On the vast majority of acoustic guitars, the top is strengthened and supported by wood bracing on the underside, most prominent of which is an X-shaped brace that is flanked by a series of smaller braces. X-bracing has been used by Martin since the mid 1800s, and this evolution from previous ladder bracing made it possible to create stronger tops that could handle the increased stress of steel strings, and ultimately allow the development of guitars such as Martin’s powerful D-28 and, later, 14-fret OM models.
The use of X-bracing began in 1843 when C.F. Martin built an X-braced guitar for Madame Delores N. de Goni, one of the finest professional guitar soloists of her time, after entertaining her in his home. De Goni was a popular performer throughout the Americas between 1841 and 1892, and she considered Martin guitars “superior to any instruments of the kind” she had seen in the U.S. or Europe “for tone, workmanship, and facility of execution.” The guitar Martin built for her was the first documented guitar built with X-bracing, establishing a standard for the countless X-braced guitars that have followed. (In 2019, Martin released a replica of that instrument, the Size 1 De Goni Authentic 1843.)
In fact, X-bracing has proven the standard for so long that just about every all-wood acoustic guitar on the planet uses some form of it—excluding, of course, ultra-boutique designs that incorporate custom bracing schemes. Martin, for example, has five different X-bracing patterns that it uses depending on whether the designated guitar features scalloped bracing, non-scalloped bracing (or its own X-Series “bow tie” plates and carbon-fiber reinforcement), and whether the neck attaches to the body via a dovetail or mortise-and-tenon joint.