Combining Woods (Tonewood Choices)

Caveat: In this article the author refers only to all solid wood guitars.  Laminates are another topic altogether.

Koa, the most desirable and among the most prized of tonewoods on the planet.  In flamed examples, breathtakingly beautiful, and offering a certain inexplicable “shimmer” that is unforgettable… and yet discussion of that wood is what prompted this article.  But before we get to that, let’s get the foundations established:

Raw cut koa
Extremely figured (curly, flamed) koa when finished.

Though there are some individual exceptions to the rule, you’ll seldom find a guitar made of just one species of wood that is exceptional. In the simplest of forms, the reason is that if you have only one species bringing something to the table, you are getting a limited range of sound.  For example, mahogany is said to push the midrange (and rightly so.) But unless you want a guitar that’s so narrowly focused on one range of the spectrum of sound, you’re going to want other complimentary materials to play a part in the sound your instrument produces.
Sitka spruce is the standard for soundboard (top) material on an acoustic guitar.  There are many reasons for that.  It’s soft and forgiving, so the luthier isn’t damaging a Sitka top as often.  It brings warmth to the table, making it a good combination with harder woods.  It’s plentiful and, therefore, affordable.   In the rest of this article, we’ll be examining how the woods combine and what other factors come into play in choosing materials for an acoustic guitar.
The most common of woods used for the body (back & sides, B&S) are mahogany, rosewood, sapele, ovangkol, Tasmanian Blackwood (recently), and maple.  Ebony is being used a bit more of late, but making a guitar body out of ebony should be done with careful consideration and the realization that the instrument may take a LONG time to open up to its complete sound potential (if it ever does, yet another article to write).  Necks are mostly mahogany, some maple.  Fingerboards are nearly all rosewood and ebony, ebony being preferred, but a bit more expensive, so most commonly found on upper and high end guitars.  Most bracing is also made of sitka spruce, because it is inexpensive and sustainable.  Adirondack is preferable for a slightly stiffer top that will be very difficult to overdrive, but there is such a thing as too much of a good thing, so one seldom chooses Adi bracing when the top is already a relatively stiff wood.
Every other aspect is purely cosmetic, and so the choices are all over the map.  If you want abalone, go for it.  If you prefer Pau abalone (more colorful) and don’t mind affording that selection, that’s fine.  Nearly every other hardwood imaginable has been used in trim, including bloodwood, ebony, purple heart, walnut, oak, maple, boxwood, koa…

Where do the woods come from?  I’ll share this video with you, courtesy of Hearne Hardwoods, to give you an idea of the scope of such operations:

Tazmanian Blackwood. Hard to tell it from Koa. Both are in the Acacia family.

(As an aside, Tasmanian Blackwood, closely related to Hawaiian koa, may prove a much more sustainable tree and it doesn’t necessarily sacrifice beauty or sound.  (The author generally prefers the sound of Blackwood, as it’s not quite as brittle.)

But I digress.  Stepping away from the eye candy, back to wood combinations:

If a wood is hard (1000+ on the hardness scale) you’ll want to temper that with something softer, and also bring another set of sonic characteristics to the table.  So you’ve got rosewood.  That’s a softer hardwood, absorbs some of the higher pitched aspects, and provides warmth.

The 3-piece back on the left was made by Joel Keefe Shoemaker, a rural US luthier.  The rosewood provides warmth, the stripe of maple is both beautiful and functional, as the harder maple is expected to provide a bit of greater clarity and a very slightly quicker bounce.  Coupled with an Englemann spruce top (cut and milled by the aforementioned luthier) this guitar has all the potential of being a very versatile and diverse instrument.  Combined with a short scale neck and Joel’s light bracing, it’s extraordinary.  It brings three woods to the table, and that amounts to three distinct layers of sonic properties.  If this guitar was built of any ONE of them, it would be dull, brittle, harsh, or some combination of those.  Instead, (and I can’t emphasize enough the importance of such materials being worked by capable hands) it becomes a masterpiece, boasting warmth and precision at the same time.  The bracing and other aspects come into play when we talk about responsiveness and dynamics, which is an article for another time.

Combining woods is essential to a full, broad sound spectrum.  All koa tends to sound thin and can really be lacking in smaller body sizes (OM or GC, for example.) Sure, they’ll open up, but why not give yourself the fullness of sound by adding other elements?

On to soundboards (tops): Sitka is warm and soft, cedar far more so, redwood even more than cedar (too much so for my taste) and sinker redwood is downright mushy.  Adironack and Lutz spruce (a naturally occuring hybrid from Alaska) are both about the same hardness, but Adirondack provides more harmonics, Lutz a crisper sound.

Note: Using the Janka scale alone isn’t functional.  There are differences between old growth and new, between different grades of each of the woods, etc.

For comparisons: Koa is very hard, for a soundboard material.  Nowhere near as hard as Brazilian Rosewood or Macassar Ebony but still… significantly harder than any spruce/softwood.  So you’ll want to pair it with a softer soundboard ideally.   But what if the soundboard is koa (or mahogany?) . That puts a serious wrench into the works, changes the paradigm.  What paradigm?  The one where we use hard wood for the body and softwood for the top.  Can it be done?  Yes, but there’s always a risk in defying convention.

This beauty was designed by the author, a combination of koa and the closely related Tasmania Blackwood, which provides greater diversity of tone than straight koa would, while reducing cost.

So it’s safe to say that any guitar featuring a hardwood body and softwood soundboard is going to bring more width of tone than any mono-wood build.    The guitar on the left was designed to provide a better sound than all koa, while reducing cost.  The matte finish allows more sound to come out, and the sapwood center was selected as slightly softer as well.  A beautiful and magnificent instrument, and an alternative to the all-koa concept.

In the overall, it’s about balance.  Balancing the hardness and clarity with the softness and warmth.

Finding that happy midpoint. It is very important that your ears and fingers do the choosing.  When you look at this guitar:

When you look at this guitar, what do you see?  Typical plain Sitka Grand Symphony body, right?

How could you begin to predict that the sound would be so unbelievable, or the back and sides would look like the pictures below?

 

 

 

But it could just as easily have gone the other way.  You could be looking at that as a top and be dazzled by it and end up buying an instrument that hasn’t got the complexity of tone to keep it interesting.

One more point to bring up in this article: It’s not fair or accurate to play a new guitar and expect that it sounds the way it will in a few weeks or months.  This is especially true of instruments made of harder woods.  They don’t take time to open up.  They take vibrations.  That same guitar could sit for years unplayed and never show you what it’s capable of.  But play it hard, get it vibrating, and it will open up fairly quickly, to present a bold, powerful richness that you never would have expected.

This article is far from a complete discourse on the subject.  There are many more factors and aspects.  It should be considered a starting point on the subject.  Feel free to comment here or wherever you may find the article, and discuss these concepts.  If you write with specific questions, I’ll be happy to reply, but don’t have the time to engage in a debate or theoretical discussion about what has been presented here.

2 Comments

  1. Yep.

    Quick question, I’ve been getting more deeply ingrained into the world of acoustics since bringing a Taylor 814 home. Just want to understand that when you were referring to wood hardness of +1000, that you were talking about the Janka Scale?

    Just trying to increase my knowledge base for future acoustic acquisitions

    Best regards!

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