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I have a question for all you voicing experts out there. Why are the bracing patterns for a steel-string so much different than a classical? You would think whatever makes a SS top stiff would also work for a classical. It seems most SS guitars all have some form of an X-bracing pattern and classicals all seem to have some type of fan bracing pattern. Is it related to the tension caused by steel vs. nylon strings?

What do you all think?

John

you hit it on the head...it is all about the tension. That is why the bridge & bridge plate nestles right in between the X brace.

Think of it this way...when strings were gut and therefore low tension, the typical bracing was ladder bracing and there were no truss rods. As steel strings at higher tensions were introduced truss rods and X bracing became the norm.

Having said that, note that, builders experimented with X bracing even with low tension strings in the 19th century and steel strings actually predate guts strings in some stringed instruments.

John,

You might find these pictures interesting. They reflect the development of bracing to match the tension on the top.



This shows the top bracing on a 1780 six string guitar, it has just moved on from the plain ladder by including the asymetrical brace below the soundhole to stiffen the treble side.



This is from a 1764 13 course lute by Brunner, and shows the early evolvement of fan bracing.

My lutes use similar but less ladder struts and fan braces.

Colin

_________________
I don't believe in anything, I simply make use of a set of reasonable working hypotheses.

If you go onto Martin's website and search around in their string section you will find they list the tension different strings have on the guitar. There's quite a difference and it's actually pretty interesting.

Roy

What is that avatar pic?

D'Addario have a good pdf resource to calculate tension for any diameter and type of string at any scale length and pitch. check at:

D'Addario tension chart

ColinColin S38406.6685763889

_________________
I don't believe in anything, I simply make use of a set of reasonable working hypotheses.

Hmm... interesting! I missed this earlier (Colin, thanks for alerting me to the pictures).

That 1780 guitar is very minimal in its bracing, do you know what the top thickness is, roughly? Beautiful shape, that guitar... there is a certain elegance to the shapes of that time which seem lost now. The replicas of such peroid instruments I've seen an played were surprising in their volume.

Francisco Sanguino sometimes had no bracing in the lower bouts of his vihuelas, but I have no information as to their top thicknesses. He did use fan struts, however, on an instrument of 1759, and this is their first known use to my knowledge.

The fan struts on the lute are very interesting... one almost wonders if something odd was happening with the spruce down there..

The more pictures of old guitars, such as above, with cracks in the upper bout by the fingerboard, really get me thinking about what a good idea reinforcing this area is. The size of the heel is also something interesting to think about. Torres also used fairly small heels at times, though not this small. I haven't seen anybody claiming this to have caused any problems (things like this are important to observe, as nowadays we seem to try to make everything as rigid as possible..., which may or may not be a good thing).

I'd love to see the front of that lute top, if possible Colin, and the rose. Are you using fan struts somewhere on your lutes Colin, or just ladder braces? Don't forget to show us pictures of your latest, either... a little birdie told me you strung up a new one recently.

Best wishes,
Joshua

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It comes down to two things, strength and sound, I think. The limiting factor in any guitar design is the static bridge torque. Cross braces don't add much stiffness against that, and the guitars that used straight cross bracing were generally small. If they tried to make them too big they just got heavy and lost sound (generally: I've seen exceptions). A brace along the top is far better at resisting bridge torque, and as soon as fan bracing came along people started to make bigger guitars with more bass. That design was pretty much optimised by Torres in the mid-19th century. Meanwhile Martin was exploring the X brace, at first on guitars that were no bigger than those of Torres (and using gut strings). The more efficient structure allowed for larger guitars and heavier stringing. It turns out that a 12 fret 000 size with a light top and bracing works very well as a Classical guitar, but it has a _lot_ of bass. Steel strings have more energy in the high frequencies, so they're a natural with the larger guitars that X bracing allows.

There are some differences in sound between X and fan braced guitars, even if all else is equal. X bracing has much more crosswise stiffness, and this changes the relationships between the resonance modes of the top. One outcome seems to be to enhance the mid-range tone of the guitar, which comes across as 'fullness' to many people. Again, this is not necessarily something that nylon strings need: usualy they appreciate enhance trebles, which comes out more from fan bracing. So there are reasons for choosing one system over the other.   

[QUOTE=Dickey] Roy

What is that avatar pic? [/QUOTE]

Take a guess.Roy O38408.0602314815

Sumpin' underwater?

[QUOTE=Dickey] Sumpin' underwater?[/QUOTE]

Yep. It"s the eye of an octopus. It was peering out of it hole trying to figure out what the heck was happening as I was zooming in for a close up. Here's a bigger image.

An eyeball only a mother could love.