Jump to content
Maestronet Forums

Belly vs Back Arching Asymmetry


Recommended Posts

On 3/19/2021 at 5:30 PM, reguz said:

Hi Don Noon. I was just waiting for when you will show upp as a Joker playing the best card. Well it is nice that you have put all earlier writing on this site. It becomes much easier for any one starting reading from the beginning.

But let me ask a question based on may unanswered question.

There have been made made statements that there will be no differens in loading with dead weight as Bruce did in the climate chamber and the condition of deflection caused by string load.

I say there is a great differens in structural behavior depending on the fact that the center in the climate chamber force the center down while string. This result in a widening of the center of the belly in the C-bout while the back  become pulled inward.

With the string load condition the end blocks become pulled upward/inward and no movement arises at the sound post. I have described how any one easy can check this. 

Why is it no one try and find out?

Comparing the two differens condition we cannot say there is no differens in de flection. 

It obvious and we must ask us can we apply the first condition for understanding the deflection of the strung instrument.

For me it is obvious what's wrong to do, the dead load condition.

Now I ask any one of you to answer and show proof that the dead loading condition produce the same deflection the string loaded instrument.

Pleas do this or accept my statement. Not answering mean to me "I don't know what's the differens".

enclosed you find the image Colin Gouhg together with G Stoppani produced when the loaded the center in their FEA. The end block remain at the same level.  The sound post hold telescoping function.

So just go ahead and convince me that I'm wrong. That's the best you can do!!!

 

2037624952_20141001Stopaniphasemovement20141001_00000.thumb.jpg.4bcc8a024d5982d47b2e7ba02e15459b.jpg

The only way to find out if your theory of the back bending and the end blocks moving is true is to make the entire back of thick cast alluminium. The neck can just slide into a pre-made motice in the alluminium top block. Nothing in the body will be able to move or flex. Now make an ordinary spruce top in the normal manner and load it and observe what happens.

But as it would be prohibitivley expensive to make a solid alluminium body, why noy buy a decent 3D plastic printer and make one with that and try out your theory ?

Link to post
Share on other sites
  • Replies 319
  • Created
  • Last Reply

Top Posters In This Topic

10 hours ago, Marty Kasprzyk said:

Whether or not the sound post moves is relative to your reference point.  There's no sense in trying to discuss something unless everybody uses the same reference point.

For example I'm sitting  here at my computer and I'm not moving at all relative to my chair, But relative to the center of the earth I'm moving pretty fast because the earth is spinning.  I'm moving even faster relative to the sun because the earth is orbiting around it and so on.  So it doesn't make any sense to argue whether or not I'm moving without specifying the reference point.

Even our basic measurements are relative to some reference for example a meter was 1/10,000,000 of the distance between the North and South poles, a liter was 1/1000 of a cubic meter, a kilogram was the mass of of one liter of water and so on.

But the big take away here is that it is easier to read something if spaces are made after a few sentences rather than having one long paragraph.

I think it is just a question of how the violin body bends and what that may mean as far as distortion is concerned. If the back is sufficiently thick/strong enough the reference point can be taken as the location of the back where the soundpost rests.

If the central back area is not strong enough to resist downward pressure of the bridge without bending then things change. I see some makers are graduating the back in that location as little as 4.5 mm. I thought about 6 mm was accepted as necessary.

As far as I can see a bit of intuition and common sense is the best way of looking at these sort of issues.

 

 

 

Link to post
Share on other sites

Det som jag tycker är mest sorgligt med denna tråd (och tidigare trådar som Don listade upp), är att Roberts forskning och insikt går förlorat i hur han själv agerar i sak frågorna. Det är ju nämligen så att det egentligen inte finns några motsägelser mellan Bruce reella observationer från Il Cannone studien och Roberts modell.

Problemen är ju fler faciterat i den bemärkelsen att detaljerade teoretiska/abstrakta modeller aldrig kan fullt ut mäta sig med enkla direkta observationer, som av förståeliga orsaker (teknisk utrustning/begränsning i exakthet), kan mäta sig mot matematik.

Helt enkelt, placera en o strängad violin att ligga på två ribbor (med botten fri från underlag),  under uppe och nedre klossar, så går ju botten ner (tillsammans med ljudpin och lock). Klossarna viks inåt, och locket, botten deformeras precis enligt förväntan. Halsen viks uppåt osv. Inget mysterium alls.

Men! Avvikelser finns i hundratusentals. Det är ju till och med möjligt att bygga en fiol, vars lock (under stallet) deformeras uppåt när man strängar upp den.

 

Link to post
Share on other sites

Hi Peter LK-G. Translated with Google you write. 

What I find most sad about this thread (and previous threads

that Don listed), is that Robert's research and insight is lost into how he himself acts on the substance of the issues. It is the case that there are really no contradictions between Bruce's real observations from the Il Cannone study and Robert's model.

 

The problems are more faceted in the sense that detailed theoretical / abstract models can never fully measure themselves with simple direct observations, which for understandable reasons (technical equipment / limitation in accuracy), can measure themselves against mathematics.

 

Quite simply, place an unstringed violin to lie on two ribs (with the bottom free from the ground), under the top and bottom blocks, then the bottom goes down (together with the sound pin and lid). The blocks are folded inwards, and the lid, bottom is deformed exactly as expected. The neck is folded upwards, etc. No mystery at all.

 

But! There are deviations in the hundreds of thousands. It is even possible to build a violin, whose lid (under the stable) is deformed upwards when you string it up.


 

OBSERVE You write about a unstringed instrument related to an outer structure it rest on. That''s the problem you do not understand. Applying string load on this condition the instrument does not start flying. Yes the center sound post/bridge move downward. I have no problem with this. Its a obvious observation. The problem is that no one seem understanding is . What deflect in relation to what?  And what you all say the center is moving down. As I wrote before the instrument laying on the table a force must come out under the center but does not happen. The weight does not increase. Instead the end blocks on wich the strings act are forced moving upward/inward in relation to the point or points that react. Most reaction is given top relate to is the sound post since the sound post does not move.  Doing an 3D Photo investigation of the instrument of course is tricky. It takes time to do IT TAKES TIME  (described earlier).They managed to do this in 3 hours 30 min. Impossible i say. So the question arises what did they do. Also this I have tried to describe. My believe is that coming around the time problem and still measure deflection is by measuring from the rib, A rib structure they decided do not deflect do not bend.

We can see this on the maps they made. Almost all green around the out line. Beside that we see tilting of the neck but also there the tilting happens at the end block a end block that not is forced upward. This verify for me that the choose the rib being unaffected by string load. Is this a assumption we can make? I can't and seek for a reliable answer but they do not answer and all of you accept their report.

 

Its is not about me . Its about what happens so we understand. Unfortunately no one  seem to have the ability coming to understand what really happens and therefor no one say any. You Peter you may do.

If you do not have access to the Bruce and co report I end them to you just give me your email adress and start studying. Compare with the these from the Lund University.

Link to post
Share on other sites
6 hours ago, reguz said:

Hi Peter LK-G. Translated with Google you write. 

What I find most sad about this thread (and previous threads

that Don listed), is that Robert's research and insight is lost into how he himself acts on the substance of the issues. It is the case that there are really no contradictions between Bruce's real observations from the Il Cannone study and Robert's model.

 

The problems are more faceted in the sense that detailed theoretical / abstract models can never fully measure themselves with simple direct observations, which for understandable reasons (technical equipment / limitation in accuracy), can measure themselves against mathematics.

 

Quite simply, place an unstringed violin to lie on two ribs (with the bottom free from the ground), under the top and bottom blocks, then the bottom goes down (together with the sound pin and lid). The blocks are folded inwards, and the lid, bottom is deformed exactly as expected. The neck is folded upwards, etc. No mystery at all.

 

But! There are deviations in the hundreds of thousands. It is even possible to build a violin, whose lid (under the stable) is deformed upwards when you string it up.


 

OBSERVE You write about a unstringed instrument related to an outer structure it rest on. That''s the problem you do not understand.

Implies that the violin will be strung up in that resting state.

I wrote in swedish to see if there was some language barrier. It's probably that too, but seems to be more of a communication problem. I don't know...? It's kind of hopeless.

Ville du faktiskt förmedla följande?

MÄRKVÄL Du skrev om ett osträngat instrument relaterat till dess yttre struktur det ligger på. Alltså du fattar inte och det är ditt problem.

(Implicerar att jag måste vara rätt retarderad som inte ens begriper enkla triviala saker)

.....

 

Link to post
Share on other sites

Your interpretation of Bruce's report is incorrect.

7 hours ago, reguz said:

Hi Peter LK-G. Translated with Google you write. 

What I find most sad about this thread (and previous threads

that Don listed), is that Robert's research and insight is lost into how he himself acts on the substance of the issues. It is the case that there are really no contradictions between Bruce's real observations from the Il Cannone study and Robert's model.

 

The problems are more faceted in the sense that detailed theoretical / abstract models can never fully measure themselves with simple direct observations, which for understandable reasons (technical equipment / limitation in accuracy), can measure themselves against mathematics.

 

Quite simply, place an unstringed violin to lie on two ribs (with the bottom free from the ground), under the top and bottom blocks, then the bottom goes down (together with the sound pin and lid). The blocks are folded inwards, and the lid, bottom is deformed exactly as expected. The neck is folded upwards, etc. No mystery at all.

 

But! There are deviations in the hundreds of thousands. It is even possible to build a violin, whose lid (under the stable) is deformed upwards when you string it up.


 

OBSERVE You write about a unstringed instrument related to an outer structure it rest on. That''s the problem you do not understand. Applying string load on this condition the instrument does not start flying. Yes the center sound post/bridge move downward. I have no problem with this. Its a obvious observation. The problem is that no one seem understanding is . What deflect in relation to what?  And what you all say the center is moving down. As I wrote before the instrument laying on the table a force must come out under the center but does not happen. The weight does not increase. Instead the end blocks on wich the strings act are forced moving upward/inward in relation to the point or points that react. Most reaction is given top relate to is the sound post since the sound post does not move.  Doing an 3D Photo investigation of the instrument of course is tricky. It takes time to do IT TAKES TIME  (described earlier).They managed to do this in 3 hours 30 min. Impossible i say. So the question arises what did they do. Also this I have tried to describe. My believe is that coming around the time problem and still measure deflection is by measuring from the rib, A rib structure they decided do not deflect do not bend.

We can see this on the maps they made. Almost all green around the out line. Beside that we see tilting of the neck but also there the tilting happens at the end block a end block that not is forced upward. This verify for me that the choose the rib being unaffected by string load. Is this a assumption we can make? I can't and seek for a reliable answer but they do not answer and all of you accept their report.

 

Its is not about me . Its about what happens so we understand. Unfortunately no one  seem to have the ability coming to understand what really happens and therefor no one say any. You Peter you may do.

If you do not have access to the Bruce and co report I end them to you just give me your email adress and start studying. Compare with the these from the Lund University.

I don't believe your interpretation of Bruce's report is correct.  People can get a distorted view of things but I don't think laser scanners do.

Screen Shot 2021-03-27 at 10.00.54 AM.png

Link to post
Share on other sites

Hi Marty. Of course you may have your opinion. But I ask you did you carfully study how Broce & Co did their investigation? I mean they in the early phase look at the instrument hold fixed in a climate chamber and loaded with a dead weight. That load looks like a upside down U. the legs down thus are in the C-bout. Since the load may turn over the instrument side ways they clamp the end blocks. We see this by the blue clams. Yes you can do so but the result of loading this way deflect the instrument in the center down while the end blocks remain at the same level. Do you say this is not different and don't produce different deflecting conditions as when it comes by loading the instrument with string load. Do the left and right side (thus the end blocks) move equal upward? Equal the conditions in the climate chamber. I say NO simply because we cannot say and proof that the stiffness of the structure on both side of the bridge/sound post are equal. But Bruce show this is what he believe.  Bruce in a email to me as an explanation write we have chosen that the rib structure does not bent. Can we do so so easy? Strings on the scroll produce a moment of force that together with the back produce deflection on back arc shape. The end block become pulled upward. What Bruce show is no moment by this moment of force. The finger board show tilting with the end block as the rotating point stil green just as the rib out line. 

Consider this. I made my study and I show this on my internet site. Now I will show you how I did finding out how to come around this problem having the vertical load conditions and the weight of the instrument. In order to only be able looking at the forces produced by the strings I hold the instrument 90 degree rotated and support on the rib and hold on bot side of the location of the sound post. Any deflection of the structure left right of the sound post now is measurable. I did this by looking on the back of my viola with holography. Very little as described string load on one string produces the deflection where it happens. The time between the first picture and the second where taken with 24 hour in between. The instrument was placed on a marble table 2,5 * 2,5 m table and build in with walls and roof so there was as little as possible infected. The  camera was connected with a computer that take picture ever 30 minutes during 24 hour. The increasing tension of the string was done by a Syncron motor (1 rotation in 1 minute) that pulled the lever 4 degree. You may see the result of the 24 hours on my internet site and pictures how the instrument was hold. 

Hope this give you some understanding the differens of handling the instrument

The holographis conditions.docx

Link to post
Share on other sites

You seem to misunderstand the whole thing. Your writingskills in english lack a lot (I'm not native english speaker but I guess others have similar difficulty reading your posts). And I guess your comprehension of english written text is not best as well. You keep repeating the same hard-to-decipher phrases and accusing evreyone else that thay don't understand. You should consider that odds are a bit higher that you are the one whoe doesn't understand the rest...

Bruce explainedthat the deformation measurements were taken from free violin on a blanket using laser scanner and then processed in computer. The blue clamps you keep mentioning were likely used in some other experiment/measuring and even uf they were used for this testing they are just rubbery plastic closing clamps that are extremely unlikely to keep body blocks from any rotation movement at all. Thay would simply rotate with the violin blocks as they touch violin with just small footprint at the edge.

The pics in your last post show your rig for holding violin and I must say your device is nice but has some fatal flaws. You place on a granite table a rig that is welded from thin floppy sheet metal. That would allow movement in tenths of mm just by looking hard at it, I wonder how you manage to tune it up without throwing any accuracy out of window. The dowel securing the soundpost position doesn't even fit the contour of violin and holds on tiny fraction of the surface which makes it very poor holding device. Tightening the bolts holding the violin would also change geometry of the whole thing. The violin is laying also on it's side on a flat thin ramp which makes it a four point - or better said two point plus two line sections contact - no good even from purely theoretical view. When you tighten string the whole structure distorts including sides and that compromises your holding position. Ideally you want to have just two or three holding points as I explained before so you have reference line or plane for displacement measurements.

Link to post
Share on other sites
5 minutes ago, Peter K-G said:

A really efficient way of preventing deformation is tapering the top ribs after upper corner blocks 

That's the sort of constructive insight this discussion needs. Probably why some makers in the past have done it.

 

 

Link to post
Share on other sites
On 3/26/2021 at 6:57 AM, reguz said:

Hi HoGo

>

Now that you agree you also know that the end block at which the strings act are forced upward/inward, simply a type of rotation dependent on the structural stiffness of the violin body. When this rotation happen the bout shapes of the belly by compression starts buckling. "Buckling" is different from "bending" is happens when a column load forces the column to bend in one ore another direction. Since the "column" on the belly already has a curved shape it vill buckle outward. However the circumstances on the end point of the  column are different. On the end blocks they are "fixed" do not rotate while on the other end we find them free .

>

Does everybody at least agree that both end blocks rotate inward when string tension is applied as shown in Colin Gough's attached FEA diagram? 

 

 

Screen Shot 2021-03-27 at 7.16.04 PM.png

Link to post
Share on other sites
9 minutes ago, Marty Kasprzyk said:

Does everybody at least agree that both end blocks rotate inward when string tension is applied as shown in Colin Gough's attached FEA diagram? 

 

 

Screen Shot 2021-03-27 at 7.16.04 PM.png

I do, and also happen to agree with a lot of Collin's research as I have confirmed some of his theoretical body mode models.

What I don't agree on is "rotated", nothing is rotated! It's bent upwards/ inwards. Rotation to me means 2pi

I also have a database of research publications from a period of 1997 to todate. Downloaded everything that has been public and some arent't public anymore. I have also read them all ;)

 

 

 

Link to post
Share on other sites
24 minutes ago, Peter K-G said:

I do, and also happen to agree with a lot of Collin's research as I have confirmed some of his theoretical body mode models.

What I don't agree on is "rotated", nothing is rotated! It's bent upwards/ inwards. Rotation to me means 2pi

I also have a database of research publications from a period of 1997 to todate. Downloaded everything that has been public and some arent't public anymore. I have also read them all ;)

 

 

 

OK, OK!    How about tip inward instead of rotate inward:    

Does everybody here now agree that both end blocks tip inward when string tension is applied as shown in Colin Gough's attached FEA diagram?

The tipping seems to be around the bottom inside edges of both end blocks. Neither of the blocks remain vertical.

 

 

 

(Sometimes I also tip or rotate off vertical)

Link to post
Share on other sites

I do. But I didn't need scans to tell me that.

However I believe that a violin should be made in such a way to keep that bending to a minimum.

It's tempting to compare the violin under string tension to an archery bow. But it doesn't behave that way because most of the bending takes place at its centre.

 

 

Link to post
Share on other sites
On 3/8/2021 at 9:47 AM, Shunyata said:

I would like to make sure I properly understand a subtlety.

The long arch has a high point in the middle of the plate and slopes down to the top and bottom edge of the plate.

For backs it seems like the arching is typically symmetrical - the top-side arch and bottom-side arch are mirror images.

For bellies it seems like the bottom-side arch is very similar to the back.  But the top-down arch is rather different.

The belly top-side arch seems to stay flatter as you move from the center, then fall more steeply once you cross the upper bout wide point.

Do I understand this properly?

yes

Link to post
Share on other sites

Whether by intention or not I suspect many violin top arches peak forward of the actual centre of the body.

For the upper bout part of the long arch to have a shorter radius of curvature than the lower part the best arrangement is to have the highest point forward of the centre.

 

Link to post
Share on other sites
14 hours ago, Peter K-G said:

A really efficient way of preventing deformation is tapering the top ribs after upper corner blocks 

Peter,

At last I got something out of this discussion. Making the taper you describe is standard practice, isn’t it? Now I can see a reason for it.

Thanks

Link to post
Share on other sites

Hi Marty. Of course you may have your opinion. But I ask you did you carfully study how Broce & Co did their investigation? I mean they in the early phase look at the instrument hold fixed in a climate chamber and loaded with a dead weight. That load looks like a upside down U. the legs down thus are in the C-bout. Since the load may turn over the instrument side ways they clamp the end blocks. We see this by the blue clams. Yes you can do so but the result of loading this way deflect the instrument in the center down while the end blocks remain at the same level. Do you say this is not different and don't produce different deflecting conditions as when it comes by loading the instrument with string load. Do the left and right side (thus the end blocks) move equal upward? Equal the conditions in the climate chamber. I say NO simply because we cannot say and proof that the stiffness of the structure on both side of the bridge/sound post are equal. But Bruce show this is what he believe.  Bruce in a email to me as an explanation write we have chosen that the rib structure does not bent. Can we do so so easy? Strings on the scroll produce a moment of force that together with the back produce deflection on back arc shape. The end block become pulled upward. What Bruce show is no moment by this moment of force. The finger board show tilting with the end block as the rotating point stil green just as the rib out line. 

Consider this. I made my study and I show this on my internet site. Now I will show you how I did finding out how to come around this problem having the vertical load conditions and the weight of the instrument. In order to only be able looking at the forces produced by the strings I hold the instrument 90 degree rotated and support on the rib and hold on bot side of the location of the sound post. Any deflection of the structure left right of the sound post now is measurable. I did this by looking on the back of my viola with holography. Very little as described string load on one string produces the deflection where it happens. The time between the first picture and the second where taken with 24 hour in between. The instrument was placed on a marble table 2,5 * 2,5 m table and build in with walls and roof so there was as little as possible infected. The  camera was connected with a computer that take picture ever 30 minutes during 24 hour. The increasing tension of the string was done by a Syncron motor (1 rotation in 1 minute) that pulled the lever 4 degree. You may see the result of the 24 hours on my internet site and pictures how the instrument was hold. 

Hope this give you some understanding the differens of handling the instrument

Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
  • Recently Browsing   0 members

    No registered users viewing this page.




×
×
  • Create New...