MIMF

Hi. I'm building my 4th acoustic guitar and just wanted input on a flat top verses a slightly domed top. Is the sound quality that much better with a domed top?

Thanks

Jeff

As I understand it, the radius on the top helps strengthen it, and the dome allows for extra movement in RH changes, helping prevent cracks....

I admit I haven't made and 'flat' tops, so I don't have data on it. From what I do know of the effects of archings, I'd hazard that the amount of dome you normally see in a guitar top won't make much difference in the sound. I'd think it would be masked by a host of other things. OTOH, living in New England I can't afford to miss any trick that could reduce shrinkage cracking, and doming does that.

If you would define what you mean by "sound quality" it might be possible to consider how to answer that question. It would still be a formidable challenge however since there are way too many variables involved to be able to isolate just that one (the amount of doming).

What I think can be said with a fair amount of certainty is that if everything else was the same (bracing design, thicknesses, same pieces of wood, etc) that the more the top is domed, the more likely it is for the main resonant frequency of the soundboard to be a bit higher. Does that make it a better sound quality ? I'm not sure the question is the right one...

Even if it's built flat, string tension will induce a little doming, so it's not exactly a flat top anyway. The difference is the amount of residual stress in the top/bracing system, and I haven't seen anything definitive on residual stress affecting sound. There's a lot of opinions, as always, but nothing more than opinions.

Hi Jeff,
I would not say the sound quality is necessarily better with a domed top. As others have said the dome does give some improved integrity to the structure of the guitar. On Classicals the doming may allow making the top thinner and lighter in weight, which usually makes for a louder instrument. As Roger mentioned, on a steel string flat top that is not overbuilt the string tension will dome the top slightly anyway.
I have built a few flat tops, and many of the old parlor guitars were flat tops, and they sound fine. Most often I "dome" the tops slightly, as I think this makes a better instrument.
Another point in favor of doming the tops is that in low humidity situations a dome top will "flatten" and a flat top may go concave.

I build both radiused top and true flat top guitars. The flat tops sound "older", more "vintage-like, and warmer overall. So far, none of them have cracked, either. Yes, a "true" flat top will take-on a bit of a tension-induced radius naturally, but it will still be considered a true flat top because the term is describing the build/design, not the result.

Consider that the radius very effectively stiffens the top, such that the tone is affected very much like you would expect from a stiffer top structure.

Interesting topic. I just started to build a batch of "Flat-Top" classicals after some e-mail conversations with Paul Jacobson. He builds flat. I observed this while doing a repair to one of Paul's guitars and asked him about it. He said he never had one crack. The string tension pulls up on the back end of the bridge and the top arches but the fron is slightly caved inwards. The Jacobson sounds a plays great.

What sort of differences in tone and stiffness arise when flat braces are glued using a radiused glue mold (instead of pre-radiused braces)? I'm debating which way to go on by current build.

I don't imagine that there is a noticeable difference in sound between a pre-radiused brace and a brace that is just glued into a curved relationship with the top. If I had to make an argument for one over the other, it would be based on efficiency of wood use or some belief that one would last longer than the other.

Have done both. One can build a flat top that is as good as a dome top, just depends on how flat and how domed. Ervin Somogyi recons either works well, depends on the implementation