Brace carving

[Dominic]

Hey all, hope you have recovered from whatever self inflicted ailments Xmas lead you into.
I’ve been sitting here in Warsaw watching the snow fall but thinking about guitars. And in particular brace carving.

Seems a few years ago it used to be popular to do tapered (sometimes misleadingly called parabolic) braces. That is carving braces gently from the X down to the ends and not scalloped at all. I used to read about it a lot on the OLF and there are articles in the Red books about it. The first few guitars I made had them before I tried scalloped bracing and have used this ever since. I like my new guitars sound better but that does not mean tapered braces are without merit. I have learned a lot since then and don’t want to discount an idea because I did not execute it well enough to get its full benefit.

The difference as I see it is that with tapered braces there is a larger stiffer area around the bridge with one flexible zone closer to the sides. While scalloped braces have a smaller stiff area around the bridge stiffening up again where the peaks are then the outer area around the sides is similar to tapered braces. Or two flexible zones. This is getting into the more mysterious engineering stuff about monopoles and dipoles etc as discussed in the Responsive Guitar by Ervin I assume.

My questions are, first I wonder why people are not using tapered braces (or at least not mentioning it much) anymore. And second, what kind of differences in sound are the two versions of brace carving aiming for, ceteris paribus. From memory Hesh made a fantastic sounding guitar using tapered braces which Bob commented very favourably on in this forum.

Cheers
Dom

[WaddyT]

I'm not a steel stringer, but IMO, most folks who scallop braces do it based on a plan and not on the basis for which it was designed. The peaks of the scallops should be a points that should limit vibration in that area, maybe to cut wolf notes, etc. These areas are at nodal points on the top, as I understand it. If they are in the wrong place, they could be a detriment to the sound, not an enhancement. Tapered braces are less likely to kill sound, but must control the top's vibration. In my experience with Classicals, most of what occurs between the bridge and the tail is bass, and treble comes primarily from the areas close to the bridge, and much of it between the wings of the bridge and the soundhole. My perceptions only, not to be confused with real information!

[Allen]

I started out using tapered braces mostly because I had no idea at all about where the peaks and valleys in scalloped braces were suppose to be placed, as well as how deep and tall they were suppose to be. Those guitars sounded better and better the more of them I built. They were pretty good in fact, but not outstanding.

Then after getting the Kent Everett DVD's I tried going with scalloped bracing. Those DVD's were a huge help explaining the what and how and why of carving the braces. The tone and response right away was much better than I was getting over my previous method.

It's a difficult thing to explain what the differences are, but it seems to have a sound that grows after the note or chord is struck.

I'm about to start carving some braces in the next day or two on a style 5 parlour so will get to try my hand at a small bodied guitar. The previous style 5 I built used tapered braces.

[Bob Connor]

We built this identical pair of OM's in early 2007. One had parabolic bracing the other scalloped.

One has since been sold bit I still have the parabolic.

The scalloped instrument exhibited better bottom end but the parabolic was much more focused in the mids and top end. It also had a much more even response as you moved up the neck.(and this was before I started using carbon fibre in the necks)

Both are still nice guitars - just depends what you prefer. The para would probably make a better fingerstyle instrument.

I've since moved in another direction with bracing so I'm not sure which I'd now prefer.

There's a pic of the parabolic bracing (the tone bars are kind of short eh ). I can't find a pic of the scallops.

2[1].jpg (161.57 KiB) Viewed 14418 times

[kiwigeo]

B**er the scallops...I much prefer Oysters.

[ozziebluesman]

Bob: I'm about to brace and close the box on a parlour size guitar using the Scott Antes plan body size and a 24.9 inch scale. My project is a cedar top 3.3mm thick and I was considering using the parabolic bracing design. My top is stiff and taps beautifully so the plan was to leave it on the thick side and brace this one light. What height is your X brace at the join please? Is there a xbrace join patch on your top? I have prepared brace stock 7mm wide for this guitar do you think that is light enough? I have never braced a top this light before so it is all new teritory for me.

Thanks Bob.

Cheers

Alan

[Bob Connor]

13mm x 6mm Alan. There was a patch applied to the joint.

[ozziebluesman]

Thanks Bob. Is your parabolic design 13mm at the Xbrace to about 2mm at the end of the brace? Also which brace ends did you tuck into the linings?

Thanks mate

Alan

[Bob Connor]

2mm at the ends would be about right. The only ones that were tucked were in the upper bout.

[Dominic]

Hey again, this thread is getting some good input. As I mentioned my early guitars had tapered braces and seemed to lack a really solid bottom end as other have observed. I didn't love the sound but an old time blues player I made a dred for loved it to bits so its pretty subjective as with everything we do. Anyway, an interesting point to consider is the purpose of the peaks.

Could the peaks just be eliminated altogether so we end up with a much lower braces in that area? Given that the soundboard around 75mm in from the side where the peaks are is pretty well supported (by it connection to the sides) and the pull of the strings with a domed top is almost directly in line with the soundboard that far from the bridge perhaps it just adds unnecessary weight. That is, its pretty unlikely a top will pull up in that region. As Waddy (and anyone who makes classical guitars) would know well, a classical guitar does not need peaks and does not seem to suffer for it although the overall construction is much lighter.

What got me thinking about this was a recent GAL journal article ( I think thats where I read it) where someone expressed the opinion that the peaks are nothing special and are in fact the result of post build scalloping originating in the early Martin days (and unthinkingly copied ever since) and are only there because that was as far as a hand could reach into the soundhole with a small plane to get at the braces. Makes you think. I get the node idea in a free plate as it can be felt but perhaps it becomes irrelevant once a top is glued to the sides. I can't feel a node on an assembled body. In fact the whole lower bout is quite active. So what do the peaks actually do? I suppose the only way to find out is to make the guitars and test it. That means getting back into my workshop which I am itching to do. So my working hypothesis is that the better bottom end people experience comes from having lower braces in the region behind the bridge plate and has noting to do with the peaks.

I don’t want to be too pedantic but these are not parabolic braces we are talking about. Perhaps very very roughly parabolic in cross section (as sections of a scalloped brace could be) but certainly not in profile and we are talking here about profile which is why I said they are wrongly called parabolic. But enough about maths.

Anyway, have fun everyone.
Cheers
Dom

[Kim]

I think that height of the peaks and their position in relation to the sides depends very much upon what you are trying to achieve from each instrument and again enters the subjectivity that prevents the perfect formula from ever revealing itself.

It has been speculated that scalloping of the braces was first undertaken by those experimenting with ways to 'open up' already finished instruments. These guys used small planes to reduce the size of bracing through the soundhole. Martin Guitars probably noticed that this practices did indeed improved the responsiveness of their instrument and so scalloping was adopted pre-assembly.....How did the 1840's CF Martin R&D guys come up with a formula to determine 'where' these scallops should be placed? That could probably be traced back to how long and skinny the forearm was of the guy who hot rodded the guitar they were copying.

Cheers

Kim

[vandenboom]

Couple of things to offer here....
Cumpiano's book adopts tapered bracing, though not strictly parabolic in cross section, more triangular, except for transverse, which is more parabolic.

Secondly, Allen referred to Kent Everett's DVD earlier. I also found lots of helpful guidelines in this resource. He proposes that the high point of a scalloped brace exist about 3" from the rim. He applies this to the high point of finger braces and the high point closest to the rim on X-braces and tone bars. His reason for choosing this distance is that when doing tap testing, he often finds nodes exist around 3" from the edge. To be honest, a part of me found this hard to take seriously, but Kent has made a lot of guitars and is highly regarded, so it was equally difficult to just disregard.
Frank

[Dominic]

Hey Frank, I agree. I think the node idea is fine with free plate tapping but I have not found dead spots around the lower bout on a built guitar box. Perhaps only where there is a peak which then makes the idea a bit circular. And classical guitars, which are perhaps played by more critical players and need to be more responsive due to lower string energy don't have them.
And as Kim said, they seem to fit the idea of guy sticking his hand in as far as he can reach.
So are the peaks needed, either structurally or acoustically? I am beginning to think not.
Cheers
Dom

[jeffhigh]

I am no acoustic expert but here are some thoughts,
As far as the effect of scalloping and the remaining peaks it is worth thinking beyond stiffness at any point along a brace, to what movement is allowed by the variations in stiffness.

Movement is not necessarily going to be greatest at a more flexible area or less at a stiffer area.

By scalloping we in effect allow the brace and top to hinge relative to the rest of the brace.
With a non scalloped brace, the bridge area is able to move up and down mainly through deformation at the ends of the braces at the sides, with the greter stiffness at the centre restricting bending.
With scalloping the effect is to create a hinge at the ends and at the middle so there is a much greater freedom of movement. this will have an effect on monople action and bass response.
I agree with Dom that whilst there may be a node at the peaks for a free plate, they are unlikely to be nodes(areas of no motion) once the plate is in place and support conditions are changed.
Whether they are necessary structurally, well I am inclined to think you do need to have an area of increased ridgidity behind the scallop to resist rotation, having a peak is one way but it could be more gradual.

[Allen]

Just to through something else into the mix. Does the peaks add enough extra mass behind a less stiff area of a brace that once set in motion it continues to move for a longer duration and a greater amplitude than it would otherwise?

[liam_fnq]

I would have thought that the peak will add both localised mass and stiffness. Mass acting to increase sustain while the stiffness acts against it. Perhaps adding mass without stiffness would have a better outcome. An experiment would be simple enough to do by adding bluetac to selective areas of the outside of the top of a finished guitar. I believe this has been done by some classical builders. I'd be surprised if it hadn't been done by flat-top builders too.

As an aside, free plate tapping has seemed a little odd to me for a while. While it's very satisfying to hear your hard work get progressively more musical with the removal of stock, I'm yet to see much point in getting to a particular point of satisfaction. That is, when the master knows to put down the brush. The simple fact is that a plate will act very differently when glued to the ribs. Of course this opens the door to plate tuning while fixed in a jig that simulates the plate being fixed to a set of ribs. Many builders do this. Next problem is that at the end of the build we glue the largest, stiffest brace to the top in the form of a bridge. The goal posts have moved again. The logical move now is to glue the bridge on before finishing. Once again the classical builders have this sussed. Many of them will glue on the bridge and string up in the white, allowing them to fine tune the instruments while in a situation that will give the most meaningful feedback possible. That is, you can play it and listen to the sound. Convention says though, that flat-top bridges are left unfinished, so the bridge is (usually) glued on after finishing.

I can't really offer a solution to my own dilemma. Perhaps I could get back to this thread in 20 years when I've got a little more experience. Stay tuned.

[Dominic]

Liam, I think you nearly answered your own question here. I read somewhere that, as you say, builders glue on a bridge and string up in a jig, (perhaps it was smallman) muck around tuning the top and then just heat the bridge off again before finishing. Easy using animal/fish glues. A lot of work but not if you can sell them for over 20k.
Cheers
Dom