Official Luthiers Forum!

I am new to guitar making and have been doing some research as I hope to make a classical guitar sometime in the near future. In some of the guitar making books I have looked at the makes put a very slight outward bow (about 2mm gap in the middle) in the sound board and back, while others left it entirely flat. What I am wondering is what is the advantage of making the sound board and back that way? Does it just increase airspace inside the guitar and amplification or does it do something else?

It is not about air space it is about structural strength to reduce the rotational affect of the bridge due to the tension of the strings. The rise is actually a dome imparted by the shape of the connecting surface of the fan braces. A dome resist the rotation forces of the bridge better than a flat plate On classical it is typically on the area around the bridge for about 3" or so past the extremes of the bridge. On a steel String it is pretty much the total top and back that is domed. That said. If you build dead flat the strings tension will pull the top in to a dome shape but you will not have the benefit of the added strength of a dome that is braced with the shape dome. Instead you have shape that is forced by the loading forces of the strings. Many great guitars are built as both dome tops and flat tops.

So know the reason. Time to research the science behind it.

There is a belief that adding some bow to the lower bout will add a little pre-stressed tension to the top, which in return will produce a more stable top over the long haul, and also increase the response of the instrument. Many, though, are built both ways with great success. Which ever you choose, will probably work fine, as when you put strings on a flat topped guitar, it becomes slightly domed from the pull of the strings on the bridge.

Welcome to the OLF, Ian, if that's your name. Others will be along to give their interpretation. See - Already happened!

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Waddy

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