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What is an Acoustic Guitar?

Interested in the acoustic guitar, but don’t know the first thing about them? In the following guide we’re going to break down exactly what an acoustic guitar is, how they work, and the different types available.


How Acoustic Guitars Produce Sound

Soundwave

Resonance

The acoustic guitar is a fretted stringed instrument, relying on resonance to produce sound through the vibration of the guitar’s strings which are then transferred to the guitar’s body and amplified via the soundboard (top of the guitar) and internal chamber of the guitar through the release of air rushing out of the soundhole

It is a member of the ‘guitar family’ which included guitars, bass guitars, and ukeleles amongst others.

When played the guitarist plucks or strums the string using a plectrum or fingers.

Pitch

Like all stringed instruments, the pitch of the notes played can be raised or lowered by the location of the fingers on the fretboard which shortens the length of string able to vibrate.  When a guitar string is shortened in this way, it vibrates faster, raising the note’s pitch.

Guitar strings range in thickness from the 1st (high E string) to the 6th (low E string). So, while there are only 12 notes in western music (the notes of the Chromatic Scale) we have available to play on guitar, the increasing mass of the strings between the 1st and 6th string results in these notes being repeated in different octaves, giving us at least 120 different frequencies, or pitches to select from.

You can read more about how the acoustic guitar works here.


The Parts Of An Acoustic Guitar

The Acoustic Guitar

An acoustic guitar consists of a neck and body. The neck features a fretboard divided into frets, each representing the notes available within an octave. The frets (the sections of the fretboard divided by the fret wires) of the guitar increase in pitch (while also becoming narrower) the further up the neck the note is played.

The Neck

The neck features a headstock that houses the 6 tuning pegs used to tune the guitar to the correct pitch for each string. The neck also usually contains a truss rod (the only exception being some classical guitars), which is an adjustment rod made from steel that runs through the neck of the guitar and can be turned counterclockwise to loosen the truss road and introduce relief to the guitar neck, or clockwise to tighten and reduce the amount of relief.

While the uninitiated may believe a dead-straight neck to be ideal, it’s important to ensure the neck contains just enough relief to allow the strings to clear the fret wires when vibrating after being plucked.

Lastly, the neck is joined to the body via the neck pocket, which on acoustic guitars is usually a mortise and tenon joint.

The Body

The body shape influences things such as volume, tonal output, and projection (the distance sound travels) and consists of an upper and lower bout, a soundboard (the top of the guitar), soundhole, bridge, saddle, and back and sides. The soundboard sits on top of the back and sides, allowing the guitar’s body to be hollow. 

Where the top meets the sides often features binding, which serves to protect the hard edges from dents and dings and also prevents the end grains of the soundboard from moisture absorption. 

Inside the body, the top and bottom of the guitar are braced, to provide additional vibrational strength to allow the guitar to handle the tension from the strings without warping.

The length of string able to vibrate is known as the scale length. The two points of contact for the string (unless fretting a note on the fretboard) are the nut that sits near the headstock and saddle which is housed within the bridge. Both are usually made of plastic, bone, or graphite, and can have an impact on the ton and projection of the guitar by the amount of vibration absorbed, that would otherwise be transferred to the soundboard. 

You can read a detailed article about the anatomy of acoustic guitar here.


How Acoustic Guitars Are Made

Optin background - Acoustic guitar patent

Acoustic guitars are made by luthiers.

Tonewoods

The process includes sourcing materials with good acoustic properties (tonewoods) such as Spruce (most common), Mahogany, and Cedar. These tonewoods are light, yet strong and this allows for greater projection, compared to wood with poor strength to weight ratio. This is particularly important for the soundboard, which is responsible for most of the soundwaves generated.

The Process

Once the materials are chosen the body is shaped, the soundhole cut, and the bracing added to the back and top, along with linings added to the sides.

The neck is usually built second and joined to the headstock using a scarf joint, while the neck is joined to the body with a dovetail joint. The fretboard, one of the most important components of the guitar is made next. The fret spacing is calculated and is crucial in terms of intonation.

Lastly, the guitar is finished with a clear lacquer, at least in most cases. Although some acoustic guitars are painted or use alternative finishing products). Next, the guitar is sanded and buffed to a fine finish and hardware such as tuners are added along with the bridge, nut, and inlays for the fretboard.

This is just a basic overview of how acoustic guitars are made, for a lengthy article that outlines the entire process (not all guitars are built the same way) you can read our complete article on how acoustic guitars are made here.


Types of Acoustic Guitars

While there are smaller guitar-like instruments available such as the Guitalele (a hybrid of guitar and ukelele) for the most part, there are 5 main types of acoustic guitar, based on size and body shape. From smallest to largest, this includes:

Parlor Guitars

Parlor Body Style

Also commonly referred to as a size 0 concert guitar. Parlor guitars are the smallest type of acoustic guitar, aside from travel guitars and 3/4 models designed for kids. The neck connects to the body at the 12th fret and the body itself is elongated compared to other body types, such as the Dreadnought. The body shape accentuates mid-range tones, and as they are usually more responsive than larger guitars with a strong fundamental tone they are particularly well suited to fingerstyle. They are also comfortable guitars to play due to their smaller body size.


Concert Guitars

Concert Body Style

Also commonly referred to as a size 00 concert guitar by Martin guitars, the concert body style is just a touch larger than the parlor and features a tighter waist which gives the guitar a rounder look.

The tighter waist facilitates a more balanced sound, and is generally considered brighter sounding than a parlor guitar, although opinions of tone are subjective.


Orchestra Guitars

Orchestra Body Style


Also commonly known as 000 or Auditorium guitars.

For a long time the orchestra guitar was the default size for guitars.  Featuring a tighter waist than both concert and parlor guitar it produces a nice, balanced sound.


Dreadnoughts

Dreadnought Body Style


While Dreadnoughts are easily the most popular acoustic body size available today, this wasn’t always the case and initial sales were quite poor. Today they are everywhere and tend to be favored by guitarists as they are capable of producing more volume than smaller models.

Due to their wide waist, the typical dreadnought looks ‘blocky’ in comparison to Parlor and Concert guitars.


Jumbo

Jumbo Body Style

Last but not least we have the Jumbo. And, as the name suggest this is a large guitar capable of producing a great amount of volume. Due to the size of the guitar and internal cavity space, the guitar tends to produce an abundance of low-end frequencies. 

Keep in mind, there are no standards when it comes to acoustic guitar sizes and body shapes. You may find some concert guitars, for example, are referred to as parlors (and vice versa) while not strictly adhering to the same standards as another concert or parlor guitar.

For a far more detailed look at acoustic guitar body styles and sizes click here.


Who invented the acoustic guitar?

Who invented the acoustic guitar?

While it’s true that the first nylon string guitar is credited to Spanish Luthier Antonio Torres Jurado, it is more accurate to say Antonio Torres Jurado standardized the guitar. This was achieved through the revolutionary bracing system he developed, known as fan bracing (the bracing allowed for the soundboard to be larger) which in turn allowed for greater volume and projection.

On the back of the first classical guitar, the first steel string acoustic was created by Christian Frederick Martin of C.F. Martin & Company, whose bracing system (X bracing) paved the way for the commercial production of steel-string acoustic guitars.

Both Antonio Torres Jurado and Christian Frederick Martin are pioneers, but the truth is mankind had been playing stringed ‘guitar-like instruments (Chordophones) for many centuries.

While there is some conjecture over which primitive instrument most influenced the eventual design of the acoustic guitar. It’s safe to say instruments such as the Kithara, and Oud played a role in influencing the design of the Lute and from there the renaissance period Vihuela, which was far more akin to the modern acoustic guitar.

Click here to read a detailed article about who invented the acoustic guitar.


Summary

If you have read over the information above, you should now have a basic understanding of what an acoustic guitar is, how it works, the different types available, and the people who played crucial roles in the acoustic guitar’s development. Remember, if you would like more information on anything discussed within this article, check out some of the links at the top of this article for a more in-depth analysis.

About Marty

My name's Marty, I've been into guitars for over 30 years. Theacousticguitarist.com is my blog where I write about acoustic guitars, music, and home recording.