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New style back bracing I think.
http://mowrystrings.luthiersforum.com/forum/viewtopic.php?f=10101&t=51495		 Page 1 of 1
Author:  Colin North [ Tue Jan 22, 2019 1:22 pm ]
Post subject:  New style back bracing I think.
This is from a Scottish professional builder (who makes very nice guitars with cylindrical plates) and looked interesting so thought I'd put it up for your perusal.
Attachment:
fullsizeoutput_107f.jpg

Blog post -
https://www.taranguitars.co.uk/blogposts/2018/10/4/developments-back-braces?fbclid=IwAR1aOyRjktDCcgL396L3yx7C68OPNfpgJNj6dWq5j5409pmofZkgoiq0Q3o

FWIW I think this may stiffen the back without adding the CF weight directly to the plate, but of course I may be mistaken.
Author:  LarryH [ Tue Jan 22, 2019 1:37 pm ]
Post subject:  Re: New style back bracing I think.
LOVE me some different. Very interesting concept, execution looks tough...
Author:  Bryan Bear [ Tue Jan 22, 2019 1:42 pm ]
Post subject:  Re: New style back bracing I think.
Interesting. That radius looks tight. those CF braces are so far away from the back it effectively has very tall braces to go with the tight radius. I bet that back is really stiff. I don't know what that really means for the guitars, just an observation.
Author:  Colin North [ Tue Jan 22, 2019 1:48 pm ]
Post subject:  Re: New style back bracing I think.
I believe he uses a back radius of 10' cylindrical normally but it looks less
Author:  J De Rocher [ Tue Jan 22, 2019 1:52 pm ]
Post subject:  Re: New style back bracing I think.
That's pretty cool. I haven't seen a brace design like that before. I wonder what the radius of the back is. I think you are correct that the weight of the CF would be effectively be separate from the back plate once attached to the rims. With the wood braces on the back being so small, it seems that the weight of the back would be reduced significantly assuming something like a standard thickness for the back plates. I wonder how that would affect the pitch of the back for those who tune the back relative to the top. In the description on the web page, it's implied that a cylindrical back is more reflective than a spherical back. I don't know why that would be so. I think that referring to these braces as "compression braces" is a bit confusing since the CF cross member would be under tension. It's a pretty interesting idea.
Author:  DennisK [ Tue Jan 22, 2019 2:06 pm ]
Post subject:  Re: New style back bracing I think.
Looks to me like it would fulfill the structural role of the back braces for the rest of the box, but leave the plate vibrating independently, as if the carbon braces weren't there at all. The free plate will feel stiffened by them, but it's the same sort of stiffness that's provided by the perimeter glue joint. On the completed guitar, the back's resonant frequencies will be much lower than they would be with regular bracing. But then the very high arch will raise frequency again, possibly back up to the normal range.

It should allow the back to move a lot more than it does with regular bracing. I bet the box tap tone sounds awesome :) But I'm not sure what it will do to the sound of the strings. High damping back wood may sound highly muffled, or it may just shorten sustain a lot, which could be interesting with steel strings. Low damping wood may give a big sustain boost, or may just make wolf notes a lot worse.

Definitely worth experimenting with. I hope he posts some sound clips of the result.
Author:  meddlingfool [ Tue Jan 22, 2019 2:38 pm ]
Post subject:  Re: New style back bracing I think.
I'm with Dennis. Once the back is attached, those straight braces would be nullified.
Author:  Colin North [ Tue Jan 22, 2019 2:38 pm ]
Post subject:  Re: New style back bracing I think.
Here's a soundclip of a standard guitar, can't find one with the new bracing.https://www.youtube.com/watch?time_continue=16&v=-DTMQA-EQlE
Author:  meddlingfool [ Tue Jan 22, 2019 2:39 pm ]
Post subject:  Re: New style back bracing I think.
But I'm sure his innovation will sell well.
Author:  Colin North [ Tue Jan 22, 2019 2:53 pm ]
Post subject:  Re: New style back bracing I think.
He has a long waiting list anyway
Author:  meddlingfool [ Tue Jan 22, 2019 3:13 pm ]
Post subject:  Re: New style back bracing I think.
Rightfully so...
Author:  ScooberJake [ Tue Jan 22, 2019 3:19 pm ]
Post subject:  Re: New style back bracing I think.
Seems like a gimmick to me. Those braces provide nothing out-of-plane to the plate, potentially not needed due to the tight radius. They will add some lateral stiffness at the rib/back glue joints, which are already very stiff. Am I missing something?
Author:  Rod True [ Tue Jan 22, 2019 3:33 pm ]
Post subject:  Re: New style back bracing I think.
Looks to me like it will hold the shape while waiting to be attached to the rim and once attached should hold the rim within it's proper place... but between the anchor points what will the back plate do... seems to me there's greater risk of the back potato chipping (is that really a verb?) with the lack of direct support coupled to the back plate...?

Looks really cool though....
Author:  Ernie Kleinman [ Tue Jan 22, 2019 3:46 pm ]
Post subject:  Re: New style back bracing I think.
Nice depth tone an sustain
Author:  Woodie G [ Tue Jan 22, 2019 5:51 pm ]
Post subject:  Re: New style back bracing I think.
The CF tie-bars (they are not braces so much as a way to apply a pure tension load to the ends of the braces and maintain a set chord length, allowing the radius of the back to vary with RH) could be a small fraction of the current cross-section and still carry the entire load...even a 1/32" diameter CF rod would do for loads in the 300 pound range, so it seems like much of the CF weight could be eliminated with a bit of knowledge of those loads. Assuming the current CF is in the 1/4" x 1/8" range, the reduction in weight from using more appropriately sized tie bars would be close to 30 grams/1 ounce.

Mr. Traugott does something similar to prevent the back from flattening along the axis of the center graft of his guitars, although it is more of a truss structure that ties into each back brace than the system that the OP shows.
Author:  LarryH [ Tue Jan 22, 2019 8:21 pm ]
Post subject:  Re: New style back bracing I think.
Not sure those are CF braces. They don't look the part in any photo I've seen and he doesn't mention CF in his post...still very interesting idea.
Author:  Woodie G [ Tue Jan 22, 2019 10:36 pm ]
Post subject:  Re: New style back bracing I think.
From the OP's initial post:

Quote:
FWIW I think this may stiffen the back without adding the CF weight directly to the plate, but of course I may be mistaken.
Author:  LarryH [ Wed Jan 23, 2019 12:56 am ]
Post subject:  Re: New style back bracing I think.
Yeah saw that, but I think Colin (the OP) is also assuming they are CF. Can't find any mention is the builder's blog post... Curious...
Author:  Colin North [ Wed Jan 23, 2019 5:08 am ]
Post subject:  Re: New style back bracing I think.
Colin follows him on FB and asked him.
Author:  LarryH [ Wed Jan 23, 2019 9:45 am ]
Post subject:  Re: New style back bracing I think.
Larry is thanking Colin for the clarification... [:Y:]
Author:  Alan Carruth [ Wed Jan 23, 2019 12:12 pm ]
Post subject:  Re: New style back bracing I think.
The straight braces are filling the function of a 'collar tie' in a roof structure. As has been said, they prevent the edges of the box from spreading out and maintain the arch of the back.

Most of the weight of the back is in the plate itself; even fairly large 'normal' braces don't add as much as you might think as a percentage. THat's why we use bracing; it adds more stiffness than weight.

In this case he's getting a lot of stiffness from the 10' cylindrical radius. This would shift the tap tones upward in pitch significantly, and cut down on the amplitude of any back vibrations: it certainly should be more 'reflective' particularly at low frequencies.

On a normal guitar the only back resonant mode that seems to add to the output is the lowest pitched 'main back' mode, which can enhance 'pumping' in the low 'bass reflex' range. I would expect that to be pretty much gone with this setup, with or without the collar ties. The higher order back modes can contribute to 'tone color', by introducing variations in output in the high range. Basically the energy to move the back comes from the top, which is the only part of the gutiar that is directly driven by the strings and that can produce sound effectively. Back vibrations tend to be 'losses', but do contribute to 'color', as I say.

In the end he seems to have gained some of the benefits of a carved arched back without the difficulty of actually carving one. An interesting setup.
Author:  printer2 [ Wed Jan 23, 2019 10:14 pm ]
Post subject:  Re: New style back bracing I think.
If I am right about the builder I think he builds as mainly reflective backs and a does a lot of laminates.
Author:  Bob Shanklin [ Thu Jan 24, 2019 10:51 am ]
Post subject:  Re: New style back bracing I think.
I switched over to a cylindrical back and top a few years ago. 10' rad for the back and 15' rad for the top.
At 10' radius the arch in a 16" wide back is only .267".
I think the camera angle and lighting in that picture are over exaggerating the arch and the depth between the CF and the brace.

Bob
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