GUITARS

The guitar is a musical instrument with ancient roots that is used in a wide variety of musical styles. It typically has six strings, but four, seven, eight, ten and twelve string guitars also exist.
Guitars are recognized as one of the primary instruments in blues, country, flamenco, rock music, and many forms of pop. They can also be a solo classical instrument. Guitars may be played acoustically, where the tone is produced by vibration of the strings and modulated by the hollow body, or they may rely on an amplifier that can electronically manipulate tone. Such electric guitars were introduced in the 20th century and continue to have a profound influence on popular culture.
Traditionally guitars have usually been constructed of combinations of various woods and strung with animal gut, or more recently, with either nylon or steel strings. Guitars are made and repaired by luthiers.

Headstock
Main article: Headstock
The headstock is located at the end of the guitar neck furthest from the body. It is fitted with machine heads that adjust the tension of the strings, which in turn affects the pitch. Traditional tuner layout is "3+3" in which each side of the headstock has three tuners (such as on Gibson Les Pauls). In this layout, the headstocks are commonly symmetrical. Many guitars feature other layouts as well, including six-in-line (featured on Fender Stratocasters) tuners or even "4+2" (Ernie Ball Music Man). However, some guitars (such as Steinbergers) do not have headstocks at all, in which case the tuning machines are located elsewhere, either on the body or the bridge.

Frets
Main article: Fret
Frets are metal strips (usually nickel alloy or stainless steel) embedded along the fretboard and located at exact points that divide the scale length in accordance with a specific mathematical formula. Pressing a string against a fret determines the strings' vibrating length and therefore its resultant pitch. The pitch of each consecutive fret is defined at a half-step interval on the chromatic scale. Standard classical guitars have 19 frets and electric guitars between 21 to 24 frets (though Ibanez has issued guitars with as many as 36 frets.)
Frets are laid out to a mathematical ratio that results in equal tempered division of the octave. The ratio of the spacing of two consecutive frets is the twelfth root of two. The twelfth fret divides the scale length in two exact halves and the 24th fret position divides the scale length in half yet again. Every twelve frets represents one octave. In practice, luthiers determine fret positions using the constant 17.817, which is derived from the twelfth root of two. The scale length divided by this value yields the distance from the nut to the first fret. That distance is subtracted from the scale length and the result is divided in two sections by the constant to yield the distance from the first fret to the second fret. Positions for the remainder of the frets are calculated in like manner.
There are several different fret gauges, which can be fitted according to player preference. Among these are "jumbo" frets, which have much thicker gauge, allowing for use of a slight vibrato technique from pushing the string down harder and softer. "Scalloped" fretboards, where the wood of the fretboard itself is "scooped out" between the frets allows a dramatic vibrato effect. Fine frets, much flatter, allow a very low string-action but require other conditions such as curvature of the neck to be well maintained in order to prevent buzz. Frets worn down from heavy use can be replaced or, to a certain extent, re-shaped as required.

Neck
Main article: Neck (music)
A guitar's frets, fretboard, tuners, headstock, and truss rod, all attached to a long wooden extension, collectively constitute its neck. The wood used to make the fretboard will usually differ from the wood in the rest of the neck. The bending stress on the neck is considerable, particularly when heavier gauge strings are used (see Tuning), and the ability of the neck to resist bending (see Truss rod) is important to the guitar's ability to hold a constant pitch during tuning or when strings are fretted. The rigidity of the neck with respect to the body of the guitar is one determinant of a good instrument versus a poor one. The shape of the neck can also vary, from a gentle "C" curve to a more pronounced "V" curve. There are many different types of neck profiles available, giving the guitarist many options. Some aspects to consider in a guitar neck may be the overall width of the fingerboard, scale (distance between the frets), the neck wood, the type of neck construction (for example, the neck may be glued in or bolted on), and the shape (profile) of the back of the neck. Other type of material used to make guitar necks are graphite (Steinberger guitars), aluminium (Kramer Guitars, Travis Bean and Veleno guitars), or carbon fiber (Modulus Guitars and ThreeGuitars).
Double neck electric guitars have two necks, allowing the musician to quickly switch between guitar sounds.

Strings
See also: Classical guitar strings
Modern guitar strings are manufactured in either metal or organo-carbon material. Instruments utilising "steel" strings may have strings made of alloys incorporating steel, nickel or phosphor bronze. Classical and flamenco instruments have historically used gut strings but these have been superseded by nylon and carbon-fibre materials. Bass strings for both instruments are wound rather than monofilament.
Guitar strings are strung almost parallel to the neck, whose surface is covered by the fingerboard (fretboard). By depressing a string against the fingerboard, the effective length of the string can be changed, which in turn changes the frequency at which the string will vibrate when plucked. Guitarists typically use one hand to pluck the strings and the other to depress the strings against the fretboard.
The strings may be plucked using either the fingers or a pick (or plectrum).

Body (electric guitar)
See also: Solid body
Most electric guitar bodies are made of wood and include a plastic pick guard. Boards wide enough to use as a solid body are very expensive due to the worldwide depletion of hardwood stock since the 70's, so the wood is rarely one solid piece. Most bodies are made of two pieces of wood with some of them including a seam running down the centre line of the body. The most common woods used for electric guitar body construction include maple, basswood, ash, poplar, alder, and mahogany. Many bodies will consist of good sounding but inexpensive woods, like ash, with a "top", or thin layer of another, more attractive wood (such as maple with a natural "flame" pattern) glued to the top of the basic wood. Guitars constructed like this are often called "flame tops". The body is usually carved or routed to accept the other elements, such as the bridge, pickup, neck, and other electronic components. Most electrics have a polyurethane or nitrocellulose lacquer finish. Other alternative materials to wood, are used in guitar body construction. Some of these include carbon composites, plastic material (such as polycarbonate) and aluminium alloys.


articles picked up from wikipedia.