There are so many options for what woods you can get on an acoustic guitar that the possibilities seem nearly endless. Today we will give a primer on acoustic wood characteristics to help start the process of narrowing down the options. It is very important to remember that many factors from finish application and type to construction technique and more have big influences on tone, so this is only a starting point.
The top (or soundboard) is the best place to start in regards to understanding acoustic guitars. The strings on any given acoustic will be under somewhere around 180 lbs. of tension. When the string is picked, the energy is transferred to the soundboard through via the bridge. This in turn vibrates the soundboard and amplifies the tone of the string. Think of the soundboard as a big speaker. If we stop right there, it becomes obvious that the soundboard probably has the biggest impact on the sound of an acoustic instrument.
- Sitka Spruce: This is the most common type of wood used for the soundboard in North America due to its abundance (for now) and great resonance. The wood comes from Sitka, Alaska and is the largest species of spruce in the world with trees growing as tall as 300 feet and a diameter in excess of 15 feet near the base. Typically Sitka has a robust, direct tone that handles most playing styles well.
- Engelmann Spruce: This species is another North American wood that works well as a guitar soundboard. There is usually an upcharge for Engelmann as the trees themselves are smaller and due to the nature of its growth, it is more difficult to get suitable tops from a log. The tone has more overtones and is particularly well suited to a softer player or a fingerstyle player. It does tend to compress when played more aggressively and is not particularly well suited to more "heavy-handed" players.
- European Spruce: European spruce looks and sounds very similar to Engelmann spruce but has a bit more headroom so can hold together better with more aggressive pickers. Some say the response is also faster as well. European spruce almost always has a premium price attached to it in North American made guitars.
- Adirondack (Red) Spruce: Adirondack is considered by many to be the holy grail of soundboard woods for an acoustic guitar and usually has a high premium upcharge. This wood is very stiff and was the choice soundboard material prior to World War II. Due to its stiffness it was used for airplanes as well and was vastly over-harvested. This coupled with the fact that the trees were not very large to begin with made this prime tonewood very difficult to obtain and it remains so today. This wood has the most available dynamic range and maintains its clarity and fullness when played softly or played with full force and a heavy pick. Generally, no species of spruce is louder or bigger sounding than Adirondack.
- Western Red Cedar: Cedar is a great choice for a fingerstyle player and is usually used on smaller-bodied guitars. Tonally it is warm and has plenty of overtones. Cedar tends to compress when played with much force but is sensitive to very light touch. Paired with rosewood back and sides, this is a glorious combo.
- Mahogany: Mahogany has been used for a long time as a soundboard material. Its tone is very midrange and punchy. In a larger guitar this can get muddy but in the right instrument it can be magical.
- Koa: Koa is very similar to mahogany but has a bit more twang to it. The tone is mid-rangy and bright. It makes for a great strummer.
After the soundboard is resonating, the sound then bounces off the back and the sides which ultimately help to shape the tone of what comes out of the soundhole and is heard. Think of the back and sides as a sort of eq. So you have a tone coming from the top that is fairly defined and then is shaped by the back and sides. There are many options here and we will cover the most common. Before we get there though, we need to address body size. Generally speaking, the bigger the body is, the louder and bassier it will be. It will usually take more power (from a pick) to get that soundboard moving too. A smaller body will be more articulate and have less bass response but take less energy to move the soundboard.
As we describe these woods, we will try to compare them to a simple equalizer such as one on a stereo (treble, middle, bass).
- Mahogany is a great wood for back and sides as it is very balanced with great articulation. For recording, this is a hard wood to beat. Bass (0), Middle (0), Treble (0)
- Sapele is very similar to mahogany but just a little brighter with a bit less bass. Bass (-1), Middle (0), Treble (+2)
- Koa is an originally a Hawaiian wood that shares some characteristics with mahogany but is more articulate and brighter. This would be like turning the bass slightly down, midrange flat, and treble slightly up. This is a beautiful wood with some particularly interesting overtones. Some times you may see it used for the soundboard too. Bass (-2), Middle (+1), Treble (+4)
- Indian Rosewood. Indian rosewood tends to have strong bass and treble response with a slightly cut midrange. This is very pleasing to a lot of people in that it is big and shimmering with nice clarity and a full tone. Bass (+3), Middle (-3), Treble (+3)
- Brazilian Rosewood: This is the Adirondack of the back and sides meaning it is considered by many to be the "holy grail" of tone woods. It is endangered from over harvesting and a really good cut of it is not common these days. It was the choice wood for many builders until the late 60's. There are also some restrictions to travel with a Brazilian rosewood guitar unless it is CITES certified. The tone is similar to Indian rosewood but with more complexity in the midrange and a tighter bottom end and sweeter top in most cases. Many believe this wood yields even more results with age than Indian as well. This always has a premium upcharge. Bass (+4), Middle (-2), Treble (+4)
- Cocobolo is a wood that shares some qualities with rosewood along with maple or koa. It has great shimmering highs but more bass response than koa or maple. Bass (+2), Middle (-1), Treble (+4)
- Maple is another choice and it is very bright tonally and visually. This is a very articulate wood that is for a bigger-bodied guitar as it tends to liven it up a bit. Bass (-4), Middle (-2), Treble (+5)
Again, there are several more choices but these are some of the more common that you will run across. Using this logic, you can see why a lot of jumbo-bodied guitars are made from maple with a spruce top. The big body is loud and powerful while the maple tames some of those strong bass tones and brings some clarity to it. Then you get a very loud, but very balanced, guitar.
These are just some starting points and we will go into more depth about bracing, finishes, more exotic woods and construction techniques in another post. Using this information should make it a little easier to at least get on the right path as far as finding "the one" acoustic for you. Every thing is relative and as we dive deeper into acoustics, we will see that luthiers are finding all kinds of ways to manipulate the sounds created by their instruments! Enjoy the hunt!