Guitar bracing
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Guitar bracing refers to the system of wooden struts which support and reinforce the soundboard and back of the instrument.
Soundboard or top bracing transmits the forces exerted by the strings from the bridge to the rim. The luthier faces the challenge of bracing the instrument to withstand the stress applied by the strings with minimal distortion, while permitting the top to respond as fully as possible to the tones generated by the strings. Brace design contributes significantly to the type of sound a guitar will produce. According to luthiers W. Cumpiano and J. Natelson, "By varying brace design, each builder has sought to produce a sound that conformed to his concept of the ideal." [1]
The back of the instrument is braced to help distribute the force exerted by the neck on the body, and to maintain the tonal responsiveness and structural integrity of the sound box.
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[edit] Steel string guitar top bracing
In all steel-string instruments the ends of the top braces taper at the edge of the soundboard. In most factory built guitars the brace tops are given a round profile, but are otherwise left unshaped. This produces a stronger top that is less responsive, but may reduce the number of warranty claims arising from damage.[citation needed] Braces are usually made from Sitka Spruce (Picea sitchensis).[2] Some luthiers use Adirondac Spruce, also known as Red Spruce (Picea rubens), in high end instruments.
[edit] X-Bracing
The tops of most steel string acoustic guitars are braced using the X-brace system, or a variation of the X-brace system, generally attributed to Christian Frederick Martin between 1840 and 1845 for use in gut string guitars.[3][4]. The system consists of two braces forming an X shape across the soundboard below the top of the sound hole. The lower arms of the X straddle and support the ends of the bridge. Under the bridge is a hardwood bridge plate which prevents the ball end of the strings from damaging the underside of the soundboard. Below the bridge patch are one or more tone bars which support the bottom of the soundboard. These abut one of the X braces and usually slant down towards the bottom edge of the soundboard. The top tone bar butts against a portion of the bridge patch in most instruments. Above the sound hole a large transverse brace spans the width of the upper bout of the soundboard. Around the lower bout, small finger braces support the area between the X-braces and the edge of the soundboard.
[edit] Brace shape and 'voicing' or 'tap tuning'
Luthiers building higher quality instruments adjust the stiffness of the top and shape the braces to maximize the response of the top while maintaining structural integrity. Tone bars and bottom halves of the X-braces may be either scolloped or parabolic in shape. Above the X-brace joint, braces usually have a parabolic shape. Experienced luthiers 'voice' or 'tap-tune' the tops and backs of high end guitars to produce optimum tone and responsiveness in the hands of the player.[5].
[edit] Scalloped vs parabolic bracing
Bracing style and shape will affect the tone of the instrument. According to luthiers Bob Connor and David Mainwaring, "scalloped braces will produce a warmer sounding bass response in the guitar with smooth mids and crisp highs. Parabolic braces will yield a quick response with a more pronounced mid range and a more focused bottom end."[6]
 Plan view of top bracing |
 Note the parabolic shape of the lower arm treble X-brace and the scolloped shape on the opposite side. |
 Top fitted to rim. Note the scolloped vintage style brace carving on this model. |
[edit] Back Bracing
The most common style of back bracing is known as 'ladder bracing.'
 Ladder bracing |
[edit] References
- ^ Guitarmaking Tradition and Technology by W.R. Cumpiano and J.D. Natelson p143
- ^ Guitarmaking Tradition and Technology by W.R. Cumpiano and J.D. Natelson p146
- ^ Guitarmaking Tradition and Technology by W.R. Cumpiano and J.D. Natelson p145
- ^ During the 1850s, X-bracing was used by several makers, all German immigrants who knew each other, and according to historian, Philip Gura, there is no evidence that C.F. Martin invented the system. See Gura, Philip, F. - C. F. Martin and His Guitars, The University of North Carolina Press, Page 106
- ^ The Luthier's Handbook by Roger H. Siminoff pp70,71
- ^ http://www.mcguitars.com.au/om.html
