Thickness of soundboard

Construction and repair of Classical Guitar and related instruments
gjo
Posts: 338
Joined: Wed Sep 16, 2009 8:48 am

Re: Thickness of soundboard

Post by gjo » Wed Feb 14, 2018 8:11 pm

Alan Carruth wrote:
Wed Feb 14, 2018 5:44 pm
I asked:
"How do you know that?"
and gjo replied:
"Well, I would call it experience "

My point is, though, that you have no 'experience' with THAT top. Simply looking at it won't tell you what you really need to know; how stiff it will be along the grain at a given thickness. Hauser had that experience, and along with his notion of the sound he wanted to get, chose the thickness that he thought would work for that top. He was, apparently, right. Would he have been able to make a good guitar with that same top at less thickness? Probably, but it would not have been the same guitar, and may not have been nearly as successful. At this point there is no way to know.
Dear Alan,

you are absolutely right, I do not have any experience with the two soundboards in question, but I would say that my nearly 40 years of selecting and buying spruce tops give me a solid base of experience to have an opinion on the soundboards of two of the most famous guitars in the classical guitar world.

With your approach and experience you might come to the conclusion that it is not possible to judge on the quality of the tops of the 1912 M. Ramirez and the 1937 Hauser. I can understand your point of view and I can accept it.

With my approach and experience I continue to be convinced that I can say a qualified word about the general quality and characteristics of a spruce soundboard. I hope you can accept my point of view and experience as well.

Tobias Braun
Posts: 18
Joined: Wed Aug 31, 2016 6:26 am

Re: Thickness of soundboard

Post by Tobias Braun » Sun Feb 18, 2018 10:12 am

Julian wrote:
Sat Jan 03, 2009 4:41 am
Thanks to all about your advice. I have read Roy Courtnall, Torres by Jose Romanillos and the 1937 Hauser plan. Actually what I was about to do (in co-operation with a local luthier) is to copy Hauser 1937 just for try-out, not to seek a certain quality guitar based on that plan. The first try was ok, but again that luthier was lack of many issues and we would like to explore further.

Now for the second try, we would make another copy of 1937 Hauser using one of the best spruce he's got, except he pared down to about 2.8mm before tuning it and putting some braces on. Hauser plan has a thickness of more than 3.00mm being 3.24mm as the thickest part. So that was how the topic derived: whether a soundboard of 2.8mm can be used for that particular plan. We all know that there are many factors that contribute to a quality sound for good guitars. We thought of using the soundboard we've got. To compensate the thinner part of the soundboard, we were thinking to increase the height or the width by ,say, 0.2mm to increase the strength, or maybe not.

We talked about dooming and flexing the soundboard which is one of the potential solution for thinner soundboard. Again, I amnot a luthier, that local luthier is more or less an amateur luthier when we get to master guitars level. So I need to explore these issues further. The best way is by practising it. I just don't have any guidance how to do it.

Anyway, I am grateful that I could have the discussions here at Delcamp forum with very valuable comments and advices for all of you.

Julian
Hello Julian,

I have followed the discussion now for a couple of days and want to add my thoughts to your post.
In my guitar making courses the 1937 Hermann Hauser is THE "basic" model for the participants. There are several good reasons - in my opinion - for it:

1. The blue prints, photos and notes of R. Brune are really good; i.e. very detailled and informative and from an academic point of view "correct" (Brune mentions repairs and admits uncertainties when measuring).
2. The photo/poster of the top gives one a good idea of the quality of the wood (have a close look - Mr. Carruth!!!)
3. And - MOST important - the CD: It gives on an "acoustic point of reference"!! I want to emphasize that aspect strongly because that really helps one after he or she has finished that model. Am I on the right track - or not?

There are countless blue prints of guitars and many of them aren't worth their price because they just lack essential information (thicknesses, doming, arching, cross sections,...). They just enable one to build just "guitar like objects"...

Knowing that I will be the "party crasher", I have to say that when participants of my courses shows up with a plan made by Roy Courtnall they have bought a "very thin soup": On first sight it looks like a guitar but...

My advice to you, Julian, is very simple: Just do it! Make two or three Hausers and see (AND listen!!) to them. If necessary, work with the thicknesses.

Good luck from Austria!

Tobias Braun

User avatar
Michael.N.
Posts: 7289
Joined: Sun Mar 25, 2007 7:28 am
Location: UK

Re: Thickness of soundboard

Post by Michael.N. » Sun Feb 18, 2018 11:03 am

But 'quality of the wood' is meaningless. You would have to define what quality means. We know that it's not grain count, that tells you very little. Straight grain? Well sure but only within reason, the vast majority of spruce soundboards sold by vendors is 'straight enough'. You usually have to go to the very low grades to obtain wood grain that meanders alarmingly. We are left with quarter sawn and runout. The point is that you simply cannot tell the qualities of the soundboard just by looking at it. Looking at it will largely give you cosmetic appearance. Looking at weak or strong summer grain growth can be pretty deceptive. You really need to either weigh /measure the stiffness or (with experience) have the piece in your hands to enable you to feel how dense and stiff it is. You can press on the soundboard of a finished guitar to judge how much flex it has but that only gives limited information. Without weighing the soundboard how on earth can you tell whether the wood density is 340 Kg/M3 (weight of cedar) or 480 Kg/M3 ? That kind of difference will have far more tonal consequences than cosmetic visual clues. If someone wants to have a guess at wood density based on appearance I'm quite prepared to plane 5 or 6 spruce soundboards, photograph them and they can use their eyes to tell us what the density and stiffness is.
Historicalguitars.

gjo
Posts: 338
Joined: Wed Sep 16, 2009 8:48 am

Re: Thickness of soundboard

Post by gjo » Sun Feb 18, 2018 1:04 pm

Michael.N. wrote:
Sun Feb 18, 2018 11:03 am
But 'quality of the wood' is meaningless. You would have to define what quality means. We know that it's not grain count, that tells you very little. Straight grain? Well sure but only within reason, the vast majority of spruce soundboards sold by vendors is 'straight enough'. You usually have to go to the very low grades to obtain wood grain that meanders alarmingly. We are left with quarter sawn and runout. The point is that you simply cannot tell the qualities of the soundboard just by looking at it. Looking at it will largely give you cosmetic appearance. Looking at weak or strong summer grain growth can be pretty deceptive. You really need to either weigh /measure the stiffness or (with experience) have the piece in your hands to enable you to feel how dense and stiff it is. You can press on the soundboard of a finished guitar to judge how much flex it has but that only gives limited information. Without weighing the soundboard how on earth can you tell whether the wood density is 340 Kg/M3 (weight of cedar) or 480 Kg/M3 ? That kind of difference will have far more tonal consequences than cosmetic visual clues. If someone wants to have a guess at wood density based on appearance I'm quite prepared to plane 5 or 6 spruce soundboards, photograph them and they can use their eyes to tell us what the density and stiffness is.
Ah Michael, is it possible that you are speaking to me?

I am far away from fighting with anybody about "experience". We all admire Antonio de Torres for the "feeling in his hands" and his experience that can not be taught as the priest Martínez Sirvent wrote in a letter to one of Torres´ descendants (you can read about this in Romanillos´ Torres book).

Experience in my opinion is one of the most important factors in learning and improving ones abilities and products, so do I - what's wrong with it? I never really cared very much for specific weight, grain count, stiffness along the grain, or whatever in a "scientific" approach might be important. For a short while I worked with a Lucchi-Meter, measured the speed of sound, recalculated my measurement to Young´s modulus, measured the weight, correlated all my measurements with each other and tried to be as complicated as I could imagine. I wasted a lot of time trying to find out and understand what all of this might be going to tell me about the most important factor in building a musical instrument - about the sound! In the end it was not very much, if not to say "nothing". All I found out was that my hands and eyes are for me quicker and better in evaluating and choosing a spruce top that I personally like and will use than all my measurements ever could have helped me.

I already admitted that I do not have any experiences with the two specific tops in terms of long grain stiffness, and I do not have any problems to admit that I am also not able to exactly give you the specific weight of a top by looking at it.

Why should I?

But I will not stop to be convinced that I can say a word about the quality of a spruce top on an old guitars when I see it.

Everything you look at tells you a story if you are willing to read or listen - and a spruce top is an object to look at as well.
Last edited by gjo on Sun Feb 18, 2018 2:01 pm, edited 1 time in total.

User avatar
Michael.N.
Posts: 7289
Joined: Sun Mar 25, 2007 7:28 am
Location: UK

Re: Thickness of soundboard

Post by Michael.N. » Sun Feb 18, 2018 1:28 pm

Well no I wasn't specifically referring to anyone. I was responding to Alan's point in that we can't tell the properties of the Hauser and Ramirez soundboards. We can tell their grain count, we can tell how straight the grain is, we can tell something about the runout but we can only guess at the density and therefore the stiffness of those soundboards. It's quite possible that the Hauser is 320 Kg/m3 and the Ramirez 480 Kg/m3 or even the other way around. It's quite possible that they are both exactly the same density. There is no way of knowing unless they are both measured but we can't tell by looking at them.
Historicalguitars.

gjo
Posts: 338
Joined: Wed Sep 16, 2009 8:48 am

Re: Thickness of soundboard

Post by gjo » Sun Feb 18, 2018 2:00 pm

Do you mean by stiffness "Young´s modulus"?

Does Young´s Modulus directly linear correlate to the specific weight/density, i.e., the heavier the stiffer?

What about "runout" in the central (joint) area? Does it affect Young´s modulus without actually affecting the density?

What about cross grain stiffness? Is a cross grain floppy top as good as a very stiff one when the long grain stiffness is equal?

User avatar
Michael.N.
Posts: 7289
Joined: Sun Mar 25, 2007 7:28 am
Location: UK

Re: Thickness of soundboard

Post by Michael.N. » Sun Feb 18, 2018 2:30 pm

Those are entirely different questions. The point that Alan and myself are making is that you cannot tell stiffness or density by simply looking at the soundboard. You might be able to draw some conclusions but those certainly will not be the whole story. Whether a maker chooses a very dense, a very light or a mid weight soundboard is entirely up to that individual maker. Some may not be concerned and just thickness accordingly. The point is that we don't know how Hauser or Ramirez approached this, in fact they may well have approached things in an entirely different manner to each other.
Historicalguitars.

gjo
Posts: 338
Joined: Wed Sep 16, 2009 8:48 am

Re: Thickness of soundboard

Post by gjo » Sun Feb 18, 2018 4:31 pm

Michael.N. wrote:
Sun Feb 18, 2018 2:30 pm
Those are entirely different questions. The point that Alan and myself are making is that you cannot tell stiffness or density by simply looking at the soundboard. You might be able to draw some conclusions but those certainly will not be the whole story. Whether a maker chooses a very dense, a very light or a mid weight soundboard is entirely up to that individual maker. Some may not be concerned and just thickness accordingly. The point is that we don't know how Hauser or Ramirez approached this, in fact they may well have approached things in an entirely different manner to each other.
Come on, I already confirmed your assumption without having problems. The terms "stiffness", "density", "specific weight", or "Young´s Modulus" were introduced to our discussion by you and Alan, not by me. Now you got me interested and I ask questions ... :bravo:

We really do not know much about the approach of Manuel Ramirez or Hauser and I never asked about this point. It was Alan who doubted that my experiences would enable me to express that in my opinion:

"The Hauser top would have done equally well much thinner in the Manuel Ramirez style and vice versa."

so let us continue discussing my statement and not shift to speculations about the approach of Hauser or Manuel Ramirez. Both never worked in the style of the other.

Alan Carruth
Luthier
Posts: 3035
Joined: Mon Dec 24, 2007 6:56 pm

Re: Thickness of soundboard

Post by Alan Carruth » Sun Feb 18, 2018 6:14 pm

Thanks for the support Micheal. I've been busy for a couple of days, and also pondering a response, and that input helps.

gjo:
I think you have to admit that your screen name is not very informative. It says nothing to me about your experience, and leaves little to go on other than the posts I read. Anyboody who knows me at all will attest that I'm not a confrontational person, and it was never my intent to call your experience into question; I simply had no way of knowing what it was.

Until I started measuring the properties of the tops I got, I really didn't know how variable they were, nor how little information you actually get visually. This is really all I've been trying to get across.

A collegue of mine took summer courses in violin making at the University of New Hampshire that were taught by the head master of the Mittenwald school, Karl Roy. Roy used to gauge stiffness by flexing in various ways, and one of the students wondered how accurate he was, so he made up a box full of small sample pieces of various sizes and measured them all. He then asked Roy to sort them out by stiffness, doing the test several times during a one-week session. He found that Roy could consistently distinguish a difference of about 3%, which is about as well as you're going to do with a good 'shop level' test. So it is possible. What's important in that is the Roy did not determine the thickness based on appearance, but on measurement that he made using his hands, and based on many years of experience. I must assume for purposes of discussion that your skill appproaches that level, and have no doubt that you can properly gauge the thickness of a top you are working on. What I find difficult to credit, based on my own extensive experience, is that anybody could properly gauge the thickness of a top on appearance alone.

gjo asks:
"Do you mean by stiffness "Young´s modulus"?

Does Young´s Modulus directly linear correlate to the specific weight/density, i.e., the heavier the stiffer?"

Yes to both questions, in a very general sense. We are, after all, talking about a natural material here, so you can't expect perfect uniformity. As it is, in using softwoods for tops we are reducing the variation by quite a lot; as it happens all softwoods have a very similar microscopic structure, so there is far less variation across softwood species than there is with hardwoods.

I don't pretend in the following to tell you anything you don't probably already know, but I'll include the explanation for clarity for those who don't.

The stiffness of a piece of material of a give size is largely determined by it's Young's modulus, which is a measure of the work required to stretch or compress it. Bending something stretches and compresses the material, especially near the surfaces. Thus the stiffness depends on the size, and particularly the thickness/height of the piece, and the Young's modulus. All else equal, stiffness goes as the cube of thickness/height, so small differences in thickness can change the stiffness a lot: 25% thicker will be almost twice as stiff, for example (but only 25% heavier, of course). This is why it is improper in a strict sense to talk about the 'stiffness to weight ratio' of a material: you need to specify the section for that. That cubic realtionship also is one of the main problems in getting accurate measurements of the Young's modulus; to get within 3% of the modulus value you need to control the thickness within 1/10% or so, which is hard when you're down in the range of normal guitar top thicknesses.

Plots I've made of the reationship of Young's modulus along the grain of various top woods to density show most samples falling close to the same line. Within the 'normal' range of densities; say from roughly 300-550 kg.m^3, it's very nearly a linear relationship. 2/3 of my samples fall within 10% plus or minus of that line, which is quite good considering normal measurement errors. These values are quite repeatable, again, given the influece of things like humidity changes.

Late wood tends to contribute more to density than Young's modulus; the outliers that are stiffer than expected tend to have relatively narrow latewoood lines. Heavy latewood, and particularly 'reaction (compression) wood' goes the other way. Note that this is not grain count, but the relative width of the early and late wood. So there's one thing that you can see that is a rough indicator of stiffness to density. Another is run out, which reduces the Young's modulus, as you'd expect.

Note that all of the softwoods I've tested fall on the same line for lengthwise Young's modulus vs density. That includes 'usual suspects' like Western Red Cedar, Engelmann spruce, European spruce, Sitka spruce, Red spruce, and Redwood, as well as soome things like White pine, Western Hemlock, White spruce, and some others. Other properties vary; both Redwood and WRC have much lower damping than the spruces in general, for example, but in terms of Young's modulus and density they follow the same rule.

There is a lot of variation in density within any species. Although, for example, Western Red cedar tends to be lower in density on average (in my samples so far) than the spruces, it's not at all hard to find relatively dense WRC, or fairly light Sitka spruce.

Cross grain Young's modulus in softwoods primarily relates to how well quartered the piece is. Even a small deviation from 'perfect' quarter can give a large drop off in cross stiffness. The 'best' crosswise Young's modulus value for different trees of the same species varies somewhat, but it's hard to get enough data to sort out the variables there.

I'm presently of the opinion that having a top with the highest possible cross grain stiffness may not always be necessary, or even desireable. There are reasons to question whether it contributes much to the overall stiffness of the top over the long run, as 'cold creep' (top bellying) seems to cancel it out to some extent, at least as a structural attribute. Acoustically it's at least plausible that there is a 'best' cross grain stiffness for a given outline of top. Again, I'll say that this in my cuurrent thinking on this, and it's working pretty well, but I do reserve the right to change my mind if better data comes in. ;)

Note that all of this data comes from measurements of top half blanks. We all know how much a piece of wood can vary from one spot to another, and these measurements smear all of that variation out. That variation could have a lot to do with why a good maker would vary the thickness of a top from point to point.

So there's a long answer to your short questions.

I'll note how little of this has anything to do with the usual visual markers of 'quality' in a top, such as tightness and straightness of grain, uniformity of color and so on. In that respect it's entirely possible to have a top that is of 'high quality' but is still not as good acoustically as one that is of a lower grade. I have paid top dollar for 'high quality' tops that I considered barely usable when I recieved them, and gotten very good tops that were very low in visual grade.

gjo
Posts: 338
Joined: Wed Sep 16, 2009 8:48 am

Re: Thickness of soundboard

Post by gjo » Mon Feb 19, 2018 7:39 am

Thank you very much for taking your time to answer my questions.

I do agree that the usual wood dealers visual grading of soundboard material often does not relate to my expectations of "quality". When I started I followed some of the common belief that "the more expensive the better" and "the more and narrow grain lines the better" which rapidly changed when I started to go directly to the sawmills and selected my stock from large numbers of pre-selected material in different gradings. Like you I often recommend to beginners to start in lower grades and trying to get a tactile and visual "feeling" for the material. Lower grades can offer great bargains when one has the occasion to select from a good stock. In another thread I quoted a friend who in a discussion about "Master Grade" mentioned that he has passed all the mastership examinations so every top he selects for his personal use finally is "master grade". In the past I bought some master grade tops from Switzerland that I was not happy with and I have not used them by now. The second and third grade tops I bought from the same source (I do not remember how many As) were much more convincing for me and I made some beautiful sounding and looking guitars with them. I learned a lot about the structure and quality of spruce tops when, together some friends, we were given the chance to select trees in a sawmill and were involved in all the work converting a tree into soundboards. I also learned why an expensive top is so expensive with all the steps starting with debarking, cutting to length, splitting wedges and cutting the tops on a large circular saw - in the end only a very small part of the tops was really good material. I am very happy that I had the chance to be involved in the whole process and all this contributes to what I call my "experience".

And now we are off topic - sorry.

Alan Carruth
Luthier
Posts: 3035
Joined: Mon Dec 24, 2007 6:56 pm

Re: Thickness of soundboard

Post by Alan Carruth » Mon Feb 19, 2018 6:52 pm

gjo:
I suspect that if we got together we'd be likely to be in agreement about what made a 'good' top. And you're right; actually processing out a tree or two is a real education!

There are lots of reasonably reliable ways to pick out a good top. The 'best' way is the one that works best for you. I've found that I'm one of those folks who's not as good at picking a top by 'feel' as I'd like to be, so I add in more objective measurements. It's tedious, but worth it to me.

Picking out a good top, and determining a target thickness, is just the beginning of making a fine guitar, of course. We're lucky in having designs to work with that have already done a lot of the work for us. I've taught a lot of students, and despite the fact that they sometimes don't work as carefully as I'd hope, I have yet to have somebody walk out with a bad sounding guitar. They may not look wonderful, but they work. All you need do to end up with a better than average guitar is use reasonably good wood, and reasonable care in building.

The devil is in the details. Objectively there is not much difference between an 'average' good guitar, and the best one you've ever heard, but that 'small' difference is important. That's why we spend so much time discussing the details like top thickness (how's that for getting back on track!). ;)

Stephen Faulk
Posts: 922
Joined: Tue Jul 03, 2012 3:27 am

Re: Thickness of soundboard

Post by Stephen Faulk » Tue Feb 20, 2018 5:17 am

I've been following this a few days..I'll add to the conversation on the Hauser plan- The guitar slipped and scraped up on a microphone. The top as repaired by sanding it and refinishing. It removed the scratches but also changed the top thickness quite bit. Segovia claimed the guitar was not as good after that. Bear in mind the change in top thickness in a talk about how important that is.
I have the plan and it's such a solid design you can make it with just about any thickness top, up to your judgment on how you thickness a particular top. I made a really great guitar at 2.5-2.3 mm according to what I thought that top needed to be. The design is solid, and depending on the wood you use will make a good guitar, but the design in itself doesn't mean it will sound like that Hauser even if you use a top you can leave as thick as 3 mm.

Right now I'm making a guitar out of persimmon taken from an abandoned tansu chest- I took all the hard wood out ad dimensioned it and am using it with a very good spruce top. As i took the tansu apart I noticed the wood in the carcass was 90-year old pine. Very light and stiff. I decided to make a pair. One guitar from the front wood to sell and one for fun out of the carcass wood. The top will be four pieces of fairly wide grain. But I have confidence it will sound great. Just for fun, nothing to prove.
Patience at the bending iron pays in rounded dividends!

Alan Carruth
Luthier
Posts: 3035
Joined: Mon Dec 24, 2007 6:56 pm

Re: Thickness of soundboard

Post by Alan Carruth » Tue Feb 20, 2018 6:18 pm

Stephan Faulk wrote:
"The design is solid, and depending on the wood you use will make a good guitar, but the design in itself doesn't mean it will sound like that Hauser even if you use a top you can leave as thick as 3 mm. "

The design only takes you so far. A good design will usually yield a 'good' guitar, but it is unlikely to be 'the same'. I've tried a few times to make identical guitars using flitch-matched wood and so on. So far they have ended up sounding different every time. As I tighten up on the controls they get closer, but I'm really starting to wonder whether it's even possible to make 'identical' ones. I'm quite convinced, though, that you won't do it unless you can find wood that is 'identical'. Good luck... ;)

GuitarsWeB
Posts: 326
Joined: Sat Feb 24, 2018 6:55 pm

Re: Thickness of soundboard

Post by GuitarsWeB » Sun Feb 25, 2018 9:17 pm

Read David Schramm’s write up on the Hauser guitars. Dave makes a dead on clone of Hauser’s instruments, right down to the proper V- joint in the neck.
PM

GuitarsWeB
Posts: 326
Joined: Sat Feb 24, 2018 6:55 pm

Re: Thickness of soundboard

Post by GuitarsWeB » Sat Mar 10, 2018 9:26 pm

I should have said, proper “Covered V-Joint.”

Return to “Luthiers”