Help. Question: Grain Orientation on Bracing

I've been cutting out bracing and not really thinking about it. Then today I thought, wait a minute, grain orientation might make a lot of difference and you are doing it wrong. Maybe I am over thinking this, but I think this might be important. Basically, I've been cutting my bracing so that the grain orientation is mostly parallel to the top (or back) as in figure 1 below. Now I'm thinking the orientation in figure 2 is better.

Since I am self-taught, I don't know how luthiers do this, but I think it could be important from the structural as well as acoustic point of view. Is figure 2 with the grain perpendicular (more or less) to the soundboard or parallel?

What do you real luthiers say. Poorly drawn diagram below.

figure 2 is how I do it...

Thanks Pete. I suspect that figure 2 is the way to do it. However, this is the harder way for me to resaw the billet without waste.... These billets are sold for guitar building dimensions and not ukuleles which means there is waste. What else is new. An ukulele builder in a guitar building world. Sigh...

1 is how lute bracing was done. The difference is small, something like a a 5% difference in strength iirc. I'll have to look it up.

The more I think about it, orientation 1 is just so wrong in so many ways. Structurally as well as acoustically. These things make a difference I think. Wrong structurally because a piece of timber is strongest to stress when the grain is perpendicular to the force. (well doh!) Grain parallel to a force is obviously weaker. Think about a 2 x 4 on its edge or laid flat. Which is stronger? Acoustically, vibrations should follow the grain down into the soundboard. If the grain is perpendicular and flat to the bridge then those vibrations are going to hit the hard grain lines and bounce back absorbing the string energy. I don't think this is over thinking things. These are the little things that make a difference in how an instrument stands up over time and ultimately how much volume it has.

I remember reading a GAL article, maybe a year ago, that concluded that brace stiffness due to grain orientation was negligible between the two methods illustrated. Maybe I'll look for it and post here. Like Aaron, all my bracing is split from billets and quarter sawn.

I use no.2
but I was taught that way!!

it does cause quite a lot of waste though, and lots of initial prepping

I use the best Sitka spruce I can find for bracing stock. After repairing hundred of ukes over the years, when the problem is a broken brace, 10 times out of 10 the wood used for the bracing is junk. The grain direction has everything to do with a well made brace that lasts. The number 2 drawing with wood quartered split wood with no run out is the way to go IMO.

sequoia said:

The more I think about it, orientation 1 is just so wrong in so many ways. Structurally as well as acoustically. These things make a difference I think. Wrong structurally because a piece of timber is strongest to stress when the grain is perpendicular to the force. (well doh!) Grain parallel to a force is obviously weaker. Think about a 2 x 4 on its edge or laid flat. Which is stronger? Acoustically, vibrations should follow the grain down into the soundboard. If the grain is perpendicular and flat to the bridge then those vibrations are going to hit the hard grain lines and bounce back absorbing the string energy. I don't think this is over thinking things. These are the little things that make a difference in how an instrument stands up over time and ultimately how much volume it has.

Click to expand...

You sure that's how vibrations work in wood?

I am no accoutical engineer and I make no claims to be a luthier. It just seems to me that grain on it side could inhibit transfer of vibrations. The way I'm thinking is like this: there are thermocline layers in the ocean which are caused by boundaries of differing water temperature. It was found during World War II that a submarine could "hide" below one of these thermal boundaries and sonar would reflect or bounce off the boundary layer because it deflects the vibrational energy of the sonar. Couldn't grain on its side act as a sort of sound reflector like a temperature thermocline?

No idea. I do know that Lute bracing is oriented in the manner that you think inhibits vibration. There are a lot of braces on lutes. They sound pretty responsive to my ears, although they don't have a huge amount of sustain. That could be down to the small soundboard aggregate and the amount of bracing though.
The point is that it's easy to fall into the trap of visualising how these things work when in fact the reality is quite different. A good example of this is those who think that the treble side of the soundboard reacts to the high strings, bass side of the soundboard reacts to the bass strings, as though there are two distinct sides to a soundboard. We know this not to be true. Probably best to study some musical instrument acoustics, which may not give the answer but almost certainly will help to understand how these things really work. Not that I've done it.

sequoia said:

I am no accoutical engineer and I make no claims to be a luthier. It just seems to me that grain on it side could inhibit transfer of vibrations. The way I'm thinking is like this: there are thermocline layers in the ocean which are caused by boundaries of differing water temperature. It was found during World War II that a submarine could "hide" below one of these thermal boundaries and sonar would reflect or bounce off the boundary layer because it deflects the vibrational energy of the sonar. Couldn't grain on its side act as a sort of sound reflector like a temperature thermocline?

Click to expand...

I'm interested. Do you want the the braces transferring the vibrations, or do you want them to reflect the vibrations back to the soundboard? If there's a diff, what's better: hearing the soundboard or hearing the soundboard with braces? If you want to utilize the braces to transfer sound, to where or what are you going to transfer them? I've always thought braces, (like ribs on a piano soundboard) are a structurally-necessary evil. They add strength but reduce vibrations. If built like your figure #2, are they simply absorbing more vibrations than in figure #1?

stevepetergal said:

I I've always thought braces, (like ribs on a piano soundboard) are a structurally-necessary evil. They add strength but reduce vibrations.

Click to expand...

This is a great quote and that is what I used to think. But I've realized that instead of being a structurally-necessary evil, bracing actually increases the volume and projection of the instrument. Not only does it make the construction structurally stronger, but it makes it sound better. It is a little counter intuitive for sure. However, and here is the rub, if you over brace the soundboard, it inhibits the sound. It is a balancing act and therein lies the challenge of lutherie. This was actually more or less figured out three or four hundred years ago/ After that it was just a matter of fine tuning the idea. See: Torres. See: Martin. Not so easy to do.

sequoia said:

This is a great quote and that is what I used to think. But I've realized that instead of being a structurally-necessary evil, bracing actually increases the volume and projection of the instrument. Not only does it make the construction structurally stronger, but it makes it sound better. It is a little counter intuitive for sure. However, and here is the rub, if you over brace the soundboard, it inhibits the sound. It is a balancing act and therein lies the challenge of lutherie. This was actually more or less figured out three or four hundred years ago/ After that it was just a matter of fine tuning the idea. See: Torres. See: Martin. Not so easy to do.

Click to expand...

How does it increase volume and projection. Can you describe the actual acoustics behind this?
I'm interested because I've actually built guitars without bracing, well a couple. That's two more than the vast majority of other makers though. I can't say that I noticed any decrease in volume but not that I had a side by side comparison. The theory behind bracing is that you can add strength whilst keeping the soundboard relatively thin (light), so it may work in the manner that you are thinking. Then again Torres tended to go very thin on his soundboards whilst Hauser was somewhat thicker. I don't know that Torres guitars are louder than Hausers though.
Projection is somewhat more difficult. That suggests that you need a decent sized room and someone at the other end of it, also doing an A-B comparison.
Have you done any of these tests?

Michael N. said:

Have you done any of these tests?

Click to expand...

Nope and I probably won't. This is all speculation on my part and is not backed up by any empirical evidence whatsoever. So there you have it... As an argument against what I said, how about this: If the soundboard of an ukulele is acting as a "drum head", why do you never see drum makers putting bracing underneath their drum heads? Hmmm.... So is bracing on stringed instruments a "necessary evil" for structural purposes which detracts from the "drum head"? I don't know for sure. However, what I'm pretty sure of is that if you don't structurally reinforce that top, it ain't gonna hold up and gonna warp and go all wonky after time. Something has to counteract that lateral strain.

I have always work under the assumption that the bracing helps support the sound plate and help regulate the top for sound, not depend on the braces for the sound.

No bracing.

There is one brace. The bridge. A wide piece of stiff structural wood glued to the top and that bridge seems to have particularly long wings.

No longer than a conventional bridge. It's a small guitar, narrow bridge (makes it appear long) but yes, it's a brace of sorts. None under the soundboard though.

Thanks Michael for that post. A gorgeous sounding instrument. Very delicate as one would expect. Perfect for a light touch. I would love to hear that guitar live.

My thoughts: What is supporting that top and counteracting the forces of the strings? If it is truly brace-less, then the grain of the wood has to do all the work. Also the sides to some degree obviously.... I also think the bridge is extra long to distribute the force across the top. Hard to tell as it is out of the frame at the bottom and covered by the players wrist at the top, but this might be key to the design. Does it go almost to the sides? Hard to tell.

My other thought is how this instrument will hold up over time or in changing humidity conditions and therein lies the rub with the brace-less instrument. In other words, it might sound killer for a year or two but structurally will begin to move in time which of course will cause all sorts of serious playability and structural issues.

My last thought is that I heard a little tendency to overmodulate in the trebles and got a little muddy. Must keep in mind that this is a low fi recording heard over tiny speakers which is poor sample. But this would make sense since there is little damping of the top and it would tend to vibrate for a long time. A good player could control this though and use it to their advantage. What delicate trebles!

Anyway, great post Michael. I think bracing is like a lot of things on an instrument. It is a compromise between structure and sound. Gain as much structural integrity while allowing as much freedom in the soundboard as possible. Therein lies the art.