Le Grande Arche
Most steel string guitars use about 12 braces for the top and 4 heavy braces for the back. These braces are absolutely necessary to give the thin top and back enough strength to withstand the 700N force from the strings.
Yamaha Guitar - Examples of bracing
Archtops only use 2 braces for the top and no braces at all for the back. From the 700N string tension only about 150N will be converted to down pressure on the Archtop Bridge. The way the string force acts on an archtop top is completely different from the way they act on steel string top. Two braces, a little arch of about ¾” (19mm) and a thickness of the top of ¼”(6mm) is enough to deal with the down pressure of 150N on the bridge.
Archtops are inspired on the violin family, the sound post is skipped but the whole concept is pretty much the same. A good example of natural evaluation. I always have my doubt about the arched top on the . It doesn’t give any structural advantage, it makes it much more expensive to produce and maybe most important “it looks so dammed good!” The picture shows the back of my Avant-garde top model archtop. Glossy, shiny and arched.