Luthiers - where/what is the actual "blueprint" of a dreadnought?

[Zion33]

When I think of a guitar I imagine what's in the picture on the right yet when I examine my real guitar I see what's on the left, this looks like a complex design and I'm just wondering what the logic to it is, where are the plans showing the measurements of this design etc? it seems highly complex, almost like an piece of art, the ol' dreadnaught is more like an arch-top than is perceived..

[JonWint]

If you look at guitars and plans of guitars, you will notice that modern flat top guitars don't have flat tops. The backs are even less flat.

Logic is to provide strength while minimizing weight. An arch top is carved.

http://www.lmii.com/products/media-g...lypage-noimage

I'm not a luthier.

[Alan Carruth]

There's a lot of discussion about whether it's better to make a guitar with a really 'flat' top, or to dome it. There are those who contend that truly flat tops sound better. They tend to feel that the stress built into a domed top hurts the tone.

In reality, once you put the strings on, almost any guitar top will pull up slightly, particularly behind the bridge, of course. It has been pointed out that guitars with strings tend to sound better than guitars without them, and once you tighten the strings there is stress on the top, and 'way more than what's built in by doming them, so the stress of building in a dome might be moot.

If you build in a dome of some sort there is lots of discussion about just what sort to use, and where. Again, there is a wide range of opinion about this. It seems to follow the general rule of thumb that says that the less actual data there is to back any opinion up, the more strongly it will be held.

Aside from it's effect on tone, many people feel that doming the top confers a structural benefit, in that domed tops are said to be more resistant to cracking in low humidity conditions. When a domed top dries out it tends to flatten, and may not crack until it actually flattens out. With luck, it might take a while to get that far.

So far as I know, backs are almost never made flat. Some makers, particularly in the Classical tradition that works on a 'solera', leave the edge of the rim flat, but dome the back plate. The geometry of this is tricky to get right without leaving a 'dimple' in the waist, but it can be done.

These days most folks use a uniform large radius dome, typically about 25' on the top and 15' or so on the back. The doming on the top is often flattened out above the sound hole to facilitate fitting the neck and fingerboard.

If you use a spherical radius dome on the top and back the actual shape of the side profile is fairly complex, but subtly so. It's the intersection of a sphere with a guitar outline, complicated by the fact that the body depth tapers toward the neck end. In fact, if you measure the height of the side it can be pretty uniform all the way from the tail block around to the waist, and then dip suddenly to the neck, even though, as viewed from the side, the taper is even.

All of these departures from flatness are 'small', but they're important. I tell my students that the only thing on the guitar that is flat is the headstock surface. In this, guitar making is much more akin to building a boat or an airplane than it is to furniture. Nothing is quite square, flat, or perpendicular to anything else. It keeps it interesting.

[printer2]

Woo-hoo!

The humidity in my house hit rock bottom at about 20% humidity in the winter. I built up a couple of bodies, one maple the other black locust and just checked them with a straight edge. They both domed a bit on the top and back. So I doubt they will have an issue for humidity cracks. I need to do a couple of necks for them.

[Zion33]

Originally Posted by Alan Carruth

There's a lot of discussion about whether it's better to make a guitar with a really 'flat' top, or to dome it. There are those who contend that truly flat tops sound better. They tend to feel that the stress built into a domed top hurts the tone.

In reality, once you put the strings on, almost any guitar top will pull up slightly, particularly behind the bridge, of course. It has been pointed out that guitars with strings tend to sound better than guitars without them, and once you tighten the strings there is stress on the top, and 'way more than what's built in by doming them, so the stress of building in a dome might be moot.

If you build in a dome of some sort there is lots of discussion about just what sort to use, and where. Again, there is a wide range of opinion about this. It seems to follow the general rule of thumb that says that the less actual data there is to back any opinion up, the more strongly it will be held.

Aside from it's effect on tone, many people feel that doming the top confers a structural benefit, in that domed tops are said to be more resistant to cracking in low humidity conditions. When a domed top dries out it tends to flatten, and may not crack until it actually flattens out. With luck, it might take a while to get that far.

So far as I know, backs are almost never made flat. Some makers, particularly in the Classical tradition that works on a 'solera', leave the edge of the rim flat, but dome the back plate. The geometry of this is tricky to get right without leaving a 'dimple' in the waist, but it can be done.

These days most folks use a uniform large radius dome, typically about 25' on the top and 15' or so on the back. The doming on the top is often flattened out above the sound hole to facilitate fitting the neck and fingerboard.

If you use a spherical radius dome on the top and back the actual shape of the side profile is fairly complex, but subtly so. It's the intersection of a sphere with a guitar outline, complicated by the fact that the body depth tapers toward the neck end. In fact, if you measure the height of the side it can be pretty uniform all the way from the tail block around to the waist, and then dip suddenly to the neck, even though, as viewed from the side, the taper is even.

All of these departures from flatness are 'small', but they're important. I tell my students that the only thing on the guitar that is flat is the headstock surface. In this, guitar making is much more akin to building a boat or an airplane than it is to furniture. Nothing is quite square, flat, or perpendicular to anything else. It keeps it interesting.

Okay now I understand, the back is just a cut out of a (very) large sphere, of course doing this predetermines the shape of the sides of the guitar also, well that pretty much explains the back part and the sides too.

One thing I still don't understand about the top is if it's radiused how come the side binding area is still flat and not curvy like the back binding? is it some special radius shape trick? you mentioned it being flattened for the neck joint area so I guess not..

In conclusion I think Newton's laws of physics apply, yes a domed top provides thinner braces but the top is stiffer, a flat top provides a loose vibrating top yet the braces are thicker so you can't win! I truly think this - may as well make it a properly flat top because at least then your neck and bridge will align perfectly without any strange angles to work with, my personal views on that may change but that's how I see it for now.

P.S. Any builders around who could make me a J45-ish thing with a true flat top?

[printer2]

Originally Posted by Zion33

Okay now I understand, the back is just a cut out of a (very) large sphere, of course doing this predetermines the shape of the sides of the guitar also, well that pretty much explains the back part and the sides too.

One thing I still don't understand about the top is if it's radiused how come the side binding area is still flat and not curvy like the back binding? is it some special radius shape trick? you mentioned it being flattened for the neck joint area so I guess not..

In conclusion I think Newton's laws of physics apply, yes a domed top provides thinner braces but the top is stiffer, a flat top provides a loose vibrating top yet the braces are thicker so you can't win! I truly think this - may as well make it a properly flat top because at least then your neck and bridge will align perfectly without any strange angles to work with, my personal views on that may change but that's how I see it for now.

P.S. Any builders around who could make me a J45-ish thing with a true flat top?

The front has a 25' or larger radius so the angle is less and less noticeable at the sides. Also some people sand the sides so the mating edge is at 90 degrees to the plane of the sides. So a top would have a arch to it but would be at 90 degrees at the sides. There are no set rules on how much or where or even if the builder puts in an arch. Martins are in the 40' radius area from what I remember.

Which leads me to clarify my previous post. I built the bodies with the back and top flat, no arch and now that the wood picked up some moisture it introduced an arch. So as long as the braces stay stuck in high humidity I probably will not have to worry about the wood splitting due to the guitar being in a low humidity environment.

[Frank Ford]

Originally Posted by Zion33

In conclusion I think Newton's laws of physics apply, yes a domed top provides thinner braces but the top is stiffer, a flat top provides a loose vibrating top yet the braces are thicker so you can't win! I truly think this - may as well make it a properly flat top because at least then your neck and bridge will align perfectly without any strange angles to work with, my personal views on that may change but that's how I see it for now.

Some quick thoughts:

1. A truly flat top is somewhat less stable than one built under a slight tension (radius, if you will) and can lead to a guitar that is more prone to needing to have its neck reset to maintain suitable action.

2. A truly flat top will tend to look ever so slightly concave, and as the instrument ages, may actually sink a bit, particularly in low humidity. A slight arch in top construction results in a much more pleasing appearance. Same thing with fingerboards - truly flat ones tend to look concave.

3. The folks building today's (and yesterday's) best instruments use the techniques and designs that work. Reading and thinking really hard about the problem is no match for experience in this example.

4. Radius tops don't necessarily have different braces than flat ones.

[Alan Carruth]

The actual stiffness imparted to a top via a 25' radius is probably so small as to be negligible as compared with normal manufacturing tolerances and the variance in wood. It would not make any significant difference in the bracing IMO.

[Bruce Sexauer]

Originally Posted by Alan Carruth

The actual stiffness imparted to a top via a 25' radius is probably so small as to be negligible as compared with normal manufacturing tolerances and the variance in wood. It would not make any significant difference in the bracing IMO.

It may be small, but it makes a huge difference IMO (compared to 50’). NOT negligible. And yes, the bracing looks much the same.

[Otterhound]

I must admit that I am a bit surprised .
Modern speaker designs incorporate the concept of no directly opposing surfaces .
You will find that this practice is used almost universally in instrument building .
While , the technical aspects of this were not measurable centuries ago , it was recognized and put into practice . This is evident in nearly every type of instrument from the modern guitar to the scheitholt , hammered dulcimer , violin , oud , trombone , oboe , clarinet ........ Even the cymbal and tympani drum . At the very least , opposing surfaces are kept to the minimum if not completely avoidable .
Far too much emphasis seems to be placed on the structural aspects with far too little placed on the manner in which sound waves are treated inside of the acoustic chamber .
Directly opposing surfaces create unwanted resonances in acoustic chambers with potentially bad results . Eliminate those surfaces and you have eliminated the problem/s associated with them .
There is a reason other than esthetics that musical instruments are not squares , rectangles and shipping boxes . The exception to this is the solid bodied electric guitar .
Let the slings and arrows fly .
The blueprints that you are referencing exist and are readily available . All you need do is search for them . Of course , these blueprints are subject to being tweaked .
There really are no rules . There typically are self imposed restrictions .

[printer2]

Originally Posted by Otterhound

I must admit that I am a bit surprised .
Modern speaker designs incorporate the concept of no directly opposing surfaces .
You will find that this practice is used almost universally in instrument building .

First arrow. Not so much that it is wrong, I don't know how much effect it would have. The thing with speakers is that they do not want to add coloration into the sound, kill resonances as much as possible. Instruments on the other hand use the resonances to produce their sound.

[redir]

After building about 40 guitars I started experimenting with true flat tops and I can't claim that they sound better but they do sound different. As Alan mentioned the strings pull the top up into an arch anyway. But I think it's the starting point of low stress that does... 'something?'

The trick is to build them very dry, that way they don't stress as much in low humidity. Even on my true flat tops I still arch the UTB and use an A-Bracing system so that the sound hole and forefront of the bridge to the head block is strengthened. But I don't see any necessity to increase the bracing stiffness on a true flat top.

[Ned Milburn]

Originally Posted by Zion33

Okay now I understand, the back is just a cut out of a (very) large sphere, of course doing this predetermines the shape of the sides of the guitar also, well that pretty much explains the back part and the sides too.

Not always...

Many guitars are made with a gentle "fold" in the back at the waist, so that if it were made with radius dishes it would have 2 different angles for the radius dish - one for the lower bout (flatter when compared to the top's plane) and one for the upper bout (more of an angle compared to the top plane).

Got it...??

[Ned Milburn]

Originally Posted by redir

After building about 40 guitars I started experimenting with true flat tops and I can't claim that they sound better but they do sound different. As Alan mentioned the strings pull the top up into an arch anyway. But I think it's the starting point of low stress that does... 'something?'

The trick is to build them very dry, that way they don't stress as much in low humidity. Even on my true flat tops I still arch the UTB and use an A-Bracing system so that the sound hole and forefront of the bridge to the head block is strengthened. But I don't see any necessity to increase the bracing stiffness on a true flat top.

So if you build your flat tops with different bracing, you can't really comment that the flat top creates the different sound... It is more likely that the A bracing vs X bracing creates the main audible difference in sound...

Would you not agree...??

[redir]

Originally Posted by Ned Milburn

So if you build your flat tops with different bracing, you can't really comment that the flat top creates the different sound... It is more likely that the A bracing vs X bracing creates the main audible difference in sound...

Would you not agree...??

The lower bout bracing is the same. I use A-Bracing above the sound hole.