Back bracing question

[rogthefrog]

In most guitars I've seen, the back braces are pretty wide and squat.

My understanding is that you get more stiffness per unit of height than width; and many top braces are tall and skinny to take advantage of that (more stiffness for a given brace weight if they're laid out skinny edge down).

What's the reason for backs often not having tall and skinny braces?

[SteveS]

Tradition.

[rogthefrog]

Why did said tradition originate? It's obvious when handling a piece of wood that taller pieces are stronger, so it's not some new scientific discovery.

[billgennaro]

I tend to go for guitars that have very resonant backs, as opposed to those that display more of a reflective back (or somewhere in between resonant and reflective). All of my guitars have tall, thin back bracing and are built by single luthiers. I haven't experienced any mass produced guitars with the resonant back quality that I desire, and they all seem to have thicker/flatter back bracing.

Just an observation that I have made. Perhaps some luthiers will chime in with their thoughts.

[charles Tauber]

Originally Posted by rogthefrog

What's the reason for backs often not having tall and skinny braces?

Short answer: it gives the sound and strength the maker wanted.

I use narrow taller braces. It seems to work for me. I also use mahogany back braces 'cause it seems to work for me. One could wax poetically about theory, but, the bottom line is use what works, by the definition of "what works" that you use.

[John Arnold]

I believe Martin used wide flat lower back braces for a couple of reasons.
The wider braces provide more gluing surface so the braces can stay glued under varying humidity. This is more of an issue on the wider lower bout. The shorter braces are more flexible, which can allow the back to belly more or less depending on humidity, instead of cracking.
This increased flexibility enhances bass response, which was especially important on the smaller guitars that Martin was making in the 1800's. Bass response has always been a hallmark of the Martin sound.

[printer2]

Lower braces should add more mass than stiffness to the back as compared to taller braces resulting in a lower resonant frequency.

[dekutree64]

I've been using tall and thin back braces so far, but lately have been moving more toward fat ones in hopes of increasing overall humidity tolerance.

In low humidity, it's the plate wood that gets stressed, and in the extreme case it cracks. In high humidity, it's the glue joints that get stressed. The plate toughness is inherent to the wood, but the joint toughness can be increased by having more glue area. So bracing dry for low humidity tolerance, and using wide braces for high humidity tolerance should be a good combo.

It's not really an issue for exceptionally stable back/side woods like Honduran mahogany and quartersawn rosewood, but one of my current guitars is flatsawn Malaysian blackwood, which will serve as a good test of the theory.

[rogthefrog]

Thanks everyone, lots of sensible thoughts and lots for me to ponder.

[mirwa]

The back and sides are merely creating an air chamber nothing more nothing less, so long as everything is stiff enough to resist being pulled apart, then it will suffice, yes before others start, different chambers create different tones but in essence its just a chamber.

So most bracings are all about what looks nice, when viewed through the sound hole

Steve

[hat]

Originally Posted by SteveS

Tradition.

Not sure on that. My '54 Gibson has very thin, tall back braces.

[printer2]

Originally Posted by mirwa

The back and sides are merely creating an air chamber nothing more nothing less, so long as everything is stiff enough to resist being pulled apart, then it will suffice, yes before others start, different chambers create different tones but in essence its just a chamber.

So most bracings are all about what looks nice, when viewed through the sound hole

Steve

The back does more than seal the box if built as a live back.

[John Arnold]

Tradition.

Not sure on that. My '54 Gibson has very thin, tall back braces.

Gibson used the wider back braces on the jumbo sized guitars until the early-1940's. So it just depends on which traditional period you are referencing.

[arie]

Originally Posted by rogthefrog

Why did said tradition originate? It's obvious when handling a piece of wood that taller pieces are stronger, so it's not some new scientific discovery.

from the farm and the dock. i have this theory that the x brace came about from the barn door, and the back ladder braces came the inside of a row boat.

[Alan Carruth]

I've used a number of back brace schemes over the years. When I went back to 'ladder' bracing I started out using all tall narrow braces. As I worked on the backs to 'tune' them I found that I was shaving down the two lower ones quite a lot to get the the back resonances to work the way I wanted and at the pitches I was after. They looked pretty puny to me, so I started using wide braces for the two lower ones for more strength. Just like Martin...

"When the problem is old, the old solutions will nearly always be best (unless some new technique has been introduced) because it is inconceivable that all the designers of ten or twenty generations will have been fools."
David Pye.