A well made guitar back will vibrate and add power to the instrument’s full tonal range through sympathetic vibration with the soundboard. An easy way to hear this is to play a well made guitar so that it’s back can vibrate freely, then play it again with its back muted by your stomach and chest. The difference in tone should be clearly apparent.
The back is first thickness sanded to proper joining thickness, then joined. After the two halves become a whole, the guitar shape can be cut out and thickness sanded to close to its final thickness. A scraper usually is the best way to finish the surface of the back, since it yields a smoother surface than the scuffing action of sandpaper.
Next, a center strip of mahogany is glued for reinforcement. The strip is then given a round profile and grooves are cut for the braces. The braces are shaped with a curve and are glued and clamped to the back with a cradle to give the back a curvature. Without this curvature, the guitar would crack easily due to humidity fluctuations.
After the back braces are glued, they are shaped and scalloped and the back is ready to attach to the ribs.