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Is this arching wrong ?


Arsalan

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10 hours ago, Andreas Preuss said:

Not quite. There are quite many Cremonese instruments which suffer from a sunken-in top plate. (Or pulled up end blocks, depending how you see it.)

As above via Timoshenko, buckled. The more they buckle the more they can buckle if you keep applying forces and torques. But buckling does not imply lack of vibrational ability any more than arching does.

As sound is in air, a very very small propagating fluctuation in the total pressure, so vibrations are analagously small propagating disturbances in elastic solids.

There's DC plus AC.

Resistance plus reactance. 

 

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6 hours ago, reguz said:

Dear Marty. Did you study how C Gough constructed the instrument? There is no scoop shape and the belly shape with cross over radii has chord line on the outline. There neither is lining on the rib that follow the instrument rib inner line. I had long discussion with C Gough about this "instrument" and how he handled it making the Mode shape condition. I cannot learn much at all from this long report. Of course, C Gough make no calculation faults. The result is based on the input data. I hope any of you can make us of what is shown in the report.

Colin Gough mathematically modeled with "cubic third-order Bezier curves" his FEA violin shape which was based upon the 1715 Titian Strad violin(http://strad3d.org/overview.html) and how he did this is described in his JASA paper on plate modes (attached).

His arch shapes are symetrical and look like violin arch shapes to me without all the age distortions and bulges we often see in old violins.

Colin's fea.png

Violin Plate Modes JASA, Nov 9, 2015.pdf

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As a matter of interest I stacked some front arching templates, which I think are fairly standard, to see what they looked like. And, even taking into account the doubling of height and absence of corner extensions, I can't see what relevance Colin Gough's drawing might have to an actual violin arching. Perhaps I'm missing the point.

 

DSC_0004.JPG

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Divide his heights by two and neglect your edges and they're kinda sorta.  But I think you're on the right track - once it passes a certain point I think we're talking more about background and prejudices, and visual aesthetics.  If you selected any 50 instruments that were generally agreed to be excellent, how many different principle arch profiles do you think you'd find?

I'm curious, however, how Figure 7 relates to the decreasing hyponasal tonal quality as the sound hole opens up, observed in a video experiment.  Maybe it doesn't...

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16 hours ago, sospiri said:

But Stradivari's ribs are very thin with wide tapered linings. He did this for a reason. Not just to make the ribs easier to bend. The violin is distorting laterally when it's played.

I am sure that all what Antonio Stradivari did on his instruments was for good reasons and it worked as a whole. But this doesn’t mean that it’s the only possible solution. 
 

In my view a few classical constructional features came from practical and/or aesthetic considerations rather than pure acoustical considerations. 
 

It was convenient to build the ribs on an interior mould in a symmetric form. Symmetry was for aesthetic reasons. The interior mould was the most convenient tool to reproduce instruments at the same size. Makers in Cremona certainly perfected this concept to the limit. 
 

My point is that if we alter the rib construction with carefully ‘calculated’ alterations we can build instruments differently in terms of ergonomic aspects, and I dare to say sound projection. (That’s still to be tested)

I came up with an arch shaped asymmetric form using balsa and .4 birch plywood which is definitely stiffer at slightly lower weight than normal rib garlands. I think this makes it possible to make the top plate thinner and lighter than normal. 

 

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If I understand it correctly Gough used the same one cross profile defined by simple Bezier curve just scaled it to fit height and width at it's position on thelong axis. The illustration shows the height doubled (so the various profiles could be seen in it).

From my (amateur) lloking at violins I see that majority violins don't have the same curvatures all along the plates, this results in an odd arch near end of long arch. May look OK in central parts but the ends will deviate from "normal" arch at the U/L bouts.

Andreas, have you tried using strategically placed "ropes" to stiffen the garland? Some flat top guitar folks use sticks inside the body against the string pull so their tops can be lighter and presumaly more responsive but I guess some "wires" stretched across the garland could counteract some of the forces on arched top instruments allowing lighter top as well.

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12 hours ago, David Burgess said:

 

Regus, there is no single clear answer. It is only you who seems to be obsessed with the notion that there is.

All depends on which point one chooses as their stationary point of reference. Most makers choose a different one than you do, possibly because moving endpoints seem to radiate a lot less sound than more central moving areas. Deal with it, and maybe learn a little something from it, if such a thing is possible for you. :)

Dear David. It is what you in your thinking believe. I do different I look at the technical solutions. The lower bout shape is much bigger the upper. to hold it simple we may expect that the upward movement on the end blocks may become different. Already that makes it difficult when you say we look on what happens in the center, If the instrument as they support on the end block deform as described above the vertical placed sound post most certain will tilt. What is it you can withhold you coming to any understanding. My point is the end block will move upward with bending of the back over the sound post. I have shown this in a vector diagram that make static equilibrium condition. If you like to check the diagram it works as follows. The string tension is given a specific length in mm by an arrow. All forces in the diagram thus are related to that mm of stress on the string

2016 vector forces.jpg

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9 hours ago, Marty Kasprzyk said:

Colin Gough mathematically modeled with "cubic third-order Bezier curves" his FEA violin shape which was based upon the 1715 Titian Strad violin(http://strad3d.org/overview.html) and how he did this is described in his JASA paper on plate modes (attached).

His arch shapes are symetrical and look like violin arch shapes to me without all the age distortions and bulges we often see in old violins.

Colin's fea.png

Violin Plate Modes JASA, Nov 9, 2015.pdf 5.66 MB · 6 downloads

Dear Marty and Dennis. With all respect for what Gough does he could have shaped the arching by many different techniques but all are related to HIS TITIAN model. What quality does his arching hold and HOW did Gough do perform the results he shows. IS THERE string stress on his model? I do not say I am better I only show that there is structural quality on the model I found. I came back on what I found about what the STL framework produce.

Maestro 2.docx

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Reguz, I fail to see how endless repetition of the same thing will make your beliefs any more viable (unless one is unusually susceptible to propaganda tactics). Are you, perchance, someone who emigrated to Finland from the old Soviet Union, or from Russia? When I visited Russia, there were still some older Soviet-era people around who seemed to be stuck in such dogmatic insistent tactics. The younger people would take me aside and apologize for this behavior.

Maybe you should try taking your shoe off and banging it on the table? :D

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39 minutes ago, reguz said:

 With all respect for what Gough does he could have shaped the arching by many different techniques

You genuinely should have a great deal of respect for Gough's work. And then strive to have more than such a superficial understanding of what he has accomplished. 

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5 minutes ago, David Burgess said:

Reguz, I fail to see how endless repetition of the same thing will make your beliefs any more viable 

Yes.

Exactly.

:wacko:

We all know plates buckle and ribs buckle. It all seems to be a good thing until it goes too far.  It probably is the mechanism of 'settling in'. 

There are other interesting things to discuss. 

 

 

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1 hour ago, Andreas Preuss said:

I am sure that all what Antonio Stradivari did on his instruments was for good reasons and it worked as a whole. But this doesn’t mean that it’s the only possible solution. 
 

In my view a few classical constructional features came from practical and/or aesthetic considerations rather than pure acoustical considerations. 
 

It was convenient to build the ribs on an interior mould in a symmetric form. Symmetry was for aesthetic reasons. The interior mould was the most convenient tool to reproduce instruments at the same size. Makers in Cremona certainly perfected this concept to the limit. 
 

My point is that if we alter the rib construction with carefully ‘calculated’ alterations we can build instruments differently in terms of ergonomic aspects, and I dare to say sound projection. (That’s still to be tested)

I came up with an arch shaped asymmetric form using balsa and .4 birch plywood which is definitely stiffer at slightly lower weight than normal rib garlands. I think this makes it possible to make the top plate thinner and lighter than normal. 

 

Rib stiffness in the thickness durection is proprtional to width X thickness^3 as discussed above but ribs are much stiffer in the width direction where stiffness is proportional to width^3 X thickness, maybe 900 to 1000 times stiffer in that direction.

So the coupling between plates in the vertical direction is very strong already compared to relatively weak coupling in the direction in the plane of the plates.

So why is it ( thickness) so important? And what happens if you make ribs 25% wider instead of 25% thicker. 

--- I know, the air volume complicates everything. It has to be a rhetorical question. 

BTW this could throw some light on the question of whether rib buckling us significant. A rib permanently buckled to the extent that the max deflexion is greater than the thickness can be less stiff in the strictly vertical direction. 

Elastucally buckled ie sprung??? Don't know. 

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1 hour ago, LCF said:

Yes.

Exactly.

:wacko:

We all know plates buckle and ribs buckle. It all seems to be a good thing until it goes too far.  It probably is the mechanism of 'settling in'. 

There are other interesting things to discuss. 

 

 

Dear LCF. I asked C Gough how it is possible changing curve lenght as shown by him happening in split seconds.

No answer.

20141207 Frequency deflection C Cough20141207_00000.jpg

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1 hour ago, LCF said:

Rib stiffness in the thickness durection is proprtional to width X thickness^3 as discussed above but ribs are much stiffer in the width direction where stiffness is proportional to width^3 X thickness, maybe 900 to 1000 times stiffer in that direction.

So the coupling between plates in the vertical direction is very strong already compared to relatively weak coupling in the direction in the plane of the plates.

So why is it ( thickness) so important? And what happens if you make ribs 25% wider instead of 25% thicker. 

--- I know, the air volume complicates everything. It has to be a rhetorical question. 

BTW this could throw some light on the question of whether rib buckling us significant. A rib permanently buckled to the extent that the max deflexion is greater than the thickness can be less stiff in the strictly vertical direction. 

Elastucally buckled ie sprung??? Don't know. 

I don’t know either and I stopped trying to find out. 
The only thing I know is that my new rib construction works. You  may have a look in my thread about the new concept violin and how I approached step by step a new rib structure. There is a sound graph which should at least make clear that it’s a functional violin. 

 


Logic brings you from point a to b, imagination everywhere. 

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14 minutes ago, reguz said:

Dear LCF. I asked C Gough how it is possible changing curve lenght as shown by him happening in split seconds.

No answer.

20141207 Frequency deflection C Cough20141207_00000.jpg

Maybe because it's not 2D but 3D, things happens crosswise too. Besides, it's a computer model and everything is magnified. The purpose of his study seams to be comparison to the Titian and finetuning FEA.

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20 minutes ago, reguz said:

Dear LCF. I asked C Gough how it is possible changing curve lenght as shown by him happening in split seconds.

No answer.

Gough has probably learned from experience that there is no point in answering you. Nothing will change, and you will just continue insisting and haranguing.

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5 minutes ago, Andreas Preuss said:

I don’t know either and I stopped trying to find out. 
The only thing I know is that my new rib construction works. You  may have a look in my thread about the new concept violin and how I approached step by step a new rib structure. There is a sound graph which should at least make clear that it’s a functional violin. 

 


Logic brings you from point a to b, imagination everywhere. 

Thanks Andreas, I have already been following your workbenchvseries with interest.

 

It is dull and prosaic but suspect that simple bit of stiffness logic wrt the ribs might have some interesting stories to tell us about how violins work.

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2 minutes ago, Peter K-G said:

is this what you want to discuss?

 

principledeformationsonlenghtaxis.gif.15ddec7c0034790f6b96b710a83b7815.gif

Deform.thumb.PNG.d59363988301e527549a277c5ad5eae0.PNG

Peter K-G  that's good for the static  lengthways string load. 

Now you need to find the corresponding animation at right angles to this showing how the small rocking motion due to string oscillation  drives the heart of the soundboard via the bridge. A bridge cannot transmit much motion in a direction at right angles to its face, no significant vibration in the direction of the string tension.  That's the design, why it is so thin compared to its width. It is flexible in the string direction and rigid at right angles to the strings and parallel to the bow.

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48 minutes ago, Peter K-G said:

is this what you want to discuss?

 

principledeformationsonlenghtaxis.gif.15ddec7c0034790f6b96b710a83b7815.gif

Deform.thumb.PNG.d59363988301e527549a277c5ad5eae0.PNG

 

52 minutes ago, David Burgess said:

Gough has probably learned from experience that there is no point in answering you. Nothing will change, and you will just continue insisting and haranguing.

 

52 minutes ago, David Burgess said:

Gough has probably learned from experience that there is no point in answering you. Nothing will change, and you will just continue insisting and haranguing.

 

52 minutes ago, David Burgess said:

Gough has probably learned from experience that there is no point in answering you. Nothing will change, and you will just continue insisting and haranguing.

David, as you can see on the figure more happens. In order to understand at least I need to know if the structure is driven by string load. If this is the case another question arises. The lenght of the sound post. The movement on the C-bout rib structure. You may have the answers so let us know. 

 

55 minutes ago, David Burgess said:

Gough has probably learned from experience that there is no point in answering you. Nothing will change, and you will just continue insisting and haranguing.

 

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Just now, reguz said:

 

 

 

David, as you can see on the figure more happens. In order to understand at least I need to know if the structure is driven by string load. If this is the case another question arises. The lenght of the sound post. The movement on the C-bout rib structure. You may have the answers so let us know. 

 

 

Yes certainly in the dynamic condition the movement = frequency we see at the bridge top. Alike action in the direction of the string lenght will happen,

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58 minutes ago, LCF said:

Thanks Andreas, I have already been following your workbenchvseries with interest.

 

It is dull and prosaic but suspect that simple bit of stiffness logic wrt the ribs might have some interesting stories to tell us about how violins work.

The figures above show where the F-hole influences the behavior of the lenght beam between the two end blocks. The function technically the F-hole holds is the the lenght beam consiste opf three part of which the two on the bout shape hold principally equeal lenght about 162.163 mm and the structure on the !island about 32-35 mm.

The  "two"  and the "one" on the island I epect must hold equal stiffness. The "two" buckle outward and produce bulging shape and the "one" flattens the cross curve between the F-hole and along the lenght axix a downward movment as result. The behavior on the "island" thus is more complex the other "two". This dynamic behavior requires a flat top between the sound post and the upper F-hole so a shorter chord line may become produced just as it will be on the other "two". The behavior is possible affecting in positiv manner by reducing stiffness on the edge og the F-hole  wing. (my experience) 

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1 hour ago, Peter K-G said:

is this what you want to discuss?

 

principledeformationsonlenghtaxis.gif.15ddec7c0034790f6b96b710a83b7815.gif

Deform.thumb.PNG.d59363988301e527549a277c5ad5eae0.PNG

Why is it that N Harris obeserved by measuring that the back plate becomes longer and the top plate shorter+

If we accept as the most makers do make a thicker location where thesound post stay on the back we there have better resistant for the bending.

All around the sound post becomes pulled upward so also the similat location under the bass bar. When that happens that structure move upward and puches on the  end blocks . The chord line try becoming longer.

That is the result N Harris found when we did his measuring.

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1 hour ago, reguz said:

Dear LCF. I asked C Gough how it is possible changing curve lenght as shown by him happening in split seconds.

No answer.

20141207 Frequency deflection C Cough20141207_00000.jpg

Harris observed the back chord line became longer. Read what I explained. On this figure we see a twisting of the end block in spit second. What happens with the neck and finger board?

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1 hour ago, LCF said:

Peter K-G  that's good for the static  lengthways string load. 

Now you need to find the corresponding animation at right angles to this showing how the small rocking motion due to string oscillation  drives the heart of the soundboard via the bridge. A bridge cannot transmit much motion in a direction at right angles to its face, no significant vibration in the direction of the string tension.  That's the design, why it is so thin compared to its width. It is flexible in the string direction and rigid at right angles to the strings and parallel to the bow.

Those images are from reguz website, just trying to move the discussion forward.

I have no clear opinion, other than it feels over simplified. Things happens in 3D.

It cannot be explained only from 2D side view and lengthwise deformation.

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