It is obvious that a guitar top and top braces must counter bending moments and shear forces caused by the pulling forces of strings and that one consideration in bracing design therefore has to be that a bracing system must have sufficient strength to withstand those forces. It also is obvious that when a player picks a guitar string, string stretching and relaxing oscillations are transferred as force oscillations via a saddle to a guitar's bridge and then to a guitar's top and top braces. Because the braces help to communication those force oscillations to various areas of a guitar top, it is obvious that bracing design changes will be apt to affect both the strength and qualities of sound produced by guitar top vibrations.

It also is obvious that braces have some additional affects on guitar sound qualities. They add weight to and stiffen a guitar top, both of which would affect top-surface resonances. Though the affect should be relatively minor, it also is obvious that space occupied braces reduces the effective volume of a guitar box, which of course functions as a complex cavity resonator, and a slight reduction in resonant cavity volume would slightly increase the resonant frequency of the lowest frequency mode of cavity oscillation and could either increase or decrease the resonant frequencies of higher resonance modes. Furthermore, it also is obvious that energy lost as heat when wood alternately stretches and compresses affects guitar sound sustain times and that because bracing design changes can either increase or decrease the rate that vibrational energy is lost as heat, bracing design can affect the sound sustain times of guitars.

Though most guitar players probably haven't thought about issues associated with guitar bracing in this detail, there is little doubt that most players would expect guitars with different types of bracing to have different sound characteristics. However, guitar bracing differences can affect something else that is very important to players that most probably don't know about. It is something that in retrospect I should have realized, but that I had never thought about.

I asked Peter Tsiorba about differences between various types of top bracing during a recent conversation and was surprised when he mentioned how much bracing design can affect guitar "playability." That surprised me, because it was something I had never considered and it explained something I have wondered about. Players often focus on fret-related issues when they think about playability (low action, neck and fret alignment, string alignment, etc.). However, anyone who has played many different guitars knows that some are much easier to play than others because of the amount of force required to pick and depress strings. There are big differences in that respect between my guitars. It is much more difficult to pick and depress strings on my Ramírez classical than on my Ramírez flamenco guitar. The forces required to pick and depress strings on my Contreras flamenco guitar are somewhere in between those other two.

That is an important consideration that I had never before related to guitar bracing differences. It could be an especially important consideration for beginners who haven't developed the finger strengths most experienced players have or for anyone who suffers from arthritis other physical problems that making playing difficult.

Maybe everyone else has been aware of this and I have been the only one in the dark, but Peter Tsiorba's comment was "I opening" to me and I thought others would be interested in it. Peter knows a lot about guitar design and construction. We are fortunate to have his participation in this forum.

-Bob

Have you tried light tension strings on your Ramírez classical and Contreras flamenco guitars to make them easier to play?

Mendoza

Mendoza, I know your question was directed to Bob, but it might interest you that my experience with light tension is they require a higher action and I find that harder to play than a very low action with medium tension. For example on the Dominquez with low tension a clearance of 3.2mm is required at the 12th fret on the E6, whereas with medium tension I can take it down to 2.6mm which is easier and faster to play for me. It also seems to me that the low tension has a duller sound.

I agree with what Sam wrote. What he described also has been my general experience.

Furthermore, it seems that if the top of a guitar is too rigid, whether because of bracing, characteristics of the wood used, top thickness, or characteristics of wood finish, more force will be required to flex the top a given amount, but lower-tension strings will act on the top with less, rather than more, force. Imagine an extreme example where a guitar top was made of thick steel that would take an extraordinary amount of force to flex and the strings were thin rubber bands that applied very little change of force to the top when they were picked. A guitar like that would produce very little sound and the sound it did produce would be much different than the beautiful sound of a well made guitar.

It seems to me that a guitar with a stiff top probably needs higher-tension strings for good results whereas good results probably can be obtained with lower-tension strings on a guitar that has a more flexible top.

-Bob