Long Arch Drawing

[Don Noon]

3 hours ago, Michael_Molnar said:

Another question is why are the highs restored?

I have no proof, but I think it relates the the transient damping change caused by a change in static load (and I would classify re-arching as a change of internal wood stress).  Somewhat like resetting the instrument to "new" status, slightly.

Re: back distortion, I think it is much more difficult to judge if a convex arch has become 2mm more convex, vs. a top that has gone from 1mm convex to 1mm concave.  Figured maple is certainly more prone to distortion compared to straight-grain spruce, but backs are also normally much thicker than tops (if you ignore the bass bar).

To me, this Strad looks extremely bulged out in the soundpost area.  And probably wasn't re-arched, as it isn't as obvious as the top and doesn't directly mess with the setup.  But since we can't tell what the original back arch was, it can only be a guess. (But this bulge is much more pronounced on the side with the soundpost, and not on the bass bar side)

[Michael_Molnar]

I agree that the damping dissipates (relaxes) after reshaping the top. This suggests to my way of thinking that the plate contour might be one parameter for tone generation, but the wood properties are also a significant parameter.
 

Also, I think we may be overestimating the back long arch that becomes a tad more convex in old violins. It’s probably a small effect.

[David Burgess]

22 hours ago, reguz said:

I strongly believe there is a great misunderstanding when people say

“God bless, look at how sunken that top is!” if there is any of that than please explain why the back does not show any outward deformation! Not on any of them showed.

But the back does show outward deformation in the soundpost area. You need to open your eyes!

[Don Noon]

In the image I showed above, I'd say the distortion was several millimeters.

[GoPractice]

22 hours ago, Don Noon said:

Could be both.

Severe distortion can screw up fingerboard projection, string clearance, and bridge height, which are important things for playability and sound.  It seems sensible to re-arch, rather than messing with those other things to follow a sinking top.

All other things being equal (which they can't be), my single datapoint is that re-arching initially attenuated the highs, but recovered after a while to be about the same as pre-rearched, which was very good.  I'm sure there are others who have more datapoints.

My perception of anexpensive rearching on a familiar instrument was that the instrument sounded newer, a bit brash. The G-string was more pronounced and less nuanced. The projection was definitely re- adjusted to higher position during the restoration. The instrument was apart, so quite a few things were adjusted.

This was possibly 3 months after the work was completed. A year later, playing that instrument ( borrowed ) in a cavernous space, the instrument sounded smoother in the higher octaves but strong.  

What sounded like a smooth softer older instrument pre- repair, I heard it on several concerto performances, the instrument was louder and easier to produce sound. After the repair the sound was more powerful and stronger in the higher positions. It was less work to play. The owner of the instrument was more guarded in that it was not the instrument he had known for decades, one that had been purchased. He knew the instrument would sound different after the restoration, and the work had to be done. It was an early 1700s northern Italian instrument. It lost some of the glow for presence in tone. I think it was a little difficult making that adjustment for him. Double stops sounded more out of tune to him ( which indicates restoration of higher frequencies ) and expressive softer passage were lost because the sensitivity of the instrument was much higher. What sounded dark previously was much brighter.

The work had to be done. The saddling was at the point that I sort of cringed when he hit bit big chords. It also was sensitive to weather, where humidity killed the sound. He rarely performed during hot summers in the east. The value ( relative to the increases ) of this non-identifiable Italian was dropping year after year.

This is just a subjective observation of the sound. And the playability was certainly different as it felt like ( more than the sound ) a completely new instrument. I would think it was the higher projection mostly because I hear and felt similar changes. It also indicates to me the differences in how we expect the instrument to behave. Visibly it was excellent work.

I would think that this was the sonic direction of most of these restorations for very old instrument. 

[reguz]

Dear David Burgess. You write "But the back does show outward deformation in the soundpost area. You need to open your eyes!" and hope that I open my eyes. Yes, I do and try to come on an understanding how such deformation becomes produced. When you stay on a plank you being the sound post and bind a rope on the ends of the plank and start pulling the plank will bend and you produce an upward force under your feet. A moment of force becomes produced and the structure of the plank will react special. Highest bending us under your feet. Withstanding a high bending you can reduce by graduating the thickness of the plank locally under your feet and less close the ends of the plank. Now looking at the back of the violin an upward force becomes produced on the sound post that withhold. On the violin we have a condition that is in rest no movement in any direction of the sound post, equilibrium. this means surrounding structure may become pulled upward but not the sound post. IF, WHEN the structure around the sound post is weaker the surrounding structure wider out that structure close and around the sound post will deform and that is what you may see. It is caused by the upward bending over the sound post NOT THE pressure on the end of the sound post down. 

[David Burgess]

4 hours ago, reguz said:

It is caused by the upward bending over the sound post NOT THE pressure on the end of the sound post down. 

Meh. Depends on what part of the fiddle you wish to use as a frame of reference. One could say that the soundpost area of the back remains stationary, and that the rest of the instrument gets sucked toward heaven. Or one could say that the majority of the instrument remains stationary, and soundpost area of the back gets pushed out. The second description is much more intuitively useful to me, and more easily and conveniently demonstrated.

[reguz]

Dear Don. the deformation you described is exactly what I explaned earlier. The end block pull the back over the sound post. Since the sound post is out of center the structure sideway on the sound opposite side cannot move as much as the structure does say on the other side of the center line. So that structure become pulled up higher. We can see this on the enclosed image. My opinion is that we can preserve for such deformation by graduating that structure thicker. Thus it must be the oposite location that must be made thicker so that structure cannot be forced in upward direction.

Sradivarius 1727.docx

[reguz]

Dear David Burgess. My opinion is different simply because the instrument does not increase in weight when strings pull on the instrument. There arise no upward and no downward movement. Lay the instrument on the table with a scale under. increase the string tension. does the weight increase? Does the rib support for a downward movement?

No also the rib should move down. The secret of the sound post is that it makes equilibrium state. I have made a vector diagram that explain how the forces act. The length of each arrow in mm is the force so finally the sum of the downward force must have an equal upward force otherwise the instrument starts to fly or???

You may pull on the handles and make another shpe but equilibrium is alwayus there.

Hope you can accept what happens

vectordiagram.docx

[Don Noon]

There is ~20 pounds of vertical force on the bridge due to string tension.

~10 pounds of that is on the treble foot

The top won't provide much resistance, due to the F-holes eliminating a lot of crossgrain support

Therefore there will be an appreciable constant vertical load transmitted to the back, thru the post

No vector diagrams or long paragraphs needed.

[reguz]

Dear Don. You are right. a constant vertical load is transmitted to the back thru the post. What the vector diagram shows is how this downward load becomes produced. The string tension produce a "resultant force" How the force of the strings act on the end block show that the string force can be seen as a resultant force. minor upward but also directed to the point where the downward resultant act. these two forces directed to the bridge/sound post as it is on the figure produce another resultant force directed upward. This resultant force together with the two vertical directed forces on the end blocks produce they the equilibrium state. The two vertical forces thus act on the underside of the sound post. If these was any force coming out it either make the structure moving downward = increasing weight or upward. If that force is bigger the weight of the instrument it will fly. Perpetuum mobile??  I hope everyone can "read" the figure!! But Don you did not explain what the vertical load on the back does! Movement? Explain your opinion on how equilibrium arises

[David Burgess]

Regus, you sound like a "book-learned-only" sort of mechanical engineer, one who compensates for their lack of intuitive  acumen by falling back on making things more complicated than they need to be.

One of my best friends was a mechanical engineer and department head, responsible for hiring and firing the engineers in the company. From his experiences, he told me that he much preferred to hire people who could basically come up with a solution out of their head in 30 seconds, versus those who had to take hours or days doing pages of calculations, and still get it wrong.

So I agree with Don that no long paragraphs or vector diagrams are needed, if one really knows what they are doing.

Don is really good at "cutting to the chase". You, on the other hand, seem more interested getting people to watch you engage in your mental masturbations.

[Don Noon]

3 hours ago, reguz said:

But Don you did not explain what the vertical load on the back does! Movement? Explain your opinion on how equilibrium arises

It should be intuitively clear to anyone what a constant punch load would do to the back plate, especially when we have visual evidence of what it does.  If someone doesn't think it's obvious, then vector diagrams and verbal arm-waving are just going to make things even less obvious, and pointless.

[Dennis J]

Surely there is enough longitudinal force or leverage on the upper and lower blocks to force bending at the middle bout which could result in the slumping seen between the sound holes. It comes down to whether the middle bout is strong enough to adequately resist that force.

[reguz]

Dear Don

This is typically you. You cannot accept that there may be persons how like to understand things by seeing things expressed other than by a CONSTANT PUNCH. In fact, that punch is a load on a column.

So if you like to express your selves better the sound post also give an equal punch on the belly in upward direction  without producing any movement.  NO MOVEMENT on the sound post and that is what the vector diagram shows.

 

[David Stiles]

In regard to the vector diagram, it is incomplete.   The back; chords AF and FE would be in tension.  So I can't see why they would bow outwards.  Soundpost GF is in compression.

[reguz]

Dear David Stiles. If the vector diagram is incomplete, you must be able to show what final force makes the equilibrium condition. Yes, you are right the AF Fe structure become bend this deflect. This deflection on AG and GE is called buckling. So, these four-structure become loaded thus a force that tends to strain or deform o structure. Since it happens on a violin, we must accept this happens on the violin body an extreme complex shape. When a curved shape as you find on AFE become bend over F there will arise stress condition. On AGE we find different condition. AG and GE become loaded by compression like the load condition on a column. That is technically called buckling stress.

How much these AG and GE buckles depends on several technical conditions. A major is of course the stiffness of AG and GE but an many respects depending on what bending is allowed by AF and FE. By graduating the stiffness on these structures, we can find another behavior of deflection and stress on AG and GE.

Since the curves shown happens on the length center line, we do not know how lateral structure on the violin body affect what happens. These structures named bout shapes are very different in shape and thus we must accept the curves all may deflect different and thus the arising stress conditions may become quite different. This is not easy controlling and certainly affect the dynamic behavior and the outcome of the mode shapes of frequency.

It is easy to find out what happens when you shave away some structure on the surface of bout shape and play a special frequency again. This give you the possibility improving the outcome when you have the basic understanding of what is described above.

Hope this make sense to you.

[reguz]

For those of you for many years ago now got complete wrong information about what happens on the back plate by the sound post take a close look starting at 7:15. He principally claim that the rib (thus the frame work you see) support the back and make the movements shown posible. This never can happen on any violin as shown in the video. Jack Frey is a highly educated in physics.

 

[reguz]

Please search and listen to

il mistero del grande violin 2021

on Youtube

[James M. Jones]

For those that would like another detailed conversation about the  long arch , check out the long arch thread in the pinned threads section at the top of this page , 12 pages of goodness. 

[MikeC]

I don't see a pinned thread on arches where is it?   

I'm blind in one eye and can't see out of the other one.  

[James M. Jones]

5 minutes ago, MikeC said:

I don't see a pinned thread on arches where is it?   

I'm blind in one eye and can't see out of the other one.  

Look right above the most Current thread , pinned with a green pin says “reference thread links , “ click on that and six or seven topics down you will see one “long arch” loads of good stuff , Bruce Carlsons  pictures are worth the time just by themselves. 

[MikeC]

16 hours ago, James M. Jones said:

Look right above the most Current thread , pinned with a green pin says “reference thread links , “ click on that and six or seven topics down you will see one “long arch” loads of good stuff , Bruce Carlsons  pictures are worth the time just by themselves. 

Thanks!  I found it.  

[Michael Darnton]

It's a lot easier to reshape spruce than maple and maple deformation seems less critical in comparison, though it can make fitting posts really difficult.

[Peter K-G]

On 4/8/2022 at 11:56 AM, reguz said:

For those of you for many years ago now got complete wrong information about what happens on the back plate by the sound post take a close look starting at 7:15. He principally claim that the rib (thus the frame work you see) support the back and make the movements shown posible. This never can happen on any violin as shown in the video. Jack Frey is a highly educated in physics.

 

 

On 4/8/2022 at 12:31 PM, reguz said:

Please search and listen to

il mistero del grande violin 2021

on Youtube

You just have to give Robert some credit, he is a VERY stubbern guy!

I do not agree with his "static" view of the violin, but I think he might have the "maths" right?

One major flaw is to think, that a model would fit any wood.

As you all know by now, I think... the long arch, the shape.... etc. has to be made as the specific wood you work with offers