Jump to content
Maestronet Forums

Belly vs Back Arching Asymmetry


Recommended Posts

1 hour ago, Marty Kasprzyk said:

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.

:)

So, not playability, but paddleability!

Still, very cool!

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

Top Posters In This Topic

1 hour ago, Marty Kasprzyk said:

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.

So..., did it sound harsh when you hit it with a bow, or was it when you hit the bow with it?

Link to post
Share on other sites
10 minutes ago, Mark Norfleet said:

So..., did it sound harsh when you hit it with a bow, or was it when you hit the bow with it?

That's a good question.  

Canoes have a similar longitudinal arch shape and I suspect they would sound the loudest when you impacted their center area rather than at the bow or stern ends-- analogous to having the bridge in the center of the plate.

Link to post
Share on other sites
16 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.

 

 

 

 

 

Or that the sides move inward. Which they do.

Link to post
Share on other sites
On 3/10/2021 at 12:46 AM, David Beard said:

Which David? We are both David B.

You spoiled the next, (I agree with David B B))

In any case, this (flatter top in the middle) has been going on for numerious threads and what I truelly agree on, is that some is intentional "straighter" in the middel was!

The "tuner" in me would do that as, the spruce is delicate in this matter. The caution for me is that, not too thin for the density.

I'm sure the Amatis knew exactly, what they where doing,...

Link to post
Share on other sites
8 hours ago, nathan slobodkin said:

Or that the sides move inward. Which they do.

The bulging upper bout theory seems so implausible to me on so many levels, and I have not yet seen any convincing explanation about how it might come about.

Anyone looking at profile drawings of the top long arch can see differences of shape, even of about a millimetre, when one profile is laid over another. But identifying such differences on a glued up instrument is not as easy.

I would say the fullness of the arch in the upper bout (by which I mean the part of the arch between the widest part of the bout and the neck) would have to differ by at least 2-3 mm to be readily apparent to an experienced luthier.

And the idea that the strongly supported (by the upper block and ribs) part of the arch could somehow bulge up by longitudinal  compression is just not possible.

Or that the ribs at the level of the top plate would, under longitudinal compression, move inward doesn't make sense. If it were possible for them to move, which it is not, surely they would spread.

 

 

 

 

Link to post
Share on other sites
12 hours ago, HoGo said:

>

>

 

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

Nah, I do it for free.

My mission is taken from Start Trek: "To boldly go where no fool has gone before." 

 

 

 

 

 

 

 

Link to post
Share on other sites
On 3/9/2021 at 2:44 AM, Shunyata said:

Looking at the other discussion, I can see this topic is a real can of worms.

The short answer seems to be that what I am seeing actually exists in old instruments.  Whether I should duplicate it is another matter.

Yes, a can of worms.

i am not replying to any of those word fights but want to add a few things to consider.

Just by the structure the entire violin has to deform. This just becomes clear if you imagine everything to be very thin and flexible (or much thinner than it actually is)

How round the long arch of classical Cremonese instruments were from the beginning is IMO impossible to say. Just the fact that some of those instruments got a slightly concave arch in the center which was certainly not there when the violin was made, shows that long time stress does deform the top.

i was long time convinced that there was a flatter zone in the center. However I never thought that this was really straight as a ruler. Not so long ago Torbjorn Zethelius presented his view of a round top arch based on the fact that you can see it on the best preserved strads. He showed side views of the messiah and lady blunt. This gave me to think. 
 

in practical terms I think we have always to see arching in combination with thickness graduations. Doing right now experimental things with archings I can only say that many types work better than what I would have thought. As long as you don’t go to unusual extremes. You can ask yourself the question if a top arch a little flatter in the center will make for the whole structure of the instrument a significant difference and speculate about the reasons why. You can ask yourself as well the question what weights more for possible deformation arching shape or thickness (thinness). 
 

I am speculating right now if ‘good sound’ is nothing else than calibrating the violin in a way that stress is in some regions higher than others and those zones have the ability to produce the overtone range we are seeking for a vibrant sound. 

 

Link to post
Share on other sites
On 3/11/2021 at 6:48 PM, 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.

Wood can both stretch and compress. And the bulging is not just in the upper bout. It occurs in in the lower bout too, as one would expect from the forces involved.

8 hours ago, Dennis J said:

I would say the fullness of the arch in the upper bout (by which I mean the part of the arch between the widest part of the bout and the neck) would have to differ by at least 2-3 mm to be readily apparent to an experienced luthier.

I think you  are underestimating the perceptive abilities of some of the more highly-trained and experienced luthiers. When one has spent hundreds-to-thousands of hours making or refining violin archings, things become apparent which are not to the casual observer.

Check Davide's distortion picture again (re-posted on page two) and see if that helps you. Or follow through with the violin experiment I suggested. It's difficult to learn if one isn't willing to put in the work, and observing the changes for yourself can produce insights which are difficult to derive from theorizing alone. Some of the people I've taught have learned best when I suggested something, and said, "Try it for yourself". And they did. So that's what I am suggesting for you.

Link to post
Share on other sites
15 hours ago, Dennis J said:

The bulging upper bout theory seems so implausible to me on so many levels, and I have not yet seen any convincing explanation about how it might come about.

Anyone looking at profile drawings of the top long arch can see differences of shape, even of about a millimetre, when one profile is laid over another. But identifying such differences on a glued up instrument is not as easy.

I would say the fullness of the arch in the upper bout (by which I mean the part of the arch between the widest part of the bout and the neck) would have to differ by at least 2-3 mm to be readily apparent to an experienced luthier.

And the idea that the strongly supported (by the upper block and ribs) part of the arch could somehow bulge up by longitudinal  compression is just not possible.

Or that the ribs at the level of the top plate would, under longitudinal compression, move inward doesn't make sense. If it were possible for them to move, which it is not, surely they would spread.

Your understanding of violins under pressure is... mostly misunderstanding. Impossible for ribs to move??

Arches bulging under longitudinal pressure not possible??

First, the top moves like a goddamn pringles chip on choppy sea. its not being delicately bounced up and down perpendicular to the feet of the bridge. Check out the Strad 3D stuff to see how a top really moves.

Second, start from the other end of your "understanding." From the fact that everything you don't believe is possible to happen happens constantly, consistently, and in surprising variation when instruments warp out under time and pressure. Then walk back to your idea that violins are made of completely homogenous load-bearing materials which only change shape in ways that make sense to you. Understand why these "impossible" things happen and you'll understand how to build an arch that fails into being tonally successful.

Also, grab a pin arching gauge and make a violin. check the arch after 10 years. it bulges.

 

Link to post
Share on other sites
16 hours ago, Dennis J said:

The bulging upper bout theory seems so implausible to me on so many levels, and I have not yet seen any convincing explanation about how it might come about.

Anyone looking at profile drawings of the top long arch can see differences of shape, even of about a millimetre, when one profile is laid over another. But identifying such differences on a glued up instrument is not as easy.

I would say the fullness of the arch in the upper bout (by which I mean the part of the arch between the widest part of the bout and the neck) would have to differ by at least 2-3 mm to be readily apparent to an experienced luthier.

And the idea that the strongly supported (by the upper block and ribs) part of the arch could somehow bulge up by longitudinal  compression is just not possible.

Or that the ribs at the level of the top plate would, under longitudinal compression, move inward doesn't make sense. If it were possible for them to move, which it is not, surely they would spread.

 

 

 

 

Dennis,

 I am quite ignorant of physics and will leave the theoretical explanations to the several people on this forum who know a lot about that. However I have made hundreds of instruments and have looked carefully at musical instruments six days a week for the last fifty years. Your belief that a qualified violin maker can't see differences in shapes of less than 2 mm is absurd. We see and correct bumps in arching of 0.1 mm every time we make an instrument. I will state with certainty that violins do distort in many ways including bulging upward in the centers of the bouts of the top, outward at the center of the back and both in or out at the junctures of the ribs and plates. As I said before we see relatively pristine  examples of old instruments from which we can see original arching concepts and we can easily see subsequent deformation on other examples. As far as how to make instruments today I am quite content to make instruments using the same shapes used by classical makers and which will deform over the next two hundred years into the shapes seen on the best preserved and best sounding examples remaining extant. 

 

 

Link to post
Share on other sites
18 hours ago, Dennis J said:

The bulging upper bout theory seems so implausible to me on so many levels, and I have not yet seen any convincing explanation about how it might come about.

Anyone looking at profile drawings of the top long arch can see differences of shape, even of about a millimetre, when one profile is laid over another. But identifying such differences on a glued up instrument is not as easy.

I would say the fullness of the arch in the upper bout (by which I mean the part of the arch between the widest part of the bout and the neck) would have to differ by at least 2-3 mm to be readily apparent to an experienced luthier.

And the idea that the strongly supported (by the upper block and ribs) part of the arch could somehow bulge up by longitudinal  compression is just not possible.

Or that the ribs at the level of the top plate would, under longitudinal compression, move inward doesn't make sense. If it were possible for them to move, which it is not, surely they would spread.

 

 

 

 

 

I will completely concur with Nathan's and David’s statements and observations, having been in the business for a similar period of time.

That the bulging of arches seems implausible to you is fascinating and leads me to suspect that you may not have had a lot of experience with older instruments.  I say this because there is plenty of evidence when one is working on older instruments that they do indeed bulge and deform under the fingerboard (and tailpiece).  Apart from simply observing the changes that happen in individual instruments that I've taken care of over decades, there is the very common problem of the joint between the top and the upper block coming open.  Often this is not noticed and dealt with and can, in the long term, result in a significant gap between the bottom edge of the upper block and the top even with the seams appearing to be closed from the outside.  When that joint does stay sound, it's not unusual to see a crease or area of smaller radius in the arching at the lower end of the block .  Additionally, when there is a lot of bulging under the fingerboard that is left unaddressed, it's not unusual to see cracks in the top near the edges of the fingerboard that are open the most at the peak of the bulge and do not extend below the fingerboard or to the edge of the top.  If those are not and indication of arching deformation in the upper bouts, what are they an indication of?  I have for some time been taking care of two violins with these sorts of cracks and doing my best to keep them from buzzing until the owners are willing and able to have the necessary work done.  They both happen to be made by members of the Gagliano family.

Yes, it is possible.  At least in this hemisphere.

Link to post
Share on other sites

I have no experience handling old instruments and not much in making instruments. So I'm careful in what I say. I'm not talking about old compromised violins with partially detached glued surfaces, only about sound ones and their arching, specifically at the uppermost end of the top arching. I'm not the only one here casting doubt on the bulging theory at that point of the arching.

It's clear that there are examples where distortion of the top occurs where the central area has become concave rather than convex. To the point that the bridge leans forward.

That must be caused by weaknesses in the top and/or back arching. I suppose that failure is not very common but it shows that things are finely balanced in that area. 

Generally arching is a grey area in violin design and there are some quite subtle design aspects involved which aren't even discussed. I'm happy with my understanding of it, but I'm sure that a lot of makers are not confident of how to handle it. And those who are aren't telling.

Whatever the case I think that early makers knew exactly the important design requirements. It's just a matter of pinning down what they were.

 

Link to post
Share on other sites
4 hours ago, Dennis J said:

I have no experience handling old instruments and not much in making instruments. So I'm careful in what I say. I'm not talking about old compromised violins with partially detached glued surfaces, only about sound ones and their arching, specifically at the uppermost end of the top arching. I'm not the only one here casting doubt on the bulging theory at that point of the arching.

It's clear that there are examples where distortion of the top occurs where the central area has become concave rather than convex. To the point that the bridge leans forward.

That must be caused by weaknesses in the top and/or back arching. I suppose that failure is not very common but it shows that things are finely balanced in that area. 

Generally arching is a grey area in violin design and there are some quite subtle design aspects involved which aren't even discussed. I'm happy with my understanding of it, but I'm sure that a lot of makers are not confident of how to handle it. And those who are aren't telling.

Whatever the case I think that early makers knew exactly the important design requirements. It's just a matter of pinning down what they were.

 

You are obviously not interested in learning so there is no need to discuss this with you any further.

Link to post
Share on other sites
11 hours ago, Dennis J said:

I have no experience handling old instruments and not much in making instruments.

Then why are you coming from the presumption that those who do have a lot of that experience are wrong? What would be the downside of approaching it from the other direction?

A couple of years ago, I attended a racing school in Nevada. Now why would I do that, since I have already spent some time on racetracks, and had been driving high-performance cars and motorcycles for decades? Because I presumed that I had barely scratched the surface, compared to a real, professional race car driver.  As it turned out, these instructors, driving slower cars than the attendees were driving, could put distance on us any time they wished, while holding a microphone in one hand, keeping an eagle-eye on their rear view mirror to give those behind them a constant stream of tips over the radio on how to go faster, while keeping track of who was in each car. "Dave, you hit your apex early, and your inside tires should have been up on the curbing."

I could have responded, "Nope, I've given this a lot of thought, looked at some photos of that corner, and the line I took is faster. Besides, it makes no sense to go up on the 'rumble-strip' curbing since it only makes sense that this would reduce traction and make the car slower", (to this guy who has lapped that track hundreds-to-thousands of times). :lol:

Link to post
Share on other sites
7 minutes ago, David Burgess said:

Then why are you coming from the presumption that those who do have a lot of that experience are wrong?

You are overlooking the experience that can be gained from sitting in an armchair by the fire, night after night, combined with reading numerous pamphlets while sat on the toilet rolleyes.gif.8758ab487165f4f683d8e2686516f184.gif

Link to post
Share on other sites

How do you decide the shape of the arching at the upper or lower ends of the top is distortion rather than maker's intent.

It's easy to understand how pressure from a sound post can distort the top between the ffs but it is prevented from doing so by by being the right length and by the downward force of the bridge.

I would say that the whole body of the violin bends under string tension. And it would bend away from the base of the sound post because that is the strongest part of the structure.

That could induce sinking in front of the bridge or other distortions in that area. But the upward force needed to change the shape of the upper arching at its widest place or higher would have to be very considerable. And how is that directional force generated?

If there is no bulging distortion at the ends of the arching the only distortion of any significance is the sinking in front of the bridge.

 

 

 

 

Link to post
Share on other sites
1 hour ago, Dennis J said:

That could induce sinking in front of the bridge or other distortions in that area. But the upward force needed to change the shape of the upper arching at its widest place or higher would have to be very considerable. And how is that directional force generated?

Lay a piece paper flat on a table. Push the ends together, ....

Oh wait, I already suggested that way back on page one. Have you done  your homework yet, or do you like to just go in circles? :rolleyes:

"How can you have any pudding if you don't eat your meat?" :lol:

Link to post
Share on other sites

This is a genuine question with no preconceptions about the preceding discussion. Since there are existing f  templates of Stradivari, would it be possible to compare the average widths of the f's on Stradivari violins to the templates in cases where there is a flat plateau in the front long arch. I would expect that if the central area had sunk from the original and the width of the front plate remains the same as the back, the average width of the f's would be narrower than the templates. It might be possible to check if instruments with a shorter flat zone of the long arch had width of f's nearer the templates. This might be a ridiculous idea but it just came into my head!

Link to post
Share on other sites
1 hour ago, Dennis J said:

That could induce sinking in front of the bridge or other distortions in that area. But the upward force needed to change the shape of the upper arching at its widest place or higher would have to be very considerable. And how is that directional force generated?

String tension.  Please do the suggested experiment.  Then, if it wasn't mentioned earlier (I've not read this entire thread) put a coin in the center of the paper to simulate downforce from the bridge and do it again.  At that point it should be completely evident.  If it's not you are, for some reason we cannot know, unwilling or unable to let go of your beliefs and open yourself to the possibility of learning.  

Link to post
Share on other sites

Reading through this thread it occurs to me that maybe a simple fact got buried - that the entire violin body bends like a banana under tension. If, for example, you measure the arching height of a 300 year old back, to get a better idea you would normally measure it both along the center line, and across the arch, because those are two different numbers - it's higher along the arch than across it. Presuming the back was what we would all consider relatively flat when it was made, this means the back arch is slightly rounder than it was when it was made. The same forces are obviously at work on the rest of the instrument, which is why ribs bend and bellies bulge. 

Another thing that hasn't been mentioned is that the bar, especially if it's under tension, will keep the bass side of the upper and lower bouts pulled down somewhat more than they otherwise would be, which means that the belly on the opposite side gets pushed up. This effect can be amplified by replacing the bar with a new one with new tension, which can happen multiple times. A consequence of this is that the arch can actually appear "round" on one side of the center line, and "saddled" on the other. If you look at the fiddle from the side, and tilt it towards you and away from you, you can get very different impressions of the long arch, even with a small change in angle.  Because of this, I think it's wise to take any photo or drawing of a long arch with a grain of salt.

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

This one has deformed in a strange way, the back height has decreased and the top height has increased radically all the way to the end blocks. Some sag in the middle is visible

 

2D4F1622-1E33-4051-BDB0-4CE83ADD547D.thumb.jpeg.fc88243bf1b628d37e6d214b223bc81e.jpeg

I suggest that simplistically the top is a curved strut which is bulging in response to the compression imposed by the strings while the bottom is straightening in response to the tension.  The downward force from the bridge is then imposed on that and modifies the displacements. The cross arching provides restraint to resist these displacements.

Link to post
Share on other sites
1 hour ago, Peter K-G said:

This one has deformed in a strange way, the back height has decreased and the top height has increased radically all the way to the end blocks. Some sag in the middle is visible

 

2D4F1622-1E33-4051-BDB0-4CE83ADD547D.thumb.jpeg.fc88243bf1b628d37e6d214b223bc81e.jpeg

I think that has deformed the normal way rather than a "strange way".

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...