Acoustic Guitar

Five courses, then six strings

The guitar has no single inventor, and its ancestry is argued over. Plucked, fretted instruments with necks and soundboxes were known across the ancient Near East and the medieval Mediterranean, and the name is usually traced through Arabic and Spanish to the Greek kithara. By the later Middle Ages two types were recognised in Spain, the Moorish and the Latin guitar. Historians generally see the later vihuela and the baroque guitar as relatives within this European family, though the links between them are not fully documented.

Surviving objects show how the modern design was reached. A decorated guitar in Edinburgh, made about 1650, began as a five-course instrument, with strings grouped in pairs, and was converted to six single strings around 1800, which shortened its neck considerably. A Viennese guitar of 1829 in the same collection has a screw in the neck heel for adjusting the string angle. By the 1840s Spanish makers such as Agustín Altimira in Barcelona were building small-bodied six-string guitars, richly ornamented, that belong to the last stage before the modern type.

The guitar in its present form is commonly credited to the Spanish maker Antonio Torres, who from the 1850s enlarged the body and standardised a fan-shaped pattern of braces under the top. In the twentieth century, the nylon string replaced gut in concert instruments. Meanwhile, a separate line of development took place in the United States, where German-trained makers and their successors built guitars for steel strings, a change that reached wide use in the early 1900s.

A box tuned by its own bracing

Everything on an acoustic guitar serves one task: turning the small motion of a string into sound that fills a room. The soundboard, or top, is usually spruce or cedar, cut thin and strengthened underneath by wooden struts called braces. Back and sides are commonly rosewood, mahogany, maple or cypress. The top moves most, carrying vibrations from the bridge, while the sides and back reflect and colour them, and the round soundhole lets air move in and out of the body.

Classical and steel-string guitars diverge in their internal structure. Classical guitars use lighter bracing, often in a fan pattern, with a wide fingerboard and strings of nylon or nylon-wrapped fibre tied to the bridge. Steel-string guitars tolerate far more tension, so their tops are usually braced in an X pattern, and their necks normally contain an adjustable metal rod to counter the pull. Scale length, the sounding length of the string, is typically around 650 millimetres on a classical guitar and a little shorter on many steel-string models.

Why nylon and steel speak differently

A plucked string releases its energy quickly, so a guitar note rises sharply and then decays. Nylon strings have lower tension and greater softness, producing a warm, rounded tone with a gentle attack. Steel strings store more energy, giving a brighter, more ringing sound with longer sustain and more audible upper partials, the faint higher tones that colour a note. Players change tone further by where they pluck: close to the bridge sounds thin and bright, nearer the soundhole rounder and fuller.

The body shapes the result through its resonances. The air inside the box, the top plate and the back each vibrate at preferred frequencies, and the balance among them gives a guitar its character. Larger bodies generally emphasise the bass, while smaller bodies often sound more focused in the mid range.

Six open strings and a rising neck

Standard tuning runs, from lowest to highest, E2–A2–D3–G3–B3–E4, mostly in fourths with a single major third between the third and second strings. Guitar music is written an octave higher than it sounds, so the written low E is E3. With about nineteen to twenty frets, the practical range spans roughly E2 to B5, and higher on instruments with a cutaway, a scooped shoulder that allows access to the upper frets.

Timbre changes along each string. Open strings ring longest and most freely, while notes high on the neck sound tighter and shorter. Natural harmonics, produced by touching the string lightly at certain frets, give bell-like overtones, while alternative tunings such as open G or drop D change which open strings ring and so alter the instrument's resonance.

Right hand, left hand

In the usual right-handed arrangement, one hand creates the sound and the other shapes the pitch. Classical players pluck with the fingertips and nails, often holding the guitar on the left thigh with a footstool, and they use rest strokes and free strokes to balance melody against accompaniment. Folk and popular players may strum with the fingers or a flat pick, and many play fingerstyle patterns that alternate a steady bass note with melodic figures.

The fretting hand presses strings against frets, forming chords or single-note lines. Techniques such as the slur, where a note is sounded by the fretting hand alone, and the barre, where one finger stops several strings at once, are central to the instrument. A capo clamped across the neck raises every open string at once, which lets players transpose without changing fingerings. Flamenco adds rapid rasgueado strumming and tapping on the top, which is protected by a thin tap plate.

Family resemblances

The flamenco guitar is a cousin of the classical model, typically lighter, with cypress back and sides and a lower string height that favours a dry, percussive tone. Archtop guitars use carved or pressed arched tops with f-shaped sound holes and were developed in the United States in the early twentieth century, and resonator guitars embed a metal cone in the body to gain volume. Twelve-string guitars double each string, and baritone models are tuned lower than the standard instrument.

Many related instruments grew from the same root. The Brazilian and Portuguese viola is a separate plucked instrument, often with doubled strings, and should not be confused with the bowed Viola. The Ukulele and Mandolin share the fretted-neck design in smaller formats, and Latin American relatives include the charango and the guitarrón. Electric versions, chiefly the electric guitar, keep the six-string layout but rely on amplification.

Song, dance and the concert hall

Few instruments move so easily between settings. In Spain the guitar is at the centre of flamenco, where it accompanies singing and dance, and in Latin America it underlies many regional song traditions, including bossa nova. Solo classical repertoire includes works by Spanish and Latin American composers, and the guitar also appears in chamber groups, from duos to quartets, and in concertos that pair it with an orchestra.

Steel-string guitars dominate American folk, country, blues and singer-songwriter music, where the instrument typically supports a voice. In jazz, acoustic guitars were a fixture of early rhythm sections, and in popular music they sit alongside drums, bass and keyboards.

Wood that reacts to weather

Because the top is very thin, an acoustic guitar responds quickly to changes in humidity and temperature. Wood that dries out can crack or shrink away from the fret ends, while damp conditions can raise the action, the distance between strings and frets. Many makers suggest keeping a guitar in a stable room at moderate humidity, in a case when it is not in use, and away from radiators, windows and closed cars.

Routine maintenance is simple. Strings lose brightness as they collect skin oils and corrode, so they are replaced when the tone dulls. Wiping the strings and fingerboard after playing slows this. Adjusting the neck rod, cutting a new nut or bridge saddle, or repairing a crack is work for a trained luthier, since mistakes are hard to reverse.

Details from the workshop and the archive

• A Spanish guitar made in Barcelona in the 1840s, now in London, is inlaid with mother-of-pearl hunting and courtship scenes, and once belonged to a daughter of the Argentine leader Juan Manuel de Rosas.
• The Edinburgh guitar of 1829 carries a printed label naming the guitarist Luigi Legnani as the model for its design, a reminder that performers influenced makers.
• When the c. 1650 guitar was converted to six strings, its neck was cut from about 305 to 223 millimetres, which damaged its engraved ivory panels.

Terms used in this entry

action

The height of the strings above the frets, which affects comfort and tone.

bracing

Thin wooden struts glued inside the top to strengthen it and shape how it vibrates.

capo

A clamp placed across the neck that shortens all the strings at once and so raises the pitch.

course

A pair of strings tuned together and played as one; early guitars often had five courses.

fan bracing

A pattern of braces radiating like a fan under the soundboard, typical of classical guitars.

luthier

A maker or repairer of stringed instruments.

rasgueado

A flamenco strumming technique in which the fingers flick outward one after another across the strings.

saddle

The strip, usually of bone or plastic, set into the bridge that supports the strings and marks their sounding end.

scale length

The vibrating length of a string from nut to bridge saddle, which affects tension and feel.

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References

1. Berklee Online. How Classical Guitar Arrived in Spain and Then the Rest of the World - Berklee Online Take Note. online.berklee.edu/takenote/how-classical-guitar-arrived-in-spain-and-then-the-rest-of-the-world
2. Victoria and Albert Museum. Guitar | Altimira | V&A Explore The Collections. collections.vam.ac.uk/item/O58876/guitar-altimira
3. University of Edinburgh, St Cecilia’s Hall. "Guitar" — St Cecilia's Hall (Staufer, 1829). collections.ed.ac.uk/stcecilias/record/96044
4. University of Edinburgh, St Cecilia’s Hall. "Guitar" (c. 1650, converted from five courses). collections.ed.ac.uk/stcecilias/record/96020

Sources were consulted for facts and context; the text is original. See Sources and Methodology.