Guitar-bodied octave bracing

[tom.gibson]

From what I can gather, it seems most people making archtop guitar-bodied f-hole octaves are using X bracing (whereas the 'mandolin-shaped' octaves, like Webers, more typically use tonebars). Is there a good reason for this? Does anyone have any experience, good or bad, with using parallel bracing on these beasts?

[Michael Lewis]

There isn't a clear answer as so much depends on more than the style of bracing. All things being equal (they never are) parallel bracing tends to reinforce the 'long the grain' strength, and the X bracing spreads stiffness across the grain more.

Do you want a clear and punchy response, or a smooth, full, and warm response? Both styles can work well if the instrument is made properly. Also both styles can be dogs if not well done. Your choice of materials, arching, graduations, and all the rest of the structure will effect the sound and tone you get.

[tom.gibson]

Thanks Michael. 'Clear and punchy' is more the idea, which made me think of parallel bracing, then got me wondering why X-bracing seems more common on GBOMs. I've used both sorts of bracing on normal sized mandolins, and I realize it's only part of the equation, but I was curious to see if anyone had any thoughts/experiences/experiments to share on bracing these big fellers...

(We're talking here about a 21.5" scale, 14" lower bout, 3" depth, around 20mm arch height...)

[tom.gibson]

Just noticed Mike Black does X or parallel on his. Maybe I was wrong to generalize...

[peterbc]

I'm working on an octave now (my first) and I was planning on doing parallel tone bars. I have the Benedetto book that suggests running them under the bridge adjuster posts, but if I do that on an octave the tone bars look pretty close to the center of the instrument. I also noticed that mandolin bracing can have asymmetrical tone bars, with one bar not going under the adjuster. What's the reason for these different methods, and what are the differences in tone and stability?