Subwoofers take many shapes and sizes, depending on the size and aesthetics of the listening environment. In general, the objective is to build the most vibration-resistant enclosure, in order to provide housing for a speaker that can move the large amounts of air that our ears perceive as bass sound. If you want to build your own subwoofers for a home entertainment system or car audio system, there are many plans and kits available.
To Port or Not To Port
There are five types of cabinet designs for building a subwoofer box. By far, two are the most popular: sealed and ported.
The sealed box is often seen in stores as a front- or down-firing speaker in an enclosed cabinet. When these are powered by an internal amplifier built within the cabinet, they are called powered subwoofers. When an amplifier is not built in, the subwoofer is a passive. Both are designs for large speakers, from 12 to 18 inches.
Ported subwoofers produce more bass with less amplifier power than sealed designs. They are also more difficult to build, owing to the addition of the port, or hole, that is in the box to augment the reproduction of very low frequencies. Ported designs are larger than a sealed box. They use the same loudspeaker, but require more precise adjustments, referred to as tuning, and more bracing within the cabinet for rigidity against vibrations from the production of low-bass frequencies. Ported subwoofers are also either powered or passive, depending on whether they include a built-in amplifier. Ported, vented and bass reflex are used interchangeably to describe this type of speaker.
Subs Go Anywhere
Human ears cannot discern the direction of bass sounds. That's why subwoofers can be front firing, rear firing or down firing. Subwoofers can therefore be placed anywhere in a listening environment, and take shapes other than the traditional rectangle. This lets them serve as end tables or coffee tables without affecting audio performance.
Subwoofer Box Materials
Birch plywood has always been good for manufactured speakers since the mid-1940s. Three-quarter- to one-inch plywood is used on all surfaces. More recently, MDF (medium density fiberboard) is a preferred do-it-yourself material. MDF is denser than plywood, making it good for subwoofer box construction. MDF is also more expensive than plywood, and creates a lot of dust when sawed into pieces. Both materials can be found at home improvement stores such as Home Depot or Lowe's, which will cut the material to size for you for a small fee. Sonotube, a reinforced cylindrical cardboard for pouring cement, is also available to create round subwoofer designs.
Box Building Tips
Glue, screws, caulking and patience are required to produce high-quality subwoofer enclosures. Each joining of cabinet surfaces should be clamped and allowed to fully dry before proceeding further. Speakers should not be installed in cabinets until the final step, as gases emitted from caulk while drying within a cabinet can eat away at speaker surrounds. Finally, there are many vendors of pre-made cabinets. Two good ones are Madisound and Parts Express. There are also speaker building software programs to aid the design process. A popular software program for Windows computers is WinISD. For precisely tuning the cabinet to reduce unwanted vibrations and sounds, ThieleSmall.com has a database of more than 5,000 different speakers. Finally, finish the cabinet with the wood veneer, paint or stain of your choice. There are many, many of these to choose from too.