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Old 06-06-2010, 02:05 AM
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Thomas Erickson Thomas Erickson is offline
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Question Question about braces

I'm wondering about braces in a flat back bass; I know it has been covered before on this forum, but I didn't find quite what I'm looking for -

I'd like to know what people are thinking in regard to the top brace and the break, for a bass that has one - should the brace always be placed directly over the break, to reinforce it? I've read suggestions that three braces is generally suitable; in this case, should the top brace still support the break even if that leaves a fairly good amount of the rest of the upper bout bare, or would it be better to locate it lower where it would cover more width (or add another brace)?

Thanks for any thoughts...
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Old 06-06-2010, 02:33 AM
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Quote:
Originally Posted by Thomas Erickson View Post
I'm wondering about braces in a flat back bass; I know it has been covered before on this forum, but I didn't find quite what I'm looking for -

I'd like to know what people are thinking in regard to the top brace and the break, for a bass that has one - should the brace always be placed directly over the break, to reinforce it? I've read suggestions that three braces is generally suitable; in this case, should the top brace still support the break even if that leaves a fairly good amount of the rest of the upper bout bare, or would it be better to locate it lower where it would cover more width (or add another brace)?

Thanks for any thoughts...
In the case of a definite upper angle break and especially if the Back has a cut there I think a brace there acts as a support piece to avoid or prevent the angle break area to crack because they often do.

As far as how many braces or the style of bracing that depends on a few things which include the size of the bass, the condition of the back, the strength of the wood species, the thickness of the wood and in some cases the tone desired in replacing or modifying the current bracing system.

On my 4/4 Prescott when it was restored it got two upper braces with one on the break. The 7/8 Hart ended up with just one upper brace as that's all it needed. Two other more modern basses that were restored has the bracing system changed to a single modified X-system. The Mougenot I have is between a 7/8 and 4/4 by French standards and that has only the original single center wide Stair-step 8" wide center brace. The brace system during the back restoration will get a normal center brace, a lower bout brace and a single upper bout brace. The upper and lower being shaped like a Bass bar rather than the wide flat style too often used in many basses which add too much wood, weigh the bass down and choke a bit of sound in the process.

You basically have to guess what will work best in the Bass you are working on. The more you have seen, done, changed, altered and had success and failure with, the more you will know to equate what the current bass needs.
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Old 06-07-2010, 07:36 AM
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Lightbulb addition..

On some of my basses that were restored, the angle break does NOT have a brace there. My Hart for one has Linen over the break and a few long vertical 'finger' patches over the joint in places. I think in this case it was determined than the Back was very strong and in near mint condition and didn't need any more wood added than necessary. It has a center brace of normal width and a lower brace shaped like a bass bar.

My Lott copy bass has a modified single 1/2 X style brace with a bass bar shaped piece opposite it on the bottom as well. The upper angle break has mainly just Linen across it.

I would have to put both of these up on the Bench to better map out and explain things. Also, my Panormo school bass which is a round back has spaced out Studs across its break point as did my previous owned attributed Dodd/Betts bass of which was pointed out to me 'done in the style of Panormo'.

All in all, there is NO standard way. Those that put 3, 4 or 5 braces in by measurement alone are just not thinking things over all the way. Depending on where you and your bass live, the bracing might need less support so that the Back can breathe and move a bit rather than having something come apart.

Consider the sound of the bass before the job, the strength and thickness of the back, its repairs and condition of them, the size of the bass including length of the bouts and their width and then just take a guess at what would be enough to hold it together and not too much so as to hamper its vibration of sound transfer. Unless you continuously do it over and over in several ways on the exact same bass and do nothing else each time but alter the braces, it would be impossible to tell what the differences are. Weigh your options and 'why' and choose a sensible method.

I have seen more ways to brace a back than I could list.
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Old 06-07-2010, 10:36 AM
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if you build a slight convexity into the flatback - maybe only 4-6mm over the entire width, the break becomes very rigid and strong. After bending the break, I re-cut the kerf to give it straight sides then glue in a fillet of wood. so i dont think in this case a brace is necessary at that point. i would rather save weight and brace further down to give the back its convexity.

however if the break is old, damaged or frail, then a brace there is an obvious choice.
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Old 06-07-2010, 01:35 PM
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Originally Posted by wayne holmes View Post
for my 2cents-brace it--anything that will help it keep its shape -a break in the wood is going to be vulnerable to loose its shape and come apart as many do that I have seen-good luck-good question
The Angle Break at the top to loose its shape? I don't think there is much stress there at all. Mostly what I have seen is at the lower bouts on a flatback with the wider part of the wood is trying to breathe and when it moves, something somewhere gives.

I have never seen any problem develop in an upper Angle break within MY time. I have seen old basses with problems and repairs but I think it takes a long time or an accident for something to happen. If the wood is very thin or the break cut or bend poorly done or ill-supported than maybe it will fail sooner than later. This IS the original way Bass instruments were made as developed by D'Salo from the Viol.

On the original Posters question we are not totally sure if he is making a Bass and asking how to do the Back or fixing a Bass new or old. Of course making a bass, roundbacks of any arch from shallow to severe if done fairly well will see less problems over time than a flatback, period.

For me, I prefer a Roundback with low arch and a semi-center brace as well. In place of the angle break I prefer some type of gradual bend towards the neck. I don't see how cutting across the back for an upper bend is a good thing for the long hall regardless of how well its done.
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Old 06-07-2010, 02:10 PM
Adrian Levi Adrian Levi is offline
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Is it possible that the differences in sound between flat back vs round has to do more with the crossbars found on a flat ? I have often wondered about this seeing as so much importance is placed on the ribs and plates vibrating as freely as possible ....?
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Old 06-07-2010, 02:31 PM
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Lightbulb ??

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Originally Posted by Adrian Levi View Post
Is it possible that the differences in sound between flat back vs round has to do more with the crossbars found on a flat ? I have often wondered about this seeing as so much importance is placed on the ribs and plates vibrating as freely as possible ....?
Who is to say? Unless you change the Back of an exact Bass and test it after it settles in with one of more brace systems or as many as you try, the comparison is not between Backs but between Basses.
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Old 06-07-2010, 07:10 PM
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Quote:
Originally Posted by Adrian Levi View Post
Is it possible that the differences in sound between flat back vs round has to do more with the crossbars found on a flat ? I have often wondered about this seeing as so much importance is placed on the ribs and plates vibrating as freely as possible ....?
Don't assume that a braced flatback vibrates less than a roundback. A back arch is carved differently to the arch on a top; it is much stiffer, and a different wood. And as Ken says, many are now bracing the roundback as well. And there are flatbacks without a break, and these could be - depending on the bracing - somewhat less rigid than flatbacks with a break.

There are so many variables its hard to generalise. Everything in a bass contributes to the way it sounds.
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Old 06-07-2010, 08:26 PM
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Interesting stuff, thanks all for posting.

Quote:
Originally Posted by Ken Smith View Post

On the original Posters question we are not totally sure if he is making a Bass and asking how to do the Back or fixing a Bass new or old. Of course making a bass, roundbacks of any arch from shallow to severe if done fairly well will see less problems over time than a flatback, period.
Not building a bass yet; just got to wondering if the break was generally considered a weak point that should be reinforced from the get-go, or if placing a brace there is more a matter of routine and/or to solidify older basses that are weak or damaged.
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Old 06-07-2010, 11:19 PM
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Quote:
Originally Posted by Thomas Erickson View Post
Interesting stuff, thanks all for posting.



Not building a bass yet; just got to wondering if the break was generally considered a weak point that should be reinforced from the get-go, or if placing a brace there is more a matter of routine and/or to solidify older basses that are weak or damaged.
Each Back will need what it needs. It is up to the Luthier to determine that. Balancing strength and tone combined is not so easy. It must be in its best condition and best repair. As Matthew mentions, there are so many factors that create the sound. Equally, there are so many things that can kill it as well.

In any the piece of wood used for the Back (or Top as well) you have density, thickness and arch. If the Back is dense and well arched, it cannot be overly thick. If soft weak wood, it cannot be too thin. If so, it needs arch and some bracing. You need to balance those three items. How well the woods were dried before the bass was made and how much tension if any is in the carcass matters as well. If you force wood, it will fail and you loose sound along the way.
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Old 06-09-2010, 08:14 AM
Arnold Schnitzer Arnold Schnitzer is offline
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Two prominent makers I know of do the following with their flatbacks: Cut a narrow groove across the back where the bend will be; install a cross brace just at the lower edge of this groove (across the back); bend the back crease, using the cross brace as a kind of fulcrum; glue the upper part of the back to the rest of the already-assembled corpus. No reinforcement whatsoever of the bend. I'm wondering what you guys think of that method.
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Old 06-09-2010, 08:39 AM
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Well, it's a neat way to get it done, and I like the idea of bending the break straight onto the ribs just as i like bending the ribs straight onto the mold. It doesn't allow for over-bending the break though - as you know, sometimes its nice to overbend and allow the wood to spring back to correct shape. And unless they fill the crack somehow it leaves a very thin bit of wood at the break. I don't know how strong that would be after 50 years of drying out - no weaker than rib stock I guess - and I suppose supported by a brace it's fine.

Kai-Thomas Roth in the Strad show how he puts a break in an "arched" back to reduce rib depth; he ends up with a compound curve which will be inherently strong and stiff. Then he fills the crack with glue and sawdust and finishes with a linen strip.

I prefer my method of filling the saw kerf with solid timber.
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Old 06-09-2010, 05:00 PM
Eric Rene Roy Eric Rene Roy is offline
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I've never liked the bend on flatbacks. Why build in a weak point? Why add anything that stops the back from vibrating freely??? I understand the ergonomics of it, the tradition of it, etc...but I like the idea of doing it through a greater rib taper from end block to neck block and keeping the back vibrating more.

I've always likened the crease on a flatback like the creases they add to a car's hood or fender. The crease on the hood of a car adds rigidity, keeping the panel from vibrating at higher wind speeds and making it stronger without overly bracing it on the inside. I think keeping the plate vibrating freely can only be beneficial to the tone.

I'm not sure if there has been any Chladni studies on bass plates the way they do violins...but I have to imagine the bend making a pretty big disruption to the lines of the plate.

Thoughts?
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Old 06-09-2010, 05:25 PM
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i don't feel that the back plate works in the same way as the top plate. I'm not sure that it has to vibrate in the same way.
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Old 06-09-2010, 05:58 PM
Eric Rene Roy Eric Rene Roy is offline
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I'm not saying it does or needs to vibrate like a top. I'm saying why reduce its own resonant capabilities.
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Old 06-09-2010, 10:35 PM
Ken McKay Ken McKay is offline
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There have been studies showing how flat back and carved back plates vibrate. There is a big difference! However, interestingly though neither experts nor non experts could successfully tell the difference between the two in blind listening tests.

iirc the difference is that properly graduated, carved violin style bass back plates have even resonances that are equally space apart while flat backs with cross braces have distinct peaky resonances from the braces stiffening effect.

Keep in mind though that these listening tests were the same model basses with either a well made carved back or a well made flat back bass.

My take on this is that a carved back has the smoothest, most even response but the flat back can be constructed in a way that has evenly spaced resonances by bracing it to flex in a similar way.

Smoother or more even resonances are not superior to a more "reedy" or peaky, viol sounding bass, only different.

I try for evenly spaced resonant back. I use thin, light braces that are X shaped and curved to a radius, resulting in the back being dome shaped which create about a half inch of curve from end to end and side to side. Even the area above and below the break angle is curved in the dome shape. The reason is to mitigate against cracks and to create a flat back that behaves like a carved one.
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Old 06-09-2010, 10:42 PM
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Quote:
Originally Posted by Arnold Schnitzer View Post
Two prominent makers I know of do the following with their flatbacks: Cut a narrow groove across the back where the bend will be; install a cross brace just at the lower edge of this groove (across the back); bend the back crease, using the cross brace as a kind of fulcrum; glue the upper part of the back to the rest of the already-assembled corpus. No reinforcement whatsoever of the bend. I'm wondering what you guys think of that method.
I am not sure it is any better or worse than just bending without cutting the groove.

How steep is the bend? How thick are their backs?
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Old 06-09-2010, 11:49 PM
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Quote:
Originally Posted by Ken McKay View Post
Smoother or more even resonances are not superior to a more "reedy" or peaky, viol sounding bass, only different.
Right.

Quote:
... curved to a radius, resulting in the back being dome shaped which create about a half inch of curve from end to end and side to side. Even the area above and below the break angle is curved in the dome shape. The reason is to mitigate against cracks and to create a flat back that behaves like a carved one.
... similar to my approach, and to the construction of a roundback, you are making quite a rigid shell, inhibiting "pumping" vibration very strongly. very different to the top plate with its inbuilt flexibility at the edges. It may feel like the back is vibrating, but I think this will be largely the resonance of the whole, via the ribs. The endpin material, density and weight of the bass (inertia) will affect how much vibration is felt through the back, and how much impedence there is in the shell.

But the outcome is, as usual, hard to predict!

I feel that the back, like the bridge and neck, has a filtering and reflecting effect more than an emitting effect. No proof of this though, just a feeling. The laws of conservation of energy and momentum say that for every movement there is an equal and opposite movement, and you can't create something out of nothing, so I would think that the MORE the back is a moving component, the less the top will move for any given energy input.

If the free vibration of the back is that advantageous, I'm wondering why anyone hasn't built a bass with identical top and back plates; identical materials, grads and arching?
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Old 06-09-2010, 11:54 PM
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Lightbulb same what?

Quote:
Originally Posted by Ken McKay View Post
Keep in mind though that these listening tests were the same model basses with either a well made carved back or a well made flat back bass.
I had 6 modern basses here one day, all the same model with roundbacks. No two sounded alike and they were quite close to each other in wood and measurements. A flatback on one would be as different. You cant compare different basses and point to the back style as the reason for anything. It's only one component.

The first basses made in Brescia 400 years ago were flatback with an angle break. What kind of basses they were we don't know for sure but now they are Double basses and each costing more than my house.

Like I said, my opinion is that each bass made or repaired should be looked at individually and not as a model to be done one way unless you are making production basses in plywood or even carved.

I have 5 flatback basses right here in my office. Two English, two Italian and one German. Three of them have angle breaks. No two of these 5 basses have the exact same bracing system. Only one of them would I change anything inside and that is only because it was repaired a long time ago. The other 4 were all recently re-braced one way or another.
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Old 06-10-2010, 12:13 AM
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That's why I love basses so much
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