How to build a subwoofer box to specifications? (That Really Works)

There are so many benefits attached to doing things yourself. It’s this same love for DIYs that’s brought us here to the point where we can freely show you how to build a subwoofer box to specifications by yourself. While DIYs might not be for everyone, it wouldn’t hurt to try.

Besides, building a subwoofer box yourself would save you a lot of money, and you’ll also whip it up to your taste. Ready to create a cool subwoofer box for your Subwoofer? Then let’s get kicking into it.


Designing a Subwoofer Box

When it comes to building subwoofer boxes, there are a few factors you should consider. Of course, you’ll need to consider the size of the Subwoofer before you start to cut the wood into the shape of the Subwoofer.

But that’s on the general front. Specifically, you’ll need to determine your box’s internal and external dimensions to carve out the perfect box for your Subwoofer.

While the process of determining the external dimensions of the box only requires essential measurement, getting the interior dimensions requires you to channel your inner math genius.

In plain words, you’ll need to do a bit of math. Hold on, don’t freak out! The math required here is quite basic, and we’ll show you how to do it. So, keep reading.

Related: DIY speaker kits

What’s the minimum depth of the box?

Before you start to cut into your box, you need to determine your box’s minimum depth. That is the first step to determine the external dimension of the box.

When we talk about the depth of the box, you can get it by measuring the front-to-back of your Subwoofer. But that’s not all. You have to add two additional inches to the depth measurement you’ve obtained from measuring the Subwoofer.

Adding the extra inches is a great way to avoid ugly surprises, as you would have to mount the Subwoofer into the box from the front. The extra inches would come in handy during fitting.

Related: How to test subwoofer

What’s the minimum height and width? 

The next thing to do after you’ve figured out what the depth of the Subwoofer is, proceed to determine the most diminutive height and width of the box.

The easy way to do this is to refer to the user manual of your Subwoofer. Depending on the Subwoofer’s brand, the manufacturer would write the height and width on the manual.

However, not every subwoofer manufacturer sees the need to include this detail in the manual. Hence, if the manufacturer doesn’t highlight the height and width of the Subwoofer on the manual, you’ll need to measure the woofer to determine the least width and height.

The simple way to do this is to measure the Subwoofer’s frame diameter. Of course, when noting the frame diameter, add a couple of inches to create space for when you mount the woofer in the box.

Your Vehicle’s Space: 

Your car might not come with sufficient space for your Subwoofer, and that’s fine. It shouldn’t stop you from installing the Subwoofer in your car.

So, you should create space in your car for the Subwoofer to fit in. Since you now have an idea of the external dimensions of the box, you can determine just how much space the Subwoofer would need to occupy in your car.

Proceed to measure the depth, width, and height of the space you’re willing to set aside for your woofer. If you have to turn the box into a wedge-shaped box, you’ll also need to consider how deep the top and bottom of the box must be to fit into the car space you created for it.

Once you’ve determined all the necessary dimensions for the car space, proceed to make any adjustments you need to make on the car.

Related: How Does A Subwoofer Work

Determine the internal dimension. 

Now, you have to activate your inner math genius to determine the box’s internal dimension and volume successfully.

But first, we start with the internal dimension. To begin, let’s devise random numbers for our external dimension. The reason? The figures from the outer dimension are an integral part of determining your internal dimension.

Regular boxes (precisely rectangular boxes)

  • Depth: 13”
  • Width: 15”
  • Height: 14″

Wedge-Shaped boxes.

  • Depth 1: 6”, Depth 2: 9”
  • Width: 19”
  • Height: 15”

With the above numbers of the external dimension of our imaginary box, we can figure out the internal dimension and volume of the box. Note that when you’re using this guide, swap these random numbers above for the actual external dimension of your box.

First, subtract 2 inches from the thickness of the wood you chose for this project. We’ll recommend that you use a 3/4 thick MDF wood for this DIY project. However, if your woofer is about 8″ or less, you should use 1/2 MDF wood.

But there are other wood types that you can use. We’ll discuss that later on in the article. For now, follow this process.

If the thickness of the MDF wood you’re using is 3/4 (as recommended), you’ll need to multiply 2inches by 3/4, which is the wood’s thickness. Then, you should deduct the result from the external dimension of the box.

Related: How to connect a subwoofer to an old amplifier

In practice, it’ll look like this;

2­­ x 3/4= 1.5

Then, subtract 1.5 from each of the box’s dimensions. Check below to see the result you’ll get.

Regular boxes (precisely rectangular boxes)

  • Depth: 11.5”
  • Width: 13.5”
  • Height: 12.5”

Wedge-Shaped boxes. 

  • Depth 1: 4.5”, Depth 2: 7.5”
  • Width: 17.5”
  • Height: 13.5”

The above table displays the actual internal dimension you’ll work with to successfully carve your box.

There’s a formula that’ll help you determine the internal volume. The formula is height x Width x depth = Cubic Volume.

Note that the Height, Width, and Depth to be used is the internal dimension and not the numbers from the external dimension. Hence, the cubic volume for a regular/ rectangular box would be;

12.5” x 13.5” x 11.5” = 1,940.625 cubic inches.

For a wedge-shaped box, there’s a bit of a twist in the process of determining the cubic volume. The reason is the two-depth dimension that a wedge-shaped box has.

Hence, you have to determine the average depth before you can determine the volume. To determine the average depth, you need to add the two depth dimensions of the box and divide them by 2. So, here’s what you’ll have in terms of the formula.

Depth 1 + Depth 2 / 2 = Average depth

4.5” + 7.5” = 12”

12/ 2= 6”

After dividing the total depth by 2, the average depth is 6.”

Then, proceed to insert the average depth into the cubic volume formula as the depth dimension of the wedge-shaped box. what you’ll get is,

13,5” x 17.5” x 6” = 1,417.5 cubic inches.

But there’s more! You have to convert the cubic inches into cubic feet to help you quickly determine the volume on the box. You’ll have to divide the cubic inches of the boxes by 1728 (which is the number of cubic inches you’ll get in a cubic foot)

For the regular/ rectangular box: 1,940.625 / 1728 = 1.123 cubic feet

For the wedge-shaped box: 1,417.5 / 1728 = 0.820 cubic feet.

A note of warning: ensure the volume is the same as the manufacturer’s recommendation. If it’s not, implement the required adjustments, then figure out the box’s final dimension.

Check to be sure that it still fits perfectly into the car space you created for it. If it does, it means you’ve completed the designing and calculation stage. So, you can proceed to the next step.

Related: How to install tweeter

Considering the Material to Build a Subwoofer Box

The materials you’ll need to build sub boxes include

  • 3/4” or 1/2 Medium Density Fiberboard (MDF). The MDF inch to use depends on the size and inch of your woofer. Alternative materials include fiberglass or plywood.
  • Circular Saw or Table Saw
  • Jigsaw
  • Carpenter’s glue
  • Electric drill
  • Speaker terminal cup
  • Silicone Caulk
  • A pair of compasses
  • 2” drywall screw
  • Tape measure and a straight ruler
  • Pencil
  • Furniture Clamp
  • Wet rag
  • 1/2″ and 3/4″ sheet metal screws
  • Coarse sandpaper

How to build a subwoofer box to specifications (step by step)

Cut out the necessary Parts:

Start by cutting out the essential parts of the box. These parts include the front, back, and sides of the box. Ensure you cut out perfect squares that are flat and smooth. You’d create an easily sealable box as a result. Your table and circular saw would come in handy for this part of the task.

Related: what is a subwoofer

Mark the front opening for the Subwoofer: 

Using the compass, make a circular marking on the front opening for the Subwoofer. Give your woofer a solid mounting surface by trying out the double-thickness method. You’ll need two identical pieces to achieve double thickness for the front part.

Strengthen the front pieces:  

if you settle for double thickness, use the carpenter’s glue and sheet metal screw to hold the two identical pieces together. Although the front pieces are already strong, you can add bracing to increased strength. However, you’ll need the bracing more on the front pieces if you’re not deploying the double-thickness method.

Cut-out the Markings: 

Drill through the markings you made on the front pieces so that your jigsaw can cut through the marking. Then, cut out the shape of the markings to have your woofer opening. Repeat the same method you used to create the woofer opening to create a space at the back for the terminal cup. Proceed to install your terminal cup and a silicone caulk bead around the rectangular edges of the terminal cup opening. Make the silicone caulk firm with the sheet metal screw.

Fit the other pieces together: 

Start by pre-drilling holes into the different pieces of the wood before joining them together. While putting the pieces together, overlap the smaller parts of the box with the largest pieces for strength. Piece the parts together with the carpenter’s glue and fit screws into the pre-drilled holes to ensure the box closes firmly.

Further, Fasten the box together: 

You’ll need your cordless screw and 2″ drywall screws to fasten the pieces further together to form a perfect box. Of course, some of the carpenter’s glue would slip out while you attach the screws. You can get rid of the glue with a wet rag. Once you’ve fastened the box to your taste, check the square alignment. Do you have a perfect square, or the square looks a lot misaligned? If you’ve got an ideal square box, proceed to the next stage. If not, use a furniture clamp to restore the box’s perfect square shape.

Fit the Subwoofer into the box: 

Put your Subwoofer into the box. If it tightly fits into the box, expand the opening with coarse sandpaper. Then, use a pencil and the Subwoofer that’s still in the box to mark the holes you’ll use to mount the woofer. Once you’ve successfully marked the holes, take out the woofer and pre-drill the holes. Screw your screws into those pre-drilled holes.

Fit the Subwoofer in: 

Before you fit in the Subwoofer, successfully seal every part by putting a silicone caulk bead on the internal seals and round the edges of the opening. Wait for 24 hours, then fit in your Subwoofer. Run the speaker wires through the terminal cup, and you’re good to go.

Related: Midbass vs Midrange

Wrap Up

There you have it! Although it might seem like a complicating process, building a subwoofer box is easier than you think. You have to get familiar with the math angle. Then, learn the necessary tools and equipment you’ll need to build the subwoofer box from scratch.

You’ll also need a good teacher. With our guide that teaches you how to build a subwoofer box to specifications in detail, you’ll never go wrong. Follow all the steps, understand the math equation necessary to carve your box to specification, and you’re good to go.

It’s that easy, and you can whip out your Subwoofer without breaking a sweat.

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