Determining the proper scallop design and brace stiffness is a VERY subjective subject. So many methods and theories are used that a complete discussion on this page is not possible (and probably not worthwhile). Woody, and all luthiers, must start with a rational plan and then work from experience, intuition and feel. There is one piece of advice, however, that all instrument builders should follow... "Work scant". Proceed with carving braces only after drawing the intended shape of the scallop on the brace... stop...think about what you're doing... proceed again and stop again... Before you think that you've taken out enough... stop.
I've taken a couple of photos where the shadows of the braces show the length and depth of the scallops. Many, many guitars have been made without scalloped braces and they sound great! Some luthiers believe that scalloping braces is incorrect and weakens the brace unnecessarily. Martin used to scallop braces quite a while back (in the 1930's and 40's). Then they quit. I've restored several Martins from this vintage in which everything but the scalloped bracing needed repair. Martin now produces very good sounding instruments without scalloped braces, but their HD models feature scalloped bracing (something for everyone).
The idea of scalloped braces is to reduce the mass and stiffness of the brace thereby changing the resonant frequency of the top. This sounds logical. As a professional engineer, I am intrigued by the measurement and modification of resonance to influence tone. The resonance of the entirely assembled and finished box of the guitar, however, would seem to me to be the critical resonance impacting tone. The resonant frequencies of the free-standing component parts of the guitar (top, back, sides, neck, etc.) are significant, but how these components interface with each other and the volume of air within the box is the final test. The physics of the many variables impacting sound and vibration in guitar is beyond our scope here.
Back to the Basics:
Notice, in the upper bouts, the cross braces are not scalloped. This is the area of critical structural resistance to the torque generated by the pull of the strings on the top. Keep the upper portions of the cross braces at full height and strength.
In October the goal was to put braces on the five tops and backs started last month. Also in October, at the Richmond Folk Festival, I met and talked with Wayne Henderson (guitar maker). He is a very unique person. That was great fun. Then, back at the shop, an old (50's) Gibson ES 150 came off the rack and had some renovation work which will be discussed here on a later date.
By the end of November I will be finished with the top and back bracing and, perhaps, some side bending. Winter is a good time to be in the shop burning Thanksgiving calories.
So be thankful... out loud and in your actions. As always, send me your questions but at a new email address.
See you next month.