1. Bracing Structural Quality:
First in brace functionality is to protect the top or back from deformation when pressures are placed on the plates. Pressure can be either from string tension or atmospheric pressure. Atmospheric pressure can be more devastating than string pressure because as wood swells from excess moisture or shrinks from a lack of moisture, this movement will exceed any size brace with which you attempt to counteract the movement. So as you can see Humidity Control is VERY important not only for a finished instrument, but the Shop Humidity is critical as well.
2. Bracing Sound Production:
Secondly bracing is used to enhance the tone that is produced by vibrations produced from the strings. This string vibration travels through the saddle, through the bridge, and results in causing a vibration of the entire soundboard. Soundboard bracing turns this uncontrolled vibration into well ordered channels and directs the vibration throughout the entire top, though the sound hole reflecting from the back plate and even getting a contribution from the neck and sides.
Bracing is made from a number of materials, some of which are Sitka Spruce, Red Spruce, Adirondack Spruce, Western Red Cedar, Spanish Cedar, German Spruce and more…. Usually the bracing is made from the same species wood as the top material. So for Sitka Spruce soundboard, Sitka Spruce bracing would be used. This is not a hard and fast rule however. Many fine guitars are made from mixed top and brace wood species – my guitars included. For a long time I made my bracing from Western Red Cedar and placed them on Spruce Top and Cedar Tops with great results.
Selection of Brace Characteristics:
Being that the braces are such important elements in stringed instrument construction, extra care should be taken in the choice of brace wood. My preference is to buy a billet (portion of a split tree trunk) and hand-split the bracing myself. That way I can control the vertical quality of the grain, eliminate run-out and hand select the best pieces. As I said earlier, I make the case for absolutely vertical grain for my braces – no runout and very tight grain patterns – typically 20 – 30 per inch. This way I gain the most structural value and at the same time minimizing the brace mass to produce a fine, quality-sounding top plate.
What About the Back Plate?
Same goes for the back plate. Look for the vertical wood, Popular choices of bracing wood species are: Honduras Mahogany, Maple, Cedar or Spruce. All have great resonating qualities and are structurally sound. I personally lean toward the same wood I use of the Top Plate.
The Last Word:
So bottom line is choose your brace wood carefully, be picky, and you will improve the sound and structural capabilities of your guitar.