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reguz

Why arching shape?

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30 minutes ago, Michael Appleman said:

The arch resists the downward pressure of the strings on the bridge as well as the lengthwise squeeze on the top and stretch on the back. Flat topped fiddles have been tried as well as just about every form of arch one can imagine. After a few centuries, a consensus has been reached about what sort of arch tends to give what sort of sound. If you want to ignore all of the experience accumulated since Andrea Amati started making violins nearly 500 years ago, feel free! Do try making a flat violin and if it works better than Stradivari or Guarneri arching, the world will make a beaten path to your door!

Why does the arch resist the pressure of the strings?. No answer from you. You look backward 500 yeasr but do not give a technical answer. WHY do we need arching shape!!!

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Now many of you start thinking, That's good. hopefully some one ask what I thinks about this problem. No one does!! Why? because you now better without explaining anything?

Ask yourselve does the instruments load increase by the downward load on the bridge?

What happens?

What is meant arching shape should or must produce?

This is what my very early question is about!!

No one did give an answer!!

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46 minutes ago, Peter K-G said:

Because that's what happens when you put pressure on a flat top box with flexible sides. A pyramid like top would push outwards

Yes, a downward load is observed but what happens with the stress condition making equilibrium?

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An arched top doesn't work very well unless you use a bass bar brace.  If you have to use a braces why bother using an arch?

This violin flat top is 1.7mm thick Paulownia wood and weighs about 43 g.

 

No 31 top.jpg

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http://blog.feinviolins.com/2012/02/arching-great-curves.html

take a look at this article.

An arch distributes the stress of downbearing from the strings, where a flat top would have all the pressure concentrated under the bridge where it would break. Try it.

this way, the belly can distribute stress whilst still being flexible whereas a flat top requires many supporting beams, stiffening it in many directions. Even so, the violin requires a soundpost and bass bar for support and to distribute vibrations effectively. 

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5 minutes ago, David Beard said:

Take a physics course.  Then follow what happens from the stretched strings.

If this is an answer on my topic questions this is not an answer. Its comes from a person who do not no nothing.. Take a physic course yourselve.

Give a proper explanation or be quite.

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21 minutes ago, reguz said:

If this is an answer on my topic questions this is not an answer. Its comes from a person who do not no nothing.. Take a physic course yourselve.

Give a proper explanation or be quite.

Might I  suggest you do two things.

1. re ask your question in a coherent manner, being specific and precise . 

2. stop coming across in such an abrasive manner, it's not really conducive to an adult conversation. It just makes you seem nuts or drunk or maybe both. No one wants to engage that in any serious way.

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With the strings tuned, try lifting the bridge.  Or, using a solid body electric or mute violin, put your finger under a bridge foot and tune up to pitch.  

You will find the bridge feet are indeed under a force pushing toward the top. 

However, the bridge on a violin isn't being shot through the air like an arrow from an archery bow, so the downward forces from the strings are being balanced by counter forces from physical distortion, primarily of the top, bass bar, and back.

When not being played, all parts of the violin find static balance, but many parts are somewhat flexed, countering forces from the stretched strings.

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OK. Jezzupe. My question is

Why do we need arching shape?

What bennefit does it produce?

What can we learn from arching shape contra a flat plate?

What technical secret do we understand of the function of arching shape.

I'm not abrasive in your sence I just like to get proper answer on my question. When they do not come I'm disappointed!!

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2 minutes ago, David Beard said:

With the strings tuned, try lifting the bridge.  Or, using a solid body electric or mute violin, put your finger under a bridge foot and tune up to pitch.  

You will find the bridge feet are indeed under a force pushing toward the top. 

However, the bridge on a violin isn't being shot through the air like an arrow from an archery bow, so the downward forces from the strings are being balanced by counter forces from physical distortion, primarily of the top, bass bar, and back.

When not being played, all parts of the violin find static balance, but many parts are somewhat flexed, countering forces from the stretched strings.

David, Lay the instrument with not tensioned striongs on a scale and measure the weight.

Now bring the strings into tension at pitch and measure the weight again.

Did the weight increase? Ask your selve what structure is movin. All stress remain inside the instrument.

What does the stress bring about?

It does not matter if you have a flat plate structure or arching structure the condition describe remain the same.

What happens with arching structure, belly and back, and what benefit do we understand?

That is my question.

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A serious answer:

Obviously, there are many ways one might support the string load, so one could say that isn't the reason a violin is arched.    But also remember, not all "violins" have been arched (i.e. Chanot)

"Reasons" for things aren't always a straight shot. Sometimes they're physical and objective, but sometimes they go to muddier philosophic or social territory.

A violin is largely culturally defined.  If you define a violin as any object tuned as a violin, unfretted, played with a bow, and about violin sized, then you can make many different physical configurations.

But for many, a violin is more specific than that.   The basic configuration of sound post, bass bar, bridge, and arched plates, and soundhole are part of the definition.

So on that level, one can say a violin is arched as part of its centuries-old cultural definition.    

To me, that is the real answer.

However, arched plates have many consequences.  But again, it's not that other solutions aren't possible, but just that they would step outside our specific cultural definition of a violin.

Some consequences of arched plates:

* Greater ratio of air volume to plate area.

* less physically direct connection of plate centers to sides

* geometric cupping of the convex arched area of plates

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4 minutes ago, reguz said:

OK. Jezzupe. My question is

Why do we need arching shape?

What bennefit does it produce?

What can we learn from arching shape contra a flat plate?

What technical secret do we understand of the function of arching shape.

I'm not abrasive in your sence I just like to get proper answer on my question. When they do not come I'm disappointed!!

Well, frankly I've got my feelings about such things, and have moved beyond such things, I don't waste much time with thinking too much anymore...except once and awhile when I'm here, and I just don't have the inclination to get more involved in this conversation

But if you have something to say, by all means say it, I'd hate to see someone with something important to be said be ignored because of the way they come across....

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1 hour ago, reguz said:

Peter I asked a question but you do not give a technical answer. Give a technicalö answer,please!

 

1 hour ago, jezzupe said:

I think you need to do some reading about structural engineering

 

26 minutes ago, reguz said:

David, Lay the instrument with not tensioned striongs on a scale and measure the weight.

Now bring the strings into tension at pitch and measure the weight again.

Did the weight increase? Ask your selve what structure is movin. All stress remain inside the instrument.

What does the stress bring about?

It does not matter if you have a flat plate structure or arching structure the condition describe remain the same.

What happens with arching structure, belly and back, and what benefit do we understand?

That is my question.

With my basic structural engineering education and "sunt bondförnuft" the flat top will colapse inwards because suronding structure is stretched and bent. On a violin in really really complexed ways that are individual to every particular violin. But of cource there are some common prominant bending stretching in general on a violin because of its shape. 

I don't see that you have a question, because you allready know all this, read your web site many times.

Over and out :)

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28 minutes ago, reguz said:

David, Lay the instrument with not tensioned striongs on a scale and measure the weight.

Now bring the strings into tension at pitch and measure the weight again.

Did the weight increase? Ask your selve what structure is movin. All stress remain inside the instrument.

What does the stress bring about?

It does not matter if you have a flat plate structure or arching structure the condition describe remain the same.

What happens with arching structure, belly and back, and what benefit do we understand?

That is my question.

Again, no matter how much or little you believe you know physics, study some more.

1) Weight change isn't relevant.

2) When a moderate force pushes on something that doesn't appear to move or break in response, what does happen is the immobile object compresses/flexes/distorts somewhat, creating countering restoral forces.

This is what happens when you lean against a wall, or when you don't fall through the floor.

 

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2 minutes ago, jezzupe said:

Well, frankly I've got my feelings about such things, and have moved beyond such things, I don't waste much time with thinking too much anymore...except once and awhile when I'm here, and I just don't have the inclination to get more involved in this conversation

But if you have something to say, by all means say it, I'd hate to see someone with something important to be said be ignored because of the way they come across....

Well Jezeepe, First of all the sound post does not move by the increasing downward load on the bridge. The bridge at the tremble bridge feet move a little. The bridge feet at the bass bar may or can move up or down. This depend on the stiffness of lenght arc shape and the bass bar that actually is an reinforcement with the function not producing deformation in the center between the F-holes.

Then what is happening?. Well since the strings principally act on the  end blocks they become pulled upward and inward. More onward and little upward. The inward pressure produces buckling on the lenght arc shape and this pruduces an upward force under the bridge feet. Together with the upward force on the end blocks a state of equilibnrium always is present and there is no change in the weight of the instrument thus no dopwnwadr movement under the sound post. I have studied the circumstances  and made a vector force diagram where you can see how string load produces forces. In order not to make it not to complex I placed the bridge on the top of the sound post. What happens with the belly and back? Well the belly becomes compressed by buckling and vbecome stress in a complex condition. The back withhold the endblock moving upward and by reducing the stiffness of the back the comprssionon the belly increases and with this the stress condition on the arching shape oneach side of the sound post.

The figure explain the circumstances. Loweing the arching high ask for higher string load or less thickness in order to deflect and produce stress condition over the bout shapes. This stress is not ONE but many hundreds of stress condition and they will respond on a specific frequence playes as well as the string respond on the stress condition producing a frequency. 15-20 frequency can be played withinONE second and its due to the stress conditions on the two bout shapes the isntrument respond and produce vibrating condition. BUT during the playing action the end block move up and downs an produce a dynamical state. The combination of that state and the stress condition on the bout shape predict the quality of the responding instrument. Hope this explaination give soemthing thinking about.

2016 vector forces.jpg

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22 minutes ago, Peter K-G said:

 

 

With my basic structural engineering education and "sunt bondförnuft" the flat top will colapse inwards because suronding structure is stretched and bent. On a violin in really really complexed ways that are individual to every particular violin. But of cource there are some common prominant bending stretching in general on a violin because of its shape. 

I don't see that you have a question, because you allready know all this, read your web site many times.

Over and out :)

Peter, Read my earlier given expålanation with a vector diagram that explain why we need arching shape.

Peter stretch means LENGHTENING. NO lenghtening n the violin is found well build.

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5 minutes ago, David Beard said:

David, you are still thinging of action and reaction om mother soil. A structure as far as it is aboutv the violin outside the structure. The violin has no supporting structure as you think about.

Applied forces on the nd blocks become orientated producing comprssion on the bridge and the sound post, not equal as you can see on the vector diagram shown earlier

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This thread looks like a smoldering dumpster to me... but since I have some background in structures, and have built a flat-plate violin (that collapsed), I feel I should open the lid of the dumpster and throw something in.

Structure:  flat plates can only support normal loads by bending stiffness, which is plenty weak in thin plates.  The arch then creates a loadpath putting the wood in compression, which is plenty stiffer.  Additionally, when a flat plate bows under load (which it must), the wood then goes into tension, and you get crossgrain splitting.  That is how my flat-plate violin died.  You can increase bending siffness of flat soundboards with bracing, but even flat-top guitars aren't really flat, and have a slight convexity to them (at least as they are first made).

Acoustics:  arching changes the shape of the modes, and it varies with frequency.  Below a certain frequency, the arched shape is more rigid and the antinodes are enlarged.  At higher frequencies, the effect diminshes, and how that happens depends on the radius of curvature and the speed of sound of the wood, with some contribution from bending stiffness.

Now I close the lid and walk away.

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Reguz--

 

Modes.

A structure will tend to move in ALL the available ways possible, the balance favoring path of least risist.

You have analyzed ONE of a number of perspectives.  The one you take begins from seeing the post as immobile.   There is nothing wrong with looking from that view, but it DOES NOT have any special priority above looking at any other point as an immobile reference.

There are many modes of flex or vibration in a violin.  And they pretty much all play roles.

******

One can only go so far considering real systems only theoretically.   

We can easily get lost or disoriented in theoretic thought.  The farther we try to go without grounding back in real observation the more likely to get turned around and off track.  

We're lucky to live in a time when real motion studies of violin plate motions are readily available to us. (google Borman i.e.)

You should spend some good time watching these.

You will find that the activation of various modes of motion in real plate observations is frequency dependent.   

A further thing to consider is that while it is theoretically valid to take any point you choose in a system as an immomible reference, there is nevertheless considerable virtue in prefering a reference that yields a comparatively simpler or more elegant perspective.  Thus there is nothing wrong with choosing the Moon as reference for the motions of our solar system, or the Earth, but a simpler understanding emerges if we choose the Sun.

In a similar way, if you watch plate motion studies from many frequencies, you will find that in some modes of motion the soundpost is easily viewed as immobile, but in many other modes not so.  Similar with the corners.   There basically are no parts that aren't mobile in some of the modes.

 

 

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