Do classical backs need to be radiused?

[XxJoshxX]

Hey guys, first post here.
My name is Josh, im 14, and Ive built a few electrics, but want to start my first acoustic soon. Im just about done planning out the build. I'm planning a multiscale classical with a Venetian style cutaway, but a bit sharper. Since I cant afford a bending iron, and I dont want to try to build one that wont work as good, Im going to do laminate sides. Now the question, I know that classicals have radiused backs, but I havent been able to find out why. Is it really necessary? I think that it would complicate things with the laminated back and sides.
Heres my latest build.

[CoolerKing]

I have no idea about the classical, but it assume it needs a small radius. Beautiful work on the electric!

[LouieAtienza]

One thing about doming is that it can give the back wood "room" to expand and contract. It also has an aesthetic purpose, as it just looks "right," an undomed back can look sunken in at times. Doming also provides strength; a comparable undomed back will not be as stiff so a domed back can be made with thinner wood.

[David Wren]

I agree with the answers above, but there is some precedence for flat backed classicals, notably Ignacio Fleta's instruments (at least the two examples I've come across in my career).

[Ned Milburn]

Originally Posted by David Wren

I agree with the answers above, but there is some precedence for flat backed classicals, notably Ignacio Fleta's instruments (at least the two examples I've come across in my career).

David, did you notice any issues with the Fleta guitars that could have been attributed to not having a radiused back?

[John Arnold]

The main issue is a sunken or cracked back from shrinkage. This is more of an issue with the more unstable woods like Brazilian RW. The Fletas I have had in the shop had only a slight back arch, but they were Indian RW, which is much more stable.

I think that it would complicate things with the laminated back and sides.

Not really. Laminating the back makes it only slightly more stiff across the grain. It is still thin enough to flex when curved braces are glued to it. There are literally millions of Asian laminated guitars that have some back arching.
OTOH, there is no issue of having a flat back that is laminated, since the lamination reduces the shrinkage.

[redir]

Honestly I think it would be more difficult to laminate sides then to bend them. My side bender consists of a 3in copper pipe (free) and a blow torch, perhaps $15. I've built over 50 guitars with it.

Also based on your image (nice guitar) and that you already have a few electric guitars under your belt then I doubt you will have a hard time arching braces for a back. It's really not as hard as you may thing.

Either way will work and good luck. Also post pics of your build process.

[David Wren]

Originally Posted by Ned Milburn

David, did you notice any issues with the Fleta guitars that could have been attributed to not having a radiused back?

Hi Ned ... if memory serves ... both backs were very slightly concave (not a good look!). They seemed to be hanging together fine though.

[Dan of SC]

I think any acoustic guitar top or back needs a slight dome. It's just way more stable.

[Ned Milburn]

Originally Posted by David Wren

Hi Ned ... if memory serves ... both backs were very slightly concave (not a good look!). They seemed to be hanging together fine though.

Thanks David. Both Serge DJ and I recently saw a newly built classical guitar with a concave back (possibly/likely due to humidity issues when building), so I was curious about its possible longevity problems and cracking.

BTW, I sent you a brief private message just to say hi.

Cheers!

[John Arnold]

Hi Ned ... if memory serves ... both backs were very slightly concave (not a good look!). They seemed to be hanging together fine though.

Fleta is in Barcelona, so it is likely that the guitars were built in relatively high humidity. This is the recipe for sunken backs (and tops). I do know that he switched from Brazilian to Indian RW earlier than many other guitar makers....maybe because of stability issues.

[redir]

Originally Posted by Dan of SC

I think any acoustic guitar top or back needs a slight dome. It's just way more stable.

I've started building true flat top steal string guitars. I know the bracing is totally different then the backs but it works quite well and it has a different tone. So far I really like it. Classical's still get an arch and backs in all cases I arch as well.

[gpj1136]

In what way is the tone different I've been curious about this. Is it more fundamental, or stronger bass ? Have you notice stability issues ? Does it tend to break up when played hard ? A lot of questions But I've been thinking of trying this also.

[redir]

Originally Posted by gpj1136

In what way is the tone different I've been curious about this. Is it more fundamental, or stronger bass ? Have you notice stability issues ? Does it tend to break up when played hard ? A lot of questions But I've been thinking of trying this also.

Well it's always difficult to use words to describe guitar tone. Having said that I find the flat tops to be more responsive. I find them to sound already played in, vintage if you will. They have a warmer sound and a nice balance. I've only built five guitars like this so far but from the first one I've noticed this. I use an A-Brace system and I bend the top from the sound hole to the head block so as to get teh neck angle right, it's not even really noticeable. Sort of like pliage on a Selmer. The top will get an arch anyway due to string tension.

It's not better than an arched top it's just different.