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I am curious about the opinions people have about the pros and cons of leaving soundboards on steel string guitars flat. I know of several respected builders who do not put a radius to them. In the past I have used a 25 foot radius dish for them, but am considering trying a truly flat flat top. I've been happy with the sound I've had with the radiused tops, but I'm curious about other ways of doing things.

It's a different tone. Go for it.

Mario, I know the reason of humidity and seperation for back and assumed (not a good thing sometimes) same reason for top, is there not a that much of a problem with tops relative to seperation and cracking whatever one wants to call it. I have used 60ft on several and have been really thinking of going to that. I know a guy that does them all flat and he always had problems, but I think that was his fault in build and then display with it hot and dry all the time then into 60-70% humidity and then back to hot and dry for several days to weeks at a time.
What kind of tone change does it give?

many fine vintage guitars are true flat tops. many builders stilll build steel string as flat tops. While true that dome construction does add strength. I read someone who said "a well built flat top in infonatly better tha any poorly built dome top." The point was that failure does not come from the fact the top is domed or flat. I comes from poor construction.

I would imagine that doming it makes for more of a treble response, and truly flat tops would have more bass response. Is this correct? Are there other ways that the tone would be shifted?
I think I recall Kevin Ryan saying his tops were truly flat at last year's ASIA symposium. I heard one of his guitars, and it was just great.

Huss and Dalton on their web site mention that on the non-traditional HD models that they dome the top which they say enhances the midrange.

The only problem that I had with a true flat top is the break angle of the fingerboard where it joins onto the guitar....If I ever do it again (which I doubt) I would put a decorative wedge in between the fingerboard and the top.....Sounded good though....Larry

I only make true flat tops.

You cut the angle into the rims to set the neck properly. So there is an angle from the top of the sound hole forward but it's flat.

I don't see any issue with humidity or strength with a true flat top guitar. The doming of the top is not required to resist the pull of the strings, proper brace placement and size does this. Extreme humidity changes will effect any guitar, radius top or flat. Maintaining RH after the guitar is finished is just as important as while building.

Like Mario says, a true flat top gives a different tone. Try it out, I love the tone of a true flat top.

Olson, Ryan and Hoffman have been building true flat tops for well over 20+ years each respectively (more in Hoffman and Olson's case, maybe Ryan too).

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Rod,

Are the tops still truly flat after the guitar has adjusted to string tension (say 6 months to a year down the road)? So if you put a straight edge across the guitar just behind the bridge it would still be flat on the top everywhere?

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Ohfercryinoutloud..... A little common sense, please.

If you build with flat braces on a flat top, it's a flatop, no matter what happens with time and string tension.

Ohfercryinoutloud..... get back in yer pram grumpy with the other six. Did I say it wasn't a flat flat top???

Rod - it was a serious question. You might find this post on the UMGF interesting - it's mainly talking about backs but but also has some interesting stuff on old Martin and Gibson tops - flat or otherwise. Warning it's long (that's truly long) but interesting (thats truly interesting).

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". . . the one thing a machine just can't do is give you character and personalities and sometimes that comes with flaws, but it always comes with humanity" Monty Don talking about hand weaving, "Mastercrafts", Weaving, BBC March 2010

Dave, the pull of the strings certainly raises the top, I'd say about 1/16" at the most. And of course without strings it goes back to being flat.

I'll take a look at that read UMGF, thanks.

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Sorry Rod my friend I couldn't resist........... If you were employed as a weatherman would you predict scattered patches of darkness tonight diminishing toward morning with scattered patches of light?

I know..... shut-up Hesh.........

Ya, I was kind of thinking that second part was redundant

As for your second remark/question, I'll only answer that question live and in person in Toronto on Friday night. Want the answer, get your a$$ on the train

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Rod, do you have a particular process for putting the angle into the rims? Anything specific to keep the angles consistent?

Yes Craig I do.

I'll dig around in the archives as Paul Woolson asked this question a couple years ago.

here's one discussion on it

here's my tutorial of sorts

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As to my question, what does it do with the tone or sound. I have no problem with flat top or radii in top. I just was wondering about the change in tone or whatever as opposed to radius top from flat.

I was just thinking/wondering, if flat is different than say 22ft, how much could one mess with anywhere from flat to 15ft and change tones as a design thing and what the GENERAl change is. Guess it is time to get with the different builds and see and go from there.

I know the 60ft top I have is "thinner or brighter" to my ear anyway, than the one with 22ft top. But then again they are of different woods, and the bracing scheme is much different. The 15 is deeper and more bass, I guess a fuller sound. Is that the general change, if built same woods and bracing would the flat be brighter than the 15?

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Stan the higher the number of the radius the closer it is to being flat.. a 15' radius will be more arched than a 60' . I just posted because I thought you were thinking the other way ..if not just ignore me as I am rambling ... Jody

Well Stan, I'll give you my understanding of the flat/radius tone differences, although admittedly I might be talking out of my arse.

Anyway, some assumptions first. Making two guitars of the same materials and size, top plate of the same stiffness (measured by some means of course) and the braces being of the same stiffness (also measured by some means) and than both sets of braces carved to the same stiffness, attached with the same glue etc... (trying to eliminate any potential for differences here).

Now the radius'd top will have slightly more tension IMO, although the brace gluing surface is arched, the top plate isn't and it wants to pull back to flat even though the braces are arched. Now the brace is stiffer than the top plate and will generally hold the plate in it's arched position. So with slightly more tension the guitar should sound tighter (kind of like a drum or a string under tension). Now the top which is not radius'd will not have any tension because the plate is already in it's natural plane. The guitar should sound looser (again like a loosely pulled drum head or a string under less tension).

Of course you'd really have to build two identical (and I mean highly identical) guitars but with differing tops (radius'd and truly flat) in order to determine the differences in tone. Now any difference in top plate stiffness, brace stiffness and I think you can't attribute much of the difference in tone to the arch or flatness of the top. I also think that the tone of the guitar can be more easily tuned by the shape and carving of the braces.

Pick a method (flat or arched) and try different brace designs, size and stiffness. The tone will change between each variance in design.

Like I said at the beginning though, this is my limited understanding and I may well be talking out of my butt

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Regarding cutting the angle into the upper bout for the proper neck set-I've been using a jig that has proved quite accurate for me. It should work fine for either a flat top or a top with a radius below the soundhole and flat above which is what I do. Hopefully this link will get you to a description.

http://kennedyguitars.com/%20Kennedy%20 ... 20Jig.html

Terry

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Rod, the tension imposed on the top plate by flexing it into a small arch is really minimal. The much bigger issue is the stiffness inherent in the arch shape vs. flat. But even if you built an arched top that was more lightly braced and similarly stiff, I've come to believe that they would still sound different, probably due to the way they want to move. That's just theory but it's based on a bunch of practical experience.

Also, you say that the brace holds the top in an arch because the brace is stiffer. That's not quite right. Take two pieces of wood the same size and glue them together bent into a dished form and they will stay bent. Glue an arched brace to a flat top on a flat surace and it will come out pretty flat. They may spring back a bit but, like any bent lamination, they will basically want to hold that shape.

In my experience, a warm, open sound is more inherent in a flatter top and an articulate, bright sound is more inherent in rounder tops. But that's just one variable and warmth can obviously be had in domed tops and brightness can be had in flat tops. It's just one more thing to play with.

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Yes Kent, I agree that the tension imposed on the top plate by flexing it into a small arch is minimal. I do agree also that the stiffness of an arched shape is greater then that of a flat shape. Again though, we are talking about such a small arch that the difference in stiffness between the two is also very minimal. If we could build two guitars with the exact same components of the exact same properties we would produce two guitars that would sound different, and that would be the difference in the stiffness caused by the arching of the top and the stiffness of the flat top. I agree again that the arched top would be marginally stiffer, by how much though, I have no idea.



This of course depends on the stiffness of the two pieces being glued together, the shear strength of the glue holding them together and the size of the arch. The two pieces which were flat and glued together in a dish will not hold the same arch of the dish, rather they will be somewhat flatter because the two pieces want to hold their original shape. Now glue three or more pieces together and you start the laminating process where the glue line starts to add more shear strength to the shape of the pieces. Use a glue that is notorious for creeping and over time the pieces will flatten out somewhat (depending on the size of the pieces and their inherent stiffness of the pieces before the stress of arching them were induced). This of course is all of minimal dimensions but still happen.

When I worked at the cabinet shop, we made lots of curved desk fronts and we used a minimum of 5 ply's glued up in the arched shape. I was told that the lamination of multiple thin pieces glued in the arched shape was what held the shape. We also used the crazy brown glue (some sort of animal glue) that cured incredibly hard.

Two thin pieces have in of themselves little stiffness. And of course we've talked about the cubed rule allot and how adding height increases the strength of the brace. Take a 1" thick flat piece and glue a 1/2" curved brace to it and yes, the brace will conform to the flat surface, and visa versa.



I also agree with you here Kent. It's all part of the system. Take a heavily braced flat top and it will sound bright and tighter, on the other hand, lightly brace a flat top and it will sound more open and warm.

I honestly think it has more to due with the bracing than it does with the arch or lack of same of the top.

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It's a matter of preference. I know folks like Olson build great guitars and I've played quite a few of them. I've never found one that I personally considered outstanding though. The few Hoffmans and countless other true flat tops I've usually felt the same about, though there have certainly some that have really shone through to me (one of Ryan's I found particularly exceptional). Again, it's not better or worse, it's personal preference. I would take a 30's AJ with the massive Gibson radius over a much flatter D-28 or D-18 just about any day.

Describing the tone is almost futile - as many know I'm rather fed up with trying to make subjective, metaphorical descriptions of tone with words that will mean totally different things to different folks. Of domed tops, I may say they project in a more focused way, more clarity and shimmer, tighter - not as much boom and midrange, maybe a bit less force on average, not as open, but can still a nice, warm, more focused punch to the low end. My words, my observations, my preferences. Someone else may apply the same descriptions to the opposite instruments, and it would be just as valid as my own. Now I can certainly see and understand why a flat top would be more appealing to players and styles other than my own, but I like a fairly steep dome.

As to structure and stability, I would say the compound radius certainly adds a different strength and stiffness to the top. It may not be an enormous difference, bus still I would not be comfortable bracing or scalloping a true flat top quite so lightly as I may a steep radiused top, both for tonal and structural reasons. As to stability, well, I'm not sure I would say arched will move less than flat, but with a crown you will have a much wider buffer zone before cracks occur should it get dry. The action will drop and it will start to buzz like mad, but it will be less likely to sink inward and/or split. I find domed tops easier to coax in to recovery if they suffer from dryness as well.

The impact of soundboard's crown on tone in pianos is an excellent example, and has been common since at least the early-mid 19th century. The piano maker I work with intentionally leaves his boards flat though, both for reasons of tone and historical accuracy. You can often find demo soundboards in piano shops to show the crown's impact on tone. Typically a tuning fork mounted to a small rectangle of spruce, which is mounted to legs that can be squeezed in to arch the board. The change in tone and volume is quite incredible to see in real time. Of course these demo boards are an extreme dramatization, as it's an unbraced piece of spruce that is shifted from flat to an incredibly exaggerated arch to demonstrate, but it's interesting none the less.

If you really want to know, build a few guitars in batches of two at a time. If possible use consecutive cuts of wood and as close construction as you can manage, but with one crowned and one flat. Obviously there will not be perfect controls, but even doing one pair you might gain some good insight. Build a couple pairs and you may see enough in trends to be more an authority on the topic than most others.

Different strokes.... A guitar can be incredible to some, but just not be for me. And like I said, there are some true flat tops that I've found incredible, but on the whole I go for the heavy dome.

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I've done just that as well as subbing out a flat top for a domed top on the same test body. That's what my observations were based on.

For what it's worth, I also do as someone else suggested and brace my flat tops at a lower humidity to help with the going concave issue. I recently took my test body (with a fairly flat top) with me to Arizona. The top is unfinished and one night I went to bed forgetting to put the guitar back in the case. 10% humidity. In the morning, the top was quite concave and the strings were resting on the fingerboard. No cracks but it sure looked ugly. Fine now though.

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