How The Back and Sides of Guitars Influence Tone

Clearly, the choice of wood selected for the soundboard (top) of an acoustic guitar plays a large role in determining the guitar’s tone, along with volume and projection, but less is understood about the back and side woods and the influence these wood pairings have.


In this article, we hope to demystify the topic and clearly explain the influence the back and sides have on your guitar’s tone.

Fundamentals of tone

Before we take a look at individual woods and their characteristics, I’ll first explain the basics of guitar tone as it relates to the acoustic guitar.

When we play a note on the guitar, we are producing vibrations that manifest all the way across the frequency spectrum. This will be comprised of a ‘fundamental’, which is the note you are playing as well as a series of harmonics.

Overtone Series

For example, an A note will vibrate at 110hz, 220hz, 440hz, etc depending on the octave the note resides in. This will be the loudest frequency produced, which is why our ears interpret it as an A note. But in addition to this fundamental frequency, additional frequencies are also produced (see above), which we call harmonics, and the makeup or composition of these harmonics determines the tone of the instrument.

This is essentially why two different instruments e.g. a piano and a guitar sound quite different despite playing the same notes.

Sotaking the idea that the frequency response of an instrument determines its tone, what affects the frequency response of a guitar?

The short answer is, everything!

From the tonewoods selected, along with the guitar’s scale length, whether you play with a pick or your fingers, how aggressively you attack the strings, the bracing type, the body style and size, and about a hundred additional factors.

In short, just about everything affects the tone of the guitar to some degree.
Where the topic starts to cause friction amongst guitarists is in how much these different factors affect tone.

The reality is that while the back and sides do affect the tone, the actual difference between different woods is not that substantial. When compared to other factors such as body size or your technique, it makes little difference and you should certainly not dismiss a guitar as a potential purchase because of the back and sides.
Other elements like the bracing pattern and the top wood affect the tone far more substantially.

Stability, resonance, and sustain

That’s not to say the back and sides shouldn’t be given consideration. One of the most important aspects the back and sides bring to a guitar is its stability. When a guitar is well constructed and has a nice stable frame with solid bracing, this results in increased resonance and sustain. While these are not directly tied to frequency output they are, nevertheless, important in relation to tone.

A guitar that has a rich sustain and high vibrational resonance can offer several benefits. Firstly when a guitar is stable and resonant, it will be more responsive. There’s nothing worse than playing a guitar that seems flat and lifeless. This can also play into other aspects such as projection when playing unplugged, and how good it sounds when placed in front of a microphone.

Aesthetics

We’ve established that while the back and side woods do affect tone in terms of frequency output, as well as tonal qualities such as sustain and resonance, they do so in a fairly minor manner. So you should never buy or avoid a guitar based on its back and side woods.

This is actually a good thing as it gives us the freedom to pick those back and sides woods based on other criteria, and one of the most important elements is the aesthetic and visual look of the wood.

When you have a guitar that looks gorgeous, and every time you see it sitting there on the stand you just feel compelled to pick it up and jam – this is an extremely valuable quality.

So finding an instrument that appeals is very important and definitely should be one of your criteria for the woods you choose for your instrument.

HPL and composite materials

Aesthetics - Back and Side of Taylor Acoustic Guitar
Layered Walnut

Another important thing to keep in mind is that not all guitars nowadays use just solid wood, there are a few other types available that can offer some unique qualities.
For example, if you are looking for a more budget-orientated guitar, you will commonly find instruments that use an HPL (High-pressure laminate) back and sides which is essentially paper that gets pressed together in sheets and combined with a resin glue at a very high temperature.

This creates a very solid and robust finish that’s exceptionally resistant to things such as humidity and temperature changes. This is even more important on entry-level and budget guitars as the nature of their cheaper construction mean they’re more susceptible to being affected by weather and humidity, so to have the means to counter that is a very powerful thing.

HPL and laminate back and sides can offer more practical and real benefits to the stability of a guitar with a very minimal compromise to the overall tone of the instrument.

Many of the larger modern manufacturers such as Martin and Taylor are using these on their entry-level instruments now as a way of achieving a high level of functionality without the cost increase that comes with solid wood.

Common Back and Sides Tonewoods

In the world of guitar making, we have a lot of wood types to pick from. Each wood species has its own tonal quality and visual style, and by combining certain woods together we can create a balance that is both tonally pleasing and visually striking.
Let’s take a look at the most common woods used and their general tonal character.

Rosewood

Rosewood

Certainly one of the most popular choices in acoustic guitar construction. While there are many specific species of rosewood the two most popular types you will see are East Indian Rosewood which is oftentimes the cheaper option, or the more premium Brazillian rosewood.

They both have a luxurious deep red tone to them, with Brazillian rosewood having a darker and more complex woodgrain. Unfortunately due to difficulties with growing and harvesting Brazillian rosewood due to the more stringent regulations around its use, it’s become less common over recent years.

East Indian Rosewood on the other hand is more accessible. It has a slightly lighter hue and a less complicated grain, you’ll commonly see multicolored purple/red and grey highlights throughout the wood.

Despite its dark and luxurious appearance, rosewood offers a bright and balanced tone with a little less emphasis on the mids, making it have a warmer and more pleasant sound when compared to something like maple.

Mahogany

Mahogany

Easily identified by its rich and dark red/brown color. Mahogany is known to add a great deal of low-end to any guitar it’s used on.

Companies such as Martin and Gibson started to use Mahogany back in the 1930s and at this time it was a cheaper alternative to rosewood. But this perception of mahogany being a more budget-orientated wood choice has basically disappeared now to where people really just choose based on which one they like the look of.

It’s also a harmonically rich wood which allows it to sound punchy, and clear, and typically won’t get drowned out by other instruments. But it is also balanced enough to where it doesn’t poke out in any particular area of the frequency spectrum.
A solid and reliable choice for both sides and back.

Sapele

A wood you’ll seldom see used in electric guitar production, but quite common on acoustic guitars. It’s an African wood that is somewhat similar to mahogany, but it’s a little bright in looks and can have darker ‘stripes’ running through it.

Tonally it picks up a bit of that midrange without sacrificing too much warmth. This makes it ideal for playing styles with high dynamics, but it still also retains enough of that sparkly top end to make it cut through in most musical scenarios.

Maple

Maple

Maple is one of the rarer woods we see used in acoustic construction. It’s an extremely dense wood and as such tends to not vibrate as well which translates into a shorter note length or faster decay.

But it is also extremely bright, snappy, and punchy giving it a lot of life and vibrance to its sound. Ideal if you really need to make something pop and project.

Koa

Considered a more premium wood Koa is one of the most expensive tonewoods used. It’s very common to see Koa used on guitars that have special runs or limited edition productions.

Koa is also considered a ‘live’ wood, this means that its tonal characteristics change over time. When you get a factory-new Koa guitar it usually sounds quite bright, but as you spend time with the instrument it will settle in and develop more warm and mellow low-end frequencies which many find appealing.

It’s a balanced wood that is highly sought after thanks to its appealing look.

Walnut

Walnut is another less common tonewood that sits somewhere close to Koa in terms of characteristics but is generally a little cheaper and easier to acquire.

It has a very rich appearance that many luthiers fall in love with because of its natural beauty and how easy it is to work with.

It’s a reasonably balanced wood but has a slight low-end bump which makes it a warm and pleasant-sounding wood.

Common wood pairings

Technically any combination of wood can work just fine, but there are certainly a few particular combinations that you’ll encounter more frequently than others. Here’s a quick rundown of some ‘tried and true’ classic wood combinations you’ll often see used.

Spruce top with mahogany back and sides

Commonly found on a lot of the very high-end Martin guitars. The spruce top is where all of the brightness and projection comes from while the mahogany back and sides offer that nice low end and warmth to create a balanced sound.

Spruce top with rosewood back and sides

Used for a similar effect to mahogany but you should find it has slightly less bass and a little more mid-range articulation. it also looks more visually striking. although this is of course subjective.

Full mahogany

Full-bodied and harmonically rich, guitars that comprise a mahogany top, back, and sides not only look beautiful, but they will also sound full and rich. However, will lack slightly on the top-end spank, ideal for more subdued playing. Commonly used on some high-end Taylor guitars.

Spruce top with walnut laminate back and sides

Sitka spruce is one of the most popular tops for the high-end sparkle and projection it adds. Here it’s complimented by laminated walnut which is incredibly durable and stable. Ideal for the working musician.

Closing thoughts

While in the grand scheme of things the back and sides of a guitar only play a relatively minor role in terms of tone, in terms of construction the back and sides play a big role, and as explained above this all have somewhat of an impact on tone, projection, and volume.

With this in mind, it’s well worth spending some time finding which woods you like the best and trying to find an acoustic that combines those woods together. But remember wood choice is just 1, albeit major, piece of the puzzle.

Marty

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My name’s Marty. I’ve been into guitars, songwriting, and home recording for over 30 years. Theacousticguitarist.com is my blog where I write about everything I have learned along the way.