Official Luthiers Forum!

I keep stats, or notes on....everything. With my memory I'd forget where to put the strings without notes. I've never experimented with domes, but I've done "sister" guitars with a Dovetail neck and bolt on. I made everything weigh the same, and deflection tested everything. They sounded very similar but not alike. I've also done bridge experiments on a single guitar. I started out with a small, light pyramid bridge and used 3 different sizes and weights. To my ears it sounded the best with the middle sized bridge, but tone is subjective. I had a hard drive die with my recordings. I've got a BIG 44 gram bridge on that guitar now and it sounds like it's stuffed full of socks. I plan on re finishing the top, and putting the "middle" bridge back on it sometime. I'm currently working on 4 "sister" guitars. I had 2 local customers who wanted indentical guitars, except one guy wanted EI Rosewood, and the other wanted Braz. They've been argueing about which one will sound the best since they were started. I've added Panama Rosewood and Honduran Rosewood to the list. I hope to have all 4 done in the next month or so.

_________________
I didn't mean to say it, but I meant what I said.
http://www.brackettinstruments.com/

Take the arched piece of wood...now turn it around so the concave face is facing the kicker. Not stronger. That's the orientation of the arch relative to string pull.

This reminds me of the Maginot Line.

_________________
Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services

[Take the arched piece of wood...now turn it around so the concave face is facing the kicker. Not stronger. That's the orientation of the arch relative to string pull.

This reminds me of the Maginot Line.

Your wrong !
it's still stronger !
especially when braced .
Any loose (flat) piece of wood is easier to break than an equal piece with an arch ,

We all know what happen to the maginot line .
That's a very bad comparison !
Mc

_________________
Mike Collins

Doesn't a flat top get pulled into a dome rather than dish when strings are put on? I agree that there is some vertical component of stress on the top, but it is minuscule compared to the 150+lbs pulling sideways on the bridge (against the dome). Someone needs to draw up a force diagram of a bridge under string tension. I'm assuming the most important thing to resist is bellying rather than being pushed straight down, and an arch is essentially pre-bellying the bridge (giving it a head start).

I think the benefit is the opposite of what we're talking about, actually. By arching the top, you're pre-empting the first bit of bellying by starting the guitar out at that point...which means it might move less over time. It's like the pre-load on your suspension.


Mike: That's just not so. If I take a piece of flat wood which would have taken, say, a 20lb weight in the middle to snap and induce an arch in it by pushing down in the middle...you're saying that it will now take -more- than 20lbs additional weight to snap? An arch is stronger in only one direction, like the ML, and weaker in the other.

_________________
Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services

Doming isn't about resisting catastropic breakage from karate kicks, it's about resisting surface warp (twist) due to the pull of the strings over time. A flat soundboard can (and does) twist over time: it bends downwards between the soundhole and the bridge, and up below the bridge (known as "bellying" I believe). A slightly domed soundboard (N.B. domed, not just bent cylindrically along the grain) offers significant resistance to this twisting. The main string tension force isn't acting perpendicular to the surface of the soundboard at the bridge, it's an angular force, almost parallel to the plane of the soundboard, thus, the doming that is in common use (with the soundboard higher at the bridge than at the sides) IS in the right direction to oppose the string tension. The physics/math of this is well understood and should not be the subject of further debate IMO. As for the difference in TONE that doming a soundboard has, that's fairly subjective. My own personal view is that the doming allows me to make the soundboard thinner and yet still offer more resistance to "bellying" than a flat soundboard. My owns observations lead me to believe that the lighter I can make any moving part of my instruments, the better the instrument's "response" will be. That is, its impulse response (attack) will be faster, its dynamic range (from quiet to loud) will be greater, and its frequency response curve will be extended at the high frequencies as compared to an equivalent instrument with a heavier flat soundboard. Of course, I don't have any hard scientific evidence to back this idea up at all - it's just that everything I ever learned about control theory, impulse and frequency response, and dynamic range in electronics seems to be relevant and apply to the guitar as as mechanical system.

Let's debate!

Cheers,
Dave F.

_________________
Cambrian Guitars

"There goes Mister Tic-Tac out the back with some bric-brac from the knick-knack rack"

-

I'm not going to say that every discussion about domes or flat tops degrade to which one is "best", we are all too experienced to be that blindered. It is hard to say what a bad-sounding guitar is, but I know it when I hear it.

I've built the last several years with X's and other braces evenly arched at 25'R, but not with dishes. Even my wife tells me they all have a similar sound.

So this last guitar I built a semi-arched top, arched in the upper bout, flat in the lower. It has a strikingly different sound than the earlier ones. I like them both, and now will have another arrow in my quiver for the customer who asks for a certain sound, another way to shape it.

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

I think an arch is stong in both directions -convex side is resisiting the load because of the stiffness and the concave side is resisting because it's basically a bowl shape.

I'm no scientist; but I have made flat tops and arched ones.
The arched ones sound best to me and my clients.
Plus they can take allot more stress that low humidity causes than a flat top.
I think it's like cars -it's a matter of preference -an individual taste
that will make you decide which you like.

mike

_________________
Mike Collins

I think a belly (within reason) is not that big of a deal whereas the dip in front is not something to be taken lightly. I think any arching counteracts the dip in front better than it resists a belly. The UMGF thread is a great one. I don't use a dish either to profile the sides and that thread gave me some great info.

_________________
Burton
http://www.legeytinstruments.com
Brookline, MA.

Are radius dishes actually bad for tone?

No.

I would hope that one chunk of sage advice passed on from those experienced luthiers here, to those of us with less experience, is that big blanket statements about "good" and "bad" tone are all 100% subjective.

Listen to a wide variety of guitarists in various genres, and you'll notice that they each select instruments that are "just right" for them, or just right for particular songs - and many of the guitars sound vastly different.

Which guitar has bad tone?

Dennis

_________________
Dennis Leahy
Duluth, MN, USA
7th Sense Multimedia

I agree with you on the humidity thing, and the sound thing is subjective (my three favourite guitars are two flat and one domed top, and I'm sure the top 10 would probably be a mix as well).

The reason the convex side of an arch is stronger is that many materials, like wood and stone, have higher compressive than tensile strengths (it's harder to crush them than pull them apart). In a perfectly formed arch, the load can be nearly 100% compressive. Invert the arch and you invert the type of the load (it becomes nearly all tensile load) and for wood and stone the tensile strength is much lower. You can prove it to yourself with a simple experiment if you don't believe me.

_________________
Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services

I hear a lot of people say domed tops split less than flat ones but does anyone have real evidence of that. In my experience, the vast majority of top splits occur at bridge ends and fingerboard edges. Those are areas where there is a stress concentration combined with differential expansion/contraction and I can't see how a dome will change that. I rarely see splits out in the middle of a top and I've never seen one split in the middle and nowhere else. And if it did, I bet it would be due to a brace glued across the grain and not a lack of doming.

I get the theory behind the argument but there's more than one way to look at it. Anyone done a side by side test or have some other empirical evidence?

_________________
http://www.chassonguitars.com

"Flat top guitar" is a misnomer, IMHO.

We can build a guitar as flat as we want, but the moment we move the guitar to an environment in which the RH is different from the RH in our shop, the top is either going to become convex (if the RH is higher than the shop) or concave (if the RH is lower than the shop). The only time a guitar will ever have a true flat-top is when it rests in an environment in which the RH is at EXACTLY the right point to make it flat. (If we braced the guitar flat, then this will be exactly the same RH as the shop RH when we braced it; if we braced it in a radius, then this will be lower than the shop RH.)

So, ANY guitar (including those built with flat tops) will have a radius in the real world. The only thing you change by building a radius into the guitar to start with is the amount of radius it has at any given RH, and the RH point at which the radius changes from convex to concave.

Bob: The bridge is trying to rotate around it's long axis,thus is being forced down into the upward arch. This is one area that the dome shows it's importance.

_________________
A person who has never made a mistake has never made anything!!!

Kent Chasson wrote:
"I hear a lot of people say domed tops split less than flat ones but does anyone have real evidence of that. In my experience, the vast majority of top splits occur at bridge ends and fingerboard edges. "

I'm in New England, and this is 'guitar hell'. I know at least one maker who doesn't like to ship guitars to New England. I see cracks all over tops, and the big season for crack repairs is February and March, when the low temperatures and humidities of mid-winter have really had a chance to get through. I used to build flatter than I do now, and just spring things in with a lot of clamps a la Sloan. I've had fewer problems since I started using radius dishes. So, while I don't have 'real' scientific evidence that it works, I'm pretty well convinced that a domed top helps. I need all the help I can get.

Thanks Allen.

I've built mostly radiused but I have flat-tops in New York and Minnesota (same problems as New England) and have yet to see any splits in any of them. Only splits I've seen is in repair work. Maybe I'll mock something up one of these days and see what happens side by side.

_________________
http://www.chassonguitars.com

If it's rotating around the long axis, the other half is being pulled up away from the upward arch.

I'm not saying an arched top has no merit, but nobody's actually tested any of their theories on why or how well it works VS a flat top so far as I can tell. Assuming the same bracing, can anyone put some numbers on this? The bracing may well be much more important. The difference in stiffness or resistance to deformation between arched and flat might be less than the difference gained by adding or subtracting a tiny bit in height to the X brace for all we know (and it's not that unlikely!)

_________________
Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services

As a repair tech I do see more "flat" tops that suffer top cracks than do domed ones. This is also something that is more to areas of humidity changes of which I am one.

_________________
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

One of the best sounding and most responsive guitars I have made had a concave top. It was one of my first builds and I did not deal with humidity properly, so what started as a convex top turned into a concave top.


It could have been the added stress. Perhaps we are all messed up and should build concave. Let me know how that works for you......

_________________
"An adventure is only an inconvenience rightly considered. An inconvenience is an adventure wrongly considered." G. K. Chesterton.

Interesting. It seems most responses are justifying why they use a radius instead of how the radius affects tone (the original question). Maybe that's because it's difficult to describe tone........

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

Daryll Young wrote:
"Interesting. It seems most responses are justifying why they use a radius instead of how the radius affects tone (the original question). Maybe that's because it's difficult to describe tone........"

That's certainly part of it.

What Todd said about deflection probably also holds for tone: the relatively small amount of arching we use is unlikely to have any major effect, and could easily be swamped by the normal variations in wood, and build practices.

Bob's right, we need some data. The problem is that, as usual, it will take a pretty big study to get enough data for a reliable conclusion, and even then, people will still argue about it. I note that RM Mottolla's study on ports has been called into question by one of the 'name' makers in the lastest American Lutherie, and that based on absolutely no hard data. He even admits that he finds blindfold tests 'un-nerving' since he can't hear things he 'knows' he's supposed to. Hmmmmm.

Alan, I thought that letter by KH was very a transparent set of impressions, especially the part about being "un-nerved" about blind tests because possibly (and I am paraphrasing here) an Estaban guitar could come out the winner.

All guitar builders should be so honest about what they do. I remember an article written by RE Brune' where he stated that building guitars was of no importance in the large scheme of the world.

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

I build with dished but not radiused forms. I do this ONLY because I am duplicating Selmer guitars of the 30's->50's and I am duplicating their arching patterns. I have attached a picture of one of my top molds. I can tell you from my perspective that if you didn't have to do it this way, you would be nuts to not use radiused dishes. What a incredibly simple way to put an arch in a plate/glue plates on/shape braces/blah blah blah... I bet it takes me a hell of a lot longer with a huge amount of added complexity compared to someone that uses radiused forms.

If you want to do it the way I do.. Hey it's a free country... But I would recommend that you go straight to your doctor and tell him you are having problems making rational decisions.. maybe he'll prescribe you something.

Regards, Peter

David Newton wrote:
"I thought that letter by KH was very a transparent set of impressions...
[snip]
All guitar builders should be so honest about what they do. "

I agree about that part. My problem is really with his first paragraph: "What do you do when a "scientific" study directly contradicts your own experience? Which are you more inclined to believe, a statistical body of "evidence" or your own ears?"

I've been thinking a lot about that letter in the last few days, and mulling an answer. Properly, that should be done in AL, so I won't go into all of my thoughts here. What it boils down to is that RM did a good job, so far as I can tell, with his science, so for KH to belittle that aspect by putting things in quotes is something of an insult. In the grand tradition of scientific invective it's hardly more than a pin prick, though.

What you have to realize, however, is that all science is provisional, and every experiment has limits. RM did a good job as far as he went, but the conditions and limitations of his experiment mean that his results are only valid in a limited set of circumstances. I suggested one such limitation to him in a letter before he published the article; perhaps if he had included it in the article it would have been an improvement. KH also raises some valid objections, about the instrument itself, for example. These are real issues, and all of them could be addressed.

The way to address them would be to do a better experiment.

We're not trying to tamp down dissent here, or create a 'new fundamentalism'. We're trying to understand how these things work, and why people like some better than others. Instead of kvetching in the letter column KH, or anybody else, could simply do a better experiment, and show why RM is wrong. I'll put in a warning, though: NOTHING is more time-consuming than science.

I'll also let everybody in on a little secret: if you do want to do that experiment, the first person you should get in touch with is RM Mottolla, and right after that you should e-mail me: we'll both be happy to help. Once you get it done, send it along to Tim at GAL headquarters, and he'll be happy too.

Of course I can't disagree with you, Alan, you have the most thoughtful, even tempered reasoning of any one I've ever conversed with.

My broad impression of KH's criticism, if it is that, is a questioning of the whole matter of trying to nail down with scientific study any aspect of a subjective thing, such as tone. He could have done that with one sentence like I just did, but I guess felt obligated to drag it out.

I think you know in which camp I am, as if it mattered, that of "tone study" is best left to those who are in that other camp, I hardly have enough time to build the next guitar, much less fiddle around with something that, at best, would give me manual dexterity practice.

I love to read the letters and articles the other camp publishes about their experiments. The numbers and graphs are mostly lost on me, but I do carefully read the introduction and summary.

One day, I will have to put a sound port in one of my guitars. I imagine it will be elliptical, on the upper bass bout, facing the player, and about 1 1/2" x 4". I like the look of John Monteleone's. I have no doubt it will affect the player's heard tone.

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