Gibson Hummingbird

What's “under the hood?” Cellphone, car or guitar... the components you can't see will often have a big influence on how gear performs. An acoustic guitar may well be “old” technology, but that doesn't mean its build doesn't matter anymore. And when it comes to the “invisible” insides of an acoustic guitar, a key component is bracing.

Strong construction, strong tone

An acoustic guitar body is essentially a speaker, an electric-less amplifier. To do this job properly, the top of an acoustic guitar needs to move – like a speaker cone – but it also has to be strong, so it doesn't implode.

An acoustic's body wood is usually thin – typically between .080" and .135" thick – and made of light wood, such as Sitka spruce. Light woods are desirable because they don't dampen the vibrations of the guitar body. When the strings are played, they vibrate the bridge, which transfers energy to the guitar's top. But a totally un-braced (un-strengthened) thin top couldn't handle the tension and pressure of those steel strings, so bracing is essential.

Back Bracing

Acoustics have bracing on their backs (and often sides) as well as tops. But back bracing is generally simpler. Back bracing is mainly designed for strength only, and is usually ladder bracing. The term is self-explanatory – it looks like a ladder, with a central brace running the length of the guitar's body and ladder “rungs” running the width from side-to-side.

Here you can see simple ladder bracing inside a Gibson Acacia L-00.

Gibson L-00

Again, there are compromises. Fatter braces provide a bigger gluing area for more strength but will make the back more rigid. Makers who like their bodies' backs to vibrate as much as possible may go for braces that are more slender (less glue contact) but taller (extra strength). And, of course, you can see back bracing so take a peek and see what sort your box has.

Top/Soundhole bracing

Early guitars employed ladder bracing for tops, too. Of course, the central brace couldn't (aesthetically, at least!) extend under the soundhole, so that meant the center brace was split in two. The solution? X bracing.

X bracing has been the predominant industry standard since the early 1900s (there remain exceptions) and again, there are subtle difference between guitars and between builders. 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. Finger braces are usually placed around the soundhole.

Brace Width and Wood?

Gibson has been perfecting the tonal imprint of bracing styles for decade. In very general terms:

• The narrower the brace footprint, the brighter the tone.

• The wider the brace footprint, the less bright the tone.

• A softer brace material will sweeten the tone but also increases bass response – it allows longer, low frequency waves to move the top more easily.

• A harder brace material will increase top stiffness also increasing treble response but reduce bass.

There are then differences between modern and vintage styles of -bracing. For example, Gibson Acoustic’s Hummingbird Vintage sports a single X bracing pattern similar to the design inside vintage Gibson J-30s. This traditional pattern delivers a balanced midrange tone, with unbiased lows and rich, clear highs.

Modern X bracing has non-parallel braces on the lower bout, as pictured here by an excellent blog on the Gibson Montana acoustic facility by Gibson online dealer The Music Zoo.

Gibson bracing

The Music Zoo blog praises Gibson's traditional approach to acoustic guitar craft, noting “how old school the Bozeman factory still is. This could be a scene from the 1950s.” There is a subtle difference between bracing on “modern” and “vintage” voiced Gibson models. That said, there is no right or wrong, it just depends what you like to hear.

As always, the only judge to listen to is... your own ears. But quality matters. Every Gibson acoustic features hand-scalloped, radiused top bracing inside the body, a feature normally found only in limited run, hand-made guitars. By scalloping each brace by hand, the natural sound of the acoustic is focused more toward the center of the body, enhancing the instrument’s sound projection.

These days, you shouldn't really have a “problem” with acoustic guitar bracing, especially not with Gibsons. New fads come and go, and some makers' elaborate alternative methods of bracing seem to split opinion. Use too much wood bracing and you're simply reducing the resonance of the top. And on a guitar with the finest tonewoods, you don't want that!

So get to know a little bit about bracing and tonewoods and you'll know your own Gibsons that much better. Be sure to join the discussions at the Gibson Acoustic Forum for in-depth talk on bracing.