Ribs (also called braces or belly bars) are attached to the bottom of the soundboard on 
the side opposite the bridges. The ribs stiffen the soundboard, strengthening the side-to-side gluing of the individual soundboard planks which are only three-eighths of an inch thick. The ends of the ribs are tapered to ensure that the edge of the sideboard does not become too rigid. The ribs are usually made of spruce, sugar pine, or some other kind of soft wood. They are spaced four to six inches apart, and are glued to the soundboard in a direction that runs at a ninety degree angle to the individual soundboard planks (see picture at right). The ribs also help maintain the crown of the soundboard.
the side opposite the bridges. The ribs stiffen the soundboard, strengthening the side-to-side gluing of the individual soundboard planks which are only three-eighths of an inch thick. The ends of the ribs are tapered to ensure that the edge of the sideboard does not become too rigid. The ribs are usually made of spruce, sugar pine, or some other kind of soft wood. They are spaced four to six inches apart, and are glued to the soundboard in a direction that runs at a ninety degree angle to the individual soundboard planks (see picture at right). The ribs also help maintain the crown of the soundboard. 
