Guitar Bracing – Designing Balance
A guitar’s internal bracing is one of the most important elements of a guitar and is sometimes overlooked. Also called tone bars, these structural wood braces are located immediately under the top. As their name implies, their purpose is to add stiffness and strength to the guitar’s thin top as well as help define its acoustic voice by influencing different movements. An instrument maker will shape and carve a series of braces in order to strengthen the top to disperse the energy from the strings. From an engineering perspective, there are many adjustments that a guitar maker can apply to a piece of wood for it to function as a supporting brace while making an efficient guitar. The most successful guitars move a lot of air, absorbing the least amount of string energy, and do so in a very balanced and beautiful way.
There are as many different variations of guitar bracing as there are guitar makers. Some famous guitar making families defined their sound and style through a very specific and distinct bracing design that was practiced for generations. Other makers spend their time using guitar bracing as a platform of exploration. Just as every piece of wood is uniquely different, every maker has a method and approach to bracing a guitar, whether good or bad.
Koentopp Traditional Classical Guitar Bracing
We can summarize the tonal spectrum of a guitar on a scale with bass on one side and treble on the other. A guitar player would have a negative reaction to a guitar that was unbalanced with more bass than treble, or viceversa. The best instruments encompass the whole spectrum. The difficulty in building a guitar is that the bass frequencies move in a completely different way than how the treble frequencies move through a piece of wood and the guitar has to do both successfully. When these frequencies are all balanced, clear, and working harmoniously, the result is a successful instrument. Some guitars are, in nature, heavier on one side of this spectrum and it is up to the maker to supply a bracing design that will bring it back to a balanced state.
Bracing in a flat-top guitar is different than an archtop guitar because it serves multiple functions. It is there to support the top from the strong forward pull of the strings and unify the top into a stiff surface. As the tone bars disperse forces across the surface of the top, they influence the top to vibrate in different ways. By studying the way bass and treble frequencies originate and escape a guitar, the bracing can be designed to bring out a desired quality.
An archtop guitar acts differently than a flat-top. The strings are fixed to a tailpiece which is attached to the back rim of the guitar. As a result, the forward pull of the strings is dispersed through the majority of the guitar’s body and not solely on the top. In this situation the force acting on the top is in a downward direction at the bridge. The braces support and unify the top but they do not need to be designed to counter the pull of the strings.
Koentopp Chicagoan X Bracing
Many people know the archtop as a beautiful and organic shape. When carved correctly, it’s true beauty lies in perfect mathematical curves relating to each other across the top and back surface of the guitar. The more perfect these archings, the more efficient the guitar becomes and the more the top acts as a major brace structure.
An arch, when designed correctly, is one of the strongest load bearing structures. Centuries ago, violin makers had mastered this “golden curve” and as a result, the arching became more mathematical, as did the bracing. Controlling the arching, the height, and the parameters of these curves, leaves the maker with a controlled way of experimenting with tonal possibilities just like adjusting the profiles of bracing bars.
Violin Bass Bar by Master Violin Maker, Michael Darnton
I always examine guitars closely when I receive them for repair or reconditioning. I often stick my fingers through the f-holes to feel the profiles of the tone bars. Even on some high end custom guitars there seems to be little consideration for both the bracing and the arching. For instance, a brace should never be flat on top or shaped like a rectangle in a cross section unless a makers goal was to add extra mass or absorb more energy. Removing the upper corners of a rectangle and rounding it to more of a bullet-like shape does nothing to jeopardize its load bearing strength but does, however, remove one-third of its energy absorbing weight.
A guitar maker can control a braces’ strength by manipulating its height. If you remove a quarter amount of a wooden board’s height you loose half of its structural load bearing strength. With certain principles like this in mind, classical guitar makers control a guitar’s voice not only by choosing a brace layout but by manipulating brace profiles and their related heights.
The design of a traditional classical guitar makes it more conducive to low frequency movement. When I am building a classical and conceptualizing my bracing I do so to bring out the trebles and create balance. I keep in mind all variables and converge them as the guitar comes together. I first pick woods that I believe will give me a good platform of color and timbre and start me in the right tonal direction. I then choose different pieces of brace wood, with different stiffness’, and work with them to bring the guitar into a balanced focus. My methods change from guitar to guitar but the idea is always constant.
In order to make a successful guitar, more attention must be paid to the design and construction of the bracing, including the arching of the top of the guitar. The bracing should focus on the whole idea of the guitar; balancing the entire tonal spectrum. This is an art of controlling stiffness and influencing different kinds of movement. A maker has a palette of sound voicing that they can choose from by adjusting the profiles, dimensions, and layouts of a guitars internal bracing (which I will discuss in greater detail in a future post). In my opinion, success of an archtop’s bracing is dependent on the efficiency of its arching. The more efficient the guitar is in all of its parts, the more delicate and influential the braces become.
Hi Dan
Thank you so much for sharing some valuble information.I do really appreciate it.
I am a self taught guitarmaker From Cape Town ( South Africa ) and have just completed my 14th guitar.
Everytime after having completed a guitar I feel that there is something I could have done better to improve on the sound. The idea that I am getting is that all the time my guitars sound just seems to be too tight.As If the wood just not want to move freely enough. I can hear that there is a hidden sound quality there, but somehow it is locked into the guitar.
I have read everything you have mentioned in your piece on GUITAR BRACING – DESIGNING BALANCE and will for my next guitar certainly apply these good ideas into it. Espacially reducing enery absorbing mass that I can remove by giving the braces a nice parabolic shape over all.Somehow I think I knew this already , but I feel that I have confirmation now that I have read your piece. My guitars seem to have uneccessary lots of sustain. Some people might think this is very desirable, but in my opinion this is not always true.Maybe this is also why I have too much mass in the braces over all.
This is also my first time corresponding with a luthier elsewhere , so I am not quite sure if you perhaps write back to me.
Any way thanks again.
Best regards
Foster
Foster,
Thanks for your reply! Your guitars look very nice and I am impressed with your work. You are definitely on the right track. I will email you with a more in depth response. Thanks again for posting.
Great advice! What kind of wood are you making this guitar from?
Thank you so much for your comment! I am not certain which guitar you are asking about. The classical guitar in this post was made with Cocobolo and European spruce. The x-braced Chicagoan pictured here model was made with European spruce and maple. Thanks again! -Dan
It is good to find somebody who is thinking about bracing and tops in a logical way, methodically applying scientific and engineering principals, not just intuition. I have been “thinking” about and sketching classical guitars for years, studying everything I can find, learning from the old masters; but your article seems to tie it all together. I see many luthiers incorporating this knowledge, though I think some just copy without understanding.I am a retired engineer, well acquainted with structural issues and design requirements, and I am struggling to find quantitative information relating top and bracing structural and dynamic properties. I feel that if we know and can express these requirements numerically, then we can trim and shape braces and top to achieve the desired qualities of mass, stiffness, resonance, etc. I believe Robert Godin is on to something useful with stiffness testing of bare guitar tops, but there must also be an accompanying set of “rules” for completing the bracing in order to produce the desired top, ready to put on the guitar, and to have confidence it will sound and play the way you want it to. Yes, this is where science can take the art and intuition of guitar making even farther. If you have such information, please let me know about it. I want to start building guitars for myself.
Thanks so much for the comment Gary! My bracing methods have been developed through my education and experience working with violins and cellos. In the string instrument world, the window of success seems to be much narrower. It is very obvious when small changes are made to a violin. My technique takes many things into consideration, bass and treble top vibrations, top flexibility, and the overall stiffness of the top. I do use the same technique and start with a certain range of measurements that I have found work best for me. The trouble with all guitar making is that it is equally an art mixed with science. No two pieces of wood are the same. Take this and mix it with hand made construction, with hand carved arching, there are few constants here. If a guitar maker is successful the one thing that surfaces are common characteristics in their work with each instrument representing a new, unique, and wonderful energy.
I use math and relationships to lead me in the right direction, to guide me on the right path and to leave references for me. Up to a certain point, it is about feeling and understanding. Making decisions based upon your past successes and experiments. Math, physics, and science, can lead one to making a really efficient instrument but I feel that there is still an equal amount of intuition and instinct that flows through the makers hand.
The way one person works, the way one person fits a brace to the top, from the start of an instrument to finish, has everything to do with the final product. Math and science are important guides.
Thank you for an informative article. I am interested in bringing out the bass end of the spectrum because I am building an acoustic / electric, and the peizo pickup doesn’t get the bass very well. I use my guitars to record, and I am looking for that special balance of acoustic and electric. my guitars have two outputs into two tracks. What kind of bracing would bring out the bass. Thanks again.
I like Gary’s comment. Particularly stiffness and resonance. Is this a secret that I should be aware of.
Thanks for the comment Tom! There are a lot of critical parameters that come into play. An x-brace will certainly support lower frequency movement however, there are other things you can consider as well like scale length, size of the resonance chamber, sound hole placement, etc. There is no one solution to this problem which is why it remains so fun for all of us;) Ervin Somogyi has written an extensive amount of information on responsiveness. I would recommend you check out his teachings if you have not already. Good luck!
Hello. I have a question. Concerning top bracing material, in a well made guitar should the bracing material be the same as the top, i.e., should an Adirondack top have Adirondack bracing, or an Alpine top have Alpine bracing? What are the advantages/disadvantages of mixing woods, i.e., an Alpine or Adirondack top with Sitka bracing. Thank you for your help.
Thanks for the question David! There isn’t really a definite answer or given method. Every maker has his or her own way of choosing woods for a particular instrument. Sometimes I don’t want my bracing to be really stiff and sometimes I do, and wood from the same species can even have drastic differences in tone and stiffness. These types of decisions are the true reasons that guitar making is an art. There are not advantages/disadvantages to using one wood over the other with a certain top wood. There are sonic differences between different species which depend on the strength to weight ratio and this is natures menu. I think the best brace wood in any condition, needs to be uniform and straight grained as possible.
Picking the right materials can help a maker define a certain sound and choosing the right bracing is only a fraction of it. One gains this knowledge over time, working with different woods and getting familiar with their qualities.
We would hope that a chef, who chooses to have his chickens delivered from a certain farm, respects them enough to make an unbelievable delicious dish, but that is not always the case:)
Thank you for the very good thread of thoughts on bracing. This is my first archtop and i’m working from the Benedetto book which is a good starting point. I am doing a round/oval hole with x bracing because I like the look and will be doing a bolt on neck. This allow access so I can make changes or correct mistakes. My question or interest is have you any experience with the varying the height of the bracing. Lets say I do 1/4″ or even 3/16″ wide, by 1″ or 1/1.25″ deep at the maximum point on the brace. Do you think the extra depth of the brace would then act to baffle the sound in the chamber/box. As A carpenter I know that strength is greater with the material is on edge. The thinner the brace the less contact there is with the plate and strength could be made up by additional depth. Any thoughts? I know I should not try to reinvent the wheel on my first guitar.
Hi Andrew! Sorry for the late reply! You ask a good question and you kind of answered it in your comment 🙂 As you stated, a thinner beam can be much stiffer than a wider beam if it is taller. If you take away 25% of a beams height it can loose about 50% of its strength. I believe this is one of the categories that makes guitar building more of an art and supplies the guitar with the evidence that is was made by the human hand. Every maker has a way that they carve a brace and voice a top; it is something that becomes very personal (This is more evident in flat top guitars, where the bracing has more of an impact on the voice of a top) I’ve been doing this for 15 years and I am still experimenting with different bracing shapes and profiles. I think of the guitar as a complete system, made up of smaller components. What makes things difficult is that our materials keep changing. Over time, if you keep at it, you will start seeing continuity between your work and how certain designs change the voice of the instrument. In a nut shell, I carve my braces a little taller under the bridge, and feather them out as they reach the rims. Think about the top as a speaker membrane, you want it to bounce effortlessly with a smooth flexibility. In my mind, I think the best guitars seem like they want to explode but still have plenty of strength to support the stress of the strings. Some makers call braces in archtop tone bars, because they act more as a tone changer than they do as a structural brace. Good luck to you! –Danny
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Hi,
Does the fan pattern eliminate the need for a bridge plate?
Thanks,
Jim
Hi Jim,
No it doesn’t. The bridge plate, along with the bracing, helps unite the top with the movements of the bridge.
-Danny
nice