F-512 Belly Bulge?

[Rayk]

All quality acoustic guitars have a radiused top, as stated above. Even if you go to a guitar shop, take a brand new, just out of the box decent, or better, quality guitar, the top will have a curve to it (i.e. radius). If you were to take all of the strings off, the top will still have a curve to it. So will the back. It is the way acoustic steel string guitars are made.

I cannot say anything for or against Saga guitars, as I have never seen one in person, nor heard one. But I would sincerely doubt that they are completely flat topped guitars, as measured with a straight edge laid across the lower bout. There are so many problems induced by a completely flat top that it makes it almost impossible to create a structurally stable steel string guitar. Not that it can't be done if you want to go out of your way to do it; with enough top thickness and heavy enough bracing, you can do anyting you want, but it won't be anything anybody would want to listen to.

I can take a pic of the Blueridge as the straight edge is flat across its surface .
I’ll also check my other models .

Saga says what Saga says ! Lol

Here’s the link to Ryan guitars anyone is free to ask him if he made flat top acoustic guitars 10 yrs ago as of now his site only mentions the back being so .

Over all it makes sense to build radius tops and backs so it would be in any mass produced companies interest to build this way to prevent future or near future issues along with custom builders .

I’ll take some pics after work .

Edit : found this post from Tom rest in peace bud .

Tom Doerr Registered User Join Date: Feb 2012 Location: Saginaw, Michigan Posts: 247

To my knowledge Ryan, Olson, Charis are all flat tops. Traugott, Somogyi and myself radius the tops. I personally use 30' pretty much the same reasons why Petros does it. __________________ Tom Doerr

 

[adorshki]

I can take a pic of the Blueridge as the straight edge is flat across its surface .
I’ll also check my other models .

Saga says what Saga says ! Lol

Here’s the link to Ryan guitars anyone is free to ask him if he made flat top acoustic guitars 10 yrs ago as of now his site only mentions the back being so .

Over all it makes sense to build radius tops and backs so it would be in any mass produced companies interest to build this way to prevent future or near future issues along with custom builders .

I’ll take some pics after work .

Edit : found this post from Tom rest in peace bud .

​

Tom Doerr Registered User Join Date: Feb 2012 Location: Saginaw, Michigan Posts: 247

To my knowledge Ryan, Olson, Charis are all flat tops. Traugott, Somogyi and myself radius the tops. I personally use 30' pretty much the same reasons why Petros does it. __________________ Tom Doerr

What's the bracing pattern on those? Ladder? Top outline size (are they smallbodies)?

 

[Rayk]

What's the bracing pattern on those? Ladder? Top outline size (are they smallbodies)?

My blues are a dread a OM and a jumbo

 

[Christopher Cozad]

Most has been said, but I believe I can add a little more to this discussion...
It is very uncommon (and has been for a very long time) to build a steel string acoustic guitar with a perfectly flat top. Nylon string? Yes. Steel string? No.
Why? To counteract the forces acting to fold the average steel string acoustic guitar in half, an undesirable amount of structural support must be added, which has a devastatingly negative impact on tone.
Consider a bridge: a perfectly flat bridge will tend bow downward under its own weight, let alone after adding the weight of pedestrians, cars, etc. to it. Flat bridges require much structural under girding. By deliberately radiusing (arching) the surface, the span is exponentially strengthened without requiring additional support.
Consider a soundboard: a perfectly flat guitar top will require a lot more bracing to keep it from collapsing downward, inward, toward the back, under tension of the strings. Extra bracing adds unnecessary weight and the soundboard runs the risk of having the tonal equivalent of a rubber band stretched across a 2 x 4. By deliberately radiusing (arching) the board, it becomes significantly stronger without having to add more bracing support.
How much radius is added?
Imagine a large circle, 50 feet in diameter (from one edge to the other, as measured through the center point using a straight line) . Its edge is curved. That curve is measured as the distance from the outermost edge to the center of the circle, half the diameter - or - its radius. Our 50 foot circle has a 25 foot radius, and this just happens to be a very commonly used measurement when building soundboards today. A 30 foot radius would use the curvature of a 60 foot circle, and so on. The radius of a guitar back is typically tighter (based on smaller circles), such as a 15 or 20 foot radius (30 or 40 foot circle, respectively).
The "flattop guitars" of old, such as the 1970s Guild acoustics, all had radiused soundboards and backs. But the radius was "flatter" than is commonly seen in today's guitars, based on the curve of a larger circle. Every soundboard I have removed from guitars of that era lays nicely without rocking or flexing into my 52 foot radius dish.
My mentors taught me that "flatter is louder". That does *not* translate into "build a perfectly flat soundboard". What it did eventually translate to in my shop was to use a much larger radius (100 foot circle) which is a "flatter" curve. I started with a 25 foot radius, then began to "flatten" those tops over time. I learned to strengthen the bracing, accordingly, without sacrificing tone. Today I use a 52 foot radius for most all my guitars. There is definitely an "arch" in all my guitar tops, and an even more visible arch in my guitar backs. These guitars are lightweight and very, very strong - without being so overbuilt (to prevent collapse) that they sound dull and lifeless.
I would accompany Kostask, saying "All steel string acoustic guitar soundboards are radiused", adding that some are much "flatter" radii than others.

 

[wileypickett]

Most has been said, but I believe I can add a little more to this discussion...
It is very uncommon (and has been for a very long time) to build a steel string acoustic guitar with a perfectly flat top. Nylon string? Yes. Steel string? No.
Why? To counteract the forces acting to fold the average steel string acoustic guitar in half, an undesirable amount of structural support must be added, which has a devastatingly negative impact on tone.
Consider a bridge: a perfectly flat bridge will tend bow downward under its own weight, let alone after adding the weight of pedestrians, cars, etc. to it. Flat bridges require much structural under girding. By deliberately radiusing (arching) the surface, the span is exponentially strengthened without requiring additional support.
Consider a soundboard: a perfectly flat guitar top will require a lot more bracing to keep it from collapsing downward, inward, toward the back, under tension of the strings. Extra bracing adds unnecessary weight and the soundboard runs the risk of having the tonal equivalent of a rubber band stretched across a 2 x 4. By deliberately radiusing (arching) the board, it becomes significantly stronger without having to add more bracing support.
How much radius is added?
Imagine a large circle, 50 feet in diameter (from one edge to the other, as measured through the center point using a straight line) . Its edge is curved. That curve is measured as the distance from the outermost edge to the center of the circle, half the diameter - or - its radius. Our 50 foot circle has a 25 foot radius, and this just happens to be a very commonly used measurement when building soundboards today. A 30 foot radius would use the curvature of a 60 foot circle, and so on. The radius of a guitar back is typically tighter (based on smaller circles), such as a 15 or 20 foot radius (30 or 40 foot circle, respectively).
The "flattop guitars" of old, such as the 1970s Guild acoustics, all had radiused soundboards and backs. But the radius was "flatter" than is commonly seen in today's guitars, based on the curve of a larger circle. Every soundboard I have removed from guitars of that era lays nicely without rocking or flexing into my 52 foot radius dish.
My mentors taught me that "flatter is louder". That does *not* translate into "build a perfectly flat soundboard". What it did eventually translate to in my shop was to use a much larger radius (100 foot circle) which is a "flatter" curve. I started with a 25 foot radius, then began to "flatten" those tops over time. I learned to strengthen the bracing, accordingly, without sacrificing tone. Today I use a 52 foot radius for most all my guitars. There is definitely an "arch" in all my guitar tops, and an even more visible arch in my guitar backs. These guitars are lightweight and very, very strong - without being so overbuilt (to prevent collapse) that they sound dull and lifeless.
I would accompany Kostask, saying "All steel string acoustic guitar soundboards are radiused", adding that some are much "flatter" radii than others.

Thank you for this.

Based on what you've seen, does the radius of this guitar (as seen in the first post) seem high to you? I can only compare it to Westerly era 12-strings, which is what I'm most familiar with, but it appears more rounded than those. But I have no idea what radius Guild might have been building into their guitars in 2021.

 

[Christopher Cozad]

It certainly appears to be more curved than the 12 string Guilds of yesteryear. Like you, I am unfamiliar with recent production models. But, as you rightly identified in your first post, "bellying" is distinct from "radiusing". Which are we seeing, or are we seeing both?
Those mentors of mine also taught me "No belly, no tone". I subsequently began to think about that prime real estate of the soundboard, the beachfront property of the lower bout behind the bridge, like the fuel bladders in the wings of the SR-71. You know how the wings droop so low when the plane is taxiing such that wheels are necessary to prevent the wingtips from dragging the ground. And they leak fuel like a sieve. That is, until airborne (under pressure/under tension), where everything balances out.
Of course it is possible to have insufficient bracing and/or too thin of a soundboard such that the "belly" eventually rips (I have photos - but these are intended for Mature Audiences Only).
Short of such a disaster, so long as the neck metrics are correct and the bridge is of sufficient mass and the saddle is tall enough - and everything is (relatively) stable under string tension, a swollen belly only contributes to the sweet sound that guitar is going to yield.

This guitar looks to me to have a tighter radius (more curve) than the older 12 strings and is showing some bellying (which I don't have an issue with, per se). You addressed the belly test in your post. Overall, it may amount to "more bubble" than we are used to seeing. But it all may be perfectly fine for that instrument.

 

[Rayk]

Most has been said, but I believe I can add a little more to this discussion...
It is very uncommon (and has been for a very long time) to build a steel string acoustic guitar with a perfectly flat top. Nylon string? Yes. Steel string? No.
Why? To counteract the forces acting to fold the average steel string acoustic guitar in half, an undesirable amount of structural support must be added, which has a devastatingly negative impact on tone.
Consider a bridge: a perfectly flat bridge will tend bow downward under its own weight, let alone after adding the weight of pedestrians, cars, etc. to it. Flat bridges require much structural under girding. By deliberately radiusing (arching) the surface, the span is exponentially strengthened without requiring additional support.
Consider a soundboard: a perfectly flat guitar top will require a lot more bracing to keep it from collapsing downward, inward, toward the back, under tension of the strings. Extra bracing adds unnecessary weight and the soundboard runs the risk of having the tonal equivalent of a rubber band stretched across a 2 x 4. By deliberately radiusing (arching) the board, it becomes significantly stronger without having to add more bracing support.
How much radius is added?
Imagine a large circle, 50 feet in diameter (from one edge to the other, as measured through the center point using a straight line) . Its edge is curved. That curve is measured as the distance from the outermost edge to the center of the circle, half the diameter - or - its radius. Our 50 foot circle has a 25 foot radius, and this just happens to be a very commonly used measurement when building soundboards today. A 30 foot radius would use the curvature of a 60 foot circle, and so on. The radius of a guitar back is typically tighter (based on smaller circles), such as a 15 or 20 foot radius (30 or 40 foot circle, respectively).
The "flattop guitars" of old, such as the 1970s Guild acoustics, all had radiused soundboards and backs. But the radius was "flatter" than is commonly seen in today's guitars, based on the curve of a larger circle. Every soundboard I have removed from guitars of that era lays nicely without rocking or flexing into my 52 foot radius dish.
My mentors taught me that "flatter is louder". That does *not* translate into "build a perfectly flat soundboard". What it did eventually translate to in my shop was to use a much larger radius (100 foot circle) which is a "flatter" curve. I started with a 25 foot radius, then began to "flatten" those tops over time. I learned to strengthen the bracing, accordingly, without sacrificing tone. Today I use a 52 foot radius for most all my guitars. There is definitely an "arch" in all my guitar tops, and an even more visible arch in my guitar backs. These guitars are lightweight and very, very strong - without being so overbuilt (to prevent collapse) that they sound dull and lifeless.
I would accompany Kostask, saying "All steel string acoustic guitar soundboards are radiused", adding that some are much "flatter" radii than others.

So what’s the limit as to seeing or not seeing a radius on a top and or using a straight edge to detect it ?

 

[Christopher Cozad]

Excellent question, Ray. How much radius is too much? How much belly is too much?

I am of the camp that says so long as the instrument is stable (no loose braces, the board in front of the bridge isn't ploughing down into the soundbox, the back of the bridge isn't ripping loose, the wood behind the bridge isn't tearing (forward belly) or splitting (belly side-to-side), and it sounds good (I know, that is pretty loosey-goosey), then the guitar is probably fine.

I am going to lay out several guitars, different makes and models, and take measurements, both with strings under tension and strings loosened. I'll post the results.

 

[Rayk]

Excellent question, Ray. How much radius is too much? How much belly is too much?

I am of the camp that says so long as the instrument is stable (no loose braces, the board in front of the bridge isn't ploughing down into the soundbox, the back of the bridge isn't ripping loose, the wood behind the bridge isn't tearing (forward belly) or splitting (belly side-to-side), and it sounds good (I know, that is pretty loosey-goosey), then the guitar is probably fine.

I am going to lay out several guitars, different makes and models, and take measurements, both with strings under tension and strings loosened. I'll post the results.

Well I guess for others that’s great info . I want to know at what point will you not be able to see a guitars radius .

So I can physically see a radius on tops but some are much harder to see . if we/I use a straight edge and there’s no noticeable deflection ( is that the right word ? ) then what would the radius be .

Also laying a straight edge across the backside of the bridge especially under string tension would add numbers to said radius or to one that may not have a said radius right ?

 

[Nuuska]

Also laying a straight edge across the backside of the bridge especially under string tension would add numbers to said radius or to one that may not have a said radius right ?

Steeper curve means smaller numbers - other than that you're right.

If you put the straight edge behind the bridge so that it has equal gap on both edges - and measure the gap and width of the bout at said line - you can calculate radius using this formula.

X = ( a2 - b2 ) : 2b

X = radius
a = half of the width of bout
b = gap at edge of bout

 

[kostask]

The Dana Bourgeois article mentioned a few things that I should have put into my post (#19), above.

-I made the assumption that this was a wood guitar. Composite (i.e. carbon fibre) topped guitars may not have or need a radiused top.
-I also glossed over the obvious point that I was talking about an acoustic guitar that was in good shape. A severely dried out guitar may indeed have a truly flat top, but that is something that is to be avoided, because top cracks will soon be developing, along with other possible structural issues (loose braces, bridges coming unglued, etc.) Most likely, it won't sound good, and will have crazy fret buzzing as well.

 

[Rayk]

Steeper curve means smaller numbers - other than that you're right.

If you put the straight edge behind the bridge so that it has equal gap on both edges - and measure the gap and width of the bout at said line - you can calculate radius using this formula.

X = ( a2 - b2 ) : 2b

X = radius
a = half of the width of bout
b = gap at edge of bout

Yeah Ray speak activated ! Lol I’m not interested in what the radius is . I’m just trying identify that’s it’s there .

I might be wrong but I’m thinking that the center of a radius top is between the bridge and tail block not at the bridge or just behind it.

In the case of a guitar actually having a flat top using a straight edge behind a bridge under tension would/could show a hump implying a radius .

Otherwise my other question was to ask what radius would not be detected by a straight edge or by eye ?

 

[Christopher Cozad]

... I’m thinking that the center of a radius top is between the bridge and tail block not at the bridge or just behind it.

During construction of a wooden steel string acoustic guitar, a solid wood soundboard is laid, face down, into a very shallow concave wooden or metal "bowl" or "dish" and the braces (pre-shaped to conform to the curvature the bowl) are glued and clamped in place. That dish has been hollowed out to a pre-determined curvature for just such a purpose. When the glue dries and the clamps are removed, the board retains the curvature of the dish, now a convex curve when viewed from the front/face/top of the soundboard. The word "radius" simply refers to a measurement of how much curvature is pre-determined for that soundboard.

In the grand scheme of things the curvature isn't a lot. But it is enough to assist in keeping the top from collapsing while keeping the bracing as light as possible/practical. Everyone uses some curvature/radiusing, but not everyone uses the same curvature/radiusing.

For most X-braced acoustic guitars, the "center" of a radiused top is a point just behind the X-brace. On the front face of the soundboard, this translates to a point just in front of the bridge, not behind it.

The entire soundboard inherits the curvature/radius, however, due to the nature of X-brace design, and there being a massive section of structural material removed (called the "soundhole"), the surface area between the front of the bridge and where the neck joins the body (beneath the fretboard extension) ends up being much less curved (it is "flatter") than the area behind the bridge, once the guitar is assembled.

When the strings are attached and under tension, the bridge "rocks" forward, slightly. Because the cross of the X-brace is right there in front of the bridge, the front edge of the bridge is prevented (hopefully) from ploughing down toward the back. The area of the soundboard between the tailblock and the front of the bridge is tightened, stretched, and pulled upward. The amount of that upward movement above and beyond the pre-determined curvature is referred to as "bellying."

"Bellying" on top of (in addition to) the built-in, pre-determined curvature is what most of us are witnessing when we do the straightedge test. Adding to what Kostask already said regarding the condition of a guitar, "bellying" may be more noticeable in one guitar than another. In some cases, "bellying" may not be reduced (much, or even at all) after loosening the strings. "Bellying" is not radiusing, though it adds to the visual "bubble" we see, mostly visible in the lower bout. "Bellying isn't a bad thing, per se.

The center of the "Belly" would be at a point behind the bridge.

In the case of a guitar actually having a flat top using a straight edge behind a bridge under tension would/could show a hump implying a radius .

I am unaware of any modern guitars that have been deliberately built having a perfectly flat top. There is always a pre-determined curvature/radius, albeit very slight. It should be visible by laying a straightedge across the lower bout of an unstrung guitar, directly behind the bridge and perpendicular to the centerline that runs from the headstock to the tailblock. When viewing a radiused top, the straightedge should be "high-centered" behind the bridge. It should rock, as in, it should not lay flat. It should not touch both binding edges.

Otherwise my other question was to ask what radius would not be detected by a straight edge or by eye ?

None, to my knowledge. If you can lay a straightedge across an acoustic guitar soundboard and detect no radius whatsoever, especially in the lower bout, I would suggest you have discovered either a damaged guitar or one built by an unconventional pioneer.

 

[Prince of Darkness]

Out of interest I took a straight edge and did some measurements on my F-240E. Measured just behind the bridge, there is a drop of about 5mm between the centre and the edges. With the straight edge place lengthways, there is no discernible drop from the 14th fret position to the bridge, but there is another drop of about 5mm by the lower edge of the body.
The structural issues associated with curvature, or the lack of it, also apply to the back, which is why Guild archbacks (much more curvature than any "flat" top) require no bracing, but flatbacks, whether solid or laminate, do

 

[Christopher Cozad]

Out of interest I took a straight edge and did some measurements on my F-240E. Measured just behind the bridge, there is a drop of about 5mm between the centre and the edges. With the straight edge place lengthways, there is no discernible drop from the 14th fret position to the bridge, but there is another drop of about 5mm by the lower edge of the body.
The structural issues associated with curvature, or the lack of it, also apply to the back, which is why Guild archbacks (much more curvature than any "flat" top) require no bracing, but flatbacks, whether solid or laminate, do

What you are seeing is common for most X-braced acoustic guitars. If you lay your straightedge along the side of the fretboard and push it up to the bridge, ideally, there *should* be no light showing between it and surface of the guitar - it is expected to be flat along that plane. I have a high-end Taylor that is not flat; the front plate (soundboard, top, face) drops down into the box away from the straightedge. This does not necessarily guarantee an impending implosion; in fact, it may stay stable in its current position for another 30 years. But, then again, it may not; it may continue to implode. The whole point of the X-brace is to prevent such a collapse.

Pre-formed archbacks, as well as carved archtops, do not typically require any bracing, just as you have said. That convex curvature is intended to provide the structural strength necessary to mitigate collapse. These are pretty cool designs.

I have not come across any acoustic guitars having perfectly flat back plates, including those that are commonly "ladder" braced (where 3 to 4 heavy braces are spaced somewhat equidistant down the back, and perpendicular to the centerline). The backs of these guitars typically have even more convex curvature (a "tighter" radius) than their respective fronts do (not counting the "bellying" bubble effect). And yet, as you have pointed out, they most certainly require bracing. It is the (pre-shaped, curved) bracing that "shapes" them into that curvature. Check both planes, both down the centerline (from the neck heel to the tailblock), as well as across the back perpendicular to the centerline. I would be surprised if you detect no convex curvature whatsoever.

 

[wileypickett]

Thanks for taking the time and trouble to explain all this to us Christropher!

 

[Westerly Wood]

What's wrong with a large belly? Jim Morrison would be ok of a little, even a larger belly bulge...

 

[Christopher Cozad]

Thanks for taking the time and trouble to explain all this to us Christopher!

You are most welcome, Glenn.

I was that kid that disassembled his parents expensive Magnavox mahogany console stereo because he wanted to understand "how" it worked. What I did learn was that such an education can be very costly (my dad was an "old school" cop). But I was not deterred. I learned how to put things back together, again (I had tremendous motivation to learn quickly). I paid the price(s) and kept taking things apart, graduating to experimenting in order to "improve" them. My earliest efforts were definitely not improvements, but I got better as I grew older. Once I discovered that there were a lot of folks out there who knew things I didn't, I wasted no time gleaning everything I could from those that were willing to share. I ended up concentrating on a few topics that were of particular interest to me, one being acoustic guitar construction. I figured everybody wanted to know what I was learning, so I taught what I knew - whether they asked, or not. LOL Eventually, that became a habit. Now, it's just what I do.

 

[Rayk]

During construction of a wooden steel string acoustic guitar, a solid wood soundboard is laid, face down, into a very shallow concave wooden or metal "bowl" or "dish" and the braces (pre-shaped to conform to the curvature the bowl) are glued and clamped in place. That dish has been hollowed out to a pre-determined curvature for just such a purpose. When the glue dries and the clamps are removed, the board retains the curvature of the dish, now a convex curve when viewed from the front/face/top of the soundboard. The word "radius" simply refers to a measurement of how much curvature is pre-determined for that soundboard.

In the grand scheme of things the curvature isn't a lot. But it is enough to assist in keeping the top from collapsing while keeping the bracing as light as possible/practical. Everyone uses some curvature/radiusing, but not everyone uses the same curvature/radiusing.

For most X-braced acoustic guitars, the "center" of a radiused top is a point just behind the X-brace. On the front face of the soundboard, this translates to a point just in front of the bridge, not behind it.

The entire soundboard inherits the curvature/radius, however, due to the nature of X-brace design, and there being a massive section of structural material removed (called the "soundhole"), the surface area between the front of the bridge and where the neck joins the body (beneath the fretboard extension) ends up being much less curved (it is "flatter") than the area behind the bridge, once the guitar is assembled.

When the strings are attached and under tension, the bridge "rocks" forward, slightly. Because the cross of the X-brace is right there in front of the bridge, the front edge of the bridge is prevented (hopefully) from ploughing down toward the back. The area of the soundboard between the tailblock and the front of the bridge is tightened, stretched, and pulled upward. The amount of that upward movement above and beyond the pre-determined curvature is referred to as "bellying."

"Bellying" on top of (in addition to) the built-in, pre-determined curvature is what most of us are witnessing when we do the straightedge test. Adding to what Kostask already said regarding the condition of a guitar, "bellying" may be more noticeable in one guitar than another. In some cases, "bellying" may not be reduced (much, or even at all) after loosening the strings. "Bellying" is not radiusing, though it adds to the visual "bubble" we see, mostly visible in the lower bout. "Bellying isn't a bad thing, per se.

The center of the "Belly" would be at a point behind the bridge.



I am unaware of any modern guitars that have been deliberately built having a perfectly flat top. There is always a pre-determined curvature/radius, albeit very slight. It should be visible by laying a straightedge across the lower bout of an unstrung guitar, directly behind the bridge and perpendicular to the centerline that runs from the headstock to the tailblock. When viewing a radiused top, the straightedge should be "high-centered" behind the bridge. It should rock, as in, it should not lay flat. It should not touch both binding edges.



None, to my knowledge. If you can lay a straightedge across an acoustic guitar soundboard and detect no radius whatsoever, especially in the lower bout, I would suggest you have discovered either a damaged guitar or one built by an unconventional pioneer.

Ok got ya , thanks

 

[Rayk]

Oh hear some quick picks of the Blueridge . At the bridge which is lifting and needs a reset there’s a slight hump behind the bridge over all its relatively flat but there is no string tension as they are removed because of the bridge coming up . I used a level as it was longer than my straight edge . Lol zoom in if ya can .

Oh my other 2 blueridges do have a radius top though not overly noticeable. The jumbo is 2010 , the dread 2014 and OM is 2016 .