Top Braces

[Mbryan]

Watched a video by Dana Bourgeois voicing and scalloping top braces on a dread. He didn’t scallop the treble X brace. He briefly mentioned it was for balance. Wondering how this help him achieve his goal? Does that give the treble’s more thickness? Or how it would affect the outcome?

[printer2]

Have you emailed him?

[Mbryan]

Originally Posted by printer2

Have you emailed him?

Don’t have his email. Not even sure if he would reply. Lol

[redir]

In theory a stiffer top will produce more highs. I'm not one to argue with Dana Bourgeois but my understanding is that in practice there really is no bass side and treble side of an acoustic guitar. It's not like the seam down the middle is some sort of magical line that separates bass and treble. The whole top works as a unit. But leaving one of the X-Braces stiff will stiffen that overall unit and make it brighter.

[printer2]

Originally Posted by Mbryan

Don’t have his email. Not even sure if he would reply. Lol

I am sure the company has one. Not like he is hiding his bracing like some others do. It sounds like a question that should not take long to answer. I have found the luthier community to be fairly friendly to each other, worth a try. I am with redir though.

[warfrat73]

The is the rationale the give on the website:
"A unique x-bracing system that scallops only the bass-side braces while the treble braces are shaped and tapered, to enhance bass-to-treble balance in a large guitar."

[Alan Carruth]

I took a workshop on tap tuning with Dana a few years ago, and he graciously allowed me to use my setup to look at Chladni patterns (resonances) on the top he brought as an example. Basically, what leaving the treble side of the 'X' brace unscalloped does is to increase the symmetry of the top.


If you try to bend the top along it's two diagonals in the lower bout you'll see that in one direction you only have to bend one leg of the 'X' brace, but on the other diagonal you have to bend both the 'X' brace and both 'tone bars'. It's stiffer in one direction than the other.

You can look at the way the top vibrates at it's tap tone pitches by using 'Chladni patterns'. The top is supported on foam pads at the edges where it is not moving, and a signal generator producing a pure tone at the desired pitch is used to drive it with a loudspeaker. A small amount og glitter or sawdust sprinkled on the top will bounce off the parts that are moving, and gather along the 'node' lines where it's not, forming the Chladni pattern.

Most guitar tops will tend to form a pattern in the shape of a 'ring-and-a-half': a ring in the lower bout and part of a ring across the upper bout. You get the clearest 'tap tone' when the ring in the lower bout is 'closed' and has no kinks caused by discontinuities in mass or stiffness distribution. When both sides of the 'X' brace are scalloped it's hard to get that ring to 'close', but leaving the treble side level works much better.

The 'closed' ring pattern, and others like it, tend to be associated with a more 'clear' or 'bright' tone. The added stiffness on the treble side doesn't itself produce more highs: if the tone bars ran at the opposite angle you'd get the same result by leaving the bass side of the 'X' unscalloped. The symmetry produces a top that is more able to vibrate at high frequencies. I use a symmetric 'double 'X' top brace pattern, and get good terebles by scalloping both sides of the main 'X'.

[Mbryan]

This is very interesting and informative.

[Mbryan]

Originally Posted by Alan Carruth

I took a workshop on tap tuning with Dana a few years ago, and he graciously allowed me to use my setup to look at Chladni patterns (resonances) on the top he brought as an example. Basically, what leaving the treble side of the 'X' brace unscalloped does is to increase the symmetry of the top.


If you try to bend the top along it's two diagonals in the lower bout you'll see that in one direction you only have to bend one leg of the 'X' brace, but on the other diagonal you have to bend both the 'X' brace and both 'tone bars'. It's stiffer in one direction than the other.

You can look at the way the top vibrates at it's tap tone pitches by using 'Chladni patterns'. The top is supported on foam pads at the edges where it is not moving, and a signal generator producing a pure tone at the desired pitch is used to drive it with a loudspeaker. A small amount og glitter or sawdust sprinkled on the top will bounce off the parts that are moving, and gather along the 'node' lines where it's not, forming the Chladni pattern.

Most guitar tops will tend to form a pattern in the shape of a 'ring-and-a-half': a ring in the lower bout and part of a ring across the upper bout. You get the clearest 'tap tone' when the ring in the lower bout is 'closed' and has no kinks caused by discontinuities in mass or stiffness distribution. When both sides of the 'X' brace are scalloped it's hard to get that ring to 'close', but leaving the treble side level works much better.

The 'closed' ring pattern, and others like it, tend to be associated with a more 'clear' or 'bright' tone. The added stiffness on the treble side doesn't itself produce more highs: if the tone bars ran at the opposite angle you'd get the same result by leaving the bass side of the 'X' unscalloped. The symmetry produces a top that is more able to vibrate at high frequencies. I use a symmetric 'double 'X' top brace pattern, and get good terebles by scalloping both sides of the main 'X'.

very interesting. Do you have a pic of the double X pattern? Thanks

[Alan Carruth]

I have them, but need to figure out how to post pics from my computer on this list.

[BlueBowman]

Originally Posted by Alan Carruth

I took a workshop on tap tuning with Dana a few years ago, and he graciously allowed me to use my setup to look at Chladni patterns (resonances) on the top he brought as an example. Basically, what leaving the treble side of the 'X' brace unscalloped does is to increase the symmetry of the top.


If you try to bend the top along it's two diagonals in the lower bout you'll see that in one direction you only have to bend one leg of the 'X' brace, but on the other diagonal you have to bend both the 'X' brace and both 'tone bars'. It's stiffer in one direction than the other.

You can look at the way the top vibrates at it's tap tone pitches by using 'Chladni patterns'. The top is supported on foam pads at the edges where it is not moving, and a signal generator producing a pure tone at the desired pitch is used to drive it with a loudspeaker. A small amount og glitter or sawdust sprinkled on the top will bounce off the parts that are moving, and gather along the 'node' lines where it's not, forming the Chladni pattern.

Most guitar tops will tend to form a pattern in the shape of a 'ring-and-a-half': a ring in the lower bout and part of a ring across the upper bout. You get the clearest 'tap tone' when the ring in the lower bout is 'closed' and has no kinks caused by discontinuities in mass or stiffness distribution. When both sides of the 'X' brace are scalloped it's hard to get that ring to 'close', but leaving the treble side level works much better.

The 'closed' ring pattern, and others like it, tend to be associated with a more 'clear' or 'bright' tone. The added stiffness on the treble side doesn't itself produce more highs: if the tone bars ran at the opposite angle you'd get the same result by leaving the bass side of the 'X' unscalloped. The symmetry produces a top that is more able to vibrate at high frequencies. I use a symmetric 'double 'X' top brace pattern, and get good terebles by scalloping both sides of the main 'X'.

That is fascinating. First time I’ve read why some choose a double-X.

Alan, I always enjoy reading your posts, and I truly appreciate how you bring a scientific mind to the acoustic world. A “thank you” doesn’t even scratch the surface for all the great information I’ve learned from you.