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Belly vs Back Arching Asymmetry


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On 3/9/2021 at 11:40 PM, David Beard said:

Again, in 2D the idea appears viable.

But, in 3D, the extra height at the ends also affects the cross arching.  How do they get broader?  And, why aren't the angles in the channeling more effected.

Since the claim is that ALL classical examples went through various degrees of similar distortions, ALL the chanelling should be skewed at the extremes of the bouts.  So, why don't the examples show that?

Also, if the plates are just deformed, why does fairly significant pushing in or pulling out of a free plate at the ends yield similarly visible degrees of enhanced and reduce temporary distortion?

What do you mean by "how do they get broader"? What is "angle in channeling"? What are "extremes of bouts"?

Wood is plastic and will deform (to some degree) in any direction if forced. You can force a flat plate into arched top with enough pressure (and steam).

As I stated I work mostly on arch top mandolins and what you see in older instruments with thin tops ia just bulge (sometimes surprisingly high) between bridge and tailpiece and the recurve under tailpiece sinks. Block definitely rotates slightly and often the joint between back and ribs opens below endpin. The rest of the shape or arching is basicly unaffected. It acts as if you pushed clay...I restored few like this using cast and reshaping it to press the arch back and add breast patch extending to the tailpiece end. Otherwise they would slowly deform back in few months under string tension and ultimately the top joint would pop open or recurve break across.

I don't understand the last cited sentence at all... What do you mean by that?

It's easy to do simle test with VSO and see what happens when you clamp the body with a sash cramp and tighten... use wdged between top and cramp bar to simulate pressure of bridge... You can easily measure the gaps between the bar and the top an also the amount of clamping distortion....

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6 hours ago, HoGo said:

No one stated that in this or the other thread.

Unless it gets edited, the post immediately before I said this refers to rounded top arches.

Pleas read before accusing me of not reading 

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6 hours ago, David Burgess said:

Why do you keep inventing my positions, when I've posted my real ones in both threads? Are you looney-tunes or something? :rolleyes:

So then you agree that carving rather than distortion is the primary cause of the top long arch character we see today in the old instruments?

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1 minute ago, David Beard said:

So then you agree that carving rather than distortion is the primary cause of the top long arch character we see today in the old instruments?

Nope. The fact is that nobody knows, and especially not you, since you have only recently been dragged, kicking and screaming, into the realization that violins distort, despite still lacking the realization that they will distort a heck-of-lot under certain conditions.

I think HoGo summed it up nicely, comparing your view with that of someone  who sees an old dented and rusted car, and believes that it must have been made that way. :lol:

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6 hours ago, HoGo said:

  

What do you mean by "how do they get broader"? What is "angle in channeling"? What are "extremes of bouts"?

Wood is plastic and will deform (to some degree) in any direction if forced. You can force a flat plate into arched top with enough pressure (and steam).

As I stated I work mostly on arch top mandolins and what you see in older instruments with thin tops ia just bulge (sometimes surprisingly high) between bridge and tailpiece and the recurve under tailpiece sinks. Block definitely rotates slightly and often the joint between back and ribs opens below endpin. The rest of the shape or arching is basicly unaffected. It acts as if you pushed clay...I restored few like this using cast and reshaping it to press the arch back and add breast patch extending to the tailpiece end. Otherwise they would slowly deform back in few months under string tension and ultimately the top joint would pop open or recurve break across.

I don't understand the last cited sentence at all... What do you mean by that?

It's easy to do simle test with VSO and see what happens when you clamp the body with a sash cramp and tighten... use wdged between top and cramp bar to simulate pressure of bridge... You can easily measure the gaps between the bar and the top an also the amount of clamping distortion....

Hi HoGo,

Yes, would deflects it position.  And yes, wood can be plastic and hold a deflection under the right circumstance.

However, will defelect or flex, it does not readily stretch.

The long arches we are discussing do not exist in isolation.   Each point alond the long arch is also the highpoint for a corresponding cross arch.   If distortion lifts a point on long arch, it also is lift the high point of the corresponding cross arch.  If we are going to talk about distortion lifting the long arch toward its ends as it approaches the top and bottom blocks, then we are also talking about lifting the high points of the corresponding cross arches.

The problem is that in many of the historical examples, these corresponding cross arches are also full and broad.  That's something that is simple to carve, but can't happen from distortion.  Lifting the long arch and simultaneously broading the corresponding cross arches would require stretching the surface area of the wood, and that doesn't happen.

Lifting the long arch would not broaden the corresponding cross arches, but pull them toward a more peaked general shape.

The same dynamics distorting the long arch with significant lifting at the ends, or significant depression nearer the middle bridge area, would either distort the shapes of the corresponding cross arches, or/and distort the channel areas near the edge of those cross arches.

I hope that helps.  

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7 minutes ago, David Burgess said:

Nope. The fact is that nobody knows, and especially not you, since you have only recently been dragged, kicking and screaming, into the realization that violins distort, despite still lacking the realization that they will distort a heck-of-lot under certain conditions.

I think HoGo summed it up nicely, comparing your view with that of someone  who sees an old dented and rusted car, and believes that it must have been made that way. :lol:

You're lying and distorting.  Always from the beginning I give distortion its due as a secondary actor.  You just didn't take note.

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For years, I've been publicly discussing these aspects of arching.

All along I've including the caveats that: 1) I'm presenting an hypothesis, and 2) distortion is real but not a primary factor.

I will be glad when a mixture of authoritarian misrepresentations, insistence of position, and bullying is no longer fashionable or acceptable public discourse.

Again, my hypothesis is that maker choice and intentional carving are the primary factors behind the character of long arches we see in the old making.

I will continue to publicly lay out the case for this.  

Your position seems to be that I am less experienced than you and should shut up.

That isn't going to happen.

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36 minutes ago, David Beard said:

I will be glad when a mixture of authoritarian misrepresentations, insistence of position, and bullying is no longer fashionable or acceptable public discourse.

 

Then why don't you stop doing it? :lol:

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1 hour ago, David Beard said:

You're lying and distorting.  Always from the beginning I give distortion its due as a secondary actor.  You just didn't take note.

Saying someone is lying has no place on this kind of forum. You  and Burgess have different views on this subject and apparently some difficulty communicating.

 Obviously the top plates of violins are carved with a flatter arch in the middle lengthwise. Equally obviously the tops distort over time exaggerating this. Thus it was and always will be.

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2 minutes ago, nathan slobodkin said:

Saying someone is lying has no place on this kind of forum. You  and Burgess have different views on this subject and apparently some difficulty communicating.

 Obviously the top plates of violins are carved with a flatter arch in the middle lengthwise. Equally obviously the tops distort over time exaggerating this. Thus it was and always will be.

If Burgess believed and agreed with what you just said, there would be no conflict.

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18 hours ago, Bran Latebarie said:

Here's an alternative theory.  Design is based on a Bruneschelli dome.  The big flat area provides no structural strength and is not meant to be under much tension or compression.  It's like covering the skylight in the Florentine dome with a thin membrane.  This allows the violin to have a big, thin area in center and acts kinda like a drum.

 

Revolutionary design for the period.  Before this they typical Florentine arch is characterized more like the back of a violin.  Much thicker in the center than at the edges.

This is pretty contemporary with the golden violin age and everyone would have known about the Bruneschelli dome, 1420.  Still cutting edge today.  Can't do better without steel reinforcement.

dome.jpg

arch.jpg

If you wanted to prevent buckling and bending a good way of doing it is to avoid using any longitudinal curved arch and just use a straight extruded like cross arch like you see with corrugated metal sheets or one of my violas

Screen Shot 2021-03-11 at 3.53.43 PM.png

images.jpeg

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The reason that this distortion subject causes so much conflict is that the buckling hypothesis at the upper bout is so commonly accepted. It's an article of faith or belief that should not be challenged.

There have been a couple of posts here that clearly point out the weaknesses of that hypothesis.

 

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6 minutes ago, Wood Butcher said:

I suspect that you haven’t handled many old instruments.

I can imagine how someone who has handled a lot of old instruments could have misapprehensions reinforced.

 

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On 3/11/2021 at 11:11 AM, David Beard said:

I will be glad when a mixture of authoritarian misrepresentations, insistence of position, and bullying is no longer fashionable or acceptable public discourse.

Again, my hypothesis is that maker choice and intentional carving are the primary factors behind the character of long arches we see in the old making.

I will continue to publicly lay out the case for this.  

Your position seems to be that I am less experienced than you and should shut up.

That isn't going to happen.

In 10-20 years many of the people will not be remembered. 

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I've never said that violin tops don't distort just that the upper bout arching, say at its widest, bulges upward. That could only happen if the surface area there increased. The arching would have to stretch.

My view is that the whole body bends at the waist or at the sound post/bridge area. And that causes a deviation from a convex to concave area in front of the bridge. That distortion is the only one obvious as far as I can see.

I should qualify "causes a deviation." I think the area in front of the bridge is susceptible to sinking anyway apart from any body bending influence. And that concavity is probably mostly confined to the central area between the ffs. I'm sure there are plenty of luthiers who would be more familiar with distortions in this area than I am.

 

 

 

 

 

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11 hours ago, Rue said:

Very cool!  :)

What's the story on that one? How does it play/sound?

It sounded terrible--shrill, harsh.  Way too much high frequency stuff from being way too stiff.

From this I concluded that the purpose of the classic curved longitudinal arch was to create large nearly flat areas near the ends of the top and bottom bouts.  These flatter and more flexible areas produce a more likable low frequency sound.

However  this viola did have very good playability.  I found if I gripped it with the concave shaped back facing the stern of my canoe I could get a powerful stroke.

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45 minutes ago, Marty Kasprzyk said:However  this viola did have very good playability.  I found if I gripped it with the concave shaped back facing the stern of my canoe I could get a powerful stroke.

I suspect that if you dramatically increased the string length it would become much more efficient.  Clarity might suffer though.

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17 hours ago, David Beard said:

However, will defelect or flex, it does not readily stretch.

The long arches we are discussing do not exist in isolation.   Each point alond the long arch is also the highpoint for a corresponding cross arch.   If distortion lifts a point on long arch, it also is lift the high point of the corresponding cross arch.  If we are going to talk about distortion lifting the long arch toward its ends as it approaches the top and bottom blocks, then we are also talking about lifting the high points of the corresponding cross arches.

The problem is that in many of the historical examples, these corresponding cross arches are also full and broad.  That's something that is simple to carve, but can't happen from distortion.  Lifting the long arch and simultaneously broading the corresponding cross arches would require stretching the surface area of the wood, and that doesn't happen.

Lifting the long arch would not broaden the corresponding cross arches, but pull them toward a more peaked general shape.

The same dynamics distorting the long arch with significant lifting at the ends, or significant depression nearer the middle bridge area, would either distort the shapes of the corresponding cross arches, or/and distort the channel areas near the edge of those cross arches.

Sure the long arcehs don't exist in isolation. The whole thing just deforms in multiple directions. The measurement plot from D.Sora shows just measured (scanned) displacement perpendicular to plane of ribs with fixed points apparently at upper and lower ends of back (that is on new violin before/ after stringing, on violins iunder tenssion for few centuries the deormation and material creep will be definitely much more exagerrated and widespread over whole structure). There is no need for any excessive stretching of the wood for this to happen. For the biggest deviation in my sketch I posted earlier you only need 0.6mm total lentgth shortening, that is 0.3mm at each end IF the width of violin follows the length we can guess the amount will roughly follow ratio between length and widths which means reduced width of approx 0.2mm at each of widest bouts... That is hardly measurable amount and seasonal shrinking/expansion can be much larger than that. Just look at need of shortening ribs to follow long term shrinking of top.

12 hours ago, Dennis J said:

I've never said that violin tops don't distort just that the upper bout arching, say at its widest, bulges upward. That could only happen if the surface area there increased. The arching would have to stretch.

My view is that the whole body bends at the waist or at the sound post/bridge area. And that causes a deviation from a convex to concave area in front of the bridge. That distortion is the only one obvious as far as I can see.

You still think the edges don't move. They do. Some stretching is there as well and cracking or open joints can be result of this - especially those nasty ones that are closed at both ends - often they can be closed only when the arch is pressed back simultaneously with clamping.

Wood does behave like a modeling clay to some degree and allows wild deformations over large surfaces like violin plate.

 

Marty, do the best traditional makers pay you to test all the weird ideas so they don't have to? :-)

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