How to Build a 15-Inch Custom Sub Box

Written by allen coleman
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How to Build a 15-Inch Custom Sub Box
(Hemera Technologies/ Images)

Before building a custom enclosure for a 15-inch subwoofer, there are a few things you want to take into consideration. The box for a 15-inch subwoofer is going to be fairly large, so the first thing you want to check is if there is enough room for the enclosure in your vehicle. All subwoofers have recommended air space (volume) inside the enclosure for the best sound quality, depending on the type of enclosure. Before getting started, check your speaker's owner's manual for the recommended box sizes.

Skill level:

Things you need

  • 3/4-inch medium density fiberboard
  • 2-inch drywall screws
  • Sheet metal screws
  • Carpenter's glue
  • Silicone caulk
  • Jigsaw
  • Electric drill
  • Speaker terminal cup
  • Speaker wire

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  1. 1

    Calculate the airspace of your enclosure by multiplying the height times length times width of your box. Use inches when calculating your airspace. If your box is 22 inches high, 20 inches wide and 24 inches deep, you would multiply 22 x 20 x 24 to get your total volume in cubic inches. Now divide that number by 1728, which is 1 cubic foot (or 12 x 12 x 12). That will convert your number from total cubic inches to total cubic feet. Keep in mind your the front of your box must be at least 18 inches high and 18 inches wide to accommodate the 15-inch speaker going into it.

  2. 2

    Cut the 3/4-inch MDF board for your top, bottom and sides of your box to the measurements needed. Cut three pieces for the ends You want to cut support for your box for a 15-inch subwoofer with an interior brace the size of an end piece.

  3. 3

    Attach the two pieces of MDF for the front of your enclosure with carpenter glue. Make sure you cover the pieces enough to seal the pieces together. Set the pieces aside to dry.

  4. 4

    Secure the to pieces of MDF that you will use as the front of the box by screwing in several sheet metal screws around the edges of the MDF. Place a screw about every 2-inches around the MDF.

  5. 5

    Trace a circle on the piece of MDF you will be using as the front of your box. Drill a hole using your electric drill, and a large bit on the inside perimeter of the circle you just traced out. Cut out the circle starting at the hole you drilled using a jigsaw.

  6. 6

    Trace the speaker terminal cup on the piece of MDF you are going to use as the back. Cut the hole, then secure the speaker terminal cup to the MDF using the hardware included.

  7. 7

    Line up the MDF piece that will be the bottom and one side. For the greatest strength, overlap the larger sides of the box to each of the smaller sides. Place marks on the edge of the MDF where your screws will go to secure the sides to the bottom piece. Repeat the process with the remaining three sides and then the top piece.

  8. 8

    Pre-drill all screw holes in MDF.

  9. 9

    Glue the box together, first using carpenter's glue, before you add the screws to ensure airtight bonds.

  10. 10

    Screw in 2-inch wood screws in the new holes. Glue may squeeze out of the seams -- just wipe it off as you go. After securing all the screws around your box, set it aside to let the glue dry.

  11. 11

    Seal all the cracks and seams inside the box by running silicone caulk along all the internal seals so your enclosure is airtight. Set aside the box so the caulk can dry.

  12. 12

    Place the subwoofer into the box to make sure it fits. With a pencil, mark all the screw holes around the subwoofer onto the enclosure. Remove the speaker and drill out the holes.

  13. 13

    Connect the sub to the speaker terminal cup on the back of the enclosure. Use enough speaker wire to run wire from the back of the sub to the terminal cup. Attach the positive and negative leads on the sub, then connect the positive and the negative wires to the speaker terminal cup leads.

  14. 14

    Return the subwoofer to the enclosure, and line up the holes around the sub with the holes you drilled earlier. Screw in all the screws to secure the subwoofer to the box.

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