How to Build a Subwoofer Box – Step by Step Instructions

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Due to the increasing popularity of customized sub enclosures, we thought that compiling some in-depth information on how to build a subwoofer box will help you through the processes of planning, building, and detailing a subwoofer box of your choice.

Learning how to make a subwoofer box helps you to prepare to customize your audio system without spending a fortune. All you’ll need is a few essential tools, materials, and the appropriate hardware.

Factors to Consider when Designing a Subwoofer Box

While you look for the right materials and equipment for the project, you’ll also be considering the desired size of the subwoofer you want to construct, as well as where it will be placed, mainly if you have limited space in your car. Another important consideration concerns the subwoofer for which you want to build a box. What are the maximum and minimum enclosure recommendations for this subwoofer? Let’s look at these factors in more in-depth details:

  • The minimum depth of the box

By depth, we mean the measurement from the front to the back of the box. To determine the minimum depth of the box, measure the depth of the subwoofer, and add 2 inches. The figure you get is what you are going to work with as the minimum depth.

  • The minimum height and width of the box

To determine the minimum height and width, you can measure the frame diameter of your subwoofer, or you can check the user manual for specifications. You should include additional extra space if you intend to use a mounting grille.

  • Available space in your car

The size of the box will largely depend on the space available in your vehicle. You’ll need to measure the height, depth, and width of the area you intend to place the subwoofer to enable you to determine the size and shape of your subwoofer box. You can now sketch the box using the dimensions you have gathered so far.

  • Internal dimensions

To get the internal measurements, subtract the thickness of the wood you are using from the external dimensions. For example, in our case, we are using 3/4″ MDF, this means you’ll need to subtract 2×3/4″ from each measurement. You can then use these dimensions to determine the internal volume in cubic inches, i.e.,

Cubic Volume = Height x Width x Depth

Convert what you get into cubic feet since most manufacturers recommended the box volume in cubic feet. This is achieved by dividing cubic inches by 1728. Ensure that the volume matches the manufacturer’s and, if not, make the required adjustments. Once you’ve made the adjustments, determine your final dimensions, and you are now ready to build your box.

Materials required

  • 3/4″ MDF – this is the recommended size unless you are using a more massive subwoofer or multiple subs.
  • Electric drill
  • Jigsaw
  • Table saw/ circular saw
  • Carpenter’s glue
  • 2″ drywall screws
  • 1/2″ and 3/4″ sheet metal screws
  • Silicon caulk
  • A pair of compass
  • Pencil
  • Tape measure and a straight ruler
  • Speaker terminal cup

Building the Subwoofer Box: Step by Step Instructions

Step 1

On the MDF board, measure and cut the main pieces of the box, i.e., front, back, and sides. You can use a table saw with a carbide-tipped blade or a circular saw, but you need to ensure that the cuts are square. Smooth and flat cuts will help to ensure that your box seals properly.

Step 2

After you have your pieces with you, use your compass to mark the cut-out for the subwoofer on the front part. If you are using double thickness, you should have two identical front pieces. Also, make the markings on both parts. Most people prefer the double thickness method since it provides a sturdy mounting surface for the sub. Ensure that your sub will fit snugly into the opening.

Step 3

Secure the two front pieces (if you choose the double-thickness for the front panel) using plenty of carpenter’s glue and some sheet metal screws. If you are not using double-thickness, you’ll need to use bracing in the internal seams of your box for added strength. The simplest method of adding bracing is using 2″x2″ strips of lumber on the seams before you attach the top and bottom. You can also use bracing with double-thickness MDF, especially if the box is big, not forgetting that the box will be exposed to extreme pressure.

Step 4

Use your drill to make a hole on the inside of the circle you traced with the compass. The hole should be big enough for the jigsaw to fit. Use the jigsaw to cut out the circle, and with that, you have the woofer opening. Using the same method, drill a rectangular hole in the back panel for the terminal cup. Install the terminal cup and run a bead of silicone caulk all around the edges. Screw it into place using sheet metal screws.

Step 5

Now that you have both the front and back pieces complete, you can now fasten the other pieces together. MDF is prone to splitting, so you should pre-drill holes for the screw in each piece before trying to attach them. When fastening, ensure to use plenty of carpenter’s glue as this is what permanently seals your box. Also, it is essential to note that the largest pieces should overlap the smaller parts of the box to ensure maximum strength.

Step 6

At this point, you can use your 2″ drywall screws and the cordless drill to fasten the pieces further. This might squeeze out some of the glue, but you can use a wet rag to wipe it off. If you find out that the box is out of square, you can use a furniture clamp to pull everything back into alignment. After you have screwed and glued everything together now, you have a box.

Step 7

Put the subwoofer in the box and see if it fits. If it is a tight fit, you can use coarse sandpaper to make the opening a bit larger. With the subwoofer still inside, use a pencil to mark holes where you are going to mount the sub. Remove the sub and pre-drill holes for the screws.

Step 8

After the glue has dried, run a bead of silicone caulk all around the edges and on the internal seals to ensure that everything is sealed. Let the box rest for about 24 hours before you put your subwoofer back inside. The silicon caulk produces acetic acid fumes in the process, and this can destroy subwoofer surrounds. You can then put your subwoofer in and hook the speaker wires to the subwoofer through the terminal cup.

What an awesome subwoofer box we’ve made!

You can make yours now.

Building a subwoofer enclosure is somewhat a straightforward process, but you’ll need to familiarize yourself with carpentry and power tools. Start by calculating the dimensions, then sketch the size and shape of your box based on the size of your sub and the space available. You can then follow the above steps. Once you fulfill all conditions, you can finish off by adding a covering of your choice from auto paint and auto carpet to vinyl or leather. With that done, your subwoofer box is ready for use.