How an Acoustic Guitar Works

The acoustic guitar is an intriguing instrument. It is incredibly versatile and can be used in many different kinds of music and styles, from pop, country, blues, and many more.  But have you ever wondered how an acoustic guitar works?  Today, we’re going to talk about how the acoustic guitar makes all its beautiful sounds and why it works.

How Sound Works

Parts of the guitar

So how does an acoustic guitar produce sound?

How Sound Works

Before we dive deep into how an acoustic guitar works, let’s talk a bit about how sound works.  Whenever you hear a sound, whether it is birds chirping, the rev of an engine, or people talking, a vibration is made.  This vibration causes air molecules to displace and compress again and again until the energy from the initial vibration is gone.  The molecules that are displaced cause molecules near them to also displace and compress.  This creates a travelling sound wave.  

This sound wave reaches your ear and causes a vibration in your eardrum.  The nerves in your ear travel to the brain and interpret the sound.  

Now, this is a simplified description of what is going but now we can talk about how an acoustic guitar produces sound.  

Parts of the guitar 

Let’s go into the parts of the guitar and how they are important to the sound the guitar creates:

Top (Soundboard)

Guitar top, Yamaha FGX720SCA

The top (or the soundboard) of the guitar, is by far the most important part of an acoustic guitar.  It is cut into a figure 8 and made thin and flexible enough for it to vibrate but strong enough to handle the high tension of the strings.  

The type of wood that is used has a huge influence on how the guitar will sound.  Some more commonly used wood in acoustic guitars are spruce, mahogany, maple.  Spruce woods produce bright and responsive sounds in an acoustic guitar.  Mahogany produces full, rich, woody sounds.  And maple produces rich mid and bass tones in an acoustic guitar.

The top of the guitar can also be reinforced with braces on the underside of the wood.  This means the braces would be on the inside of the guitar.  How the braces are arranged has a huge impact on how the top vibrates.  As a result, creating different sounds.  

Braces inside the guitar affect the way a guitar sounds.

How the wood is cut and constructed to create the top can also influence the sound of an acoustic guitar.  

Strings and pitch

Strings on the guitar

While the top of the guitar is the most important part of the guitar, there wouldn’t be and music coming from the guitar without the strings.  There are many qualities that allow the strings to produce different pitches.  

The first quality is its mass.  The more mass a string has the slower the string travels.  The slower the vibration, the lower the pitch.  The lower the mass, the faster the string travels and the higher the pitch the string makes.  

The next quality is the tension.  The higher the tension in the string, the higher the pitch of the string.  This can be seen as you tune up the guitar. The string becomes tighter and tighter until the string becomes the correct pitch.

The final quality is the length of the string.   The shorter the string the higher its pitch becomes.  This is apparent in the way we play the guitar by placing our fingers in the spaces between the frets to temporarily cut the string short.  The closer we put our finger to the soundhole on the fretboard the shorter the string becomes and the higher the pitch of the note.

Neck and Fretboard

A Guitar Neck

The neck and the fretboard are what give the guitar its wide range of sound.  The neck needs to be cut in a way that allows it to survive the high tension of the guitar strings.  Because steel strings create higher tension, the neck on the acoustic guitar is constructed with a truss rod to help withstand the tension of the strings.  Classical guitars don’t usually have a truss rod due to less tension created by nylon strings.  

The fretboard is another thin piece of wood that is placed on the top side of the neck to allow the guitarist to make the strings shorter and create different pitches on the guitar.

Body Shape

The shape of a guitar's body helps to shape its sound.

The shape of the guitar also contributes to how the guitar sounds.  The bigger the body of the guitar the louder the sound.  The depth of the waist affects the sound of the guitar as well.  A more pronounced waist will create a tone that is rich in bass and mids.  

So how does an acoustic guitar produce sound?

An acoustic guitar produces sound by causing a vibration on the strings.  This vibration creates energy which is transferred through the saddle and into the soundboard.  The soundboard now creates vibrations which cause the air inside of the guitar to create a soundwave that bounces around inside the guitar and out the soundhole.  

So there we have it.  Now we know how an acoustic guitar works.  

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