Abstract: A guitar soundboard assembly is comprised a plurality of internal braces attached to an inner side of a soundboard for resisting warping. The soundboard is relatively thick for a longer useful life. The braces include two cantilever braces extending between opposite sides of the soundboard. Each cantilever brace is comprised of an elongated bar supported in a spaced position behind the soundboard by a pair of mounting blocks at its ends. Although the soundboard is relatively thick, the portions between the mounting blocks of the cantilever braces are free to vibrate, so that it can vibrate as much as a thinner conventional soundboard. The bases of the mounting blocks of the cantilever braces are slightly angled relative to each other to arch the soundboard forwardly for further increasing stiffness and resisting cave in.