Anatomy of an Acoustic Guitar

Acoustic Guitar Anatomy

The diagram above shows the anatomy of an acoustic guitar. Some guitars may vary e.g. many classical or flamenco guitars will not feature a pick guard or truss rod. But for the most part, the components listed below are common on all acoustic guitars.

Headstock

Headstock

The headstock (also referred to as the ‘peg head’) appears at the top of the guitar neck. Its purpose is to provide a home for the tuning machines. The area at the top of the headstock also provides space for the manufacturers branding. Classical guitars, and some small body acoustic guitars feature slotted headstocks.
 
Headstocks usually comes as ‘straight’, ’tilted’ or ‘scarfed’. Straight headstocks are the least expensive to make as they utilise a single piece of wood. They do not apply as much tension to the nut as a tilted headstock and this can affect tone. Because of this, straight headstocks are not seen on high end acoustic guitars very often.
Most guitars feature tilted headstocks. The pitch of the headstock being between 9 and 15 degrees. The greater the pitch the more pressure applied to the strings over the nut. Many believe this increases sustain.
 
This is also the case for slotted headstocks. As the string angle is further emphasised placing more downward pressure on the nut. Scarfed headstocks are like titled headstocks, but are made from two pieces of wood. This often results in better structural integrity.

Tuning Machines / Machine Heads

Tuning Machines

Tuning machines (also referred to as tuners, tuning pegs or machine heads) are used to tune the guitar.
 
Tuning machines are ‘geared’. This means they feature a cylindrical peg (tuning post) sitting inside a pinion gear. When the pegs are wound the tension increases or decreases on the individual strings, depending on the direction turned.
 
The amount of tension applied per turn is measured as ‘gear ratio’. A gear ratio of 12 to 1 means, for every 12 turns of the tuning peg the machine head cylinder turns a full 360 degrees once. The higher the number, the more control you will have over tuning.
 
Tuning machines come as either ‘sealed gear‘ or ‘open gear‘. Acoustic guitars often feature ‘open gear’ tuners. Electric guitars tend to utilise ‘sealed gear’ tuners more often.

Nut

Nut

The nut is at the headstock end of the guitar’s fretboard and is usually made from hard plastic, bone or graphite.
 
The nut plays a very important role. It is the string’s last point of contact before the tuning machines. Because of this, it transfers the vibration of the strings to the guitars neck. Along with the saddle the nut also controls string spacing as all strings sit in slots cut into the nut.
 
The nut slot depth is an important consideration. It differs based on the thickness of the string. For example, the low E string requires a deeper slot carved out of the nut than the high E string.
 
If the nut slot is too shallow the guitar string may come out of the slot. If the slot becomes too deep over time the string may come into contact with the fret wires causing fret buzz. A nut slot cut too narrow can contribute to tuning instability. This is because the string will not slide through the nut slot easily if bending the string.

Neck

Guitar NeckThe guitar’s neck is home for the headstock, tuning machines, fingerboard (fretboard) and strings.

Necks are either fixed using glue (set neck) or bolted directly on to the body. In the case of acoustic and classical guitars, this is almost always glued in place.

The longer the neck, the longer the scale length (the distance between the saddle and nut). Generally speaking, the shorter the scale length the ‘warmer’ the tone, whereas the longer the scale length the brighter the tone.

The wider the neck, the more area the fretboard utilises. Generally guitars manufactured to be played with the fingers e.g. classical and finger style guitars feature a wider neck to provide more space between the string making it easier to play individual strings. Most steel string acoustic guitars utilise a 43mm neck width measured at the nut and commonly referred to as nut width. Classical guitars on the other hand will typically be over 50mm in width at the nut.

Necks also come in different depths (e.g. the thickness of the neck) and shapes (e.g. the roundness of the underside of the neck), known as neck profiles. (C, V, and U for example).


Frets and Fret wires

FretsThe frets of a guitar refer to the areas between the metal fret wires located on the fretboard, used to separate the guitar’s fretboard into semi-tone intervals.

Most guitars utilise 21 frets, however, some electric guitars have 24 frets.

Fret wires are shaped like a mushroom or ‘T’ with the top section sitting on the fretboard and the stem embedded into the neck itself. The top of the fret wire is rounded to aid playability and is referred to as the crown.

Fret wires come in a variety of sizes, from tall, short, skinny and wide. This chart shows most available fret wires for guitars and other stringed instruments.

Fret wires can wear over time, particularly if the guitar is used regularly. When this occurs, frets may need to be replaced or repaired. This is known as fret dressing which involved levelling and reshaping the top of the fret wire.


Fret Markers / Inlays

Fret Markers / InlaysFret Markers (also referred to as inlays or positional markers) are located on the guitar’s fretboard and indicate specific frets of the guitar’s neck. This allows the guitarist to orientate the guitar’s neck with more surety.

Typically guitar inlays will be found inset onto the 3rd, 5th, 7th, 9th, 12th, 15th, 17, 19, and 21st frets.

Inlays are seen in a variety of shapes, however, most typically are either square, trapezoid, or dots. In the case of dots, the 12th fret of the guitar usually contains two dots to indicate the octave. Inlays are made from a variety of materials including, plastic, mother of pearl and abalone to name just a few. Inlays are usually not seen on classical guitars.

Fretboard side dots are dots found on the side of the guitar fretboard at the same locations on the neck e.g. 3rd, 5th, 7th, 9th, 12th, 15th, 17, 19, and 21st frets


Truss Rod

Truss RodThe truss rod is the metal tensioning bar running through the centre of the guitar’s neck that can be adjusted to modify the amount of relief or bow in the guitar’s neck. The image to the left shows a cross section image  of the guitar neck, with truss rod running through the middle of the neck.

Generally speaking electric guitars and steel string acoustics will require a truss rod however many classical guitars do not due to less tension being applied to the neck due to less tension being applied to the neck when using nylon strings as opposed to steel strings.


Fretboard / Fingerboard

FretboardThe fretboard (also referred to as the fingerboard) is the section of timber laminated onto the main area of the neck. It is usually manufactured from maple (more commonly seen on electric guitar fretboards and necks) or rosewood.

Pressing the strings against the fretboard creates individual notes e.g. melody. Pressing multiple fingers against the fretboard at designated frets produces harmony or chords.

In the case of acoustic guitars, the fretboard has traditionally been rosewood, for high end classical guitars, the choice is often Ebony. Rosewood is particularly popular as it is an oily timber, ideal for reducing tension between the fingers and fretboard and is credited with contributing to producing a warmer tone.

 Rosewood is becoming a less common fretboard material. Recent CITES regulations designed specifically to protect Indian Rosewood have forced manufacturers to explore engineered timber options and in most cases, these have shown promise. .


Heel / Neck Joint

Heel / Neck JointThe heel (also referred to as the neck joint) is the where the neck joins to the body of the guitar, along with the sides of the guitar body.

For acoustic guitars, in the majority of cases the neck will be glued, using a dovetail joint, a particularly effective type of joint commonly used on acoustic guitars.

 


Back and Sides

Back and SidesThe back and sides of an acoustic guitar are usually paired. Rosewood, maple and mahogany are often used with mahogany being an ideal timber due to being a hard but workable timber.

The back and sides make up the stable elements of the body, with the soundboard or top wood responsible for vibrating and resonating sound.


Lower Bout, Waist and Upper Bout

Upper Bout, Waist and Lower BoutAcoustic guitar bodies comprise of an upper bout, which is the top half of the guitar and a lower bout (the bottom half of the guitar). The bouts are separated by the waist, which is the narrow section located between the two bouts.

The shape and size of the body of an acoustic guitar influences the playability of the instrument with regard to how comfortable the guitar is to play. More importantly, the body shape and size influences the tone of the guitar as it affects the internal ‘air resonance’ of the guitar. For example, a wider lower bout lowers air resonance and gives more definition to the low end tonal output of the guitar.

* Tone is influenced by a number of contributing factors. Body shape is just one of these.


Sound Hole

Sound HoleAs the name implies, the sound hole is the hole located on the guitar’s soundboard.

In the majority of acoustic guitars, this is simply a circular shape but variations known as F-Holes are also seen in some acoustic guitars (mainly jazz acoustic/electric guitars and electric guitars).

Gypsy guitars (Selmer guitars) tend to have an elongated sound hole, while some manufacturers such as Bourgeois and Martin feature select guitars with larger than normal sound holes.

Contrary to popular opinion the sound hole is not solely responsible for the guitar’s sound, this typically originates from the body of the guitar, in particular the soundboard, however, the sound hole opens up the body to allow greater resonance and facilitates the release of internal ‘air resonance’.


Rosette

RosetteThe rosette refers to the decorative rings located around the sound hole.

While many likely believe this to be decorative only, rosettes are actually both decorative and used to reinforce the timber around the sound hole, which otherwise would be subject to cracking.


Pick guard / Scratch Plate

Pick GuardThe pick guard (also referred to as the scratch plate) is located to the underside of the sound hole of the guitar body, and as the name implies is used to ‘guard’ or protect the guitar’s body from the pick, that over time would otherwise scratch the guitar’s surface.

Pick guards are typically constructed from three separately laminated pieces of plastic (three-ply) and come in a variety of different shapes.

In the case of classical guitars, these are usually not used, as classical guitarists tend not to play with a pick. In the case of flamenco guitars however, the pick guard is replaced with a clear protective plate referred to as the golpeador that protects the guitar‘s soundboard from the more aggressive strumming patterns flamenco music incorporates.


Binding

BindingBinding, refers to the strip (vinyl, PVC plastic, amongst other materials) that is seen on the edge between the guitars top and sides. It is also sometimes seen on the back of the guitar and also the neck. If the neck features binding it is referred to as a bound neck.

Binding serves three purposes. firstly it provides a decorative element between the sides and soundboard. Secondly it protects the edges of the guitar which are most prone to impact and lastly it shields the open grains of the timber used for the soundboard preventing the absorption of moisture.

  • Faux binding is when binding has been imitated using either the timber of the guitar‘s soundboard or paint.
  • Purfling is similar to binding, however it is usually the thinner strip located on the inside of the binding usually consisting of a contrasting color.

Soundboard

SoundboardThe soundboard is an essential part of the guitar‘s anatomy and refers to the top of the guitar’s body, which houses the bridge and sound hole.

Acoustic guitars use resonance to project sound. The soundboard resonates due to the bridge being fixed to the soundboard which vibrates due to the guitar strings running directly over the saddle which is located in the middle of the bridge.

While the choice of timber is less critical on an electric guitar due to the additional components involved in creating tone, on acoustic guitars the choice of tonewood used can play a major role in the guitar’s overall tone, resonance and ultimately volume, with timbers selected for their strength, and lightness. This is because the sound board must vibrate freely to produce sound but also handle the tensions applied by the steel strings. Soundboards utilise bracing, to add additional tensile strength.


Bridge, Saddle And Fixing Pegs

BridgeThe bridge is the part of the guitar that fixes the strings to the body and allows for the vibration from the strings to resonate through the body of the guitar, projecting sound.

Strings are typically fed through small holes in the bridge and locked in place by the fixing pegs which are pushed directly into the string holes, located on the bridge.

The bridge also features the guitar’s saddle, which is similar to the nut of the guitar and features slots for the strings.

Unlike the nut, however, the saddle is positioned on an angle with the end closest to the fixing pegs reserved for the bass strings, allowing accurate intonation. Essentially the thicker strings e.g. ‘E’ and ‘A’ require slightly more length to compensate for their additional tension when fretted due to their wider surface area.


Bracing

BracingLocated on the underside of the guitar‘s soundboard and back is the bracing. Bracing refers to the wooden struts (structural components made from spruce, or a similar light yet strong timber) that reinforce the guitar‘s top and back and influence the tone of the guitar.

Bracing supports these larger, lighter sections of timber structurally without adding much additional weight which would impact the guitars ability to resonate. Some struts are scalloped, which is an effective technique used to reduce the weight of the struts further while maintaining structural integrity.

There are many different types of bracing, including X bracing which is the most common form of bracing amongst steel string guitars. Classical guitars commonly utilise fan bracing.

Most guitar backs utilise ladder bracing, a simple form of bracing where the struts are fixed to a centre strut and run perpendicular to the strings in much the same was as a ladder.


Summary

The components of the guitar referred to above are found on the majority of acoustic guitars. There are, in many cases differences between manufacturers particularly in regard to the headstock shape, tuning pegs, fretboard timber, fretboard wire gauge, rosette style and material, inlay material, bridge design and material and of course the tone woods selected for the construction of the guitar. However for the most part the basic anatomy will be similar across different models.

All of these differences account for the range of tones extracted from different acoustic guitars and the music they are most suitable for playing. This is just one of the reasons why owning one guitar is never enough.

Enjoy the article? Got a question about the anatomy of your guitar? We’d love to hear from you in the comment section below.

4 thoughts on “Anatomy of an Acoustic Guitar”

  1. Appreciate the effort you gave to write such a beautiful post with an amazing image of the acoustic guitar. I have found a lot of other articles on the internet but those are too long and full of technical details. Your one is short and to the point which i loved. Really good work. Can you please add a subscribe option on your site please so that i can stay updated?
    Cheers

    Reply
    • Not too sure the partitions themselves are named specifically, but the bracing is made up of individual struts creating partitioned sections under the soundboard e.g. X bracing, fan bracing etc.

      Reply
  2. Nice article to describe the anatomy of acoustic guitar. The content is very good and effective. I came to know about different parts like nuts, necks, soundboard, fretboard, tuner buttons. I have to repair the wraparound bridge part of my guitar which is the main tailpiece unit of a guitar and I believe this will help me a lot.

    Reply

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