The Structure of the Acoustic Guitar
Key points in determining reverberation
Each part has an effect on the sound
A guitar functions because string vibrations resonate throughout its body. There are many important points to note in how this reverberation is controller. One could even say that each part has an effect on the sound. Some of the most important points however are the correlation between the area of the sound hole and the volume of the body, the material used for the top of the guitar, and the bracing.
Even the volume of the body has an effect on the sound
For example, if a guitar is made thicker but its shape is kept the same, its body will have a greater volume. Likewise, if the shape is made smaller but the thickness is kept the same, it will have a lesser volume. When we speak of the volume of the body, we are speaking of the amount of air inside the guitar that vibrates and resonates. Therefore, if the volume of the body changes, so does the loudness and timbre of its sound.
What is the bracing?
Pieces of wood called harmonic bars are placed on the inside of the top of the guitar. The placement of these harmonic bars varies by manufacturer and instrument, and is referred to as the "bracing" of the instrument.
Bracing serves two purposes. One is to provide sufficient strength to support the tension of the strings. Bracing strengthens the top to prevent the neck from warping or part of the body from being lifted up when the steel strings are pulled. The second purpose is to create a certain timbre. Consider the height (the center portion bulges up when looked at from the side) and placement to get an idea of the sound you want. Higher harmonic bars create sharper sounds, while lower ones create softer sounds. The bracing changes the atmosphere of the sound produced by the guitar-for example, by allowing a guitarist to play in a manner that expresses depth across the entire range or to play crisply with a clean stroke.