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Why arching shape?


reguz

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  • It is a frequent occurrence for a violin maker, to have visitors who wish to try all the violins out, often for hours. Yesterday it was a gentleman from Heidelburg who wanted to test drive everything for about 3 hours. As usual, I started by standing to heel, ready to explain the history and significance of each individual instrument, but (also a frequent occurrence) he said no, he was only interested in the sound (some people have a restricted life). Whenever this happens, the respective visitor, invariably comes to unique findings, is however convinced that his/her results are definitive, after all he has just played them all.

     

    I often think that life would be far simpler, if I had a smart Alec science hat to put on, where I could just tell everybody what sounds best or not, and why. In reality, I think it is better to remain friendly and polite, and just to write an invoice for whichever one has won the lucky dip.

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9 minutes ago, Dennis J said:

I don't see comparing the arching of the violin top to an arched bridge very helpful.

But taking the analogy further, one of the major advances in bridge building was the development of the box girder. And, as a sort of box, surely the body of a well made violin should be able to withstand the loads exerted on it by the strings without buckling anywhere.

I would have thought that it would be more likely to twist than anything else.

 

 

 

 

 

 

 

Arch design experiments with low tensile strength-high compressive strength materials (stone, brick, cross grain wood) have been going on for some time.  Preliminary results indicate that robust end supports are helpful for preventing collapse.

arches.jpg

deformed arch, small.jpg

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48 minutes ago, jacobsaunders said:
  • It is a frequent occurrence for a violin maker, to have visitors who wish to try all the violins out, often for hours. Yesterday it was a gentleman from Heidelburg who wanted to test drive everything for about 3 hours. As usual, I started by standing to heel, ready to explain the history and significance of each individual instrument, but (also a frequent occurrence) he said no, he was only interested in the sound (some people have a restricted life). Whenever this happens, the respective visitor, invariably comes to unique findings, is however convinced that his/her results are definitive, after all he has just played them all.

     

    I often think that life would be far simpler, if I had a smart Alec science hat to put on, where I could just tell everybody what sounds best or not, and why. In reality, I think it is better to remain friendly and polite, and just to write an invoice for whichever one has won the lucky dip.

Well - I think as long as you get to write that invoice at the end of the session, it's win-win!

A huge part of the enjoyment, for the buyer, is tire-kicking.  And we all kick tires with slightly different agendas...

Just smile, maybe offer a coffee, and let people enjoy.  They're much more likely to pull out their credit card that way...

Caveat:  That does not include the professional tire-kickers...who only kick and never buy...dunno if you can spot those ahead of time or not...

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1 hour ago, Marty Kasprzyk said:

Arch design experiments with low tensile strength-high compressive strength materials (stone, brick, cross grain wood) have been going on for some time.  Preliminary results indicate that robust end supports are helpful for preventing collapse.

arches.jpg

deformed arch, small.jpg

What you show on the image is correct no dodt about that. But cannot compare with the forces that act on the violin. On the violin the load seen on your image comes from the string and the string act on the abututment in the case of the photo the rock structure. If your comparison would be correct the end blocks become puched away  and the chordline would become longer just as we see on the image above. Look again on my vector image a that explain what happens with the string load action. This is possible not so easy to undertsand without any knowledge but it is what it is. The arc shapes buckle outward instaed of becoming lower and wider. Hope you come to an undertsanding.

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An arch, for static vertical load, is ideal for distributed loads, but not for point loads, such as a violin bridge foot.   The center is going to cave.  To resist static loads most efficiently, you'd want:

1178608647_Staticarch.jpg.27f294880101551598555cc1631017c3.jpg

Of course, that might be (and probably is) terrible for creating a broad acoustic response.  Still, some day I would like to carve one up and see.

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29 minutes ago, martin swan said:

Then why are old backs always longer than fronts?

Attached is a finite element analyis (FEA) modeling of a violin under string tension taken from Colin Gough's reply to Mr. Zulger a few years ago.  It shows how the back is statically stretched longitudinally more than the back and how the end blocks are rotated inward and how the top plate is dished downward.  If you look carefully you should see that the C bout cross arch flairs outward.  After a long time wood creep will eventually make these shape changes permanent.

I've also attached Colin's entire reply.

Influence of static tension and differential in-plane displacements breathing mode.pdf

Static loading.jpg

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Martin, if you are able involving wood properties and "tension" wich must be compression you are welcome. The differensbetween tension and compression are the opposites.

However, the vector diagram is as simple as possible making the main conditions visible. It does not take in account that the bridge feet is NOT an extension of the sound post.

So there is much more to say but its already to difficult for many as its shows I believe. The major is showing that the end block move not the sound post.

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18 minutes ago, Marty Kasprzyk said:

Attached is a finite element analyis (FEA) modeling of a violin under string tension taken from Colin Gough's reply to Mr. Zulger a few years ago.  It shows how the back is statically stretched longitudinally more than the back and how the end blocks are rotated inward and how the top plate is dished downward.  If you look carefully you should see that the C bout cross arch flairs outward.  After a long time wood creep will eventually make these shape changes permanent.

I've also attached Colin's entire reply.

Influence of static tension and differential in-plane displacements breathing mode.pdf

Static loading.jpg

That's one hypothetical analysis of deformation. How many others can you come up with?

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21 minutes ago, sospiri said:

That's one hypothetical analysis of deformation. How many others can you come up with?

I would call it the primary analysis of deformation. The pull on the saddle/end block and the neck/nut is destine to fold it in half. Where exactly the folding will happen, the center line, will vary from instrument to instrument, but the basic physics don't change. I mean the bridge is the technical center, but there could be weakness in the material that would cause buckling away from the center. Ice does not always break where you hit it.

If you keep winding the strings, eventually the saddle and nut would kiss, assuming the violin were rubber

I've actually carved tops to intentionally do this and have had some interesting results. The fiddle may die an early death by being given a head start at folding based on the dipped arch I carved, but it is a great sounding violin.

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31 minutes ago, martin swan said:

Yes this is definitely what we see!

So it's all "B" and no "A".

>

There is indeed some of Janito's drawing "A" spreading of the C bout cross arch as seen in Colin's first illustration which is attached.  I suspect that the corner blocks might help reduce this spreading compared to cornerless violins.

Colin's first FFA.jpg

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If you get an introductory text on engineering statics the explanation will be clear.  In layman's terms the strings press down on the bridge and the bridge presses down on the top.  The bending moment (force) increases linearly with the distance from the bridge.  But this is offset by the upward pressure from the ribs to hold up the plate.  So the bending moment is strongest halfway between the plate and the bridge.  You resist this bending by either making the plate thicker at this middle distance (like the shape you carve the base bar) or by tilting the plate at this point to give you a greater effective thickness to resist the bending and shear moments.  Tilting midway in the plate is an arch.  If this doesnt make sense, get a statics book.

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4 minutes ago, sospiri said:

It's surely just one example of many potential deformations? What about deformations caused by too tight sound posts on either the belly or the back?

 

again, the primary force is that of the strings on the saddle/nut

I would call your deformation possibility a secondary force, not the primary one. 

Lets assume for a minute that we put in a ridiculously long/tight post, and then this motion starts, the most likely result is post pushing a dimple or even cracking the back, however if the bride foot is off to the side of the post underneath, the end result will most likely be the post shooting through the top as the top is generally weaker than the back material, and usually thinner than the back in these locations.

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6 minutes ago, Shunyata said:

If you get an introductory text on engineering statics the explanation will be clear.  In layman's terms the strings press down on the bridge and the bridge presses down on the top.  The bending moment (force) increases linearly with the distance from the bridge.  But this is offset by the upward pressure from the ribs to hold up the plate.  So the bending moment is strongest halfway between the plate and the bridge.  You resist this bending by either making the plate thicker at this middle distance (like the shape you carve the base bar) or by tilting the plate at this point to give you a greater effective thickness to resist the bending and shear moments.  Tilting midway in the plate is an arch.  If this doesnt make sense, get a statics book.

but,but...magic box :)

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5 minutes ago, sospiri said:

That's one hypothetical analysis of deformation. How many others can you come up with?

Sopri; i'm happy that you show these figure and the comment based on my discussion with C Gough.

First of all construct the instrument  so as Gough uses in his FEA.- It is based on the inner out line of the Titian Strad violin without corner and end blocks. He give the lengt arc redia shape and all cross sections also raddii shape from on side to the other thus having a perfect chordline under the radii. The thickness of the plates 3 mm are also radii and this give a special connection to the rib. At the highest lenght arc cross section the connection with the rib is far  more than the  3 mm thickness. it is about 4mm and become less  entering the center line wher it is some what more than 3 mm.

Cough witt telling that he uses the Titian out line is you letting to belive we deal with the Titian. The shape and conditions with out block is no violin its some thing else and we can not expect that it will function as a violin. 

Beside this Gough hols the instrument  in his FEA at the centerline  and the location of the end blocks. Now consider; when string load applies the missing end blocks move upward in relation to the sound post. BY GRAVITATION the instrument remain on the location where he support the instrument. To do so the complete structure must move down ward and Gough belive that its due to the load on the bridge and now he observe deflection. Since he hold the missing end block fixed the deformation by the downward movement casuse a widening of the belly in the C-bout will the back by the down ward movement pull in the rib. This is what the figure show and is impossible producing oin a instrument free in space. Goug and Soppan work in team and Stoppan i show the two phases when the instrument become dynamic. Widening the belly and pulling in the back. TOTALLY fault.   Since ther oare no blocks the neck tilting upward produce roptation on the rib it is connected on . On tye real instrument we have glued connection by the widdth inward about 15 mm. That connection when we study buckling condition is called FIXED and do not allow an upward buckling shown on the image above. Study the different condition as the great Mathematic professor once found out. You find picture on my internet site in one of m,y treports. So what we see above probally is possible on HIS construction but not om any vreal violin. The missing end block allow rotation of the rib structure and of course the back plate become longer. The violin does not!!

The report Gough show these figuree also show a figure where the distance between the belly and back increase/decreas. Thus you need a telscopic sound post to makle such movement. I say the distance by tehe lenght of the sound post REMAI do not change. On the figure the string has a stright horizontal connection between the nut and the bridge. In that state there is no longer a downward forec on the bridge. NO bending is present in that state. Continoing the string tension also finnally will make a straight line on the other side of the bridge. The instrument is forced in a condition like a banana with a string from end top end In the FEA analyze Gough thus produce circumstance that never arise. What is the meaning with that and how can he claim we xeal with a violin. All this a noteducated violin masker in solid mechanic jat accept and can not do other. You become cheated. I have used may hour studying what he present and had a lon discussion with Gough.

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13 minutes ago, jezzupe said:

again, the primary force is that of the strings on the saddle/nut

I would call your deformation possibility a secondary force, not the primary one. 

Lets assume for a minute that we put in a ridiculously long/tight post, and then this motion starts, the most likely result is post pushing a dimple or even cracking the back, however if the bride foot is off to the side of the post underneath, the end result will most likely be the post shooting through the top as the top is generally weaker than the back material, and usually thinner than the back in these locations.

Jezuppe; I have been explaining static conditions not the result in the dynamic state. Well aboutshooting through the top you know better but may makers reinforce the inside as you know.

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10 minutes ago, jezzupe said:

but,but...magic box :)

Jezzupe, You still do not accept that there is an equilibrium state by compression on the Bridge some what higher and the sound post. The comprssion on the sound post in may instrument is not very high. When you take of the strings and bridge the belly bend outward and the sound post tumble. On the N Harris violin in his thesis we observe a upward movement of the bridge feet staying on the bass bar. This tells me that the reinforcement that must prevent that movement this is some what weak.

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And as final words to Reguz; Sir, you may or may not be onto something, regardless, instead of trying to explain it to the world, as Martin suggested, it will be best if ou show the world, instead of try to explain it

And, as a word of advice about how you come across to others. You could be the smartest man in the world, but if you can not communicate properly with people you will be ignored.

Think of the horror of someone like Einstein or Mozart who were as brilliant as they were, but were never heard because they were ignored because of the way they came across to other people.

I'm sure that this has happened in human history, some ground breaking information was there, known, ready to be disseminated, but fell on deaf ears because the "genius" lacked the one thing that would have allowed everyone to understand , the ability to communicate with other in a way that is not offensive.

I think if you want your instruments, you work and your ideas to be taken more seriously, that, regardless of any language barriers that may be present, you must work of your style of communication.

I really feel that "it" is what is holding you back, perhaps be more introspective of the way you come across to others.

Put yourself in others shoes listening to you speak. It would have been a shame if no one wanted to hear Mozarts music because no one wanted to hear what came out of his mouth.

Always with 100% certainty, with an artist, musician, scientist, what comes out of the mouth is what precedes the presentation of what ever it is they do...

 

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23 minutes ago, jezzupe said:

again, the primary force is that of the strings on the saddle/nut

I would call your deformation possibility a secondary force, not the primary one. 

Lets assume for a minute that we put in a ridiculously long/tight post, and then this motion starts, the most likely result is post pushing a dimple or even cracking the back, however if the bride foot is off to the side of the post underneath, the end result will most likely be the post shooting through the top as the top is generally weaker than the back material, and usually thinner than the back in these locations.

When you put in a too long sopund åpost you affect the cord line from the sound post to the end block It requires a longer chord line which only is possible when the arc shape (radii) become less. When we do this we affect the stress conditions on the belly and back. That is what you do findeing the best accoustic result of the dynamic behavior producing sound baased on stres condtion on the bout shapes.

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