Making an instrument with good tone, responsiveness and projection requires making the soundboard both light and stiff.
Many types of wood can be used with good results. Often it is the unique weight and feel of a particular piece of wood that makes it suitable for a soundboard. I have had very good results using a variety of hardwoods and softwoods but not every board from a particular species of tree will have the density, weight and stiffness I prefer.
Spruce is by far the most popular tonewood for soundboards and for good reason; it is both light in weight yet very strong. Spruce has been used for making boats and airplanes because of it’s light weight and remarkable strength.
The soundboard needs to be thin and light enough to vibrate yet it also must be strong enough to be structurally stable.
Bracing helps adjust the strength and stiffness of the soundboard and back of a stringed instrument by adding stiffness and support in some areas while allowing the bulk of the soundboard to be thin and vibrate freely.
This soundboard required two braces. The braces are slightly arched and add a slight radius across the width of the soundboard. By bracing a slight radius into the soundboard I can use lighter braces to add strength without adding much weight.
This concept is similar to the design of arches and geodesic domes, the design of the structure itself adds strength without requiring much mass.
The braces are shaved down to remove any unnecessary weight. This is done with a small plane and a chisel or two. I gradually taper and shape the braces until the soundboard has the stiffness and resonance I want with as little mass as possible.
I find shaving the braces to be one of the more critical yet enjoyable aspects of making a dulcimer.