Soundboard "Center of Gravity" at bridge

[bostosh]

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?

[Rudy4]

Originally Posted by bostosh

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.

[wrench68]

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.

[printer2]

Stick on a bridge and CG will be pretty much close to the bridge. I would not think too much about it.

[Alan Carruth]

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.

[redir]

No you don't want to do that. Whenever there is a full moon you will get a wolf note.

[printer2]

Originally Posted by redir

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.

[Talldad]

Thinking aloud.

If you removed the upper bout section of the soundboard from your solid works drawing, on the grounds that it is acoustically dead…. 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.

[bostosh]

Originally Posted by Talldad

Thinking aloud.

If you removed the upper bout section of the soundboard from your solid works drawing, on the grounds that it is acoustically dead…. 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.

[bostosh]

" If you removed the upper bout section of the soundboard from your solid works drawing, on the grounds that it is acoustically dead…. 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.