Question about braces

[Ken Smith]

Originally Posted by wayne holmes

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.

[Adrian Levi]

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 ....?

[Ken Smith]

Originally Posted by Adrian Levi

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.

[Matthew Tucker]

Originally Posted by Adrian Levi

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.

[Thomas Erickson]

Interesting stuff, thanks all for posting.

Originally Posted by Ken Smith

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.

[Ken Smith]

Originally Posted by Thomas Erickson

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.

[Arnold Schnitzer]

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.

[Matthew Tucker]

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.

[Eric Rene Roy]

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?

[Matthew Tucker]

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.

[Thomas Erickson]

Originally Posted by Eric Rene Roy

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?

The break is going to affect the rigidity of the back across the top bout, yes, but there's no reason why that's going to make the back as a whole any less resonant. It isn't like the break in and of itself is going to change the mass of the back or introduce any stress into it.

As for the resonance of the back goes in general - I'm not sure it even matters much; certainly in the case of an orchestra player resting the back on his knee there's not much there to resonate! And even if it is left free to resonate, it certainly isn't being driven anything like the way a top plate is, so comparing the two doesn't make sense even with a carved back...

[Matthew Tucker]

Originally Posted by Eric Rene Roy

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?

my be wrong but that thesis "round back vs flat back" floating around a few years ago probably did this.

My thoughts on this are that chladni patterns of a braced bent plate would probably be just as good/bad as an unbent braced plate, except that the the plate would be effectively shorter. But that said, you're not going to easily get the common modes 2 and 5. And it all changes when you attach the rim of the plate to the ribs, eh.

I'll try to find a picture of the chladni pattern of my ladder-braced bent back on my first bass. As I recall it was almost a perfect circle mode centered around the lower bout. Above the C's there was very little resonance at all, perhaps if there was no break there would have been a circle mode there as well at a higher freq. But what they all mean ... that's the big secret isn't it?

[Ken McKay]

Originally Posted by Arnold Schnitzer

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?