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While guitar construction has many variations, in terms of the materials used for the body, the shape of the body, and the configuration of the neck, bridge, and pickups, there are features which are found in almost every guitar. The photo below shows the different parts of an electric guitar. The headstock(1) contains the metal machine heads, which are used for tuning ; the nut(2), a thin fret-like strip of metal or plastic which the strings pass over as they first go onto the fingerboard; the machine heads (3), which are worm gears which the player turns to change the string tension and thus adjust the tuning; the frets(4), which are thin metal strips which stop the string at the correct pitch when a string is pressed down against the fingerboard; the truss rod(5) , a metal cylinder used for adjusting the tension on the neck (not found on all instruments); decorative inlay (6), a feature not found on lower-cost instruments.

The neck and the fretboard (7) extend from the body; at the neck joint (8), the neck is either glued or bolted to the body; the body (9)- in this instrument, it is made of wood which is painted and lacquered, but some guitar bodies are also made of polycarbonate or other materials ; pickups (10), which are usually magnetic pickups, but which may also be piezoelectric transducer pickups; the control knobs (11) for the volume and tone potentiometers ; a fixed bridge(12)-on some guitars, a spring-loaded hinged bridge called a "tremolo system" is used instead, which allows players to "bend" notes or chords down in pitch or perform a vibrato embellishment; and a plastic pickguard(13), a feature not found on all guitars, which is used to protect the body from scratches.

The wood that the body (9) is made of largely determines the sonic qualities of the guitar. Typical woods include alder(brighter, but well rounded), swamp ash(similar to alder, but with more pronounced highs and lows), mahogany(dark, bassy, warm), poplar(similar to mahogany) and basswood(very neutral). Maple, a very bright tonewood, is also a popular body wood, but is very heavy. For this reason it is often placed as a 'cap' on a guitar made of primarily of another wood. Cheaper guitars are often made of cheap woods sound sterile and lifeless, such as plywood or agathis.

[edit] Pickups

Main article: Pickup (music)

Compared with an acoustic guitar, which has a hollow body, electric guitars make comparatively little audible sound simply by having their strings plucked, and so electric guitars are normally plugged into a guitar amplifier, which makes the sound louder. When an electric guitar is strummed, the movement of the strings generates (i.e., "induces") a very small electrical current in the magnetic pickups, which are magnets wrapped with coils of very fine wire. That current is then sent through a cable to a guitar amplifier.[9] The current induced is proportional to such factors as the density of the string or the amount of movement over these pickups. That vibration is, in turn, affected by several factors, such as the composition and shape of the body.

A close-up of the pickups on a Fender Squier "Stagemaster" guitar; on the left is a "humbucker" pickup and on the right are two single-coil pickups.

Some hybrid electric-acoustic guitars are equipped with additional microphones or piezoelectric pickups (transducers) that sense mechanical vibration from the body. Because in some cases it is desirable to isolate the pickups from the vibrations of the strings, a guitar's magnetic pickups will sometimes be embedded or "potted" in epoxy or wax to prevent the pickup from having a microphonic effect.

Because of their natural inductive qualities, all magnetic pickups tend to pick up ambient and usually unwanted electromagnetic noises. The resulting noise, the so-called "hum", is particularly strong with single-coil pickups, and aggravated by the fact that very few guitars are correctly shielded against electromagnetic interference. The most frequent cause is the strong 50 or 60 Hz component that is inherent in the frequency generation of current within the local power transmission system. As nearly all amplifiers and audio equipment associated with electrical guitars rely on this power, there is in theory little chance of completely eliminating the introduction of unwanted hum.

Double-coil or "humbucker" pickups were invented as a way to reduce or counter the unwanted ambient hum sounds. Humbuckers have two coils of opposite magnetic and electric polarity. This means that electromagnetic noise hitting both coils should cancel itself out. The two coils are wired in phase, so the signal picked up by each coil is added together. This creates the richer, "fatter" tone associated with humbucking pickups. Optical pickups [10] are a type of pickup which sense string and body vibrations using infrared LED light.

[edit] Tremolo arms

Main article: Tremolo arm

Some electric guitars have a tremolo arm (sometimes called a "whammy bar" or a "vibrato bar"[11] and occasionally abbreviated as trem), a lever attached to the bridge which can slacken or tighten the strings temporarily, changing the pitch, thereby creating a vibrato effect. Early tremolo systems, such as the Bigsby vibrato tailpiece, tended to be unreliable and cause the guitar to go out of tune quite easily, and also had a limited range. Later Fender designs were better, but Fender held the patent on these, so other companies used Bigsby-style tremolo for many years.

Detail of a Squier-made Fender Stratocaster. Note the tremolo arm, the 3 single-coil pickups, the volume and tone knobs.

With the expiration of the Fender patent on the Stratocaster-style tremolo, various improvements on this type of internal, multi-spring tremolo system are now available. Floyd Rose introduced one of the first improvements on the vibrato system in many years when in the late 1970s he began to experiment with "locking" nuts and bridges which work to prevent the guitar from losing tuning even under the most heavy whammy bar acrobatics.

[edit] Guitar necks

Electric guitar necks can vary according to composition as well as shape. The primary metric used to describe a guitar neck is the scale, which is the overall length of the strings from the nut to the bridge. A typical Fender guitar uses a 25.5 inch scale, while Gibson uses a 24.75 inch scale in their Les Paul. The frets are placed proportionally according to the scale length, so the smaller the scale, the tighter the spacing of the frets.

Necks are described as bolt-on, set-in, or neck-through depending on how they are attached to the body. Set-in necks are glued to the body in the factory, and are said to have a warmer tone and greater sustain; this is the most traditional type of joint. Bolt-on necks were pioneered by Leo Fender to facilitate easy adjustment and replacement of the guitar neck. Neck-through instruments extend the neck itself to form the center of the guitar body, and are known for long sustain and for being particularly sturdy. While a set neck can be carefully unglued by a skilled luthier, and a bolt-on neck can simply be unscrewed, a neck-through design is difficult or even impossible to repair, depending on the damage. Historically, the bolt-on style has been more popular for ease of installation and adjustment; since bolt-on necks can be easily removed, there is an after-market in replacement bolt-on necks from companies such as Warmoth and Mighty Mite. Some instruments, notably most Gibson models, have continued to use set/glued necks. Neck-through bodies are somewhat more common in bass guitars.

The materials used in the manufacture of the neck have great influence over the tone of the instrument. Hardwoods are very much preferred, with maple, ash, and mahogany topping the list. The neck and fingerboard can be made from different materials, such as a maple neck with a rosewood fingerboard. In the 1980s, exotic man-made materials such as graphite began to be used, but are pricey and never really replaced wood in production instruments. Such necks can be retrofitted to existing bolt-on instruments.

There are several different neck shapes used on guitars, including shapes known as C necks, U necks, and V necks. These refer to the cross-sectional shape of the neck (especially near the nut). There are also several sizes of fret wire available, with traditional players often preferring thin frets, and metal shredders liking thick frets. Thin frets are considered better for playing chords, while thick frets allow lead guitarists to bend notes with less effort. An electric guitar with a neck which folds back called the "Foldaxe" was designed and built for Chet Atkins by Roger Field (featured in Atkins' book "Me and My Guitars."). Steinberger guitars developed a line of exotic instruments without headstocks, with tuning done on the bridge instead.

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