System Design

The first step that has to be taken when you are designing your own enclosure is figuring out how much space is available in your vehicle. If you own a hatchback, for example, you will have to calculate the cubic feet of the hatch area, keeping in mind that you'll still need to be able to get to your spare tire. The space that you will have at hand will tell you the size and shape of the enclosure, which will narrow your choice of the drivers that you can use. For example, one 10-inch subwoofer usually requires an enclosure with 1 to 1.5 cubic feet of internal volume if you want the best performance, while a 12-inch subwoofer requires 2 to 3 cubic feet.

The table below lists what I would recommend for your box volumes for common-size drivers, but then again it's best to consult the manufacturer of the speakers you're considering in determining the best recommended box volumes.

TABLE 1 - Box Volumes for Common Driver Sizes

Driver Diameter (in) Enclosure Volume (ft 3)
6 0.3 - 0.4
8 0.6 - 0.8
10 1.0 - 1.5
12 2.0 - 3.0
15 5.0 - 9.0


It's very important for me to explain to you that any recommendation won't take into account the volume that will be displaced by the drivers, crossovers, internal braces, and, in the case of a vented system, the port.

If you prefer to compensate for these components, you are going to have to build your enclosure slightly larger than what your measurements are going to show you. As a rule, it's generally a good idea to increase the volume by 20 percent.

When you are figuring out the shape of your box, you should think of the ideal dimension guidelines which include: Depth-- should be 0.7 x; Width and Height-- 1.4 x Width. You should also, avoid constructing an enclosure with walls that have equal dimensions because this could result in a peak in the mid-bass area.

If the enclosure is going to be irregularly shaped, it's easier to think of its interior as a collection of conventional shapes; then you will calculate the volume for each, and add these volumes together. The second table will give you the formulas on calculating internal box volume.

For example, the volume of a box that has a slanted front (most common) is easily determined when you add the volume of the square or rectangular part of the enclosure at the bottom to the volume of the triangular portion at the top. You should also realize that it's easier to measure in cubic inches and then convert them to cubic feet.

Formulas - How to Calculate Internal Box Volume

Area (rectangle) = Length x Width

Area (triangle) = 1/2 Length x Width

Area (circle) = 3.14 x Radius x Radius

Area (circle) = .785 x Diameter x Diameter

Volume (rectangular box) = Area (of one side) x Depth

Volume (triangular enclosure) = Area (triangle) x Depth

Volume (cylinder) = Area (circle) x Length

1728 Cubic Inches = 1 Cubic Foot

28 Liters = 1 Cubic Foot




When you are making more than one driver enclosure, you'll get the best results when you isolate each driver in a separate chamber. This will help to prevent variations in speaker tolerances and input power from restricting system output. If you building separate chambers isn't actually possible, you can make sure that each driver receives the same amount of power by mounting two drivers that are exactly the same in the same cavity and wiring them in parallel.

With so many choices out there, selecting drivers can be a difficult task. It requires an understanding of specs as well as a sharp set of ears. Once you've decided on what type of enclosure you want and the right drivers youll need, map out the design on paper. This will help you to visualize the shape of the enclosure and may prevent unnecessary cutting. Before you saw, you will need to be absolutely sure that the enclosure will fit in your vehicle.