Measuring Dos and Don'tsDo . . . . take torsion bars and spare tire hold-downs into consideration.
Don't . measure beyond any bolts or curves that you can't remove.
Do . . . . take the opening that the box has to pass through into consideration.
Don't . forget that on some vehicles there may be a gas tank nearby with a sending unit that may need to be accounted for.
Do . . . . take into account that hydraulic cylinders may need up to 2 inches of play on each side of a sub enclosure when a side is dropped.
Don't . forget to take into account room for the hoses to flex when the hydraulic cylinders are filled (locked up).
Calculating Your CutsOnce you know the total size of the box that you desire to build, you'll need to calculate the size of the boards that you will need. There's no real science to calculating your cuts; just keep in mind how the boards will be oriented. One set of boards will be on the inside of another set of boards and the board thickness has to be accounted for. For example if your desired box is 13 1/2 x 13 1/2 x 13 1/2, build with 3/4-inch MDF then your cuts will be as follows:
> Two pieces 13 1/2 x 13 1/2 (typically the front and back)> Two pieces 13 1/2 x 12 (typically the top and bottom)> And two pieces 12 x 12 (typically the sides, and this cut would also be the same size of a divider on a dual subwoofer box)
What you'll notice about the cuts is that they are 111/42 inch apart and 111/42 inch is, of course, the total thickness of two pieces of 31/44-inch board. So the first two cuts will be on the outside of the box and one of them will have the speaker cut out of it. The next two cuts will on the inside of one dimension, but on the outside of the other dimension. The last two cuts will be on the inside of both dimensions.
Putting It All TogetherNow that you've calculated the dimensions and made your cuts you can dry fit all of the parts, then seal and assemble the box. A dry fit ensures that you've made all of your cuts correctly before you start applying glue and screws or nails, making a fix much more difficult not to mention messy. Once everything's confirmed you can start assembling the box. For box integrity, it's a good idea to glue every edge before air nailing or screwing a box together.
Additionally adding small braces on the inside of a box will ensure that the big bass won't eventually vibrate the box to pieces. The final step is purely cosmetic. This is the point where you decide if you want to wrap the box in carpet, seal and mold the box for paint, or simply toss the raw wood in the trunk. Whatever you choose, make sure that the subwoofer has some type of gasket between it and whatever it's screwed into. Most speakers have one pre-attached, but not having one will lead to a bad seal and poor sound quality.
Follow along as our guide takes us through the cutting and assembly of a basic multiple subwoofer enclosure and the simple things that make the finish product look finished.
Once complete the enclosure can be finished. Here, we've opted to carpet the enclosure. Take the time to the press the material down into the recess for good adhesion to the edges. After applying adhesive to both the material and the enclosure and allowing some cure time we can start to lay down the material. | 
After the enclosure has been finished we can wire and mount the speakers before placing the box into the car. |
The overall effect of the recess is subtle but it does add a clean finished look. A small basic trim panel was then laid out and trimmed to match the rest of the vehicle to complete the finished look of the rear hatch area. Our job here is done. |  |