Finally, the finale: The acoustic guitar body or “sound box is where the sound is perfected, enriched and enhanced..
In previous articles, we discussed the acoustic guitar anatomy, including the entire acoustic guitar, the neck, the headstock, and different aspects of their design and function. In wrapping up this series, the acoustic guitar body was saved for last with specific reason.
The body is the main aspect that takes simple string vibrations and adds the rich flavors of the classic acoustic guitar sounds – the beautiful combination of both wood and steel – to produce a virtually endless supply of musical possibilities throughout its history.
As the guitar is strummed, picked or plucked (or whatever style the player chooses), the vibrations of the strings travel and transfer through the bridge and saddle into the top piece, otherwise known as the sound-board. And whether one is playing a beginner acoustic like the Yamaha FG 700, or a high end Martin, the physics and process are quite the same. The bridge pins keep the strings securely anchored into the bridge for consistent tension and playability.
The soundboard is usually made of book-matches pieces of straight grained, light and strong wood. The most common candidates for soundboards are Sitka Spruce, Engelmann Spruce, Adirondack Spruce, Cedar, Koa, and Mahogany. The Spruces are all coniferous and grow in thin annual rings, giving the wood grain long, straight fibers that are evident when the trees are quarter-sawn (much like the way a pizza is cut if it were cut in 4 quarters).
These woods have been proven throughout the guitar’s history as providing the highest strength to weight ratio, allowing luthiers to produce guitar tops that are thin, strong and very responsive. Other woods, like Cedar, Koa and Mahogany are used in different applications because they impart different tones, warmth and overtones to the initial guitar sound.
Of all guitar top woods, Sitka Spruce has become the most popular for many reasons (which we will discuss in a future article). Another general reference for understanding tone woods can be found here, http://en.wikipedia.org/wiki/Tonewood .
Defining the rest of the sound box are the sides and back of the guitar. Many luthiers believe that the top of the acoustic guitar is the most important piece of wood for producing the initial tone quality and personality as well as the projection and EQ balance. As the sound resonates and interacts with the sides and back of the guitar, these different woods that are used produce what are called tones and overtones as the sound vibration interacts with the woods and picks up the “flavors” of the particular woods.
A very drastic but simple way to demonstrate the difference would be to take a mallet and strike coffee can, a plastic bucket, and a wooden box. All three objects would produce tones and overtones that are distinctly different from each other, and in essence would be characteristic of the different materials and how they respond to vibrations. The difference between tonewoods would not be as drastic, but one could understand the logic behind different woods imparting different sound qualities or flavors on the initial tone produced by the steel strings (or nylon for classical guitars).
The body of the guitar can vary by size, model, shape, depth, wood construction, internal bracing patterns, finish, bindings and purflings, giving the different manufacturers or luthiers a virtually endless combination of creative outcomes. And although the sound box is not truly a “box” shape, the body of the guitar, which consists of a top, sides and back roughly constitute a “box” which amplifies and gives personality to sound which differs based on all of these construction components or “ingredients”.
On the top or soundboard, the guitar has a sound hole surrounded by a decorative ring known otherwise as a rosette. The rosette adds both strength to the book-matched joint and can also be a place for a crafty luthier to display his or her artwork with beautiful abalone inlays or other precious materials.
The top is also protected (usually) by a polymer pick or plectrum guard which takes much of the follow through scratches from the strumming player’s pick. Additionally, the edges of the guitar, where the top and back meets the sides, is often guarded by a polymer or decorative wood purfling that is inlaid into the binding (thin edge piece).
The top of the acoustic guitar body (or the sound board), is braced underneath by one of several bracing patterns. Depending on the characteristics of the sound desired by the luthier, different woods, layout patterns, and shapes of woods (called bracings) are glued underneath the sound board to both strengthen it and help it to transmit vibrations effectively.
A few other notable mentions on the acoustic guitar body anatomy are the end pin and the finish. The end pin can be a place for a ¼ inch stereo input in the event the guitar is equipped with an internal electronic pickup. The finish, which can come in many different finishes and lacquers or polymer coats actually has a significant impact on the sound profile and projection as well.
While it is not our intention to dive into the different materials used to add a finishing coat to the guitar, we will briefly share what different finishes impart on the sound. If a luthier created 3 different guitars that were completely identical in construction, model, and woods used, but differed only in the finish of the guitar, the sound profile or personalities would differ significantly.
Gloss or high gloss guitar finishes will give the brightest and most crisp and penetrating projection of all finishes. A satin (or semi-gloss) finish will soften all of the characteristics of the final sound, giving the guitar a bit less crispness and projection, perhaps making the guitar sound a little more mellow.
The flat or “natural” finish will give the final guitar sound a dull, quiet, and subdued tone when compared to the other two finishes. Therefore, if you are shopping for an acoustic guitar and have narrowed it down to a fine intermediately priced BR 160, understand that different finishes on the same guitar can change the personality of the exact same model.
In a future article, we will talk more about specific characteristics and personalities of several popular tone woods used for tops, sides and backs of acoustic guitars. It certainly helps to understand what makes a guitar give it distinct sound and projection qualities before making an investment.