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plate flexing question


jim mcavoy
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I think it's important for folks to familiarize themselves with the Strad 3d animations {that are exaggerated } in order to get a feel for what motions are taking place during any given mode of motion. I have no "evidence" as of yet, but am starting to apply rules of fractal geometry and think that there may be great potential for it when applying it to "applications" for both analyzing motion as well as sound. There are some pretty neat papers related to fractals and music/sound. It seems quite an unexplored avenue of looking at what we do. Fractal geometry has proven itself to be an amazing breakthrough in many different fields. The key to it seems to be using a very open minded imaginative way of conceiving ways to apply it to whatever you are trying to "do".. Looking at micro antennae that are used in cell phones, and the way that by simply folding the antennae into a portion of a fractal shape, that it allows it to do what it does, makes me wonder if there is not a pre exiting fractal application that is "happening" with Strads and truly GREAT sounding instruments related to its structure and motions. Once you understand the basics of fractal geometry, and that it's basic principle is quite easy to understand, the somewhat fun and potentially difficult yet exciting part is sitting there trying to brainstorm ways that you could use it for applications of building and or applying it to motion.

 

Intriguing. Fractals pop up in so many fields, who knows ?

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Once you understand the basics of fractal geometry, and that it's basic principle is quite easy to understand, the somewhat fun and potentially difficult yet exciting part is sitting there trying to brainstorm ways that you could use it for applications of building and or applying it to motion.

I know this is a reach....Have you drilled down in the production of sound to see if this applies ....I'm thinking in the areas of self replication complete with accidents
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I know this is a reach....Have you drilled down in the production of sound to see if this applies ....I'm thinking in the areas of self replication complete with accidents

Like I say, once you sit down and REALLY  think about it, just thinking of all the different aspect and ways you might apply it are kinda....vast

 

Here are some interesting reads

 

http://cvsp.cs.ntua.gr/publications/jpubl+bchap/ZlatintsiMaragos_MultiscaleFractalAnalMusicInstrumSignalsApplicRecogn_ieeetASLP2013.pdf

 

http://phe.rockefeller.edu/perrin/fractaldimension.pdf

 

There are many fractal applications in other fields that may have crossover applications. To me it's some what like a puzzle that may be much more interconnected than first meets the eye.

 

For example, just theorizing, what if the air cavity shape is a specific geometric mimic of a particular part of the woods internal structure?  What if the woods individual fiber characteristics are a scaled down version of what we end up with on a macro level? And or a great sounding violins motion closely represents a scaled up version of individual fiber motions and or structural capabilities. Let alone looking at "Sound" in graph form and dissecting it. Mandelbrot discovered a glitch in a signal frequency while at IBM which was a major step forward in understanding transmission of data, perhaps a similar effect is happening with the transmission of frequency? It's pretty endless to think of what may or may not be applicable. Its just a interesting way of thinking about certain aspect of sound motion and form.

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I wish we could see what we think is motion or what we think is in motion.

Well we actually kinda can starting at the molecular level as described by Brownian motion, which by the way is a derivative of fractal geometry, which thus translates to Brownian noise and or the colors of noise, which of course are directly connected to frequency and sound, and then as we see when we drive sound/frequency at measured levels through our "Strad 3d" we get a certain range of motions in the various modes. I speculate that if we want our violins to sound good that we will mimic the motions of a known "great" sounding violin, as shown in the Strad 3d animations, and or, knowing that these are exaggerated motions that we can somewhat mimic by applying hand forces to the free plates. Also taking note that the entire corpus moves as one for the most part based on it's literal connection by being glued and or we can observe the motion of both the top and back, along with the garland and see the "action/reaction" events as they take place.

 

Going off this line of thinking, IF we were to think of the model used in Schleske's animations as "perfect" and therefore wanted to mimic that "way" it moves when force is applied/driven through at "arbitrary frequency" X,Y or Z, in free plate mode the best we can do to try to mimic the range of motions that we see. This will be dictated by the shape, material characteristics as well as perhaps most important the thickness as it relates to material properties.

 

For a moment let us assume we all use a homogeneous wood that was the same across the board so as the characteristic we the same for you or I, when we got to the point of being able to flex the plate in ways that mimic the animations, a macro representation, or fractal of the micro, there is this arbitrary thickness in arbitrary locations that will allow us to mimic the motion very closely to what we are watching, this is perfect, if we are too thick,it will not move like the animation, if it is too thin the range of motion will be too big.

 

To me the sound is a by product of the motion which is a by product of the energy, the sound or frequency is the caboose in the train or the last by product of all this energy transfer, so to get that great sound, we need to work backwards, so we all* know what that great sound is, the next step back is the motion that makes that sound....

 

of course all just "theoretical"

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Something I observed on pg. 8 of Ms. Hutchins work from Davide's link is when the pair of hands is flexing the plate for mode 1.  Why is the old signal generator test M5 glitter line in the way of the flexing for mode 1?  Same for flexing for mode 5 with hands pg 8, what I see is where the glitter would show up for mode 2.  What I see on pg. 8 shows for hand flexing for mode 2,  I would look into that for finding/flexing mode 1.  That's where I checked and found for mode 1 tone.  Why flex the tailblock area for mode 2?

It is impossible to isolate one mode from the others, when you flex a plate each contributes in some way.

But for me it is quite clear that when you do a twist, is mainly the rigidity of m1 that you feel, if you bend across the grain, without twisting, the m2 is the main responsible, and If you bend lengthwise will be the m5 to be subjected to stress mostly.

The tailblock area is clearly an area of bending for the m2 in the free plate.

When you do these tests is not necessary to flex with very large movements : rather, it must be avoided in order not to cause damage.

Sensitivity is the key, and that's why I said previously that they are not very reliable by themselves.

 

I also want to stress that these systems are only for modern making, not to test old violin plates, as Curious1 stressed in his post #41 in a very appropriate way :)

 

PS Just try to think of fractals gives me a headache :huh:

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A problem with the concept of plate flexing is learning it. How does one learn to "feel" what is right from reading about it? Working in a shop where the technique is explained "hands on" could work, but that is a steep learning curve, at least for me.

 

On another note, we all should try to focus on practical matters. I think the pipe dreams about fractals belongs on another forum. Well that is my opinion.  I also worry that some postings meant to be lighthearted banter could have been misinterpreted by some as a shop secret. Yes, there are some naive makers here. I could be one of them.  :lol:

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Davide,

have you spent any time looking at the transitions (flexing)in the lower bout ...longitudinal, torsional, and traverse bending ...say using clock points 3 to 9? (I and 2 points at a time)

(and conversely in the upper bout)

....not for a 300 pound gorilla

Jim

 

I tried a few times to flex at various points localized here and there, but I've never understood how do you figure out something useful, probably because I was too afraid to make cracks.

I think that there is too much stiffness in small areas and this is beyond the sensitivity of my hands.

Do you understand something from these localized flexing?

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Re: Davide's schema tap-tones.JPG

this is the way to get the actual mode frequencies on an "any Plate"...I think ...useful for testing and documentation

Well done Davide!

Jim

 

Yes, the scheme is just a reminder of where to grab and listen, valid for all plates.

I forgot to specify, perhaps someone may have thought that I do this scheme for each violin that I make, but would be useless because it would always be the same. ;)

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A problem with the concept of plate flexing is learning it. How does one learn to "feel" what is right from reading about it?

 

A major problem for me is the same problem with almost all other plate graduation techniques:  how do you know that this method (or any other method) is causing a good result (whatever that is), and not the myriad of other choices that are made in construction?  

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I tried a few times to flex at various points localized here and there, but I've never understood how do you figure out something useful, probably because I was too afraid to make cracks.

I think that there is too much stiffness in small areas and this is beyond the sensitivity of my hands.

Do you understand something from these localized flexing?

This is soft ground for me...I think it is an over-view to see how the plate is coming, if there is an evaluation, it is subtle (but there)
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The only useful information I can get from flexing plate are as follows: not moving, begins to move, it moves!!

But at this point I am still far from the final result and I still have a lot of wood to be removed, and many other factors to think about to make some decisions about what to do.

I'm not kidding, I believe that the flexing of the plate is not a system of some use in evaluating the end result, I do not think it is possible to achieve such sensitivity in a reliable way, neither after many years of practice......

The only benefit that I can see is in comparing two plates simultaneously to see which one is stiffer, but even that does not lead anywhere.

It is the same as with tap tones : use them (why not?), but don't rely to much on them.

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I'd bet the tap tone of the back on the Canone is much higher than the re-graduated ones. 
So what's the point in all the analysis when the point of making a new instrument is surely not to replicate with 
utmost tedium day after day.
'Papers' have been written about how to produce consistently 'good' plates etc....but it's jaw droppingly dull reading.  

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I'd bet the tap tone of the back on the Canone is much higher than the re-graduated ones. 

So what's the point in all the analysis when the point of making a new instrument is surely not to replicate with 

utmost tedium day after day.

'Papers' have been written about how to produce consistently 'good' plates etc....but it's jaw droppingly dull reading.  

 

But I bet that you have read them anyway..... :)

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A major problem for me is the same problem with almost all other plate graduation techniques:  how do you know that this method (or any other method) is causing a good result (whatever that is), and not the myriad of other choices that are made in construction?  

I agree, and furthermore we don't even have an established bench mark of what we are shooting for, just a general group consensus which scientifically amounts to nothing more than an opinion backed up by some similarities in squiggly line frequency charts.  

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