Luthiers: Scalloped Bracing Question
 

Hey Gang:

I was sort of arguing on another forum about scalloped bracing with another poster. His argument was from an engineer's perspective, in that scalloped bracing is flawed and not a viable solution to "tuning a top" and that non scalloped thinner braces will distribute the tone more evenly than having soft and hard spots.

Can you guys school me on scalloped bracing, why it is used over thinner/lighter braces and what advantages there are to non-scalloped braces?

I know all or most of you guys all scallop your braces.

Uh, Eugene,
I am not a builder, but I have a duck in this walk.

The shape and size of the braces, to one extent or another, is used in tuning a top.

Braces can be made smaller without scalloping, which is a certain kind of shaping that looks like a suspension bridge.

The less mass there is to the braces, the more bassy the instrument will be.

How the braces are brought to the point of having less mass will determine the tightness, or looseness, of that bassiness.

My guitar has non-scalloped bracing because I did not want a bassy sound guitar. I wanted a tighter sounding guitar with a quick, punchy response with not much sustain.

HE
http://www.howardemerson.com/

Both styles have their place. I use scalloped bracing on some models to bring out the low end a bit more and parabolic braces on other models to equal things out. Both have their pros and cons.
If I had a preference, it would be parabolic braces, because a more focused overall tone is more pleasing to my ear.

Like so many aspects of building, there are strong opinions on each side. One thing to remember, there are many different ways to successfully make a great guitar. There are of course many ways to make a bad guitar. Scallop bracing is used by many to make wonderful sounding instruments, so anyone that says it doesn't make sense is revealing more about their lack of understanding than anything else. There are builders that know how to position and shape those scalloped bracing to make their guitars sound like they want. It takes year of experience and many builds to be able to do that.
I have built both, but prefer parabolic bracing, make that parabolic lattice bracing. The term parabolic is applied in a general sense to indicate that the transition in height is very gradual, but there is no way any one's braces are actually parabolic.
From an engineering perspective, there is much more unknown than known about guitars. I'm a degreed, practicing mechanical engineer with about 30 years of experience.

Hmm. Gibson's website says the scalloped bracing on the J200 is produce a more focused sound. Now I'm really confused......

Any any event, what about medium gauge strings on a scallop-braced top? I put 013-056 mediums on my J200 and after about 36 hours noticed a bit more top lifting than I felt comfortable with.......long term use of mediums causes damaging top distortion with scalloped braces? I seem to remember reading something in Martin literature that they did not recommend medium gauge strings on their instruments with scalloped bracing.......

Yes? No?

Buc, from the Martin website:

Q: Is it safe to use medium-gauge strings on my scallop braced guitar?
A: Yes it is safe. All of our six-string guitars designed for steel strings have been tested to withstand the tension of a medium gauge string. However, since each top is unique, take note if the top starts to raise abnormally. If this happens, go back to the lighter-gauge strings.

Good post Steve, so I guess they are not "overrated" but quite crucial to many builders for achieving highly desirable sounds. Whether you like the tone of parabolic or scalloped bracing is not in question, but rather the importance of achieving certain sounds, it is indeed crucial, would you agree?

It all depends on how much the braces are scalloped. A 10% reduction in brace height reduces the stiffness by 27%.
The stiffness of individual tops can vary widely, so the suitability of a certain string gauge should always be determined on a case-by-case basis.
Scalloping loosens the top in the bridge area, while maintaining the stiffness around the edges. The result is more punch, since a smaller area of the top is excited when the string is first plucked.
Scalloped brace guitars generally have a bit less sustain than unscalloped or tapered brace guitars. There are always tradeoffs.

As Steve says, no one actually shapes braces to a parabolic curve. When I first heard the term, I asked the person using it (who I believe originated the usage) if he knew the quadratic equations for the parabolas he used. He ignored the question. I have never seen or heard of anyone who plotted a parabola and used it as a model for a brace. Conclusion: "parabolic" is just puffery; a misleading term that is being used to imply a scientific knowledge and geometric precision that does not exist. All it means in connection with bracing is 'convex.'

Scalloping is not intended to be a way of maximizing structural strength or rigidity with a minimum of mass, which is probably what the OP's engineer friend was assuming. It is a way of shaping tone by introducing a tendency toward certain nodes and antinodes in the modes of top vibration. How it does this is a matter on which there is disagreement, and which could be the subject of a lengthy treatise.

When you (scallop) or remove wood from any brace you weaken the brace. This allows that particular area of the top to be more flexible which allows it to move a greater distance, at a slower frequency and will "usually" change the bass response. Adding mass to a brace "can" have the same type of effect which sounds counter intuitive. The brace can be heavier but more flexible, based on its design which will allow the top to move a greater distance albeit at a slower speed, which will change bass response too.

If you are doubtful stick a C-clamp through the sound hole and clamp it to your bridge and listen to how bass heavy the sound of the top gets. The C-clamp didn't change the stiffness of the brace but only added mass to that area of the top. There is a difference between adjusting stiffness and mass and knowing how to manipulate both is one of the many ways to tune a top.

As the quote from Martin's literature that Placida provided us with points out, it depends on the individual top. But generally speaking, it's okay.

My 1987 000-42 has scalloped bracing based on the bracing pattern of a 1935 000-28, and it's never had anything BUT medium gauge strings on it. And I string my 1989 Gibson J-100 with mediums, as well. Again, there are no problems with it, and never have been.

So it depends on the actual top that's on the guitar, but most traditional style factory-built guitars with scalloped bracing will be fine with mediums on them, since that's within the normal, expected range of customer use.


Wade Hampton Miller

I'm not a luthier. But I can't help but notice that my three main guitars, the ones I really play, have scalloped braces. I also have a dread with tapered X and scalloped tonebars (is that the name for the smaller braces,
in the lower half of the top?) and a large jumbo with straight, but fairly low, braces (the builder swears by them) and a rosewood bridgeplate.

The quality I notice in my scalloped-braced guitars (and the two HD-28's I used to own) is not so much a louder bass, but greater clarity and transparency in the bass, e.g., playing chords in succession you hear the movement in the bass more clearly. In two of the instruments the builder (same guy) scalloped pretty deeply to balance the influence of a very stiff top.

The tapered-braced dread has much better sustain than most dreads I've played, but it's not particularly well-balanced.

All these instruments are much more mellow-sounding than the straight-braced Jumbo. But the difference could be expalined in many ways, e.g., the Jumbo is in Koa, the other guitars are rosewood (Braz and EIR)+Sitka and Curly Maple+Engelmann.

At least in the late 70's and early 80's to my ears there was a huge difference in quality between scalloped-braced and straight-braced Martin Dreadnoughts.

The "soft and hard spots" can be a way of tuning the top. That doesn't mean that all braces should or shouldn't be scalloped. Every single piece of wood is different. This goes for tops, braces, bridgeplates ect. The big guitar companies take their tops out of their big belt sanders and glue braces on them straight out of the brace making machines. (The "scalloped" braces are scalloped in a machine.)That's it. Most factory guitars are overbraced so they get predictable results. I don't know how any other small builders do but I graduate my tops.(the top is thinner around the edges.) I roughly shape my braces before gluing them on. I then do some more shaping after gluing the braces on. I do my final voicing after the top is glued to the rim before the back is installed. What I actually do to the braces depends on the individial top and braces and the tone desired.

There's thousands of J200's out there with medium guage strings. They should be OK on it.

Is there a good reason why a manufacturer would scallop their dreads, and not their similarly modeled OM's? Any ideas on this???


Ryan

OM's generally use thinner braces, therefore the desired tone might not be great with Scalloped bracing.

I know that the Martin OM-28 uses scalloped bracing while the D-28 doesn't. My Stanford dread has scalloped bracing but the OM does not. Bizarre.

Scalloped bracing on Taylor LKSM-12:

http://i583.photobucket.com/albums/s...opedbraces.jpg

http://i583.photobucket.com/albums/s...rings/lksm.jpg

Strung with 13's and rings like a bell.

Interesting discussion. Neither of my guitars uses scalloped bracing, but the Almansa uses tapered braces while the Raimundo uses straight-sided ones.

The Raimundo has more sustain. Both are well-balanced to my ear.

-brian

I'm not an expert by any stretch of the imagination, but it seems to me that tapered (sometimes called parabolic) bracing and scalloped bracing have their places. I don't think I've ever seen anything remotely close to scalloped bracing in a classical guitar.

I would think a small bodied guitar would not benefit much from the scalloping because the braces are shorter, but larger bodied guitars (i.e. dreads and jumbos) would gain more from some looser areas over the long cross braces in particular.

It seems to me that there is not much of an advantage to scalloping shorter finger braces and the like, since they are so short.

The bottom line is, bracing is an art and not a science. There is no right or wrong way to do it. The goal is to make a guitar sound a certain way, while leaving enough strength and stability in the top so the guitar will have a long happy life.

In what has been said about tapered bracing to compare with scalloped bracing? I heard a guy (builder) talking about the flamenco guitars he made and how the flamenco guitar differs to the classical. Tapered bracing =shorter sustain and scalloped bracing = longer sustain.
So from what I have heard some of you are saying ,the subject is the opposite.
I was also under the impression that a finger style guitar needed articulated notes (shorter sustain) and a faster frequency with tapered bracing. Scalloped bracing would give you a longer sustain and longer frequency.

Is it also true that scalloped bracing will give you more projection, since the plucked note is not restricted?

I am not always sure what people mean by 'tapered' bracing. To me it means the top of the brace defines a more or less straight line, and the height of the brace lessens as it approaches the rim of the guitar.

Other things being equal, scalloped braces will give less sustain than tapered. The top is more flexible, hence more readily set in motion with a greater excursion. The volume of the note rises faster, and, there being only so much energy available from the plucked string, it gets used up faster and the volume falls sooner. This is what a lot of flatpickers desire, and part of the reason why scalloped bracing is favored among bluegrass players. It also tends to be favored by fingerpickers (I'm also often not sure what "fingerstyle' is intended to mean, since it could be so many different styles) who play country blues, or others who want the bass to thump, and the notes just played to get out of the way of those that follow.

Thank you, Mr. Arnold.

I know the luthiers in this thread know who you are, but perhaps others don't.

If not, please Google "john arnold guitar," "john arnold luthier," and john arnold spruce" to get an idea.

Fran

I'll be very interested in hearing your findings with the new Stanford PSOM-10 when it arrives, Eugenius. IMO there is some very serious thought put into their design work. I would be really curious hearing Toni Goetz's input about his bracing techniques......

Ryan

Thank you, Steve. That's exactly what I had suspected all along, but a quick Google didn't turn up the info I was looking for. So, there really is no difference between "parabolic" (as a loosely used term) and scalloped braces?

There is a difference, both in shape and sound. I like the sound of both, but I like the sound of "parabolic" more.

Sorry, I must have misunderstood what you posted. So, what exactly is the difference, then? If "parabolic" implies that the "transition in height is very gradual", as you mentioned, then are scalloped braces more "scooped"?

Howard also said "All it means in connection with bracing is 'convex.'" Doesn't that imply both terms, parabolic and scalloped, are pretty much equivalent?

Seems like I'm missing something here :p

Thanks Howard,
This makes sense and clears up some things for me. I had somebody trying to convince me of the opposite way around.
Thanks!!

I would call scalloped braces "concave". Could someone post a picture of a typical parabolic setup?

I would too, but I'm assuming Howard is talking form the "point of view" of the removed portion :D

Some examples, if I may.

Scalloped:

http://www.patfosterguitars.com/agf/scalloped.jpg

What is often referred to as "parabolic", though I would call them "not scalloped" :

http://www.patfosterguitars.com/agf/para.jpg

Pat

So that's it! I've been thinking about the whole thing backwards (?). "Parabolic" refers to the actual braces, not the shape of their "scallops". No wonder Howard referred to them as convex rather than concave! :roll:

Thanks, Pat!