What radii do you build into your soundboard and back?

[Joel Teel]

Hello folks,
I'm curious to know what radii you build into your soundboards and backs?...and why you chose to use these?

I've designed my 000 and 0000, built my custom body molds, and just finished building my bending forms to use with the LMI side-bending machine. It's time to decide on my radii so that I can order my radius dishes...but I thought that I'd see what others are using.

Thanks...Joel

BTW...here's a few pics of my work so far...

[theEdwinson]

Hey, Joel,
Ever since the beginning, I've put a 15' radius on the backs and a 25' radius on the top. You know, since you asked, I'm not really sure why I've stuck with those numbers, except that I like the way my guitars look and perform with that architecture.
You may be opening up a lively conversation here; I'm looking forward to hearing what other builders have to say about this topic.

I will say that for me, the 25' top radius works very well for the way I build. And when you induce a radius like that onto a load-bearing plate, you are automatically giving it more strength against the torsion of string pull. So you can build that top thinner- actually, more lightly overall- and I think, get more tonal response from it, without sacrificing structural integrity.

Additionally, a radiused top will really help to reduce distortion over time. We've all seen old Martins and Gibsons that have bellied-up behind the bridge, and with a sunken concavity in front of the bridge. This condition often necessitates a neck reset, and/or a JLD Bridge Doctor, or other bridge work, to bring the top back to spec and get the string height back down to a manageable height. Of course, a lot of that also depends on how you brace the top...

I think the reason I settled on the 15' back radius is also a matter of strength, which allows a lighter and more responsive build; and I just like the way it looks.

I think I read somewhere that Kevin Ryan puts an 8' radius on his backs. Anybody know if that's true?

And there is the other factor of avoiding standing waves in the soundbox. Two flat surfaces facing each other might cause the sound waves to just bounce back and forth without really going anywhere- resulting in a woofy, boomy, unfocused projection. But when those surfaces are domed, the sound waves bounce around in there like excited kids on a trampoline.
There's my $ 0.02.

By the way, that is some impeccably clean work you're doing there. Clearly, you're making your jigs and fixtures to have a service life of several generations. If your son Zane decides follow you into this Craft, he'll be pretty well set up!

[Jeremy Hamm]

Hey there, way to go with the building! If you're interested in making your own dishes, they're not too difficult to make, you just need to give it a good solid morning to make the jig & get it done. I have a really lousy but informative 3 piece video on how I make mine. Check the links if you're inclined to do so!
https://www.youtube.com/watch?v=5N7FO28n3EA
https://www.youtube.com/watch?v=RFGxRx03ECs
https://www.youtube.com/watch?v=lJ87FwpoY_U
It's a nice way to save a couple hundred bucks.
-Jeremy

[tysam]

28' for the top and 15' for the back. I have tried others (25' and 20' and 28 20") but 28 and 15 seems to work the best for me.

[Szk]

I'm at 15' for the back. For the top I've got a 28' down to the bridge, than flat below.

[Howard Klepper]

Originally Posted by theEdwinson

And there is the other factor of avoiding standing waves in the soundbox. Two flat surfaces facing each other might cause the sound waves to just bounce back and forth without really going anywhere- resulting in a woofy, boomy, unfocused projection. But when those surfaces are domed, the sound waves bounce around in there like excited kids on a trampoline.
There's my $ 0.02.

Steve, the lowest note that could produce a standing wave at the distance between the top and back of a guitar has its fundamental about an octave and a half higher than the highest note on a guitar. Standing waves are something to avoid in a room (where they can cause boominess), but not a problem for a reflection between the top and back of a guitar, especially since the body is tapered. Actually, any resonance is a standing wave, and we need them, but need them well distributed.

OP, I'm impressed by anyone who can write in that nice Wright-style architect's lettering, so I'm sure you will be a good builder. And I'm currently using 30'/30'.

[Beau Hannam]

Originally Posted by tysam

28' for the top and 15' for the back. I have tried others (25' and 20' and 28 20") but 28 and 15 seems to work the best for me.

Ditto for guitars and ukes

[Rodger Knox]

For the top, it's flat to the waist and 15' radius below that.
The back is also 15'. I don't use radius dishes, just appropriately curved cauls, and glue the braces on one at a time.

[JamesO]

I've used 25' for the tops and 15' on the backs of all my guitars to date, but the current one is 30' and 15' because that's what the guitars I want to emulate use and also very close to the recommendation in Trevor Gore's book set.

[Joel Teel]

Thanks Steve,
It's a blessing, and a curse.....there's a somewhat OCD creature living inside, who forces me to make things as well as I can possibly make them.....no matter what it is that I'm making, or how important its purpose. The blessing is that I've developed the ability to create things with a high level of detail.....and the curse is that I spend way too much time building things that don't need to be anywhere near perfect. I am hopeful, though, that this compulsion will lend itself well to building guitars. 😜

Originally Posted by theEdwinson

Hey, Joel,
Ever since the beginning, I've put a 15' radius on the backs and a 25' radius on the top. You know, since you asked, I'm not really sure why I've stuck with those numbers, except that I like the way my guitars look and perform with that architecture.
You may be opening up a lively conversation here; I'm looking forward to hearing what other builders have to say about this topic.

I will say that for me, the 25' top radius works very well for the way I build. And when you induce a radius like that onto a load-bearing plate, you are automatically giving it more strength against the torsion of string pull. So you can build that top thinner- actually, more lightly overall- and I think, get more tonal response from it, without sacrificing structural integrity.

Additionally, a radiused top will really help to reduce distortion over time. We've all seen old Martins and Gibsons that have bellied-up behind the bridge, and with a sunken concavity in front of the bridge. This condition often necessitates a neck reset, and/or a JLD Bridge Doctor, or other bridge work, to bring the top back to spec and get the string height back down to a manageable height. Of course, a lot of that also depends on how you brace the top...

I think the reason I settled on the 15' back radius is also a matter of strength, which allows a lighter and more responsive build; and I just like the way it looks.

I think I read somewhere that Kevin Ryan puts an 8' radius on his backs. Anybody know if that's true?

And there is the other factor of avoiding standing waves in the soundbox. Two flat surfaces facing each other might cause the sound waves to just bounce back and forth without really going anywhere- resulting in a woofy, boomy, unfocused projection. But when those surfaces are domed, the sound waves bounce around in there like excited kids on a trampoline.
There's my $ 0.02.

By the way, that is some impeccably clean work you're doing there. Clearly, you're making your jigs and fixtures to have a service life of several generations. If your son Zane decides follow you into this Craft, he'll be pretty well set up!

[Joel Teel]

Jeremy...
Really cool video...but I was choking and in need of a glass of water just watching you make them 😋
How did you build the radius into the slides to begin with?

Originally Posted by Jeremy Hamm

Hey there, way to go with the building! If you're interested in making your own dishes, they're not too difficult to make, you just need to give it a good solid morning to make the jig & get it done. I have a really lousy but informative 3 piece video on how I make mine. Check the links if you're inclined to do so!
https://www.youtube.com/watch?v=5N7FO28n3EA
https://www.youtube.com/watch?v=RFGxRx03ECs
https://www.youtube.com/watch?v=lJ87FwpoY_U
It's a nice way to save a couple hundred bucks.
-Jeremy

[Joel Teel]

Thanks Howard,
I never developed the desire to write in cursive. When I was in high school, I was drawn to the graphic styles of lettering, and decided to develop my own personal style of handwriting.....which was also influenced by my drafting courses. I do aspire to, one day, become a good builder.....there's not much, in this world, that would make me happier.

Originally Posted by Howard Klepper

Steve, the lowest note that could produce a standing wave at the distance between the top and back of a guitar has its fundamental about an octave and a half higher than the highest note on a guitar. Standing waves are something to avoid in a room (where they can cause boominess), but not a problem for a reflection between the top and back of a guitar, especially since the body is tapered. Actually, any resonance is a standing wave, and we need them, but need them well distributed.

OP, I'm impressed by anyone who can write in that nice Wright-style architect's lettering, so I'm sure you will be a good builder. And I'm currently using 30'/30'.

[Joel Teel]

JamesO
Rodger Knox
Beau Hannam
Szk
Tysam


Thanks for taking the time to respond

[LSemmens]

I'm not a builder, but I could not help your use of the plural of radius being that of radii. From a, once, Latin student. Too many people these days do not appreciate the finer nuances of the English language. FWIW Radiuses seems to have become acceptable, just not in my vocabulary. So; thank you from a pedant.

[redir]

My top is dead flat but I arch the UTB and the whole of the top is canted from the waist to the neck block.

My backs vary but '15 is common.