Bracing 101

[Freeman Keller]

There were a couple of questions and comments on my ladder braced 12 string thread about bracing, and since I happen to have picture of all the different guitar that I've built, lets do a quick comparison.

 

I know some of the theory behind these different schemes, but would like others to chime in. Also, I won't go into a lot of detail about all the variations of each (forward shifting, Martin's A frame, many of the other things going on). These are just the basic shapes and why they work the way they do.

 

Lets make a couple of definitions - I will call anything that has primarily structural functions a "brace". I will call anything that is primarily intended to alter the sound of the top a "tone bar". Braces certainly alter the sound and tone bars can supply strength, but for now just remember the definitions.

 

First, the most common bracing pattern in the MODERN guitar world - Martin's X brace used on most steel string guitars today. Here is my version on my 6 string 000 guitar

 

 

These are 1/4 inch scalloped spruce braces in a classic X. Inbetween the X in the lower bout is a piece of maple called a bridge plate - it reinforces the area under the bridge and gives a wear point for the ball ends of the strings (maple is a much harder wood than the spruce top). The ball ends of the strings are pulling up, which pulls the lower bout up and pushes it down between the bridge and soundhole. The X very cleverly counteracts that rotational force and since it also crosses the grain, it provides strenght to the top to avoid splitting. The two braces between the sound hole and the neck are also there to avoid splitting - the extension of the fretboard is being pulled into the top at that area and could split along the grain right at the edge of the fretboard. The thin flat brace is the so-call "popsicle" - early Martins didn't have it and some people feel that is one of the reasons they sound the way they do.

 

The two pieces of spruce between the X are tone bars - yes they apply some cross grain strength to the top and they do help prevent the lower bout from being pulled up, but they are the primary places that the luthier removes wood to "tune" or "voice" the top. By "scalloping" the wood from the top of the bar its resonate frequency changes. The little braces at the sides are called "finger braces" and also serve in both a strength and tuning funtion. Scalloping any brace or tone bar does reduce its strenght considerably.

 

OK, here is my OM 12 string, also X braced, but in this case I used 5/16 wide brace and did not scallop them (which keeps them stronger). I added one more 1/4 tone bar in the lower bout, again mostly for strength. Also the top plate is 0.010 thicker than on the 6 string. It is interesting that the Martin neck block that I used extends deeper into the upper bout to reinforce that area under the fretboard extension and is notched for the popsicle.

 

 

Here is a shot of the parlor, only one tone bar and finger brace, and very deeply scalloped. I was trying to really bring out the voice of that little git - seemed to work OK (it is amazingly loud)

 

 

OK, for comparison, here is a traditional fan braced classical (in the Torres/Hauser school). Again, it has a maple bridge plate (but no pins, of course), a couple of braces that go across the grain, and the small braces that fan out across the lower bout to give strength but flexibility, as well as countering that same rotational force the X does

 

 

Now here is the one we've been talking about - a ladder braced top like the old Stella/Harmony/Sovereign built in the 20's and 30's. All you've got is big fat tall braces running across the grain, nothing to counter the rotational force at the bridge.

 

 

But wait - most of these guitar did not have pinned bridges, they had tailpieces and a simple glued on bridge. There is no rotational foruce - the string pressure is straight down. There is a maple bridge plate to keep that area from splitting out and a popsicle for the same reason, and from an engineering standpoint the bracing makes sense. Add to that that this is a very cheap way to build a guitar and you have the type of guitar that sold in Sears and Wards catalogs for ten dollars or so (at a time when a D-28 sold for $28 and a D-45 for $45). Some people feel that the sound of these old guitars is largely due to the bracing - we'll see as mine goes along.

 

I'll add one note to this - there were and are ladder braced guitars with pinned bridges. Usually they have even bigger bridge plates than mine and the theory says that the tops shouldn't last very long.

 

Last, but far from least, here is a picture of a carved top instrument - in this case my mandolin but many archtops, violins and all sorts of others are similar.

 

 

The two little pieces of spruce are tone bars, they have very little structural function (that is done with the shaping of the top). And yes, the are supposed to be at an angle to each other. Remember that a mando, archtop, violin are all floating bridge instruments - they have tailpiece and thus no rotational forces on the bridge area. After the top is carved the tone bars are scalloped to tune or "voice" the top - they actually get tuned to different notes. The wonderful old Gibson mandolins of the 20's were hand tuned by Lloyd Loar, makers today strive to duplicate what he heard.

 

Archtops frequently have a single X brace/tone bar system, violins have only one, but the funtion is still the same - the strength comes from the shape of the top, the sound from the way these little piece of wood are shaped.

 

Comments and discussion?

[Stackabones]

Cool thread, FK. I think part of my no bridge pin pet peeve has to do with ladder bracing. I love the sound! My Gitane D500 is ladder braced (as are most djanoboxes iirc) ... probably due to when they were first being built.

[Freeman Keller]

Good point, 'bones, and I should have added that the Selmer - Maccaferri gyspy style guitars are usually ladder braced (with much smaller braces than mine) but again, they have tail pieces (and those cool looking mustache bridges). They certainly have their own wonderful sound, I would assume due to this construction. That is all I know about them.......

[Stackabones]

Do you know how ukes are braced?

[LaurentB]

I never knew that the Martins D-28 and D-45 were named after their prices in dollars, very nice to know!

[jamesp]

So that's why picks are so hard to retrieve! ;-)

[Freeman Keller]

 

Do you know how ukes are braced?

 

 

Not yet, but I'll look inside my Martin and see. For some reason I think they are an X

[Freeman Keller]

 

I never knew that the Martins D-28 and D-45 were named after their prices in dollars, very nice to know!

 

 

I read that somewhere, but I just looked in one of my reference books to try to confirm it and I can't (so don't quote me on it). I do know that my Type 27 Dobro sold new in 1932 for 27 bucks.

[Gary Palmer]

 

Do you know how ukes are braced?

 

 

They vary between;

 

Tops = Fan, X, Ladder bracing and tone bars.

Backs = Ladder

[Freeman Keller]

They vary between; Tops = Fan, X, Ladder bracing and tone bars. Backs = Ladder

 

 

Thanks Gary. Now I don't need to take the strings off mine. Also, Melandy just built one, maybe he could post a picture of the bracing on his.

 

And it would be cool if some of the other builders would post picture of the insides of theirs - particularly unusual things like archtops. Just for laughs, here is the inside of a biscuit bridge resonator - no bracing but it is like the other floating bridge/tailpiece instruments. The bridge moves up and down and drives the cone, the little spirals do add some strength to it. A spider is different, however I don't have a picture (and I'm not going to take it apart to get one).

 

[missedmyexit]

Great thread thanks for taking the time Freeman.

 

What I don't understand is how you tone the top. I understand that shaving the "tone bars" give you different sounds and tones but how do you know what those tones are going to be until you put the guitar together and string it up?

 

Do you tap on the wood? If so where?

[missedmyexit]

 

Backs = Ladder

 

 

Are there any guitars that vary the back bracing? Seems like most use ladder. Someone got me Cumpiano's book for XMas but it's on back order.

[Freeman Keller]

 

Are there any guitars that vary the back bracing? Seems like most use ladder. Someone got me Cumpiano's book for XMas but it's on back order.

 

 

 

Most use ladder - it is a nice way to make the dome shape that most backs have. They are curved from side to side and the sides themself are curved from heel to tail. Since the back is in no rotational tension this seems to work pretty well.

[TESmith]

Very informative, and well explained thread Thank You!

 

Do not know if the info will ever become imortant to me or not, but it is neat to learn and IT will be of importance if I do go ahead and try my own build(s)

[JasmineTea]

 

Comments and discussion?

Yes; tonebars.

 

Tonebars don't viberate, not much anyway. They divide the top and create different sized sections on the top, each section viberates differently according to it's size.

 

Scalloping the tonebars allows the viberations from the different sized adjacent top sections to combine and create other kinds of viberations.

 

This mixing of viberations is what causes the soft, puffy, airy sound that lightly braced guitars tend to have. Like a little cloud surrounding each note.

 

Topwood; Some topwoods take less playing effort to "top-out". Others seem like you can play as hard as you'd like and never get it to breakup or distort at all. I play with a lighter touch most of the time and find that I prefer a top that does'nt need a lot of effort in order to get close to the break-up point. I find them to have a more colorful sound than the stronger topwoods, even though the stronger topwoods are much louder, or can be if you play them hard.

[Stackabones]

Thx for info on ukes!

[Gary Palmer]

 

Are there any guitars that vary the back bracing? Seems like most use ladder. Someone got me Cumpiano's book for XMas but it's on back order.

 

 

Indeed most use ladder, but the double-back technique could also be considered as a form of bracing. The primary role of bracing is to strengthen or brace sheet timber and prevent it from distorting or splitting along the grain when under stress, but can easily be overdone. A simple ledged and braced door is a good example of the way in which such applications can be used in a structural manner, but - in terms of musical instruments - bracing needs to strike the fine balance between strength and flexibility. Bracing can be lightened if we introduce an arch into the equation for strength and arching also allows plates to expand and contract more freely with humidity. This in turn can be used to reduce weight and improve tonal response. I prefer ladder bracing but opt for narrow, tall and contoured - instead of wide and short - due to the improvement in strength:weight ratio that's gained.

 

The use of a spanish heel/C-block at the heel of the neck also reduces deformation under string tension and can extend the pre-neck-reset lifespan of an instrument. This is due to the way in which it makes contact with both soundboard and back plate, whilst effectively locking them in unison with one another within the span of the upper bouts.

 

Backs generally require less bracing due to the lack of string tension induced by the presence of a bridge and one way of avoiding/reducing the use of bracing is to cross-ply veneers. This unfortunately proves expensive and pretty heavy when done using solid timber veneers and that's where double-backed technique (A glued sandwich of manmade honeycombed sheet material between two sheets of timber veneer) can come into play.

 

Tonal feedback can excel when using lighter construction in the right way.

 

Soundboard bracing can also be lightened by using the double-top technique, but finding the right balance betwen bracing and method used is - again - a balancing act.

[guitarcapo]

I've seen X braced backs too.

 

Personally I'm not a fan of scalloped bracing. I think it weakens the top and creates phase interferences between the different notes. It can sometime make for good results but nothing that is uniquely superior and the results are sometimes unpredictable. I think a better approach is just weaken the braces by thinning them or using less rigid ones.

 

Martin tried to get away from it too. But the public kept clamoring for weaker built tops. Build a top weaker and the guitar sounds better new so you get instant gratification. Martin was probably worried more down the line doing warrantee work.

 

A couple of areas that seem really critical to me that don't get a lot of attention are the thickness of the braces as they attach to the sides in the lower bout. Some luthiers thin them out to nothing as they hit the kerfing. Others notch the kerfing and have the braces thick at that point. Huge difference in sound over that little detail. Another is the end block. If the end block attaches to the top over an area that juts into the top more than the kerfing line, it can kill tone quite effectively. You really want the end block to attach to the top in a way that it makes an edge flush with the top kerfing.

The thickness of the top at the edges where they meet the sides, especially in the lower bout are very critical. That's the fulcrum where the top flexes back and forth.

You can thin there a bit more because the guitar will never distort there and the tension is distributed over a wide area. Other things like the location of the X brace from the sound hole, the size and expanse of the bridge plate, the height and width of the braces, and the size of the soundhole make huge contributions to sound. Scalloping braces sometimes makes a great guitar...but I just find the results unpredictable...and to be honest I've had guitars where one of the tone bars fell out and I couldn't hear much of a difference...maybe a touch more bass like if you used different strings.

 

To me the pattern of the braces is another area that seems overrated. I have ladder braced Harmony Sovereigns that seem to have a touch more cut bite and treble than a Martin D-18...but really close considering you're dealing with a huge change in bracing pattern under the hood.

[simplygoodmusic]

Great thread FK. While I was reading I was already thinking that I wanted to ask both about Mandolins and SelMacs. I guess you read my mind.

 

This is the kind of thread that cause my addiction to this forum.

[TXTooMuch]

This now makes more sense, thanks FK

[stormin1155]

I have four old parlor guitars circa 1905-1930. All have ladder bracing. Two have pinned bridges (Washburn 217 and the old Supertone my dad had as a kid), one uses a tailpiece, and one has a surface-mounted metal bridge. I just finished rebuilding it (neck reset, regluing some bracing, etc). They all sound good (must be the old wood). Actually, a friend of mine had an old parlor that had been rebuilt using X bracing. I didn't think it sounded any better than my Washburn.

 

Here's a closeup of the metal surface bridge on a Supertone (Sears). I'm guessing it was made circa 1930.

 

[DeepEnd]

Years ago, when I first started playing, there were Epiphone and Voxton (both made by Samick AFAIK) steel strings that had traditional pin bridges and fan bracing. How common was that?

[guitarcapo]

And then there's "Kasha bracing"

 

I tried this once on an old parlor guitar I was fixing and It didn't work for me well so I never tried again. The bridge kept twisting the soundboard under tension and it's pretty easy to see why. I could have just braced it more but the sound I was hearing wasn't all that great to pursuit it further for me. I figured if the guitar didn't sound that great , adding braces probably wouldn't ADD tone. I'm sure it works for some people but I gave up trying to figure it out.

 

 

 

 

[melandy]

Thanks Gary. Now I don't need to take the strings off mine. Also, Melandy just built one, maybe he could post a picture of the bracing on his.

 

Hey Freeman. I'm posting this from my phone and have limited ability click on links and check things out. IIRC, the StewMac uke i built had a ladder braced top, although that thing is so tiny there wasn't a whole lot to brace.

 

There is a link to the project in my sig. I'm fairly certain that I took pics of that step.

 

Thanks,

-A

 

P.S. Do mine eyes deceive me or is Lauren back?

[Freeman Keller]

Krash wants me to edit this and we'll put it up at the Annex. How about all you folks who have built sending me some pictures or links to them and we'll get as much information there as we can. Gary, 'capo, Melandy, Meandi, any one else out there with pics - preferably your own builds and information about them.

 

Also please feel free to commment on the little I know about this. I've learned most of it from experimenting, reading, and folks on the internet who know a whole lot more than I do.