Official Luthiers Forum!

I have many questions that begin with the word, "Why".

Here's one of them:

Why dome the top and back plates when that creates eternal stress in a guitar?

I understand that doming is thought to help stability and increase structural strength. But do these
advantages outweigh setting up the inbuilt stresses that result?

I remember Arthur Overholtzer saying that his best sounding, most responsive guitar was built using
parts that were glued in with very light clamping so as to introduce as little stress as possible.

Does anyone here have first-hand knowledge about this? I'm not really interested in entertaining
guesses when it comes to guitar making.

I wouldn't put too much stock in what Overholzter wrote. He had some rather strange ideas. Doming a guitar causes very little stress that is overwhelmed when the strings are tightened up. So don't worry about that. So are you a builder or are you just guessing about stuff?

I've built a few SS guitars and I'm looking for advice because I'm about to start another.

I know Overholtzer is considered somewhat of a crank but his stress idea made sense to me.
I don't necessarily trust what makes sense to me, though, because I've been wrong too many times.

Thanks.

Jim McCarthy

In regards to stress, I think it is overstated. Having to force parts to fit will build in stress, but the wood will relax over time. A guitar side with spring back if removed a few years later, no longer has spring back.

But you put strings on the guitar and that stress will be there forever. This stress can slowly make the guitar fold up. It sort of makes the idea of building stress moot in my view.

Yeah, what you say makes sense to me and maybe that's one of the reasons that as a guitar ages, it "opens up".

But I also remember reading that violins that have had their top removed years after being built, can oftentimes sound better. I interpreted that to mean that whatever stress had been built into the intrument had been relieved in removing the top. My interpretation could very well be wrong, though.

There are so many, many variables to all this it becomes confusing for me. And forgive me for asking things that those of you here with far greater experience than me have kicked around already.

I would guess that a guitar built without doming would tend to not last as long as one that has or at least the neck might have to be reset sooner and more often. But if a guitar sounds better not domed and has a shorter life expectancy - well I'd like to know that. And as you say, the internal stresses are moot because of the tension of the strings, well you're probably right. But do you or anyone else here know that for sure?

I want to say something about my first post and your response to it.

In asking a question about building stress into a guitar I was not trying to make a statement or, as you inferred, a guess. It really was a question.

I suppose that asking people to not respond with guesses can come across as offensive. It's just that on these internet forums it seems people can have a tendency to provide "answers" when all they really have is second-hand knowledge at best or their own half-baked theories at worst. It becomes impossible for someone like me who has very little practical experience in guitar making to be able to tell the real from the unreal. But even for someone who has built hundreds of guitars, has that person ever tried building one without doming it?

That's what I'm wondering.

Thanks again.

Jim

The kind of stress you do not want is where you force a part to conform to an abrupt change. For example, if the lining has and up and down line, like an X games ski slope and you clamp the top to it, you will have problems. That is one reason that gluing the top on with little blocks works so well. The sides to not have to conform to an examct shape at all. The blocks join the top to the sides, and the channel cut for the bindings removes the irregularity.

Lots of builders do not dome their tops, Jim Olson, Kevin Ryan, Charles Hoffman are among the most prominent.

There are also many types of domes commonly used; some use domed tops glued to flat rims, some use spherical domes glued to sides that are sanded to a mathcing shape, some use cylindircal domes, then there's the "pliage" style... I agree with Barry though, once the strings are on, the stress inflicted by either of these will be trivial by comparison.

_________________
Rian Gitar og Mandolin

Most notable for using both a dome top as well as a true flat top would be Bob Taylor. All the basic Taylor guitars get built with a 25' dome top, the custom shop (R. Taylor line) offer either a 60' dome or a true flat top. This is all from the R. Taylor website so you can check it out there. So, if Bob Taylor is willing to put his reputation on the line with his custom guitars, using a flat top, that speaks volumes to me.

Oh, and all of us all have relied on other's for where we are today. But I do agree that we have to experience the out come of the method used in order to give an actual account of what is or is not working.

I build with a true flat top because I like the sound it produces. I built my first few guitars with a dome, than switched and I like the sound I get from the flat top better.

I honestly don't believe that building with a dome makes the guitar 'more stable' to changes in humidity etc... Any change in humidity severe enough to reverse any doming of the plates will also cause cracks, and to fix those requires re-humidification (is that a word?) which will bring the plates back to their intended shape.

The pull of the strings pulls my tops up ever so slightly as it appears to have a dome, but when the strings are loose or off, the top goes back down to flat.

_________________
My Facebook Guitar Page

"There's really no wrong way, as long as the results are what's desired." Charles Fox

"We have to constantly remind ourselves what we're doing....No Luthier is putting a man on the moon!" Harry Fleishman

"Generosity is always different in the eye of the person who didn't receive anything, but who wanted some." Waddy Thomson

Thanks Rod.

Can you articulate the difference in timbre between a flat top and a domed?

I'm assuming you've built guitars with these differences while all other variables are the same, right?

Jim

The braces are shaped to the dome shape the glued to the top. this creates some stress on the top that a 100% flat top would not see but at the same times adds strenth to top as a dome shape can take higher loading with less deformation. The added stress on the stressed skin top is off set by the add structural strength the dome offers and its add resistance to deformation for the string pull. Like all things in this craft it is a matter balancing the pros and conns.

Let me counter that with yet another question that has always bothered me. Who says stress is necessarily a bad thing? Within the bounds of common sense, of course. I mean, we build this perfect "stress free" guitar then put 180# or so string tension trying to pull it apart, right?

As I see things, all stress is not necessarily bad. Who's to say that some built-in stress can't be used to our benefit? Some builders radius the top and glue to a flat rim. What makes this wrong?

Sorry to (slightly) hijack this thread, but it seems relevant to the conversation to me.

_________________
Wes McMillian
Santo, TX
http://www.wesmcmillian.com

It does to me too.

I suppose I've always believed something will vibrate more easily when it's relaxed and maybe that's not true.

That's certainly not true of strings: there must be tension or the thing is quietly flacid.

And it's definately not true for a drum head.

I was thinking that the additonal stress to the top caused by doming could possibly have a dampening effect. But I have no idea.

Thanks for your reply.

Jim

Please take my input with a salt lick though as I've only got 8 guitars under my belt. I have 3 with domes and 5 without and I'm sticking with the flat tops.

Well, early guitars are usually over braced and one can never have "all other variables the same" as learning to brace and shape said braces change from one guitar to the next. Having said that, I found that the domed topped guitars have a bit more of a tighter sound to it which is to be expected as the doming does offer a difference in stiffness (if all other variables be the same). Think of a drum skin, tighten it up and the pitch rises, loosen it up and the pitch goes down. Same thing with a domed top vs. a flat top. But then when bracing and shaping said braces, I (like most) tend to listen for a particular tone/pitch which honestly might negate the doming effect on the top (for sound anyway, but then I don't believe the strength in doming on a guitar theory anyway )

Honestly though, there are so many variables involved with building (top density, top stiffness at a particular thickness, individual brace stiffness, size and shape of the brace, location of brace, bridge plate density, thickness, bridge density, thickness) that it really does take a lot of effort to predict anything with 100% certainty. Having said that, these things can all be measured and over time, data can be collected and predictions can be made based on that data, however there will always be some level of speculation as to what precisely the guitar will sound like as we are working with materials that are to some degree unpredictable. Introduce 180lbs of string tension and that can change things

_________________
My Facebook Guitar Page

"There's really no wrong way, as long as the results are what's desired." Charles Fox

"We have to constantly remind ourselves what we're doing....No Luthier is putting a man on the moon!" Harry Fleishman

"Generosity is always different in the eye of the person who didn't receive anything, but who wanted some." Waddy Thomson

Even if you build "flat" in hope of no stress, the top will dome when the humidity changes......so per your thinking it would then have some amount of stress so not sure you gained anything as far as reducing stress.

Take this with a grain of salt.....but my understanding is that on violins a rod connects the top and back plates and is cut at a length that introduces a little stress in the plates that helps the sound. Someone correct me if I was told or remember incorrectly.

_________________
Formerly known as Adaboy.......

Rod and Daryl,

Thank you. Good, helpful posts. I wish guitars wern't so complicated. If they were simpler,
we could say things with certainty, and who doesn't love certainty?

STRESSSSS!!!!!!!!!!!!!! yup it is in there and you won't get it out. The guitar is in constant flux with RH changes and load bearing. When you look at a top , there are 3 very distinct areas of stress . From the bridge toward the neck block we are under compressive forces . Also there is a rotational force as the neck is being pulled by the strings. This wants to pull the back straight (tension) and push the top down Compressive and rotational. Then we have the bridge trying to rotate by the string load pulling on the ball ends and the strings pushing down on the saddle , and last but not least , you have the tensional force as the strings are pulling the wood is holding it back from the tail block , so there is no way to build a guitar that won't have stress in it.
The stress we want to avoid is the forcing of joints and bad fit. If the joint won't close dry , forcing it will not last long and that joint is doomed to eventual failure.
Doming will help with some RH movement and adds strength. Hope this helps explain some for you.

_________________
John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

Thanks for that. And what is 'wetware'? Is that the human brain?

Jim

PS Several days ago I was reading a thread - I don't remember which - where you were asking about something. You persevered, clarified your question and persevered some more. From what I remember, the responses to your question were tangential. I have alot of respect for your perseverance.

Thank you for that Filippo.

I wasn't thinking that doming vs. a flat top guitar would lessen the stresses that cause cracking. Maybe there is an advantage of one type over the other but I don't know and have never seen statistics that would cause me to believe one or the other. I was asking the question from the point of view of tone and resonance.

From my reading I find very little solid information which would suggest that one type of building is superior to another but I tend to think that probably one is, indeed, better than another.

Much of the info we are all exposed to is anecdotal and to my knowledge much of the experience that has been gained by the people who have built thousands and thousand of guitars over the last century is nowhere to be found EXCEPT, relatively recently because we are now blessed with access to forums such as this.

The books I've read tell how to do things but usually don't say why they are done that way. I think that's mostly due to the fact that most people simply want to know how how to duplicate relatively successful designs and have little interest in the explanations for why they work.

You say, "To be concerned about a design element that has been in use over 100 years, it might be helpful to look at the body of instruments and see if there is a causal effect to the 'why' question." I appreciate the advice but I don't know where to look exactly. That's why I was asking here. Have any ideas?

Thanks again.

Jim

Yes, you're right about that, Filippo. I did not make myself clear.

I will now appeal to the higher powers that Mr. Carruth stop by. He seems to be a wise one.
Anybody have a direct line to him?

Can I just throw another "theory" of mine in here (and related to the Violin part of my response later) and think that a domed top would tend to be more sensitive to string vibrations. If a top has already some stresses (or a preload maybe a better term to use) imparted to it by doming then it would only take the slightest vibration to get it too, vibrating. I build Selmer style guitars and the tops on those are almost barrel shaped by design, they use a combination of 7' & 12' domes across their width and a 25' along their length.
Here's a slightly blurry image of Selmer a top on a guitar I'm currently building.
and from the end.

You mentioned about violin tops being removed too & sounding better when glued back on. The reason for this is that there is a longitudinal tone bar that is glued to the underside of the violin's top.When these are fitted they are deliberately carved over radiused (if you can imagine the 3 dimensional radius of a viollin top) so that when it is glued it has to be "pulled down" onto the top at it's ends. This imparts a stress (or preload) to the top and makes the violin loud & responsive. After a few years a trained pair of ears can detect a drop off in the life or tone/voice of the instrument. This is because the tonebar has lost it's 'spring' over the years and is not loading the top like it used to. This is when the top of the violin is removed, the old tone bar is removed and a new "Over Radiused" is made and glued in, thereby restoring the top's reload and original responsive tone and volume.

_________________
Nick Oliver

http://www.oliver-guitars.com

Very interesting, Nick.

I believe I had read that the tops had been relieved of stress by uncoupling them from the sides. I don't recall ever reading that new tonebars had been installed. But here, in my late 50s, the memory isn't all that reliable.

Thanks for this info.

Jim

I think it likely that 'high' stress levels can cut down on the sound. I've been doing some tests that involve using a tall saddle to raise the strings 18mm off the top of a classical guitar (don't try this at home!), and it does seem to be a bit harder to move the top when it's set up like that. Of course, it's also hard to sort out all of the changes in the forces on the top when you make that sort of change, and there's a lot more of that experiment to do, so don't take that as gospel.

The question is, what's 'high' stress? Compared to what I just did to my poor test mule, doming the top is nothing. I sure don't want the job of trying to figure out just where 'normal' stress ends and 'high' stress begins.

Doming the top has one really useful effect: it makes it much less likely to crack when the humidity drops. Here in 'Guitar Hell' (New England), that's a biggie, and I'm going to keep doing my tops even if it does cost a little sound.

Just reading Alan's reply has reminded me to mention the fact that my "theory" only applies to a bridge & seperate tailpiece style of instrument (Archtoped family of instruments & Selmers e.t.c,being the styles of instrument I build) where the strings energy is driving the soundboard up & down through a floating bridge as opposed to a fixed bridge style where the bridge is being rotated/rocked by the strings. I could see that if you have too much preload on the top plate of a fixed bridge, this would have the ability to hinder the bridge in it's action of driving the plate as Alan refers to in the first part of his post.

_________________
Nick Oliver

http://www.oliver-guitars.com

Do you want to know what I think? No?

I think we should shoot the next person who starts out a steel string guitar question with "that's what Stradivarius did".

Violins are hardly relevant to anything about guitars.

Old Art Overholtzer sure made a bad name for himself, but in teaching about the "stress free" guitar, he emphasized excellent joinery, making the parts fit without forcing them together. I think that is a lesson every novice should learn, and practice.

In arching a top or back, not much stress is built in. Once sides are bent, I like them to be at rest in the forms. Don't you profile the sides before gluing on the top and back? Don't you shape the bottom of the bridge to match the top?
These are all stress-reducing practices.

_________________
https://www.facebook.com/profile.php?id=100008907949110

Thank you for that, Alan. I've let go of the notion that Overholtzer's book planted in me years ago.

Jim