A Guide to Acoustic Guitar Tonewoods

The term ‘Tonewood‘ is used to describe wood used in the construction of stringed instruments, chosen for their acoustic properties.

In the following article we’re going to explore the world of acoustic guitar tonewoods, and explain how different characteristics of timber such as density, moisture, strength and flexibility influence how an acoustic guitar sounds.

What Makes an Acoustic Guitar Sound the Way it Does?

It’s been said that everything affects tone. But what is tone?

Experienced guitarists and luthiers use very deliberate terminology to describe the sounds they are hearing, much like an experienced winemaker will use terms such as ‘bouquet’ and ‘flavor intensity’ to describe the quality of the wine they produce.

As a result, you will often hear terms thrown about such as:

  • Crisp – A combination of articulate and bright
  • Scooped – Dominant on the lower and higher frequencies with a lack of mid range
  • Nasally – The opposite of scooped with more dominant mid range frequencies
  • Piercing – Metallic sounding with emphasis on the higher frequencies
  • Crunchy – Warm and on the verge of distorting
  • Compressed – Reducing the dynamic range between louder and quiet frequencies
  • Responsive – The speed the sound travels
  • Punchy – Powerful but controlled
  • Woody – Deep, rich, lacking metallic sounding overtones
  • Airy – Spacious, not overly compressed
  • Smooth – Lacking harshness, even response
  • Brittle – Loss of clarity, on the verge of distorting
  • Articulate – Clear sounding with good note separation
  • Boomy – A combination of punchy and airy with good sustain
  • Bright – The higher frequencies are accentuated

And while it’s true that there are a lot of different factors that contribute to the sounds we hear emanating from an acoustic guitar and the terminology we use to describe it, including the size and shape of the body, the method of construction, the guitarists technique etc. All things being equal, the soundboard (the top of your guitar) and the characteristics of the wood it is built from play the largest role in how an acoustic guitar sounds.

Resonance

Resonance

When a guitar is played, the strings are strummed or plucked and begin to vibrate.

The strings pass over the bridge saddle which is connected to the soundboard by the bridge. When objects such as the soundboard and air inside the guitar body vibrate at the same frequency as the source of the vibrations – the strings, resonance occurs which amplifies the sound we hear. The strings alone just can’t push enough air around to be sufficiently loud, but when transferred to the soundboard of the guitar we then have a much larger surface area vibrating and disrupting air particles creating a much louder sound.



The resonant capabilities of the soundboard, which are controlled by factors such as density, moisture, strength and flexibility accentuate some overtones more strongly than others, coloring and affecting the quality of the sound we hear (tone), influencing the amplitude of the soundwaves produced (volume) and affecting the speed of the sound wave (response).

Other components including the back and sides, bridge and neck of the guitar all play a role in shaping the sound we hear further, but the soundboard is the most important component, behaving much like a speaker diaphragm, projecting soundwaves from the body of the guitar.

While the electrical components of an electric guitar tend this diminish this influence, the same can’t be said for acoustic guitars which must balance the need for resonance against the ability to handle tension.

This balance is critical.

For instance if the soundboard is too heavy and inflexible, the bass tones generated by the strings will not transfer effectively to the soundboard resulting in a thinner sounding guitar. Alternatively if the soundboard cannot sustain the tension created by resonance, over time it will become unstable. Resonance can be a powerful force, capable of breaking glass to destroying bridges.


The Acoustic Properties of Timber

Different species of timber possess different acoustic properties. This is due to the characteristics of the timber e.g. density, moisture , strength and flexibility.

There are many thousands of species of timber, but many are unsuitable for building guitars. To understand why some timbers are better suited than others it helps to have a basic understanding of timber growth patterns.

Hard and Soft Woods

All trees can be classified as either evergreen or deciduous. An evergreen tree is a tree that maintains its leaves year round. Conifers fall under this category (e.g. Spruce and Cedar). Deciduous trees on the other hand shed their leaves every fall and are more affected by changes in temperature and rainfall.

Evergreen and Deciduous Trees

When a deciduous tree sheds its leaves, its growth slows and the timber becomes denser and harder. This is why deciduous trees are also known as hardwoods.

Most hardwoods are unsuitable for soundboard construction as the additional density of the wood requires more energy to resonate, resulting in a dull sounding guitar that lacks volume. Mahogany, being one of the softer hardwoods is one of the exceptions here and has been used fairly regularly as a soundboard material, although it projects less volume than Spruce.

Many softwoods are not sufficiently strong enough to handle the tension placed on the guitar and therefore cannot be used for the guitars soundboard. Alternatively, some softwoods, are ideal for this purpose as they provide a good balance of flexibility along with tensile strength. Spruce is a good example of this and is one of the most commonly used tonewoods for acoustic guitar soundboard construction along with Cedar.

Incidentally, this is also why steel string acoustic guitars require pick guards. Softwoods are dented fairly easily by guitar picks. Alternatively, classical guitars don’t require pickguards as they are intended to be played with the fingers. Flamenco guitars on the other hand use a golpeador which looks much like a standard pickguard mirrored on both sides of the soundhole to protect the timber from the aggressive strumming patterns incorporated with flamenco music.

Tonal Relationships

It helps to consider the body of an acoustic guitar as similar to a drum. The top resonates while the drum shell (the sides) offer stability. Hardwoods are often used in this capacity and their tonal relationship with the soundboard also affects the sound of the guitar. Rosewood, for example, is a hardwood that is often used for the back and sides of acoustic guitar bodies and under some circumstances will accentuate note articulation, or clarity.



Changing one tonewood for another, regardless of the component e.g. top or back and sides can influence the entire sound of the instrument. This is why specific pairings exist e.g. Sitka Spruce soundboard paired with Rosewood back and sides is a fairly common pairing.


How do Tonewoods color Sound?

It helps to look at tonewoods like an engineer might assess an equalizer.

We’ve already touched on the fact that a tonewood’s characteristics can accentuate different frequencies. Mahogany for instance accentuates low and high end frequencies, while reducing or ‘scooping’ the mid range frequencies. This makes Mahogany well suited for a singer/songwriter as the guitar is more or less leaving room in the mid ranges for the vocals to fill the space.

Spruce on the other hand tends to offer a wider dynamic range due to its lightness and ability to vibrate freely.

Due to these different properties, acoustic guitars can, and often do have very deliberate tonal characteristics. Alternatively the different ‘ingredients’ in combination and their tonal relationship with other factors such as size and shape may help balance the sound of the instrument or lean it a particular way tonally. Tone, being completely subjective with regard to the acoustic guitar means there is no ‘perfect choice’ just many different colors.

The table below demonstrates how some of the different characteristics of wood manifest themselves with regard to tone, volume and response.

Property

Impact on sound

Density Density of timber affects the ‘speed of the soundwaves’ being produced. Dense timbers provide less opportunity for the soundwaves to be absorbed, resulting in greater amplitude (volume). However, there can be greater contrast between frequencies.

Softer less dense timbers tend to absorb more of the vibration resulting in a warmer more evenly balanced sound with greater sustain.

Moisture Guitars and humidity do not ‘play’ well together, which is why the storage of acoustic guitars is important. Relative humidity of between 45% and 55% is considered ideal.

In a more immediate sense, high moisture content results in damping. This means the vibrational energy produced from the guitar’s strings is reduced resulting in a duller sounding instrument, often described as lifeless.

Over the longer term excessive humidity can cause structural problems. Due to the physical changes incorporated with moisture and the way the soundboard of an acoustic guitar is constrained by the sides of the body, high moisture content may also result in physical changes to the timber and neck joint.

These changes can cause issues with tuning stability and intonation and in more extreme cases damage the guitar permanently.

This is also why binding is used on the hard edges of guitars. While binding offers protection, it also conceals the end grain of the soundboard timber which absorbs moisture at a much faster rate than other surfaces.

Strength and Flexibility Stronger more flexible timber tends to produce a wider dynamic range of tone with more clarity due to increased resonance.
What about Laminate?
Laminated timbers tend to not vibrate as well as solid timbers as they are less flexible. But they are cheaper and easier to work with as they allow the luthier to use a beautiful grain pattern on the topmost surface, utilising less expensive grades for the lower sheets.

Generally speaking the more expensive the guitar the more likely it is to be built from solid timber. Although, there are exceptions, amongst them Taylor Guitars who use laminate tops and are one of the premier acoustic guitar brands in the world today.

The Components of the Guitar

Back and sides

As already discussed, the back and sides of an acoustic guitar play an important role in terms of stability. Aesthetics also play a role. Being the largest surface area of the guitar, the back of the guitar in particular gets a lot of attention.

Tensile strength is less important, although a high degree of elasticity or flexible strength is required to initially shape the sides of the guitar. The hardness of the timber used is also important as most dents and gouges will occur on the back of the guitar.

In most cases the back and sides will utilise the same timbers. Mahogany has often been considered an ideal choice here as it tends to produce less overtones while providing sufficient hardness. Rosewood is also commonly used and can accentuate some of the lower frequencies, but in turn sacrifices some of the clarity of mahogany.

Neck

Timbers used for the neck are mainly chosen for the structural integrity. Obviously the neck of a guitar must be very stable and strong enough to support the tension from the strings while ideally being light and easy to carve. Mahogany and maple are the most common woods used, with maple more often seen on electric guitars.

Fingerboard

The fingerboard or fretboard will ideally look attractive yet be hard enough to stand up to the abrasiveness of the steel strings while also providing a smooth playable surface. Rosewoods have long been the most utilised fretboard material due to its innate hardness and oily nature, reducing tension between the fingers and the neck.

Maple is also commonly used, along with ebony, which being a less common timber is a more expensive option but contrasts nicely against natural timber surfaces due to its darker look.

Bridge

The bridge of the guitar is an important component with regard to transferring the vibrations from the strings to the soundboard, it also must be durable enough to withstand the pressure and tension created by the strings. Generally hard, dense timbers transfer energy more effectively while also being highly durable.

Rosewood and Ebony are the most common woods used for this purpose due to their density and hardness.

Soundboard Tonewoods / Top Woods

Ideally the sound board timber will be visually appealing, strong, and flexible. Quarter sawn Spruce is often used on acoustic guitar soundboards because of its resonant qualities combined with its high strength. Resin canals form within the timber once cut which enhances this further.

What is quarter sawing?

Quarter sawing refers to how the timber is initially cut or ‘ripped’. The most common and least expensive option is known as plain sawing where the length is continually cut along the same axis. Quarter sawing refers to the process of first cutting the length into quarters (think of an X intersecting the rounded grain pattern) and then being cut lengthways.

Quarter Sawn Timber

As seen in the diagram above, the end grain pattern is defined by how the timber is initially cut. A plain sawn section of timber is more likely to split, while quarter sawn timber is stronger, more visually appealing and less likely to be compromised when affected by tension.

The Most Commonly Used Tonewoods for Acoustic Guitar Construction

In the following section, we’ll take a look at the most commonly used tonewoods and describe their tonal characteristics along with the components of the guitar they are best suited to.

  • Many of the metrics used e.g. hardness, strength and elasticity are best looked at as a base of comparison between the listed tonewoods.

Spruce

Spruce

Component Soundboard
Density kg/m3
Dried Weight
Sitka Spruce – 425
Adirondack Spruce – 435
Engelmann Spruce – 385
Hardness
Resistance of wood to dents and wear. Measured as the amount of force required to embed a .444ml steel ball halfway into a sample of timber.
Sitka Spruce – 2270
Adirondack Spruce – 2180
Engelmann Spruce – 1740
Tensile Strength
Bending strength before rupturing e.g. breaking
Sitka Spruce – 70
Adirondack Spruce – 66
Engelmann Spruce – 62.2
Flexible Strength
The amount of stress required to deform the timber
Sitka Spruce – 11.03
Adirondack Spruce – 10.76
Engelmann Spruce – 9.44

Acoustic characteristics

Easily the most commonly used top wood for acoustic guitars. When compared to Cedar (another commonly used soundboard timber),  Spruce is lighter and possesses more flexible strength resulting in a bright, responsive tone with good articulation and a wide dynamic range that holds it’s tone without bocomming brittle even when strummed with good intensity.

The main appeal of Spruce, aside from its availability is its compatibility with many styles of guitar. Not to mention its ability to age gracefully and look and sound better over time.

The three most common species of Spruce used for acoustic guitar soundboard construction are: Sitka Spruce, Engelmann Spruce (European) and Adirondack Spruce. Sitka Spruce is best known for its balanced tone, whilst Engelman is typically a lighter, more supple tonewood resulting in less projection. Adirondack Spruce produces a wider dynamic range than Sitka and is considered more responsive.

Appearance

Spruce is light in color often described as blonde, or amber and features a tight grain pattern. Spruce tends to take on more of a darker, golden appearance as it ages, providing visual character to older instruments.


Cedar

Cedar

Component Soundboard
Density kg/m3
Dried Weight
370
Hardness
Resistance of wood to dents and wear. Measured as the amount of force required to embed a .444ml steel ball halfway into a sample of timber.
1560
Tensile Strength
Bending strength before rupturing e.g. breaking
51.7
Flexible Strength
The amount of stress required to deform the timber
7.66

Acoustic characteristics

Second in popularity to Spruce as a soundboard material, Cedar (a member of the Mahogany family, also sometimes referred to as Indian Mahogany) is a softer wood than spruce and as a result produces a warmer, darker, more complex sound compared to Spruce.

Cedar accentuates typically lighter sounding tones with greater response than Spruce. This makes it ideal for styles of guitar that are played with the fingers as opposed to being strummed e.g. classical and finger style playing.

Cedar is also considered strong yet light, but not to the same degree as Spruce, especially along the end grains where it can be brittle. As a result it is unable to drive the same amount of volume as the stronger more flexible Spruce and tends not to last quite as long.

This is the most likely reason you will notice many vintage acoustic guitars are made from Spruce as they tend to remain playable for much longer.

Appearance

Cedar is finely textured and tends to feature more linear grain patterns. Colors can range from a pale yellow/cream to dark with honey tones.


Mahogany

Mahogany

Component Soundboard, Back and Sides
Density kg/m3
Dried Weight
590
Hardness
Resistance of wood to dents and wear. Measured as the amount of force required to embed a .444ml steel ball halfway into a sample of timber.
4020
Tensile Strength
Bending strength before rupturing e.g. breaking
80.8
Flexible Strength
The amount of stress required to deform the timber
10.06

Acoustic characteristics

Mahogany is defined as a hardwood but it is perhaps better identified as a ‘soft’ hardwood. More often seen as a back and side pairing for acoustic guitars, full Mahogany guitars (soundboard, back and sides) aren’t uncommon however and can look very good.

In my experience Mahogany is a very natural, woody sounding tonewood. It lacks some of the initial punch of other tonewoods but emphasises the high and low end frequencies with greater prominence, whilst scooping some of the midtone frequencies.

Appearance

Most easily recognised by its deep red and pinkish hues, you will often see Mahogany used for furniture construction. Tightly grained with a uniform appearance and less discernible grain patterns it’s an attractive timber that tends to look better as it ages.


Rosewood

Rosewood

Component Back and Sides, Fingerboard
Density kg/m3
Dried Weight
Brazillian Rosewood – 830
Indian Rosewood – 835
Hardness
Resistance of wood to dents and wear. Measured as the amount of force required to embed a .444ml steel ball halfway into a sample of timber.
Brazillian Rosewood – 10870
Indian Rosewood – 12410
Tensile Strength
Bending strength before rupturing e.g. breaking
Brazillian Rosewood – 114.4
Indian Rosewood – 135
Flexible Strength
The amount of stress required to deform the timber
Brazillian Rosewood – 11.5
Indian Rosewood – 13.93

Acoustic characteristics

Rosewood (back and sides) are often paired with Spruce (soundboard) and provide a balanced yet complex tone, due to the abundance of overtones produced. Rosewood provides good articulation, especially of the lower end frequencies. It is less dominant in the mid ranges, but when paired with Spruce for example produces a balanced and wide dynamic range.

Appearance

Rosewood is a very dark (chocolate) tonewood and contrasts nicely with a lighter timber top. Rosewood is a hardwood but is also quite porous and typically requires grain filling to provide a smooth surface for finishing.

Why is Rosewood not seen as often on guitars as it once was? 

Rosewood has come under tighter import and export laws thanks to CITE regulations brought in to protect the species. As a result, rosewood is not as prominently as it once was in guitar luthiery.

I’ve experienced this first hand with my previous company having to make changes to fretboard construction as we offered rosewood as an option along with maple and ebony. And while frustrating, this is a larger issue for acoustic guitars with rosewood being not only a good fretboard option but also ideal for the body back and sides.

While frustrating for manufacturers, the restrictions are not without reason. Rosewood has long been exploited due to high demand, mostly for furniture.  In the ten years preceding 2015, it is estimated that ⅓ of all illegal timber and wildlife seizures were rosewood.


Maple

Maple

Component Back and Sides, Neck, Fingerboard
Density kg/m3
Dried Weight
705
Hardness
Resistance of wood to dents and wear. Measured as the amount of force required to embed a .444ml steel ball halfway into a sample of timber.
6450
Tensile Strength
Bending strength before rupturing e.g. breaking
109
Flexible Strength
The amount of stress required to deform the timber
12.62

Acoustic characteristics

Maple is a hard timber and accentuates mid and upper ranges with greater emphasis than Spruce or Cedar for example. It is rarely seen on acoustic guitar soundboards and is more often utilised for the back and sides along with the necks due to its strength. It is highly responsive with good compression and sustain.

Many people make the point that maple influences tone much less than other species and lacks character. As a result is harder to define.

Appearance

Another pale timber, maple has a more whiteish appearance than Spruce and often features highly decorative grain patterns. Maple is often seen as a book matched veneer on electric guitars like the Gibson Les Paul. The highly decorative grain patterns of Flamed Maple, Quilted Maple and Spalted Maple can look stunning when finished with a high gloss sealer.

What is bookmatching?
Bookmatching is the process of mirroring the grain patterns of two sections of timber, for either the top or back of the guitar body. This is done by using one section of timber half as wide as the guitar’s soundboard. The timber is then cut in half along the edge of the timber reducing the depth by half, resulting in two sections of timber with matching grain patterns. The two halves are essentially opened like a book and joined by the edges in the center to create a book matched section of timber.

Wallnut

Wallnut

Component Soundboard, Back and Sides
Density kg/m3
Dried Weight
610
Hardness
Resistance of wood to dents and wear. Measured as the amount of force required to embed a .444ml steel ball halfway into a sample of timber.
4490
Tensile Strength
Bending strength before rupturing e.g. breaking
100.7
Flexible Strength
The amount of stress required to deform the timber
11.59

Acoustic characteristics

A medium density tonewood. Wallnut produces a warm, airy, woody tone similar to Mahogany with less overtones and more prominent mid tones. It has a very even dynamic range, meaning it doesn’t accentuate one dynamic range over another, resulting in a very even sounding guitar.

 Appearance

A dark (light brown to chocolate) tonewood with hints of red and purple. It is often highly decorative, and features a tight grain pattern.

Koa

Koa

Component Soundboard, Back and Sides
Density kg/m3
Dried Weight
610
Hardness
Resistance of wood to dents and wear. Measured as the amount of force required to embed a .444ml steel ball halfway into a sample of timber.
4490
Tensile Strength
Bending strength before rupturing e.g. breaking
87
Flexible Strength
The amount of stress required to deform the timber
10.37

Acoustic characteristics

Koa is a hard, dense tonewood that accentuates with mid and upper ranges, providing good articulation and crispness in the upper ranges. It holds its tone nicely when strummed with good response, similar to Mahogany.

Appearance

Dark brown with streaks of blonde. Koa is a highly figured tonewood that looks beautiful as a soundboard. Taylor’s range of Koa top guitars in particular are very appealing.

Cocobolo

Cocobolo

Component Soundboard, Back and Sides
Density kg/m3
Dried Weight
1095
Hardness
Resistance of wood to dents and wear. Measured as the amount of force required to embed a .444ml steel ball halfway into a sample of timber.
14140
Tensile Strength
Bending strength before rupturing e.g. breaking
158
Flexible Strength
The amount of stress required to deform the timber
18.7

Acoustic characteristics

A dense, strong tonewood. Cocobolo’s density results in a bright sounding guitar with great sustain and an immediate response when played.

Appearance

Displaying a wide rage of colors from reds to purples and yellows. Cocobolo often changes colors after being cut and can be polished to a beautiful gloss like finish.


Summary

Hopefully, after reading the information above article you have a better understanding of what tonewoods are and how they influence the sound of an acoustic guitar. I’ve always considered tonewoods as filters, emphasising specific overtones while reducing others, coloring the overall sound of the guitar and governing its capacity for volume and response.

Keep in mind also, as time passes and more traditional tonewoods become scarce, and as a result more expensive, that the materials used to make acoustic guitars are likely to slowly change over time. Sustainability is already playing a role with regard to the availability of many traditional tonewoods and as more guitars are built this is only likely to increase.

Marty


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