Four types of subwoofer enclosures are available from speaker manufacturers, including the infinite baffle, sealed, ported, and band pass constructions. The subwoofer enclosure is commonly made of strong wood in the shape of a box, securely assembled with nails to prevent any rattling between the wood joints. Sound moves through the wood box to provide a deep or flat bass, depending upon the chosen type of subwoofer enclosure.
The infinite baffle subwoofer is typically installed in a vehicle's trunk or within a rear window deck. The front of the subwoofer is physically attached to a board, such as thick plywood, allowing the speaker's rear cone to hang freely within the trunk or deck structure. Unlike the other subwoofer enclosures, the infinite baffle uses the trunk or deck as the enclosure structure. The bass produced is relatively flat, but offers an inexpensive subwoofer choice for those on a budget.
Sealed subwoofer enclosures place the subwoofer within a secured box, only allowing the speaker's front cone to project outward from the box. This enclosure type emanates a firm bass, without producing a vibratory boom, in a compact enclosure design. Buyers should be aware that sealed subwoofer enclosures must have an accompanying amplifier to provide the needed power for an adequate bass output. The amplifier must match the subwoofer in power output. Lack of power can produce a weak sound, whereas excessive power leads to subwoofer damage.
Ported subwoofer enclosures use the same construction design as the sealed speaker, but the enclosure has an added opening near the cone's rear area. The opening, or port, allows the rear sound waves to emanate out of the enclosure. The movement of the front and rear sound waves together produces the low frequency bass that many music enthusiasts enjoy for rock and roll songs. The main drawback to the ported design is the need for space; the enclosure must have room for the physical speaker and a tube shape for the port itself.
Band pass designs generate the booming sound that is commonly heard from loud car speaker systems. This enclosure type uses two spaces within the box; one side holds the sealed subwoofer, and the second side has a tube for porting the sound waves. Speaker enclosure designers can alter this internal structure, adding multiple ports at different angles to achieve varying bass outputs. The louder bass boom requires a large enclosure structure, especially if numerous ports are involved.