How to Build a Subwoofer Box: Step by Step Outline

One of the best ways to add your personal touch to a car's audio system is to build a box for your subwoofer. This article is a step-by-step outline of how to build a subwoofer box. Building your subwoofer box is a cost-effective approach to achieving your desired design and fit. Only a few basic tools, hardware, and materials are required.

Ensuring your sub has the right enclosure for your purposes, whether a basic cubic box or a properly built kerfed/ported box, can make all the difference. 

Building a subwoofer enclosure is a very simple task, but you'll need to be experienced with carpentry and power tools. Calculate the dimensions first, then draw the size and shape of your box based on the size of your sub and the available space.

After that, you can proceed with the instructions outlined below. Then, after you've met all of the requirements, you can add a covering, ranging from auto paint and carpet to vinyl or leather. After that, you're ready to use your subwoofer box.

Considerations when Designing a Subwoofer Box

1. Available Space in Your Car

While you're looking for the right materials and equipment for the job, think about the size of the subwoofer you want to build and where you'll put it. Does your car have limited space? Then, the size of the box will be determined by the amount of space in your vehicle.

To design the size and shape of your subwoofer box, measure the height, depth, and breadth of the area where the subwoofer will be installed. Now you may draw the box using the measurements you've obtained.

2. Minimum Depth of the Box

When we talk about depth, we're referring to the distance between the front and rear of the box. So to calculate the minimum depth of the box, measure the depth of the subwoofer and add 2 inches. The figure you get will be the minimal depth you will work with.

3. Minimum Height and Width of the Box

You have 2 options: measuring the frame diameter of your subwoofer or consulting the user handbook for specs to calculate the minimum height and width. If you're utilizing a mounting grille, make sure you provide enough room.

4. Internal Measurements

To get the internal dimensions, subtract the thickness of the wood you're using from the external dimensions. In our case, we're utilizing 3/4-inch MDF, which means you'll have to subtract 2-3/4-inch from each dimension. The internal volume in cubic inches can therefore be calculated using these dimensions.

Height x Width x Depth = Cubic Volume

Because most manufacturers propose the box volume in cubic feet, convert what you obtain into cubic feet. Divide cubic inches by 1728 to get this result. Make sure the volume matches the manufacturer's specifications, and if it doesn't, make the necessary modifications.

Determine your final measurements after making the adjustments, and you're ready to start building your box.

Materials Required:

  • Unless you're utilizing a large subwoofer or numerous subs, 3/4" MDF is the ideal size.

  • Circular saw/table saw

  • Electric motor drill

  • 2" drywall screws

  • Jigsaw

  • Silicone caulk

  • Carpenter's Glue

  • A straight ruler and a tape measure

  • 3/4″ and 1/2″ sheet metal screws

  • A compass and a pencil

  • Speaker terminal cup

How to Build a Subwoofer Box

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Step 1

Measure and cut the main elements of the box, such as the front, back, and sides, on the MDF board. You can use a circular saw, or a table saw with a carbide-tipped blade, but be sure the cuts are square. Smooth and flat cuts will aid in the proper sealing of the box.

Step 2

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Use your compass to mark the subwoofer cut-out on the front part with all of your pieces in hand. If you're utilizing double thickness, you'll need two front sections that are similar. So make the markings on both parts as well.

Most people prefer the double thickness method because it provides a stable mounting area for the sub. Make sure your sub fits snuggly in the opening.

Step 3

Use plenty of carpenter's glue and sheet metal screws to secure the two front parts if you choose the double-thickness for the front panel. If you're not utilizing double-thickness, you'll need to reinforce your box's internal seams with bracing.

On the seams, use 2′′x2′′ strips of lumber before attaching the top and bottom. It is the simplest technique for adding bracing. You can also use double-thickness MDF for bracing, especially if the box is large, but keep in mind that the box will be subjected to a lot of strain.

Step 4

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Make a large enough hole inside the circle you traced with the compass with your drill to accommodate the jigsaw. Then cut out the circle with the jigsaw, and you'll have the woofer opening.

After that, drill a rectangular hole in the back panel for the terminal cup using the same technique. Place the terminal cup and apply a bead of silicone caulk around the perimeter. Use the sheet metal screws to secure it in place.

Step 5

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Since the front and back pieces are done, you may join the remaining pieces together. However, MDF is prone to splitting, so pre-drill holes for the screws in each piece before attempting to join them.

When fixing, make sure to use a lot of carpenter's glue because this is what will maintain your sealed box forever. It's also important to remember that the box's bigger portions should overlap its smaller parts for maximum strength.

Step 6

Use your 2′′ drywall screws and a cordless drill to secure the pieces. It may squeeze out some of the adhesive, but you can wipe it away with a moist rag. If you discover that the box is out of the square, you can use a furniture clamp to straighten things out. You now have a box after screwing and gluing everything together.

Step 7

Check to verify if the subwoofer fits in the box. If the aperture is too small, you can use coarse sandpaper to enlarge it. Before removing the sub, mark holes where you want to place the subwoofer using a pencil and pre-drill the holes for the screws.

Step 8

After the glue has set, use a bead of silicone caulk to seal the edges and internal seals. Allow the box to rest for at least 24 hours before reinstalling your subwoofer. In the process, the silicon caulk emits acetic acid vapors, which might harm the subwoofer's surroundings. After that, you may plug in your subwoofer and connect the speaker cables to it via the terminal cup.

Step 9

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Now it's time for the carpeting. You can buy a roll of grey carpet and a 3M spray adhesive from a nearby auto parts store. Evenly spray the entire back of the box with the spray adhesive, covering all of the edges. Make sure you spray the carpet's backside where it will meet the box.

Spraying both the box and the carpet and then flipping the box forward completes the process. Again, having a large enough carpet sheet makes this simple. As you go, pat down the carpet and make sure it's smooth. You won't have to cover the holes because you'll cut them out later.

When you get to the last side, and the carpet edges meet, cut along the edge with a razor blade or box cutter, making it as seamless as possible. At this point, make sure it has bonded to the edge.

The same procedure applies to the sides. Before you begin, you may need to cut some extra material off, but make sure your material reaches the edge, then spray the box and carpet. Finally, use your razor blade along the edge to cut off the excess.

Step 10

Cut the holes for the sub and speaker terminals with the razor. Connect the wires from the terminal to the sub and vice versa. Center the subwoofer and screw that down

Best Material for Making a Subwoofer Box

1. Medium Density Fiberboard (MDF)

MDF is the most common and best overall material for your car audio setup. This engineered wood is extremely long-lasting. In addition, it's dense and thick, which helps bring out the optimum sound quality from your subwoofer. Despite its weight, MDF is inexpensive and widely available.

MDF is less prone to warping, so it's the preferred material for making subwoofer enclosures and speaker boxes in general. The one drawback is that it's quite hefty, so if you intend on moving your subwoofer about much, you might want to look for something lighter. However, because it'll most likely be sitting in your trunk, you won't have to worry about this.

2. Other Woods

Pine board is a wonderful alternative to MDF if you want something that looks a little nicer and don't plan to cover it with carpet. Another alternative is plywood, which is a better choice than pine, which you should only use if aesthetics are a top priority and you want to stain it and make it look amazing.

The main concern with using different types of wood instead of MDF is warping. You may stain a gorgeous natural wood enclosure to make it look even better.

3. Fiberglass

Fiberglass is a fine choice in some situations, but it's usually reserved for highly specialized high-end installations. Fiberglass is light, robust, and can be molded into almost any shape. However, one disadvantage is that you can't have very large single box panels with it.

As a result, there's more room for error when making fiberglass subwoofer boxes, but the end result is magnificent.

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