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  #1  
Old 09-17-2021, 10:15 PM
bostosh bostosh is offline
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Default Soundboard "Center of Gravity" at bridge

Here is a question, I modeled/drew/cnc'd the soundboard plate with braces in 3D solids. The software has an option to "Model the CG" so i do, Wow, very near the bridge. on a Dreadnaught shape. This can be moved in CAD by moving the mass of the braces and is it relevant to soundboards?
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Old 09-18-2021, 06:33 AM
Rudy4 Rudy4 is offline
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Quote:
Originally Posted by bostosh View Post
Here is a question, I modeled/drew/cnc'd the soundboard plate with braces in 3D solids. The software has an option to "Model the CG" so i do, Wow, very near the bridge. on a Dreadnaught shape. This can be moved in CAD by moving the mass of the braces and is it relevant to soundboards?
I doubt it. More like a coincidence, with the constraints of basic geometry thrown in.

There are many bracing patterns (i.e. fan bracing) that would throw the idea of center of gravity out the window, as those instruments would more or less prove that any balance point doesn't necessarily coincide with the ability to provide good tone or volume.

Practical "seat of the pants" design with a bit of intuition thrown in was what lead luthier Danny Ferrington to conclude that non-symmetrical body design could produce what he considered superior response in an acoustic instrument.

Last edited by Rudy4; 09-18-2021 at 10:03 AM.
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Old 09-18-2021, 09:15 AM
wrench68 wrench68 is offline
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I love working on guitars, but i am NOT a luthier, and i have NEVER voiced a soundboard, but my guess is that moving the mass of the braces will move the nodes on the soundboard.
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Old 09-18-2021, 03:10 PM
printer2 printer2 is online now
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Stick on a bridge and CG will be pretty much close to the bridge. I would not think too much about it.
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Old 09-20-2021, 01:20 PM
Alan Carruth Alan Carruth is offline
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I think the 'Acoustic Center' of the top is more important than the CG. It's a version of the 'center of moment', like the 'sweet spot' on the bat where you get the most solid hit, and the least sting in your hands. You can fine tune the AC of the top by working with the top thickness distribution, and especially the brace profiles. A well designed and made top has the AC at the bridge location, which is not always at the widest part of the lower bout, which is often said to be the case.

It is certainly true that the bridge tends to weigh about as much as all of the other bracing on the top together, and that tends to pull the CG toward the bridge, but I'd be surprised if it was often right at the bridge on most guitars. I do recall seeing violin makers advocating something like this, but that's a different system.
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Old 09-20-2021, 01:32 PM
redir redir is offline
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No you don't want to do that. Whenever there is a full moon you will get a wolf note.
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Old 09-20-2021, 05:17 PM
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No you don't want to do that. Whenever there is a full moon you will get a wolf note.
But only once a month.
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Old 09-21-2021, 06:09 AM
Talldad Talldad is offline
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Thinking aloud.

If you removed the upper bout section of the soundboard from your solid works drawing, on the grounds that it is acoustically deadů. ish, where would the CoG move to?

Would it move to nearer the acoustic centre of the board, in line with the lower bout? That would be cool.
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Old 09-22-2021, 11:12 PM
bostosh bostosh is offline
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Thinking aloud.

If you removed the upper bout section of the soundboard from your solid works drawing, on the grounds that it is acoustically deadů. ish, where would the CoG move to?

Would it move to nearer the acoustic centre of the board, in line with the lower bout? That would be cool.
ii will try that calc.....Good suggestion
And i can add the weight of the bridge.
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Old 09-27-2021, 10:43 PM
bostosh bostosh is offline
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Default removed upper bout re-calc'd

" If you removed the upper bout section of the soundboard from your solid works drawing, on the grounds that it is acoustically deadů. ish, where would the CoG move to? "

The CG on the truncated to upper bar OM Cad 3D model moved 2.06 away from the sound hole to under the saddle.

I will analyze the Dread next.
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