It’s the 2016 A to Z Blog Challenge, so I thought I’d focus on one of my favourite subjects: Guitars. Care to join me?
So I’ll have to do a little remedial guitar anatomy to explain this one. If you remember from Guitar Anatomy 101, I mentioned that what gives the acoustic guitar its “voice” is the face of the guitar. The face is very thin piece of wood, as thick as a nickel or as thin as a dime. When the strings are plucked or strummed, the face vibrates, and, voila! The thing is that the strings are anchored to the face of the guitar by way of the bridge and, consequently, the face is subject to a great deal of stress, which would tend to distort the sound. To counter the stresses on the face, it has to be supported, but how to do that without dampening the resonant qualities of the face? This has been the question luthiers have tried to answer ever since the first gut strings were stretched across the face of the earliest instruments.
The strings of classical guitars aren’t under quite as much tension as their steel kindred, so the stresses exerted on the face aren’t as great. If you could turn a classical guitar inside out and look at the bracing under the face, you would see a series of “fingers” extending towards the bottom of the guitar, much like the ribs of a hand fan. Not surprisingly, this is called “fan bracing”.
There are two additional problems when considering steel string guitars. The first is the significantly greater tension the steel strings place on the face and the bridge, which will tend to torque the neck significantly. The second issue is that steel strings have small balls at the end that help anchor the strings to the guitar (remember that the nylon strings of a classical or flamenco guitar are tied to the bridge). These “ball ends” have a tendency to damage the underside of the face. Definitely not a good thing for tone quality or overall sound. Strengthening the face of the guitar enough to protect the face from both of these stressors would seriously diminish the tone quality of the instrument. That will never do.
Widespread use of “X bracing” has been attributed to the C.F. Martin Company, who first utilized the technique in the mid 1800s. In X bracing, the sound hole sits in the cleft of the top portion of the “X” and the arms extend down almost to the bottom of the guitar. The bridge plate, a kind of reinforcement for the bridge, is “hugged” by the lower two arms of the “X”. This configuration gives the face an enormous amount of support while minimizing the dampening effect. There have been other variations on this design, but X bracing seems to be the industry favourite.
What this bracing pattern has done is to allow the guitar to endure greater tension on the face without distortion, instability or damage. Without this bracing design, the modern steel string acoustic guitar would not be possible. The instrument would sound very different and not nearly as resonant as we’re accustomed to.