|This article does not cite any references or sources. (December 2009)|
A guitar speaker is a loudspeaker – specifically the driver (transducer) part – designed for use in or with the guitar amplifier of an electric guitar. Typically these drivers produce only the frequency range relevant to guitars, which is similar to a regular woofer type driver, which is approximately 75 Hz — 5 kHz.
The cones of these drivers typically range in size from 6.5 in to 15 in with 10 and 12 in models being the most popular. As with all loudspeaker drivers, the magnets are usually made from Alnico, ceramic, or neodymium with higher quality Alnico magnets reserved for expensive models.
A Guitar speaker cabinet contains one or more guitar speakers - as many as eight, often 10" or 12" types. A 4x12 ("four by twelve") is a guitar speaker cabinet containing four 12" speakers. A cabinet is usually mono, but may have two inputs for a "stereo" amplifier. Two speakers in a cabinet may be wired in parallel (lowering the impedance) or in series (increasing the impedance). Larger multiples will usually be series/parallel to maintain an impedance of 4 to 8 ohms. Bass guitar cabinets often have multiple different-sized speakers, such as a mixture of 12" and 15" speakers. Some bass cabinets incorporate horns.
Often what is referred to as a "guitar amp" is in fact a combo amplifier: a cabinet with speakers and a built-in amplifier. Combo amplifiers may be referred to by their speaker cabinet configuration plus the word "combo", so that "4x10 combo" means a guitar amplifier built into a 4x10 speaker cabinet.
Since the popular configurations are limited in variety, cabinet configurations are often written abbreviated without ambiguity: For example, 4x10" may be written 410, and 112 refers to a single cabinet housing a 12" speaker.
The speaker cabinets, which hold these drivers can be closed-back or open-back, along with variations such as a semi-open back 4x12 in cabinet, which may have a baffle deflecting two of the four speakers. Closed back cabinets may be acoustic suspension or bass reflex.
The sound of the speaker and cabinet is crucial to the sound of the electric guitar, so much so that it needs to be considered part of the instrument. If the clean signal from a guitar amplifier or pre-amplifier is captured directly, it is very brittle and thin, with no resonant depth, particularly from a solid-body electric guitar. A distorted signal used directly is even worse: It can be described as excessively shrill, scratchy and fizzy, completely different from the smooth tones that listeners hear in recordings or live performances.
When driven hard, guitar speakers produce complex behavior. There will be some power compression, several kinds of distortion, even mechanical limiting as one or more drivers approach their physical limits (e.g. cone excursion). A guitar speaker shows a nonlinear frequency response depending on the speaker's load, e.g. the frequency response at small amplitudes is different from those at large amplitudes.
A guitar speaker isolation cabinet contains a guitar speaker and one or two microphones in a single- or double-layer soundproofed box. These devices allow the capture of the sound of a guitar amplifier and speaker being played loud, while minimizing "bleed through" between tracks in the mix. These are almost exclusively used in recording studios and during live performances that are being recorded.
As an alternative to the isolation cabinet, there exist guitar speaker cabinet emulating circuits or signal processors (also known as direct boxes), allowing the sound of a guitar amplifier to be fed directly into recording equipment without the need for a speaker cabinet and microphone. Cabinet emulation is available in software also. Cabinet emulation is complex, but in its core essence it is equalization, which combined with a model of resonance, modeling the frequency response of the speaker as well as the internal reflections and standing waves of the cabinet.