Is this arching wrong ?

[HoGo]

29 minutes ago, Anders Buen said:

You cant deduce the dynamic response, far above the "DC level", for a vibrating body by assuming it from its static shape and static forces. If you want to see the dynamics, you have to do the dynamics.

I guess it's similar to static loading of a bridge vs. its dynamic behavior when the traffic is in action. Like the famous London millenium bridge that had to be closed the first day the walkers passed it. Just from observing deflection of the bridge you won't know how it will respond to dynamic impulses.

[reguz]

As I told before I tested during very long time by rubbing the varnish reducing the stiffness (say on the upper bout part) which increase the static stress condition on curves. When I got a negative result by rubbing on one bout area, I rubbed the varnish on the lower bout and got very good result. Continuous some time I got WULF behavior which tells me the frequency result are to close each other. Either the conditions are equal on the bouts or separated. Optimal is when both bout area participate producing the frequency with high amplitude. So, my experiences are arching shape condition with in my case the Stalls and stress condition on arching shape which influences the acoustic result. I did some of this testing together with Staffan Borseman. Thus with the ear of a very experienced player.

[reguz]

Dear Hogo. You as all other only see the action of the bridge feet produced by the stress condition on the strings. BUT there is action on the end of the strings. THEY produces buckling on the belly arching and bending on the back arching. Yesterday in a talk with Peter we look at figure 25 and 27. When you only have load condition of the bridge the you should  see  the bridge move down. This will cause a horizontal force action on the end blocks (belly) and a pulling force on the back. This is what Gough and Stoppani show happening on the cross section. THUS, as result we see the opposite I mean as it works. The belly become buckled by inward acting forces and the back "only" become bend. In such condition the volume of the box changes. In the very important dynamic state, the structure vibrates in low frequency and it will produce breathing. Not as Gough shows you. As described earlier the strings does TWO things. FREQUENCY "injection" and basic dynamic behavior on arching shape. Play the pizzicato on the G string and you can feel the dynamic. 

Tell me where I can read any from Woodhouse, Stoppani or Gough about what happens on the ends of the strings. They only see bridge action.

[Don Noon]

22 minutes ago, reguz said:

Tell me where I can read any from Woodhouse, Stoppani or Gough about what happens on the ends of the strings. They only see bridge action.

They only look at bridge lateral forces for vibration because what happens at the ends of the strings (regarding tension) is insignificant in almost all cases.  If the tension dynamically varied enough to excite body vibrations, it would also change the pitch of the note being played.  This happens on a steel-cored G string, but not appreciably for anything else.

[Peter K-G]

1 hour ago, reguz said:

As I told before I tested during very long time by rubbing the varnish reducing the stiffness (say on the upper bout part) which increase the static stress condition on curves. When I got a negative result by rubbing on one bout area, I rubbed the varnish on the lower bout and got very good result. Continuous some time I got WULF behavior which tells me the frequency result are to close each other. Either the conditions are equal on the bouts or separated. Optimal is when both bout area participate producing the frequency with high amplitude. So, my experiences are arching shape condition with in my case the Stalls and stress condition on arching shape which influences the acoustic result. I did some of this testing together with Staffan Borseman. Thus with the ear of a very experienced player.

I'm sorry to say, but this whole post looks like rubbish. No measures and incoherent talk without base.

It takes away all credibility.

[Dr. Mark]

36 minutes ago, Peter K-G said:

...this whole post looks like rubbish

It is.

 

37 minutes ago, Peter K-G said:

It takes away all credibility

It does.  People are involved now because they still think it's their thread instead of reguz's, but through incessant and unrelenting haranguing and interruption he's controlling the discussion and uses it as a soapbox for his ego.  I'm sorry to see that Mr. Noon has also yielded to temptation and has joined us sinners - I understand though.  What appear to be easily correctable errors draw one in to his doom...

"'Through me the way to the suffering city...Abandon all hope - You who enter here".

[Don Noon]

50 minutes ago, Peter K-G said:

It takes away all credibility.

That happened several years ago. 

[Don Noon]

4 minutes ago, Dr. Mark said:

I'm sorry to see that Mr. Noon has also yielded to temptation and has joined us sinners - I understand though. 

Woke up too early, and nothing to do before heading to the hospital for a relatively minor adjustment.

[reguz]

indefatigable you answer which I am grateful for but do you give any explanation how it is according to meaning? Don refers to 8 years of filing but never ever explains how he thinks a violin works. That's what should happen, otherwise it's just complaints that are of no use to anyone. So, if we're going to get somewhere, start by telling me what you know so I can learn something from you. Thank you

[Anders Buen]

4 hours ago, HoGo said:

I guess it's similar to static loading of a bridge vs. its dynamic behavior when the traffic is in action. Like the famous London millenium bridge that had to be closed the first day the walkers passed it. Just from observing deflection of the bridge you won't know how it will respond to dynamic impulses.

A bridge, like the Millenium bridge, has their first resonances close to 0 Hz (static), so not really relevant for a violin.

[Dr. Mark]

2 hours ago, Anders Buen said:

A bridge, like the Millenium bridge, has their first resonances close to 0 Hz (static), so not really relevant for a violin

https://www.youtube.com/watch?v=j-zczJXSxnw

Fixed points at the towers

[Muswell]

7 hours ago, HoGo said:

I guess it's similar to static loading of a bridge vs. its dynamic behavior when the traffic is in action. Like the famous London millenium bridge that had to be closed the first day the walkers passed it. Just from observing deflection of the bridge you won't know how it will respond to dynamic impulses.

The problem with the Millenium bridge was  lateral vibration, not the well known vertical vibration, and it had not been recognised as a design issue for bridges before.  Very slight lateral movements encouraged people to walk in such a way as to counter this. It only became a problem when the number of people was very large, such as happened on the opening day, and the synchronous walking reached a critical level.  This was later repeated in a trial to prove the computer model for remedial action when the number of people crossing was gradually increased. There are probably quite a lot of footbridges which could have the same problem but never have enough traffic.

[Anders Buen]

9 minutes ago, Dr. Mark said:

https://www.youtube.com/watch?v=j-zczJXSxnw

Fixed points at the towers

The reason why this bridge fell down was insufficcient knowledge about coupled wind and bridge dynamics, self sustained vibrations. The towers are boundary conditions and supports. Their contribution is to reflect dynamic waves. The response we see here is impossible to predict only using statics.   

[Dr. Mark]

3 hours ago, reguz said:

indefatigable you answer which I am grateful for but do you give any explanation how it is according to meaning?

Tell you what - I'll reply when

a) I can understand your question

b) The reply I would give you isn't repetitive

c) the font you use is normal size and color, and you use normal capitalization

d) I believe that the content of my reply would help push the discussion forward (see e.g. b) above)

Fair enough?  No need to reply.

[Dr. Mark]

18 minutes ago, Anders Buen said:

The reason why this bridge fell down was insufficcient knowledge about coupled wind and bridge dynamics, self sustained vibrations.

To clarify, evidently quite a bit was known about wind-induced vibrations in bridges, but such knowledge had dropped out of the engineering curriculum.  I'm attracted to the visual similarity of the bridge oscillation and the A0 mode vibration here: https://strad3d.org/st_5.html

[Anders Buen]

9 minutes ago, Dr. Mark said:

To clarify, evidently quite a bit was known about wind-induced vibrations in bridges, but such knowledge had dropped out of the engineering curriculum.

They did after this accident, I presume. Scaling experiments have been important in bridge design dynamics.

[Dr. Mark]

35 minutes ago, Anders Buen said:

They did after this accident, I presume.

Well, yes.  Waiting to close the barn door until after the horses are gone is a cost/benefit decision.  But I do need to amend my assertion - although aerodynamic forces were not well understood in the 30's, the effects of wind loading had previously been well-known to structural engineers but by the 1930's had been forgotten. 

According to https://wsdot.wa.gov/TNBhistory/bridges-failure.htm, in the section headed 'Blind Spot - Design lessons of Gertie's failure' we find, in reference to design engineers in the 1930's lack of concern with wind load:

'This trend [i.e. "Wind was not particularly important" ] ran in virtual ignorance of the lessons of earlier times. Early suspension bridge failures resulted from light spans with very flexible decks that were vulnerable to wind (aerodynamic) forces. In the late 19th century engineers moved toward very stiff and heavy suspension bridges. John Roebling consciously designed the 1883 Brooklyn Bridge so that it would be stable against the stresses of wind. In the early 20th century, however, says David P. Billington, Roebling's "historical perspective seemed to have been replaced by a visual preference unrelated to structural engineering."'

'An entire generation of suspension bridge designer-engineers forgot the lessons of the 19th century. The last major suspension bridge failure had happened five decades earlier, when the Niagara-Clifton Bridge fell in 1889. And, in the 1930s, aerodynamic forces were not well understood at all.'

[fscotte]

In no world whatsoever, in any kind of luthery, does rubbing away a little bit of varnish increase the modes in any way, that's even measurable.

Unless you're putting on about 300 coats of varnish, and 5 mm thick, there is absolutely no credibility that taking rubbing away a few thousands of an inch of varnish in a small upper bout or lower bout area is going to do anything at all.

[Anders Buen]

2 hours ago, Dr. Mark said:

Well, yes.  Waiting to close the barn door until after the horses are gone is a cost/benefit decision.  But I do need to amend my assertion - although aerodynamic forces were not well understood in the 30's, the effects of wind loading had previously been well-known to structural engineers but by the 1930's had been forgotten. 

According to https://wsdot.wa.gov/TNBhistory/bridges-failure.htm, in the section headed 'Blind Spot - Design lessons of Gertie's failure' we find, in reference to design engineers in the 1930's lack of concern with wind load:

'This trend [i.e. "Wind was not particularly important" ] ran in virtual ignorance of the lessons of earlier times. Early suspension bridge failures resulted from light spans with very flexible decks that were vulnerable to wind (aerodynamic) forces. In the late 19th century engineers moved toward very stiff and heavy suspension bridges. John Roebling consciously designed the 1883 Brooklyn Bridge so that it would be stable against the stresses of wind. In the early 20th century, however, says David P. Billington, Roebling's "historical perspective seemed to have been replaced by a visual preference unrelated to structural engineering."'

'An entire generation of suspension bridge designer-engineers forgot the lessons of the 19th century. The last major suspension bridge failure had happened five decades earlier, when the Niagara-Clifton Bridge fell in 1889. And, in the 1930s, aerodynamic forces were not well understood at all.'

There was mishap quite recently in NY (Brooklyn bridge?) where the new saftey fences did sing in the wind. I did not know about the historical suspension bridge designs and knowledge. Empirically they must have known quite a bit.

A stiff static system may tend to be stiff also dynamically. Statid ques are used in floor design, but the resonances we work on are quite low, 5-25 Hz ish. 

[Andreas Preuss]

10 hours ago, reguz said:

I tested during very long time by rubbing the varnish reducing the stiffness

You presumably mean that you reduced the thickness of the varnish to reduce the stiffness of the plate in that area. 

I once destroyed a back plate by cutting holes in the stressed zones which should theoretically make the sound collapse entirely. The overall impression was that the sound got a little worse, but the effect was to my surprise by far less than what I expected. 

10 hours ago, reguz said:

So, my experiences are arching shape condition with in my case the Stalls and stress condition on arching shape which influences the acoustic result.

How is the acoustic result influenced?

 More overtones? Quicker bow response? More sound volume?

[reguz]

By rubbing the varnish, you reduce stiffness locally and the stress conditions produced by the strings will increase the stress condition at the location you did the rubbing. I also did this together with Staffan Boseman on a viola in the white We liked improving stress conditions on the belly and by scarping on the back in the STL sector shaped the back thus become less stiff and allow the end blocks rotating more. When that happens, the belly buckling forces increase and produce the result we liked to find out about. Staffan played and I scarped and he could give proof on the result we looked for.

[LCF]

47 minutes ago, reguz said:

 Staffan played and I scarped and he could give proof on the result we looked for.

Intriguing, tell us more.

[fscotte]

An interesting concept.

On some of the mandolins I've built, I would take an orbital sander, without the sandpaper, and run it against the back plate while the mandolin is still in the white.  After about 30 seconds of this, the mandolin would absolutely sound gorgeous, easy to play, as if the orbital sander vibrations really loosened up the entire mandolin.  But by the next day the mandolin would stiffen back up and sounded the same as it did before.

[reguz]

Working together with Staffan Borseman how was the concert master for 25 years he told me that he always started payling and call it "warming upp" the instrument before the concert take place. He used the word massage like warming up the dynamic state.

[Anders Buen]

1 hour ago, reguz said:

Working together with Staffan Borseman how was the concert master for 25 years he told me that he always started payling and call it "warming upp" the instrument before the concert take place. He used the word massage like warming up the dynamic state.

Many maker specialists of more critical thinking, think that "warming up" an instrument or playin in is an the player adapting to the instrument and not the insturment to being played. Of course, it is useful to heat the strings and the neck at the holding position and the bowed strings (the strings and rosin becomes hot by bowing them) before a performance because the instrument may stay more stable in tune. The rosin melts and solidifies through the Helmholz cycle. Anders Askenfelt showed us at a conference many years ago with pictures from an IR-camera.