How to Build a Subwoofer Box
This DIY project can be a real money-saver
Erin Blanton wrote about mobile A/V gear at Crutchfield for several years, and worked as a Sales Advisor in our contact center before that. She left Crutchfield to open her own toy store, Pufferbellies, in nearby Staunton, Virginia, which continues to keep her busy.
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What you'll need
Building your own subwoofer box is a great way to get the look and fit you want, without spending a fortune. All you need is a few basic tools, hardware, and materials.
Cost for materials (not including the subwoofer)
We spent right around $25, though your costs will vary depending on what you already have in the garage.
Building our sub box took about an hour and a half. Your project could take more time or less, depending on the complexity of your box's shape, and the tools you have at your disposal.
Tools and materials
- Electric drill with bits for pre-drilling screw holes and driving screws
- 3/4" MDF (medium density fiberboard)
- 2" drywall screws
- Panhead sheet metal screws (1/2" and 3/4")
- Carpenter's glue
- Silicon caulk
- Non-hardening rope caulk
- Speaker terminal cup
Choosing your subwoofer
I chose an Alpine 10" subwoofer for my CR-V because it requires relatively little box volume.
When choosing a subwoofer, carefully note the manufacturer's recommended enclosure size, especially if you have limited space in your vehicle. The box volume tells you how big your enclosure needs to be for maximum performance from the sub. The box shown in this article was intended for my Honda CR-V, so I wanted to make sure it wouldn't take up too much space. With that requirement in mind, I chose a 10" Alpine sub. The manufacturer recommends a box volume of 0.6 to 1.25 cubic feet.
Designing the box
To determine the correct dimensions for any subwoofer box, you can follow these steps:
Determine the minimum depth of your box. Measure the depth of your subwoofer and add 2 inches. This measurement is the minimum depth of your box (in this article, the depth refers to the front-to-back dimension of the box, with the woofer being mounted to the front).
Determine the minimum height and width of your box. Measure the frame diameter of your woofer, or check the mounting template that may be included with the owner's manual, to determine the minimum height and width for the front of your box. If you plan to mount a grille, be sure to allow for any additional space that may be needed to accommodate it.
Determine the available space in your vehicle. Measure the height, width, and depth of the vehicle space that you are willing to devote to your subwoofer. If the box must be wedge-shaped to fit, you will need to know the depth at the box's top and bottom.
Sketch out your box. Now's the time to sketch your box on paper using the dimensions you've gathered. The box shown in this article is rectangular, but you may find that a wedge-shaped box fits better in your car or truck. Your sketch may look like one of these:
For our examples, let's use the following external dimensions:
Depth 1: 5"
Depth 2: 8"
Determine the internal dimensions and volume of your box. The above steps identified the external dimensions of the box. To determine the internal volume, just subtract the thickness of the wood to be used for construction. If you're using 3/4" MDF (recommended!), then 2 x 3/4", or 1-1/2", will be subtracted from each dimension.
The internal dimensions for our examples:
Depth 1: 3.5"
Depth 2: 6.5"
Calculate the internal box volume in cubic inches. Based on the internal dimensions, you can calculate the internal volume of the enclosure using the following formula: Height x Width x Depth = Cubic Volume
Let's plug in some numbers:
11.5" x 12.5" x 10.5" = 1,509.375 cubic inches
Wedge box: Since the wedge box has two depth dimensions, we need to find the average depth before we can determine the volume. To find the average depth, add the two depth measurements together, then divide by two. Remember that Depth 1 = 3.5 and Depth 2 = 6.5.
3.5" + 6.5" = 10"
10" / 2 = 5"
So, the average depth of the wedge-shaped box is 5". Plug that dimension into the formula:
12.5" x 16.5" x 5" = 1,031.25 cubic inches
Convert cubic inches to cubic feet. Since most manufacturers will provide the recommended box volume in cubic feet, you'll need to convert the internal volume from cubic inches into cubic feet. This is done by dividing the cubic inches by 1,728.
Rectangular box: 1,509.375 / 1728 = 0.873 cubic feet
Wedge box: 1,031.25 / 1728 = 0.597 cubic feet
Adjust your box's volume to match the sub's specifications. Now, compare the volume of the box you've sketched to the manufacturer's recommendation. If it's too large or too small, you can make small adjustments to one dimension until your box's internal volume matches the manufacturer's recommendation as closely as possible. Often, manufacturers will recommend a range of enclosure volumes. You can get good results with a box that's anywhere inside the recommended range.
Determine the final exterior box dimensions. Once you've identified the correct internal dimensions, it's time to add back that 1-1/2" we subtracted in step 5, to derive the new external dimensions. Double check to make sure that these dimensions will fit properly in your car, and you're ready to move on to construction.
Click on the photos to enlarge.
Finishing and customizing the subwoofer box
After finishing the box, I couldn't wait to pop it in my CR-V. After the glue and caulk had dried, we hooked it up to the rear channels of my Alpine 4-channel amplifier using 12-gauge speaker cable. It sounded excellent, and the box was definitely sturdy.
However, since naked MDF leaves something to be desired in the looks department, I checked in with Crutchfield's installation specialist, Warren Hawkins, to get some ideas on customizing a subwoofer box. He offered up plenty of inspiration and installation tips on all kinds of coverings, from vinyl to carpet and beyond!
Thanks to Kelley Blanton, and to Taylor and Boody Organbuilders of Staunton, VA, for the use of their facility and tools.