flat or curve top what is the different between

[Tygrys]

Hello all.

I'm planning to make carbon fibre guitar and I'm just wanted to ask what is the different between flat and curve top?

But please exclude the archive I know that some of steel string guitar have slightly curved top but what for?

How this would change the sound?

[murrmac123]

The principle reason for putting a curve in the top of a "flat-top" guitar is to prevent the top cracking if it were to shrink due to a change in humidity.

This is not a problem you will encounter with a carbon fiber top.

[Tom West]

A radius top also a stiffer top with can be made lighter. Something you may want in a carbon fiber top. We can't let you get away too easy........!!!
Tom

[rick-slo]

One thing anyway, with a wooden top a curved top pre-stresses the wood a bit. That tends to even out the sound a bit between bass and treble. A true flat top will favor the bass strings more. Perhaps that is true for a carbon fiber guitar also, don't know for sure.

[printer2]

The top will have a resonance frequency. With an arc to it the top will have a higher frequency than a flat top due to the stiffness added by the curve.

[Tygrys]

In summary. Curve on wooden top is to prevent deformation due to a outside conditions like dry or moisture environmen; also help to promote high tones.

In CF I wouldn't be worry about deformation from humidity.

I'm planning to build travel (3/4) size guitar with short scale about 22.84 inches (580mm)

So shorter scale will help to expose high tones but bass will be a challenge.

I crow that Composite Acoustic they are using flat top on the cargo mod, and their guitar is well responsive with low and high tones.

Could please anyone tall me what is usual curve on wooden toplanning?

[ac]

Emerald made their X7 with a curved top for more projection as archtops were built that way to project louder in bands years ago before electronic amplification was common.

Later, they came out with their X7-OS (offset soundhole) with a flat top--I think the reason was to help improve the bass response a tad.

I had both guitars for a short while and played them side by side. Sound was very close but my wife said that to her, the X7 with the curved top sounded slightly louder. This is pretty subjective but thought I'd pass it on.

The X7 with the center soundhole is discontinued and recently, he renamed the offset soundhole version with the flat top from X7-OS to X7, since there was no need to separate the two anymore. (In case you visit their website and wonder about the naming.)

[printer2]

Originally Posted by Tygrys

Could please anyone tall me what is usual curve on wooden toplanning?

25' to 40' radius.

[redir]

I think it's been pretty well covered but I just want to add that I used to build with a radius and now I prefer to build dead flat. I still put a radius in classical guitars. But for some reason a while back I decided to experiment with true flat tops and I liked the results so well that I stuck with it. After being strung up for a short while you see an arch from string tension. I've not experimented with one exposing it to wild extremes in humidity and temperature but so far they hold up just fine. I don't really know how to describe the tonal difference, they just sound different.

[Tygrys]

I like to thank you all for good and useful discussion.

Now I think I will make flat top atleast for start i may later do also curved one but if I will it will be in far future.

Ps. Another argument for flat top is that it is easier to make. :-)

One more time thank you all

[arie]

Originally Posted by Tygrys

I like to thank you all for good and useful discussion.

Now I think I will make flat top atleast for start i may later do also curved one but if I will it will be in far future.

Ps. Another argument for flat top is that it is easier to make. :-)

One more time thank you all

i would look to the CA Cargo for guidance. those guitars are fine examples of CF instruments. Don't have a lot of exposure to the Emerald i'm afraid, only played one. RainSong is another example to check out the build technique on.

one thing that i will mention is that setting a neck angle on a true flat top takes a bit more planning then on a dished top in terms of the fretboard extension.

[Alan Carruth]

Although carved archtop guitars certainly have higher pitched top resonances than flat tops, they also have much higher arches in general. Given that bridge torque imposes some curve in any top, I'd think it would be difficult at best to 'prove' that the doming many of us use on our flat tops makes any real acoustic difference. I does certainly seem to help a wood top withstand humidity changes, and that's reason enough do use it in my book.

[rick-slo]

Originally Posted by Alan Carruth

Although carved archtop guitars certainly have higher pitched top resonances than flat tops, they also have much higher arches in general. Given that bridge torque imposes some curve in any top, I'd think it would be difficult at best to 'prove' that the doming many of us use on our flat tops makes any real acoustic difference. I does certainly seem to help a wood top withstand humidity changes, and that's reason enough do use it in my book.

Don't see the logic. Bridge torque lift (and dip anterior to the bridge) is mostly behind the bridge out to a few inches. A curved top from curved braces imparts a curve to a much larger area. For example a true flat top I built (now 45 years ago) remains flat all around except immediately behind the bridge.

[redir]

Originally Posted by Tygrys

I like to thank you all for good and useful discussion.

Now I think I will make flat top atleast for start i may later do also curved one but if I will it will be in far future.

Ps. Another argument for flat top is that it is easier to make. :-)

One more time thank you all

I should mention that on my true flat top guitars I do arch the UTB as that helps get the neck angle right. There are other ways to do that. It's not really all that easier. Honestly it takes me 10 minutes with a block plane to arch the braces. I also use an A-Bracing pattern to strengthen up the area in front of the X and across the sound hole where you tend to get a lot of deformation. The string tension is always going to pull up and 'arch' the top behind the bridge which as a result will cause a lot of stress in front of it so I like the A-brace style. An arched top would be stronger in that regard.

[Alan Carruth]

rick-slo wrote:
"Don't see the logic. "

I was mostly thinking about what printer2 wrote:
"The top will have a resonance frequency. With an arc to it the top will have a higher frequency than a flat top due to the stiffness added by the curve."

In theory adding some curve to a flat plate makes it stiffer, and there can be a big jump in stiffness between 'no' curve and 'some' curve. This is particularly noticeable in the 'free' plate, especially if there's a 'ring' mode. Once you glue it to a set of sides, though, the difference becomes much less. A carved arch top, with the arch about 15mm high, is noticeably stiffer than a flat plate the same size, but once you make them into guitars the difference is not as great as you might expect. An arch top guitar I made a few years ago on the 'Small Jumbo' pattern has it's 'main top' resonance at 250 Hz, while a flat top the same size has the same resonance at 213 Hz.

By comparison, the relatively low arch of a 'domed' flat top should not make too much difference as compared with a 'flat' top. Given that there's a fair amount of variation between tops, and that brace profiling can have a noticeable effect, I suspect it would be difficult to show that domed tops are much different acoustically than 'flat' ones in any systematic way.

You can argue that small differences can be important, and that's certainly true. That arch top I mentioned does sound a good bit different from the flat top, although it's hard to say how much of that if from the arch and how much from F-holes vs a round hole. And there's always 'Feynman's Dictum': "You are the easiest person for you to fool". People really do hear what they expect to hear, especially when they have some effort tied up in the result.

I will point out that I've never made a 'flat' top. Humidity issues are such a problem here in New England that it's just not worth the risk.