The primary subwoofer parts are the woofer, also referred to as the driver, and the cabinet. Many subwoofers are active and have dedicated amplifiers. Other subwoofer parts, such as the cabinet and the stuffing, will vary by intended application. Subwoofers are typically placed into one of five main types or categories, which are as follows: sealed, ported, band pass, passive radiator, and transmission line. They may be utilized in a home audio system, an automobile audio system, or as a part of a professional audio set-up.
The woofer, or driver, is the speaker that produces the low-frequency sound that is acquired by proper assembly of the assorted subwoofer parts. Typically, the speaker size is between 8 and 21 inches (approximately 20 to 53 cm). Odd sizes may be preferred for specialized applications. Smaller drivers can be found in desktop computer multimedia systems, while much larger versions are often used in dance clubs.
Woofers are speakers designed to produce a frequency between 20 and 200 Hz. The voice coil is composed of magnets that attract and repel, moving the diaphragm to make sound. A suspension holds the diaphragm in place while allowing for just enough movement. All of these subwoofer parts are housed in a large frame called the basket, which is then installed into an enclosure or cabinet.
Cabinets can be built from plywood, medium-density fiberboard (MDF), fiberglass, or another similar stiff material. The precise dimensions of the cabinet will be determined by the specifications of the other subwoofer parts, especially the requirements of the woofer. Adjustments made to the dimensions of the enclosure will alter the resultant sound produced. Cabinets may be purchased pre-built or custom made and will sometimes include back panels for sound control and adjustment.
Within the cabinet, the remaining subwoofer parts are compiled to achieve the desired sound. A key contributor to achieving satisfactory sound is the choice of stuffing or insulation material. To help insulate the sound and protect the internal subwoofer parts, a myriad of materials, like fiberglass, wool, and polyfill, are used. Fabrics and foams specially designed for acoustic applications are also available to assist with fine-tuning.
An amplifier is employed to power the subwoofer and may be incorporated into the cabinet as one of the internal subwoofer parts or may be external to the cabinet unit. Crossover filters are sometimes incorporated in a passive system to an external amplifier. A number of subwoofers also utilize equalizers for enhanced sound control. These components can range from simple and utilitarian to complex and full of options.