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A guitar speaker is a loudspeaker – specifically the driver (transducer) part – designed for use in a combination guitar amplifier (in which a loudspeaker and an amplifier are installed in a wooden cabinet) of an electric guitar, or for use in a guitar speaker cabinet. 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. Well-known guitar speaker manufacturers include Jensen, Celestion, Eminence, Electro-Voice, JBL, Peavey, and Vox.
A guitar speaker cabinet contains one or more guitar speakers. Some cabinets contain two 10" or 12" speakers. Another popular format is four 10" or four 12" speakers. The largest guitar speaker cabinets have eight 10" or 12" speakers. 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 may include a single speaker (typically 12" or 15"), multiple speakers of the same type (common formats include 2x10", 4x10" and 8x10"). Some bass cabinets use multiple different-sized speakers, such as a mixture of 12" and 15" speakers. In rare cases, some large bass cabinets incorporate horns to boost the bass response.
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. Bass cabinets are usually closed-back, along with a bass reflex port or vent to boost low frequency response.
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's tone. If the clean signal from a guitar amplifier or pre-amplifier is captured directly (i.e., before it is sent to a speaker cabinet) it is very brittle and thin, with no resonant depth, particularly from a solid-body electric guitar. A distorted signal captured directly, without going through a speaker cabinet, is even worse: It can sound 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, which affects the sound of the instrument. 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.
Isolation cabinets and emulation devices
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 are 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 a PA system or recording equipment without the need for a speaker cabinet and microphone. Direct boxes are used more often with electric bass than with electric guitar, because the tone of a guitar amplifier and speaker is often considered to be a key element of an electric guitarist's tone. Cabinet emulation is also available in software, stompbox pedals and some guitar amps. 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.