The Essence Of Acoustic Guitar Tone

Adirondack Spruce - Ideal For Guitar Tops

Beyond the basic body style, there are quite a number of elements that go into giving an acoustic guitar its sound. Here's an excerpt from The Ultimate Guitar Tone Handbook (co-authored with Rich Tozzoli), that shows why the kind of wood that the guitar is made from makes such a big difference.
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The size of the instrument, types of strings used, style of picks, finger technique, soundboard, nut material and even the structure of the bracing inside all have an effect on the sound. However, the woods used for the top and body probably are the most important tonal factors involved in the overall sound of a guitar. 

Since most acoustic guitars are primarily made of wood, each will have it’s own sonic character and soul. Rosewood bodied guitars will sound different than mahogany, which will be different than koa. Within a subset of that picture, wood comes in many varieties from countless different parts of the world so even different species of the same wood will sound different when built into the body of a guitar. 

Back And Sides

The most important traits for the back and side wood is that it be both resonant and good at reflecting sound. Rosewood has always been considered the best wood for this because of it’s bass response, with Brazilian rosewood being the most desirable sub-species. It’s hard, dense and resonant, and flavors the tone in a pleasing way as it absorbs the vibrations from the top. The problem is that Brazilian rosewood is now extremely rare and it’s use is restricted, so other types of rosewood are now used instead.

East Indian rosewood isn’t as hard as Brazilian, but it’s the most available and also has a rich bass response, while Cambodian, Amazon, and Madagascar rosewood all have many of the same tonal properties as Brazilian and are sometimes used as a substitute. Tulipwood is also a member of the rosewood family, as is Kingwood, but they both have a problem with availability, quality, and sizes large enough to make guitars from. 

While rosewood makes for wonderful live guitars, they might not be as appropriate in the studio because they may actually have too much bass response. Mahogany, on the other hand, has a very crisp, crystalline and glassine tone that works well for recording because it’s an extremely light wood without the reflectivity of rosewood. However, each type has its strenghts and weaknesses, and both can be successfully used in studio recording situations.

Koa, from Hawaii, is another popular wood for guitar making since it has a density that falls between mahogany and rosewood. Maple has been a traditional choice for violins and many other instruments because it’s extremely hard, but for guitars it doesn’t have the resonance of rosewood and it’s tone is sometimes considered harsh. That can be tempered with the right combination of soundboard wood, however, sometimes resulting in a very projective, powerful sound. Ovankol, which is also called shedua or African teak, isn’t as dense as rosewood so it’s sound is somewhat dark sounding.

The Top

The real job of a top (called the soundboard) is to be light enough to vibrate yet be strong enough to withstand the pull and pressure of the strings. Spruce has the highest strength to weight ratio of any of the woods, which is why it’s a typical choice for a guitar top, although cedar,  redwood, mahogany and koa wood have also been used. None of them are as light as spruce however, so they produce a totally different tone.

Adirondack spruce is known for its great tone but it’s from a protected forest in New York and therefore very rare. Sitka spruce from Alaska is very strong and easily available, so it’s become a popular choice for most guitar tops. Engelmann spruce has a very light weight and produces a very open sound, but because it’s not as strong the others there’s a possible longevity problem, which is also true of cedar. 

Carpathian and Italian alpine spruces from Europe are somewhere between Sitka and Adirondack in their tonality, but they’re also rare so they come at a premium price. 

Mahogany is also sometimes used for the soundboard but it has less projection and fewer overtones than spruce, which produces a punchier sound with less bass.

Figure 10.9 Tonal Qualities Of Various Types of Woods 

Wood Type	Description
Rosewood	Great projection and balanced tone with excellent bass response.
Mahogany	Fewer overtones and less bass than rosewood. Necks are warm sounding.
Spruce	Used for tops because it’s light yet stiff. Good projection and clarity.
Ebony	Used mostly for necks. Lowest projection of all woods used for guitar building.
Koa	Used for soundboards, low projection and lots of mid-range. When ussed for back and sides behaves like mahogany with more mid-range.
Maple	Low projection, few overtones, and sometimes harsh sounding.

You can read additional excerpts from The Ultimate Guitar Tone Handbook here.

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