you can begin to build your box.
- 3). Transfer your measurements to a sheet of 3/4-inch plywood. Outline the face of your box (where the speakers holes will be cut) to the exact height and width that you need. Place your speakers face down on the board and trace around the speaker (not the speaker frame) to mark where you will need to cut your holes. Then, mark out the two sides of your box on the plywood. Do this by transferring the height and width of your box onto to plywood so the width is marked like the base of a triangle. The full height will be the front edge of the side. Mark the back edge so it is half the height of the front and then connect the two heights with a diagonal line. Mark out what will be the top face of your speaker enclosure by drawing a rectangle (or square depending on the size of your planned box) that is as wide as the front face but the height is equal to the length of the diagonal you created for the side pieces.
Speaker enclosures do not need a bottom piece. Cut out all of your pieces using a jig saw. Drill a hole inside the circles you traced for the speaker holes so you can insert the blade of your jigsaw in the circle and then cut out the holes you traced. You will have four pieces to your box: the front (with three holes, two side pieces and the top.
- 4). Assemble your box. Screw your speakers into place by attaching the frames of the speakers to the inside face of your front side of the box so the screen of the each speaker lines up with the holes you cut. Then, screw each side in place. Cut two pieces of 2x2 to fit on the side of the box so one piece will create a brace between the front and back sides of your speaker enclosure and one will act as a brace between the two sides.
- 5). Seal the box by running a bead of silicone caulk on the inside of the box at every seam formed by the pieces of your box meeting. Let the caulk dry. Cover the exterior of your box with automotive carpeting and you are done.
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