Acoustic Guitar Bracing Explained

Acoustic guitar bracing can be something of a mystery to many players, even though it's one of the defining aspects of an acoustic guitar's sound. At its simplest, bracing is a system of struts and supports that are glued to the underside of the top of a guitar in a specific pattern to provide strength to the top. More importantly though, bracing is a way of shaping the sound, voice and personality of a guitar.

When we talk about the 'voice' of an acoustic guitar, we are primarily talking about two things: the tonewoods used, and the internal bracing of the instrument. Different tonewoods will produce different tonalities - a Spruce-topped guitar will be more balanced and loud than a Mahogany-topped guitar, for example. Bracing determines how that fundamental tonality is translated to the listener. 

When the guitar is played, the strings vibrate the bridge, which transfers energy to the top of the guitar. The braces will transfer this energy across the soundboard and out to the back and sides of the guitar, and this sound is heard by the player through the soundhole. Thicker or more complex braces will absorb some of this vibration, translating to less bass and volume, whereas lighter, thinner braces will allow the sound to resonate more fully.

Without bracing, the guitar’s top would vibrate freely, producing a chaotic, virtually unusable sound. Bracing helps counteract that physical disruption. Otherwise, chords would be a mess of noisy treble tones and muddy lows.

There are a huge number of bracing patterns available to guitar players now, but here are a few of the most common.

X-Bracing

The vast majority of guitars available today have 'X-bracing', first developed by CF Martin around 1840. Prior to this, guitars used gut and nylon strings that didn't produce much in the way of tension (or volume!). With the advent of steel-stringed guitars, the need for a more stable form of bracing arose. In addition, players often wanted an instrument with more volume that could compete acoustically with violins and banjos.

The X-brace system is incredibly responsive and well-balanced while remaining strong, which is the reason that it has become so popular. It consists of two braces crossing under the sound hole and either side of the bridge forming an 'X' pattern, which provide the majority of the top’s support. Under the X-braces, there are typically two tone bars that help carry the vibrations from the 'X' to the lower portion of the guitar top., and 'finger braces' placed around the soundhole.

Martin's X-bracing patterns can also vary in position between models. In their 'forward-shifted' models (including most of the Reimagined Standard Series), the 'X' cross is moved closer to the soundhole, giving the soundboard more freedom to resonate, resulting in a warmer, louder tone. Less commonly, 'rear-shifted' X-bracing moves the 'X' further towards the base of the guitar. This gives a more balanced, intimate tone that works especially well on dreadnoughts. 

Scalloped X-Bracing

Martin's famous pre-war guitars all featured their 'Scalloped X-Bracing'. Scalloped bracing is when the luthier removes parts of the braces giving them a "scooped out" appearance. This reduces the mass of the bracing, allowing the top to vibrate more freely, producing a louder, deeper and richer sound.

In the mid 1940s Martin transitioned to straight non-scalloped braces, in part because of the reduced structural integrity of the scalloped patterns. This practice of only using straight braces continued until 1977 when Martin released the HD-28, a dreadnought guitar that featured braces scalloped similar to those in the found in "Golden Era" instruments. Since then, Martin has released many other scalloped guitars, for players that prefer a vintage sound.

A-Bracing

A-Bracing can refer to a few different patterns, depending on the builder. Lowden's A-bracing 'or 'Dolphin Bracing') is a variation on X-bracing, with the strut between the fingerboard and soundhole replaced by two diagonal braces which splay outward. 'Dolphin' refers to the ultra-thin scalloped braces which give Lowden guitars their enormous depth and volume.

Ovation also use an A-Bracing pattern, also known as 'Adamas Bracing' - rather than an X shape, the braces are arranged in a row from the soundhole or neck block to the lower bout of the guitar. Ovation has developed some fascinating bracing patterns, which are worth investigating further - click here to see some more.

Martin use an A-frame pattern on their entry-level guitars - based on a modified straight-braced X pattern, it features an angled bridge plate which strengthens the top further, for a tougher but less resonant guitar.

Ladder Bracing

In the 1920s and early 1930s, Gibson Guitars introduced their Kalamazoo and Recording King lines featuring a simple form of bracing known as ladder-bracing. With just a few strips of wood glued horizontally on the top in a 'Ladder' pattern, these guitars produced a more treble-friendly sound favoured by blues, folk and country players. Not only were these guitars cheaper and easier to acquire, they had a raw, unpolished and midrange-focused sound with fantastic projection. While they lack balance for strumming, they work exceptionally well for fingerpicking.

Ladder bracing has remained popular for these styles of music, and modern brands such as Waterloo and Gretsch still produce exceptional ladder-braced guitars that excel for blues and folk fingerpickers.

V and C Class Bracing

The biggest development in bracing of the last few decades has to be Taylor's 'V-Class Bracing' system. Developed by head luthier Andy Powers, V-shaped bracing creates stiffness along the centerline of the guitar (parallel to the strings) and flexibility across the soundboard, allowing both sides of the top to vibrate in an orderly fashion. That rigidity generates greater sustain, while the increased flexibility of the top produces more volume and power. Likewise, that even, orderly vibration pattern resolves the clashing sound waves that we perceive as imperfect intonation, where dissonance might arise out of certain chord voicings and note patterns along the fretboard.

The end result of this complex pattern is a guitar that is more even in volume and dynamics across the entire fretboard. While it may not be as loud and punchy as traditional X-bracing, it makes up for it on overtones and harmonic sweetness. It's a great all-rounder, and strumming and fingerpicking are equally balanced and full sounding, even with a light touch.

C-bracing is a new pattern based around the V-Class pattern, used in Taylor's Grand Theater guitars. This pattern emphasises the lower frequencies to produce a surprisingly powerful bass response from a smaller-bodied guitar.

Bracing Woods And Construction

Most acoustic guitar builders use Sitka Spruce for their bracing, and with good reason. Not only is it plentiful, it has a great strength-to-weight ratio, meaning that it supports the soundboard with a minimum of added weight. Many builders also now offer Adirondack spruce as a bracing option, which was used in the Golden Age guitars of builders such as Martin and Gibson. Adirondack is even stiffer and lighter than Sitka, allowing thinner bracing which translates to more resonance, bass and responsiveness.

For those wanting a truly vintage-correct tone, Martin's Authentic Bracing is the benchmark. To replicate the sound of their early 20th century pre-war guitars, Martin artificially age the braces with their VTS Torrefaction system, alongside period-correct features including thinner, 'tucked' braces and a smaller bridge plate.

The type of glue used for bracing can also vary. Most modern manufacturers will use standard wood glue, but animal protein or 'Hot Hide' glue is a common upgrade. Hide glue is a traditional method of applying braces which many believe has a 'tighter' connection between the brace and soundboard, reducing the amount of energy lost. In a finely built guitar, this small amount of extra contact can make a big difference in tone and volume overall.

It's important to remember that bracing, while important, is just one factor in the sound of an acoustic guitar. It's very easy to get hung up on individual specs in the search for your perfect instrument, and the amount of variations in bracing can be overwhelming and confusing. If in doubt, always trust your ear - or contact our knowledgable staff at info@acousticcentre.com.au.