Almost certainly one of the most, if not the most important part so of the design of a guitar are of course the strings. Whilst the shape of a guitar, its body, frets and even style of play has changed enormously over the years and as it has migrated from one country to another, the fact that it is a stringed instrument has been the case for many thousands of years. What has changed, however, is the type of material used for the manufacture of the strings, the number of strings included on the guitar, and how they are positioned or placed along the body and fret board of the guitar and neck. The traditional classical guitars and the flamenco guitars have used gut as the string in the past, although this is rarely the case today.
Modern classical guitars have replaced the use of gut for the strings with nylon instead, and in some cases carbon fibre. These are clearly more easily and cheaply manufactured, but also provide a longer life, being far less subject to wear and tear than the natural materials and fibres in something organic such as gut. Of course, not all guitars use nylon, and electric guitars particularly use steel strings instead. Not only does this provide a different sound, but more importantly, a different strength. Because the strings of a guitar are pulled very tight across the whole body, both they and the body of a guitar, especially the neck, are under a great deal of pressure and strain.
The strings of an electric guitar are under particular strain, and so nylon would simply not be sufficient as far as its tensile strength is concerned. Typically the steel strings of either electric guitars or steel strung acoustic guitars are made either from a collection of alloys, rather than pure steel itself, and these alloys usually include steel, nickel and even phosphor bronze. The strings of bass guitars are manufactured rather differently from the acoustic or electric guitars, and rather than having a single fibre or string, those incorporate into the build of a bass guitar tend to be wound instead. The strings of a guitar are strung very tightly against the neck of the guitar, and kept parallel to it for the whole distance.
Running behind the strings for almost the full length of the fret board or neck are frets, small ridges which, if the string is depressed by the finger, will catch the string at a certain, measured distance from the body, shortening the string by a mathematically calculated amount, resulting in a change of resonance or frequency that produces a distinct note. The actual method used to strum or pluck the strings of a guitar varies widely, and this can depend upon a number of factors, including the type and model of guitar, and the style of play. For example, Spanish guitars and flamenco guitars tend to be plucked, whereas some guitars are hit rather than plucked or strummed. Strumming involves pushing a nail or plectrum against the strings, usually striking all or most of the strings in ascending chromatic order.
Alternatively, individual strings may be plucked to bring out single notes, and usually in most guitar music it is a combination of these two methods which provides the backing chords and sound of the music, with the individual notes being picked out as a separate line of music. Because of the strain on the strings, it is possible that over time they stretch or loosen slightly, and so at the top of the neck is the headstock, where the strings end, and each can be tightened slightly using a turning screw. By tightening the string the length and thickness of the string is altered slightly, and this can adjust the frequency and therefore the note associated with that string. It is therefore important that prior to a performance the guitar is tuned to make sure that each string is stretched to the correct note.