Learn the Anatomy of the Acoustic Guitar
A Little History
Stringed instruments that bear some similarities to the modern day acoustic guitar have been in existence for thousands of years. But the history of the guitar can be somewhat confusing as not all scholars agree on the guitar's lineage. For example it has been proposed by many that the lute was a precursor to the guitar. However others feel the lute represents a different branch in the evolution of similarly stringed instruments. To make things more confusing, the name guitar and its etymological past variations guitarra, qīṯāra, cithara, kithara have been applied to a variety of different stringed instruments that mostly resemble a harp more than a guitar.
The modern guitar may well have ultimately evolved from some of these instruments, but the generally accepted predecessors are considered to be the 15th century vihuela and the 16th century baroque guitar. Both were developed in Spain, had hollow, waisted bodies with flat backs, a sound hole, moveable gut frets, and most commonly found with 5 or 6 doubled courses of gut strings. They were both played with the fingers or with a plectrum, although the vihuela was sometimes played with a bow.
A variety of different interpretations of the guitar appeared over the following years but the basic principles remained. They all still had strings that lie across a saddle and bridge which transfers the vibrations to the soundboard. Those sounds are then naturally amplified inside the hollow chamber of the guitar body and projected through the sound hole(s) to our ears. There were however some significant innovations along the way such as swapping the tied gut frets for ivory and later for metal.
Classical / Spanish Guitar
During the mid 19th century a luthier named Antonio de Torres created what is now commonly accepted as the template for the modern classical guitar. His innovations include making the guitar larger but with a thinner soundboard resulting in a louder, richer sound. He also perfected the fan bracing method (an internal structure that strengthens the soundboard) which is still in use today.
Whilst the classical, or Spanish guitar has not changed much in appearance and construction since its creation, gut strings are no longer used with nylon strings now preferred. The three lower (in pitch), thicker strings (E, A and D in standard tuning) are wound in silver-plated wire.
The back and sides of the guitar are typically made from rosewood or mahogany and the soundboard from cedar or spruce. The neck too is usually made from either mahogany or rosewood. Whilst the string tension of a classical guitar is less than that of a steel string acoustic guitar, thanks to their nylon strings, some models do still come with an adjustable steel truss rod within the neck to prevent it from bending. Classical guitar fretboards are commonly made of ebony or rosewood with twelve frets up to where the neck meets the body and are usually flat and wider than other acoustic guitars. There are additional frets along the remainder of the fretboard which continues up to the sound hole. Some models offer a cut-away in the body just below the fretboard to grant easier access to those higher frets. Both the nut and the saddle can be made of bone or an equivalent synthetic plastic material. Another recognisable feature found more on classical guitars than other acoustics is the double slotted headstock with three, backward facing tuning pegs on either side.
Whilst there are of course no rules restricting what styles of music an instrument can be used to play, the classical guitar has become synonymous with both folk and Latin American music. Typically played with the fingers and thumb plucking or strumming the nylon strings, the classical guitar has a warm sound when compared to its steel string cousins. Traditional playing techniques for classical guitar also include keeping the thumb of the fretting hand behind the neck and the body sat on a raised left leg (for right handed guitars) with a relatively steep angle of the neck.
A Little More History
Around the same time as Torres' advances with the classical guitar, the relatively new X bracing technique was being adopted by various guitar manufacturers including Martin, one of the oldest and most respected makers of acoustic guitars today. The majority of guitars were still relatively small at this point, but as demand grew for ever louder guitars, so the size of guitars increased. Sizes ranged from the small Parlour guitar, through Grand Concert and Grand Auditorium guitars, to the larger Dreadnought created by Martin (and the most popular style still today) and Jumbo created by Gibson. Most of these styles also have a cut-away version too.
By the 1930's, with the added strength provided by X bracing, steel strings, which had been around since the turn of the 20th century, were widely adopted and used on the vast majority of guitars (with the exception of nylon strung classical guitars of course). Other changes around this time included longer necks to allow fourteen frets free of the body, adjustable truss rods, and of course the invention of the electric guitar!
Steel String Acoustic Guitar
As the name suggests, one of the main differences when compared with a classical guitar is the use of steel strings which produce a brighter sound with more volume. All strings have a solid steel core but the four lower (in pitch), thicker strings (E, A, D and G in standard tuning) are then wound with bronze wire. Steel string acoustic guitars normally have heavier gauge (thicker) strings than electric guitars to improve projection. However, steel strings also create more tension than say nylon strings and so require a sturdier construction than a classical guitar. This has resulted in different bracing techniques which in turn can affect the overall tone of the instrument. Steel truss rods within the neck are also present in the majority of cases.
A similar selection of woods to those used for classical guitars can be found in steel string acoustic guitars. Rosewood or mahogany back, sides and neck are commonplace although maple is also a popular choice. Cedar or spruce are also the most common choice for the soundboard. Fretboards, typically made of rosewood, have fourteen frets up to where the neck joins the body with more frets beyond that point all the way to the sound hole. Cut-away style bodies that provide easier access to the higher frets are a widespread option. Whilst slotted headstocks are seen on some models, solid headstocks with side projecting tuning pegs are more common and generally pitched by varying degrees depending on the model.
Steel string acoustic guitars feature in a huge variety of musical styles from folk, blues and country through to jazz, rock and pop. They can be strummed and picked using a pick/plectrum. They can be played finger-style using just the bare fingers, fingernails, or by attaching metal or plastic finger picks to the fingers. Or maybe a combination of the two styles known as hybrid picking. As with all acoustic instruments they don't require any power source so can be played anywhere from the campfire to the studio.
One area where steel string acoustic guitars differ from each other is in the profile of the top/soundboard. In the early 20th century several guitar manufacturers, notably Gibson, experimented with archtop guitars and mandolins in a bid to increase the instrument's projection. Archtops typically have a curved, carved top with some also including an arched back too. The first models still had a round or elliptical sound hole with later models adopting violin style f-holes which further increased the volume. They became particularly popular with jazz musicians and, by the 1930s, were the preferred guitar style of the then new electric guitar.
Twelve String Acoustic Guitar
As we discussed above, some predecessors of the modern guitar had double courses of strings. This means that each string is closely accompanied by another string of the same pitch or typically an octave higher. These pairs of strings are played as one string.
In the case of the twelve string acoustic guitar, each of the regular six guitar strings are doubled. The four lower (in pitch), thicker, wound strings (E2, A2, D3 and G3 in standard tuning) are doubled with non-wound steel strings, one octave higher that sit just to the left of the regular string. The higher (in pitch), thinner, non-wound strings (B3 and E4 in standard tuning) are doubled with another identical string of the same pitch. This results in, from low to high, left to right, (E3, E2), (A3, A2), (D4, D3), (G4, G3), (B3, B3), (E4, E4). The overall sound? What some call a chorus or shimmer effect caused by the out of phase vibrations of the doubled strings.
Back in the 1920s, just before the era of the electric guitar began, John Dopyera designed the resonator guitar to increase the volume beyond that of the regular steel string acoustic guitars. The first production models under the National brand, had a metal body and, rather than the traditional wooden soundboard, used three metal cones inside the body for projection. A "T" shaped bridge sat on top of the three cones to transfer the string vibrations. The National Tricone was born. The first models had a "square" neck and were played horizontally in your lap (known as a lap steel guitar). Round necked models followed soon after.
A year or so later Dopyera left National to form Dobro and released the first inverted single cone resonator guitar with an eight legged spider bridge to transfer the string vibrations. National followed that by also building a single cone resonator guitar (but not inverted) that Dopyera had designed earlier whilst still with National. This became known as the National Biscuit due to the wooden disc that sat on top of the cone to hold the bridge. The Dobro, with its outward facing inverted cone, is the loudest of the three designs. However many players still prefer the original tricone for its tone and sustain.
The square neck models are played in the lap with strings raised very high from the neck (known as high action), with an open tuning (all strings tuned to a chord like G for example) and are exclusively played with a slide or bottleneck. The round neck models however are played in a regular acoustic guitar position but again most frequently with a slide or bottleneck and in an open tuning. Both styles are typically played with plastic or metal finger and thumb picks attached. Whilst the resonator guitar was created with Hawaiian lap-steel guitar music in mind (it was very popular at the time), it has since found its way into country, blues and bluegrass music.
Electro Acoustic Guitar
Firstly let's make the distinction here between semi acoustic and electro acoustic guitars. Semi acoustic guitars utilise a pickup but still have some acoustic qualities like a hollow or semi hollow body which can alter the overall tone of the instrument. However, they are intended to be played whilst plugged into an amplifier as they aren't very loud when played acoustically. Electro acoustic guitars on the other hand are essentially an acoustic guitar with some form of pickup, normally mounted in the sound hole, or a piezo style pickup fitted under the saddle, that allows it to be plugged into an amplifier or recording equipment.
It is worth noting that the sound hole mounted pickups function in the same way as a typical electric guitar pickup sensing changes to the magnetic field as the strings vibrate. As a result they will lose the majority of an acoustic guitar's character. Piezo style pickups sense vibrations from the strings through the saddle and bridge to the soundboard and so retain the acoustic qualities. Most models will also include a small preamp due to the weak pickup signal and so require a battery too. These are commonly found in the side of the guitar along with an EQ to tweak the tone and an electronic tuner. The jack socket to plug in the cable is normally mounted on the bottom edge.
If you want to follow up with some history and anatomy of the electric guitar, check out our Anatomy of the Electric Guitar. Also, if you are completely new to some of the terms we have just used or maybe you just feel a little rusty, why not check out our free Fundamentals of Music Theory course.