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im in the planning stage of my next build and im sort of driving myself crazy. id like to build a guitar for a friend of mine who has a pretty heavy strumming hand. what i have in mind is an adi/EIR SJ of sorts (UB 11.3", W 9.5", LB 16") - think lowden-ish 'f' shape. this is only my third guitar, so i know ultimately i need to just put chisel to wood, but ive lost site of that in the midst of all of the possible wood combinations, bracing configurations, and acoustic black magic.

what approach would you take in building a guitar with a big, full sound that is not easily over driven?

how do you move forward in building early guitars without a clear cohesive plan?

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sweat the small stuff.

Heath, if he over drives one of you'r existing guitars make the top a little stiffer as it's being driven by more energy.

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Jim Watts
http://jameswattsguitars.com

If you have a choice between 2 tops - pick the heavier/denser of the 2.. They tend to be a bit more forgiving of hard playing...

Otherwise - you can leave the top bracing a hair taller than before... or don't round/triangle shape them as much - leave them a little fatter...

Thanks

Can't advise you,
but know how ya feel.
Happens to me every time I carve braces.
When do I stop,
have I gone too far?
Tap tap tap,
now what do I do?

As truckjohn said, pick the densest top you've got, and then work it to the correct stiffness. It will be thinner then a less dense top would be, but will weigh more. That will help.

Brace it to give the 'right' tap tones: the braces will need to be a bit stiffer to keep the pitches up, due to the extra weight, and the added stiffness will help too. As John says, mske them a little wider and taller.

Use 'tapered' or 'straight' bracing rather than 'scalloped', if you can. Again, tapered bracing concentrates the mass and stiffness at the bridge, and gives more 'headroom'. You lose some 'attack', of course.

If you could tune the 'main back' tap tone so that it's around a semitone higher in pitch than the 'main top', that will help the 'attack' a bit, and give a fuller bass and midrange. Martin style back bracing, with the two lower braces low and wide, helps with this.

Then you can open up the hole a little, to raise the 'main air' pitch a bit, at the cost of a little fullness in the bass, but the benefit of some more attack and high end.

Make all of these changes SMALL. You're trying to keep things in balance, and the best way to avoid falling over is not to hold too many bricks in one hand at arm's length. A lot of small changes that all tend in the direction you want to go is the ticket.

My advice: Read Alan Carruth's advice MOST carefully. Let it soak in. Then, as you said yourself, just launch the project and apply chisel to wood. Tell your friend how to get the most out of your instrument. After that, it's pretty much up to your friend. You can't control how your friend will play this instrument. You can only give your counsel.

Alan gives great advise. I appreciate his reading his posts. Clinton

thank you so much everyone for taking time to answer. if nothing else, i think posting my concern and having some feedback helped get me out of my head a bit.

alan (and those who echoed his sentiment), a few questions or maybe just a chance to repeat what you said, if i may.

what is it about the added weight of the top that helps in the headroom dept.? while ive heard you say that density tracks pretty proportionally to stiffness, is it just weight that im looking for, or is it the stiffness that just happens to be accompanied by some added weight? will a heavier bridge help in this same way?

you mention that opening the sound hole a bit may help with more attack, how about adding a sound port? achieve the same goal? sometimes i wonder if the "client" the guitar is going to just beats on lesser guitars to get sound out of them that isnt there. perhaps if the sound felt fuller to him, he would see less need to bang on the thing. just a thought.

i wanted to say also that i appreciate your advice to make these changes SMALL. its easy to get carried away sometimes.

thanks again.

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sweat the small stuff.

Heath Blair asked:
"what is it about the added weight of the top that helps in the headroom dept.?"

That's a good question; I'm glad you asked that. We need more poeple who will ask questions, and.....










...darned if I know _for sure_. It seems to work,though. I _think_ it has to do with two things; the relative impedance of the strings and bridge, and, more, a likely shift into non-linear behavior by the top at high amplitudes.

Mechanical 'impedance' is a measure of how much movement you get out of something at a given pitch for a given force. The more massive and/or stiff the thing is, the higher the impedance. Strings have impedance too: it's a measure of how hard they can push on the bridge at a given amplitude, in a sense. If the impedance of the string and that of the top match at a given frequency, two things happen: all of the energy of the string can flow into the top, so you have no sustain, and the string can't tell how long it is, so it doesn't know what pitch to make. Bad. In general, the top and bridge have a higher impedance than the strings, and the greater the mis-match, the longer the sustain, and the lower the power, all else equal (and the more 'in tune' the guitar is likely to be, with less chance of 'wolf' notes). Using a dense top, and thicknessing and bracing it to the correct stiffness, results in a top that is both heavier and stiffer than a lower desnity top that's 'properly' braced. The energy tends to stay in the strings a little longer, and you don't have as strong an attack, but get more sustain. This is pretty non-controversial.

Scientists tend to treat guitars as 'linear' systems, for two reasons:
1) they are, pretty nearly, and,
2) it simplifies the math.
In fact, nothing on the guitar is really 'linear', although some parts are pretty close to that. In a linear guitar, if you put twice the energy into the string you get twice the sound out, no mater how loud you were playing to start with. Even discounting fret buzz, this is probably not strictly true. More importantly, it seems as though you can only get the top up to a certain amplitude before it starts to 'break up' acoustically. It's sort of like 'clipping' in an over driven amp, but probably more complex. With a heavier and stiffer top it should take more energy to get it to that amplitude, so it could be less prone to breaking up. Also, the greater impedance mis-match means that playing th strings to a certain level results in less poweer transferred in the heavier top, and lower amplitude that way.

All of this makes sense, but it's _not_ backed up by data. It's one of the many (many, many) 'science fair projects' that needs to be done on the guitar.

Alan and others,

I'm resurrecting this thread to clarify a bit about the strings. I am in pretty much the same position as Heath, in that, this is my third guitar, it is being made for a musician who plays fairly aggressively and uses medium gauge strings. I intend to follow Alan's advice on the top and bracing, and will try to tap my way to that semi-tone difference between main back and main top notes.

String gauge wasn't specifically addressed in this discussion, and I want to ask about other changes (if any) other than nut slot sizes that need to be considered or executed when building for someone who will use medium strings. Based on Alan's discussion, it seems that larger strings have higher impedance, and he discussed how to try to compensate for higher impedance in general. However, I took physics for poets in college, so I can't figure out if the medium strings when brought to pitch, produce higher pounds of tension on the neck and top (intuition tells me this would be the case, but I don't know). If so, do the added stresses from increased string tension/pull require other structural changes such as modification of the neck (I'd rather not put CF rods in, but maybe should?); which orientation to put the truss rod adjusting nut; choice of bridge plate material; extra head block depth to support the fingerboard extension part of the upper bout; etc.

Thanks, Beth

Beth, having taken physics for poets your ear may be better than mine, but if you are not already using something similar, back (and top) frequencies can be quite accurately checked by using several programs including, for iphone (strobosoft?) or computer (Visual analyser or Audacity, both free) for example. There are discussions about this elsewhere on this forum and others.
I have both but VA and Audacity, but use VA v9 as I find it quite easy to use and it gives data in a form I like, but clearer plots seem to be obtained with a half decent decent external microphone as opposed to say a laptop's internal mic.
Help on setting it up and using it are here http://www.anzlf.com/viewtopic.php?f=1&t=3696&p=44370&hilit=Setting+up+Visual+Analyser+and+capturing+a+frequency+plot#p44370
I believe you are correct, heavier guage strings produce more tension on neck and top, but as I havn't used them I can't discuss what may be needed, if anything at all.
But suspecting I had some rotation of the neck/body joint on previous builds, I do like the fretboard support extention to the neck block on the OLF SJ Plans (my current build in progress)
Good luck with the build, and enjoy it.

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The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

Given the weakness of my math chops, I probably should have taken physics for poets.... I have learned a bit sinced then, though.

A heavier string of the same material needs to have higher tension to sound at the same pitch, so, yes, medium tension strings pull harder than lights. The exact tension that any maker chooses to lable as 'light' or 'medium' is up to them, though: one makers mediums might be another one's 'medium light'. Most of the string makers have tables in their catalogs, and on line, that give the tension of theier string sets under some standard conditions.

On a guitar stiffness is more of an issue that strength per se. You're unlikely to rip the neck off the body right away by putting on a heavier gauge of strings, but the normal tendancy of things to move around will be speeded up. Adding a CF rod will help slow it down, but then you have to put more force on the adjustable truss rod (if you have one) to adjust things: stiffer is stiffer. Stiffening the neck can have other benefits aside from the structural ones, but that's another long post and I don't have much time right now.

Remember that if you up the tension on the strings by 10%, you can cut the torque on the top back down by making the strings 10% closer to the top, and that gets you back to 'normal' bracing. You still need to think about the 'footprint' of the bridge, since that takes all the tension load. I realize that, for some folks, string height off the top is a religious issue, so treating it as a variable might unleash the auto-da-fe. Be judicious. Too low might affect the tone, and too high is structurally risky, but the allowable range is fairly wide.

Colin, thanks for the link. I tried using Audacity on my current build but couldn't figure out how to really gather the frequency patterns and use them effectively. I'm going to investigate your method though, because I do want to do something more formal and accurate than tap tap tap....pluck the guitar string....tap tap tap

Alan, that pearl about the inverse relationship between string tension and string height is GREAT! I don't have enough knowledge or experience to be a purist about anything in luthiery, so I will build that little factoid into my calculations for action in the final setup. As for planning the bridge footprint...hmmm...any suggestions about tweaking the "standard" 6 string bridge for the application of heavier strings and greater tension?

Thanks guys, and I'm sorry Heath if I hijacked your thread. Hopefully this has been a useful extension of the initial discussion

Beth, it sounds like you're ready to do some reading...

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Trevor Gore, Luthier. Australian hand made acoustic guitars, classical guitars; custom guitar design and build; guitar design instruction.

http://www.goreguitars.com.au

Trevor...HA! Too right. It isn't the reading that's my problem....it's the comprehending that gets me

Beth Mayer wrote:
"It isn't the reading that's my problem....it's the comprehending that gets me."

That sounds like the world I live in!

I find experiments help me understand things much better than just reading about them. The problem is that even 'simple' demonstration experiments take time, and there's always some stuff in there you didn't expect, not to mention the 'noise'... Still, some combination of reading and hands-on experience can move you forward faster than either by itself, I think.