To improve the low frequency sound we added a subwoofer to our home theater system. The driver was purchased from Adire Audio (out of business). It is the Shiva, an impressive dual voice coil driver specifically designed for subwoofer applications. The enclosure was built from plans in an app note from Adire audio. The outside dimensions are 18” by 18” and it is 22” high. It is internally braced side to side, rear to midbrace, and front to midbrace. It has an internal volume of 88.5 liters and a Q of 0.6.
It is constructed from a single 4’ by 8’ sheet of 3/4” MDF. Due to the size and weight of this sheet I had Home Depot do a couple of rough cuts before I left the store. MDF is a great material for speaker cabinets, it is dense, very flat, and does not warp. It drills, cuts, routes, and machines very well although it can be tough on bits/blades, carbide is recommended.
MDF also tends to absorb a lot of paint. Priming and 1 or 2 coats of paint are advised.