The portion of an amplification or sound reinforcement system that houses the speakers. In instrument amplification systems the cabinet usually refers to an enclosure of one or more speakers that does not contain any of the amplification devices (an amp and speaker cabinet as one unit is generally just referred to as an “amp” or a “combo amp”).
Over the years, there have been lots of different guitar cabinet configurations, with the most common being the 4×12 (four 12″ speakers), though there have been 4×10, 2×12, 1×12, and even a 2×15. Marshall has become almost synonymous with its monstrous 4×12 cabinets, and Fender was producing 2×12 cabinets as early as 1961 for its Tremolux amp, though by the following year, the Dual Showman amp head appeared with a matching 2×15 cabinet (and yes, it was very heavy)!
Guitar cabinets have different form factors to allow for maximum projection and dispersion. For example, some 4×12 cabinets have a “slant” design where two of the speakers are tilted back to aim more at the guitarist’s ears. A “straight” 4×12 has a more vertical front panel (called the “baffle“) and is designed to project the sound more directly forward. They can have either open or closed backs, which greatly impacts the tone. In addition, they may or may not have ports, which affect the amount of bass energy they project.
Bass cabinets may come in many different configurations as well…4×10, 2×15, 1×15, 8×10, with and without midrange and high-frequency drivers (tweeters) – and the corresponding crossover circuits required to divide the input signal into multiple frequency ranges – and often feature ports to increase bottom end.
PA or sound reinforcement cabinets have all of these variables and a few more. Some may have passive crossovers built in to divide frequency ranges, they may be of the horn-loaded, or folded-horn variety with all sorts of different dispersion characteristics. They may be fitted to accept the pole of a speaker stand or have flying hardware points and/or be shaped so that many can be placed together in an array. Sizes and shapes depend a lot on the specific application the cabinet is designed for. There are cabinets designed only to handle very low frequencies that may have many large speakers (18″ or more), while others may be designed to be small and blend in with the aesthetic of auditoriums and so forth.
Monitor cabinets are also used in sound reinforcement applications. Monitor cabinets can come in the form of small wedge-shaped boxes that sit in front of performers, larger conventional PA-type boxes that sit on the side of a stage for overall fill monitoring (aptly called side-fill monitors), behind or beside drummers, etc. Again, a variety of shapes, sizes, and configurations are common.
In odd contrast to instrument cabinets, PA cabinets may have amplification systems on board and still be called cabinets, though often the term “powered” or “active” speaker is used.