A subwoofer is a piece of audio equipment designed to produce or enhance low audio frequencies such as bass and sub-bass. They are rarely used in isolation; instead, they are used to supplement other loudspeakers that produce higher frequency sounds. A subwoofer contains one or more woofers—the speaker drivers—that are mounted to a subwoofer enclosure made of wood or plastic. The quantity, size, and placement of each woofer can create a variety of subwoofer types, including horn-loaded, bandpass, and isobaric subwoofers. If a subwoofer has a built-in amplifier, it is considered an active subwoofer.
A subwoofer is technically a type of loudspeaker, though most audio frequencies are produced by loudspeakers with higher ranges. A subwoofer can produce sounds that range in lower frequencies from 20-200 Hz, like a bass guitar or a tuba. Mid-range speakers usually handle 200-2k Hz frequencies, although some are designed to produce lower frequencies as well. Tweeters produce sounds at the highest frequencies of human hearing, between 2k-20k Hz.
Another way to think about how these pieces of equipment work together is choral ranges: subwoofers are like bass singers, mid-range speakers are like tenor and alto singers, and tweeters are like soprano singers. All three types work together in harmony to create a multi-dimensional sound. Likewise, a subwoofer adds dimension to the sound mid-range and tweeter speakers produce.
Subwoofers are frequently used in home stereo systems and automotive audio installations. Commercially, subwoofers are used in theaters, nightclubs, and concert venues. Musicians and DJs often use a subwoofer in conjunction with mid-range speakers and tweeters to create a rich, custom sound for their artistic needs. Hip hop and rock music, for example, are especially popular genres to use with subwoofers to enhance bass frequencies.
It’s worth noting that the placement of a subwoofer within a room (and the shape of the room itself) can have a major impact on its performance. For example, a room might have a “bass trap” that flattens the sound’s lower frequencies, effectively counteracting the subwoofer. Different room modes can enhance different frequencies, so a room must be treated with absorbent materials and strategic equipment placement to balance the frequencies as much as possible.