My Acoustic Guitar Soundboards

by Chris Jenkins

My goal is to make a soundboard which is as light and thin as possible, which conducts sound well, and is strong enough to be sound structurally.

1. Selection of soundboard. Important to pick out tops which have as much longitudinal stiffness as possible. Ideal weight is less than 7 gm per cc. Lighter the better. Cross grain stiffness is good, but not so important as longitudinal. Tap tone is important.
 
2. Thicknessing of soundboard. Thickness to a certain stiffness. When suspended across 2 dowels 18"apart, with dial indicator placed at the center, and 5 lb wt placed 3" off center, soundboard deflects .280 inches.
 
3. Bracing.  Start with braces 3/16 inch wide and 1/2 inch high on the 0 and 00 size guitars. Slab cut Sitka braces are stiffer than quartersawn braces, so they can be shaved to a lighter weight while maintaining the same stiffness as quartersawn braces. Graphite laminated braces are stiffer than Sitka braces of the same size. However, they are heavier. When laminated braces are shaved down to the same weight of Sitka braces, the strength is almost identical.
 
4. Shaving braces. To maintain maximum stiffness with minimum weight, braces are shaved to maintain parabolic shape. Top is tuned in mold for maximum responsiveness. Braces are sanded smooth after shaving.
 
5. Bridge design and construction. The bridge is also a brace. Its most important function is to transmit energy to the top. It should be as small and light as possible, while still covering the braces. Rosewood bridges weigh about 60% as much as ebony bridges of the same size. I now only use rosewood, and weigh pieces to find the lightest pieces possible. Bridge plate is made of rosewood also, tightly fitted between the X braces, and larger on bass side so as to have more surface area contact with X brace on bass side. A thin layer of graphite is laminated o the bottom of the bridge plate to make it more wear resistant, and to make it transmit energy more efficiently to the braces.

6. Paintings on the underside of the top are optional. However, many experts have stated that they do feel the guitars with abstract art on the soundboard have a more full and balanced tone.