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Woodland

Boxy, honky nasal sound.

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56 minutes ago, Marijan Radaljac said:

Normaly, any actions which would increase the string angle would increase the puling-up force at the effort (nut) point. If you drive it far enough it will break the joint or deform the structure behind the joint (load) point, that is, plates/ribs construction. 

I think this is a key point.    If the rib assembly was perfectly rigid., there would be zero compression in the top plate with any given overstand/nut positions.   But because, it is not rigid, the force from the neck root on the top block can be transmitted to the top plate.

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Ok here's my drawing.

overstand.thumb.jpg.f944a2b8f9701e3d9b476af18a91a532.jpg

In A we have a "standard" set-up with a regular overstand - the triangle represents the neck and the block represents the body of the violin (just in case that's not obvious)

In B we have a vastly raised overstand and nut position, just so we can see what's happening. The first thing we see is that the bridge has got higher AND the string angle has increased. 

The question for me is whether the B scenario actually pulls the saddle and the nut together more than in A. And if so why ...

 

 

 

 

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1 minute ago, martin swan said:

Ok here's my drawing.

overstand.thumb.jpg.f944a2b8f9701e3d9b476af18a91a532.jpg

In A we have a "standard" set-up with a regular overstand - the triangle represents the neck and the block represents the body of the violin (just in case that's not obvious)

In B we have a vastly raised overstand and nut position, just so we can see what's happening. The first thing we see is that the bridge has got higher AND the string angle has increased.

As for the vertical line that represents the join between the neck and the body, that line doesn't bend if the glue joint is good. 

The question for me is whether the B scenario actually pulls the saddle and the nut together more than in A. And if so why ...

 

 

 

The answer is yes. 

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4 minutes ago, martin swan said:

And why? Isn't it just string angle?

 

It is a lever.  The string tension is the “effort”: the top is the “load” and the button joint is the “fulcrum”.

8B61CE88-F219-4447-97D8-523390273B1F.gif

The fartheraway the “effort” is from the “load” the greater the mechanical advantage.

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Martin, I think you are correct that the higher overstand itself is not increasing the compression on the top....since the "overstand, being simply neck root in contact with air.  itself can't push on anything at all.   Thinking more about it,  I think it is the position of the nut in relation to the  top block that is key.   Lower nut positions focus the force of string pull lower down on the top block (where the back plate may help counter it) whereas higher nut positions focus more of the force on the top of the block, trying to tip it over (and compress the top.

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9 minutes ago, Brad H said:

Martin, I think you are correct that the higher overstand itself is not increasing the compression on the top....since the "overstand, being simply neck root in contact with air.  itself can't push on anything at all.   Thinking more about it,  I think it is the position of the nut in relation to the  top block that is key.   Lower nut positions focus the force of string pull lower down on the top block (where the back plate may help counter it) whereas higher nut positions focus more of the force on the top of the block, trying to tip it over (and compress the top.

Yes, the two are tied and the nut is part of their lever..  You cannot increase the overstand, keep the projection and all the other measurements to spec, and not have the nut higher.  The “lever” starts where the strings start  (once again I believe it is where the strings originate and not the nut, perhaps one of our engineer members can correct me it I am mistaken).  For instance, if you replace the neck with a big s curve and the strings start from the same place at the end of that s curve, the “effort” would be the same.

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18 minutes ago, martin swan said:

The question for me is whether the B scenario actually pulls the saddle and the nut together more than in A. And if so why ...

15 minutes ago, Jerry Pasewicz said:

The answer is yes. 

The answer is no... if you're talking about the force on a direct line between the nut and saddle.

It IS all about string angle for that, with the force being maximum when the string angle over the bridge is zero, and the force (along the nut/saddle line) goes to zero when the string angle goes to zero (of course, other geometry restrictions prevent that from happening).

With the high overstand in drawing B, the moments (torque) on the neck block are much higher, which have to be reacted by compression in the top and tension in the back.

It's complicated, but basic mechanics.

 

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24 minutes ago, martin swan said:

Ok here's my drawing.

overstand.thumb.jpg.f944a2b8f9701e3d9b476af18a91a532.jpg

In A we have a "standard" set-up with a regular overstand - the triangle represents the neck and the block represents the body of the violin (just in case that's not obvious)

In B we have a vastly raised overstand and nut position, just so we can see what's happening. The first thing we see is that the bridge has got higher AND the string angle has increased. 

The question for me is whether the B scenario actually pulls the saddle and the nut together more than in A. And if so why ...

 

Let's say you forgot to glue the upper ribs to the top plate and had a very weak glue joint between top block and table.... in which of your drawings do you think that weak glue joint would be broken first?   In other words, which diagram would cause more of a tilting force on the top block?

 

 

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15 minutes ago, Don Noon said:

The answer is no... if you're talking about the force on a direct line between the nut and saddle.

It IS all about string angle for that, with the force being maximum when the string angle over the bridge is zero, and the force (along the nut/saddle line) goes to zero when the string angle goes to zero (of course, other geometry restrictions prevent that from happening).

With the high overstand in drawing B, the moments (torque) on the neck block are much higher, which have to be reacted by compression in the top and tension in the back.

It's complicated, but basic mechanics.

 

However, he did not say “force”, he said “pulls together”.

As you said the compression on the top is increased, therefor with the increased compression and the same string tension the nut and the saddle would indeed pull closer together. 

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9 minutes ago, Jerry Pasewicz said:

It is a lever.  The string tension is the “effort”: the top is the “load” and the button joint is the “fulcrum”.

8B61CE88-F219-4447-97D8-523390273B1F.gif

The fartheraway the “effort” is from the “load” the greater the mechanical advantage.

You seem to have your fulcrum the wrong side of the load ...

Look, I don't mean to be rude but I don't think anyone denies for one moment that there is leverage centred around the top block. I can see I'm being far too subtle.

 

Does raising the overstand/nut move the fulcrum higher up in the top block or not?

 

 

 

 

 

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3 minutes ago, martin swan said:

You seem to have your fulcrum the wrong side of the load ...

Look, I don't mean to be rude but I don't think anyone denies for one moment that there is leverage centred around the top block. I can see I'm being far too subtle.

 

Does raising the overstand/nut move the fulcrum higher up in the top block or not?

 

 

 

 

 

If you wish to consider the fulcrum to be where the tension intersects with the compression, than yes.  Raising the appui and ergo raising the “nut” moves the “fulcrum” toward the top.

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It might help to do a force diagram just around the block area.

682748277_Forcediagram.jpg.49dfbaa011b5de4fb8e1996118903d79.jpg

String force S is the same for both.  Therefore the sum of the top and back forces must be opposite in sign and equal in magnitude to the string force.

However, there is the moment to contend with, and with diagram B, the string force is much farther away from the block, and the forces in both the top and the back must rise to counteract the moment.

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10 minutes ago, Don Noon said:

The answer is no... if you're talking about the force on a direct line between the nut and saddle.

It IS all about string angle for that, with the force being maximum when the string angle over the bridge is zero, and the force (along the nut/saddle line) goes to zero when the string angle goes to zero (of course, other geometry restrictions prevent that from happening).

With the high overstand in drawing B, the moments (torque) on the neck block are much higher, which have to be reacted by compression in the top and tension in the back.

It's complicated, but basic mechanics.

 

Don, thanks for introducing the concept of torque.

OK so you are saying that in drawing B there is more torque. I get that. But is the joint not sufficiently resistant to that torque? I think it is.

I can see that it might creep over a long period of time, but I don't think that raising the nut/overstand would make a discernible difference to the properties of a violin top in the short term.

Brad, I don't think that's relevant. It's possible to hold a few tons of oak in place with one well placed screw and they will stay there for ever. The force you describe only becomes relevant if there's a failure of the "pinning mechanism". In a properly built and well glued up violin, I don't believe that raising the overstand will cause the top block to tilt more. Yes there may be more torque (I take Don's word for it) but there's plenty to resist it.

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10 minutes ago, Don Noon said:

>

With the high overstand in drawing B, the moments (torque) on the neck block are much higher, which have to be reacted by compression in the top and tension in the back.

It's complicated, but basic mechanics.

 

I don't think you will find any engineers disagreeing with Don's comments.

But  I think it's simple and basic mechanics.

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1 minute ago, martin swan said:

Don, thanks for introducing the concept of torque.

OK so you are saying that in drawing B there is more torque. I get that. But is the joint not sufficiently resistant to that torque? I think it is.

I can see that it might creep over a long period of time, but I don't think that raising the nut/overstand would make a discernible difference to the properties of a violin top in the short term.

Brad, I don't think that's relevant. It's possible to hold a few tons of oak in place with one well placed screw and they will stay there for ever. The force you describe only becomes relevant if there's a failure of the "pinning mechanism". In a properly built and well glued up violin, I don't believe that raising the overstand will cause the top block to tilt more. Yes there may be more torque (I take Don's word for it) but there's plenty to resist it.

Great.  Now all we need to do is measure or test to see if in fact the increased compression can cause the top to move.  A soundpost that gets looser with string tension would seem to prove that point.  And, if you now believe that the compression increases, there must be a point when the arch is strengthened.

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9 minutes ago, Don Noon said:

It might help to do a force diagram just around the block area.

682748277_Forcediagram.jpg.49dfbaa011b5de4fb8e1996118903d79.jpg

String force S is the same for both.  Therefore the sum of the top and back forces must be opposite in sign and equal to the string force.

However, there is the moment to contend with, and with diagram B, the string force is much farther away from the block, and the forces in both the top and the back must rise to counteract the moment.

OK this is helping a lot.

But for B to balance out, either the back has to stretch and the table contract, or both have to stay the same.

Doesn't the soundpost modify all that potential movement in arching? It's really not possible for the back to stretch (ie. the arching to flatten) without the table arching travelling up. 

It still seems to me that while all this creeps over decades, it's a remarkably stable system in the short term.

And if increasing the overstand/nut does anything to the playability of the violin, it's more likely due to the string angle than the play of these forces.

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3 minutes ago, martin swan said:

OK this is helping a lot.

But for B to balance out, either the back has to stretch and the table contract, or both have to stay the same.

Doesn't the soundpost modify all that potential movement in arching? It's really not possible for the back to stretch (ie. the arching to flatten) without the table arching travelling up. 

It still seems to me that while all this creeps over decades, it's a remarkable stable system in the short term.

And if increasing the overstand/nut does anything to the playability of the violin, it's more likely due to the string angle than the play of these forces.

Good...sorry, I know you were talking to Don.  That is what I would like to get to....what happens if we change arches, thin backs, make blocks smaller, top arch rounder, and could this account for the shop of back arching as related to top arching?

 

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Just now, Jerry Pasewicz said:

Great.  Now all we need to do is measure or test to see if in fact the increased compression can cause the top to move.  A soundpost that gets looser with string tension would seem to prove that point.  And, if you now believe that the compression increases, there must be a point when the arch is strengthened.

I'm sure I haven't set as many soundposts as you, but I'm well over a thousand. On violins they all without exception get tighter under string tension. 

 

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3 minutes ago, martin swan said:

I'm sure I haven't set as many soundposts as you, but I'm well over a thousand. On violins they all without exception get tighter under string tension. 

 

Absolutely the overwhelming majority of the cases, no doubt.  But, if one that sounds incredible, gets looser, then it makes me wonder.  And when you see it, you will now wonder as well.:ph34r:  I am not saying it is good or bad, I do not know.  But, if it can be a variable, I would like to explore it.

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10 minutes ago, Jerry Pasewicz said:

Great.  Now all we need to do is measure or test to see if in fact the increased compression can cause the top to move. 

I wouldn't even bother testing that.  Compressive stress on a curved (arched) structure will make it curve more.  Maybe not much, but it would be like doing a test to see if necks tend to pull up or pull back.

10 minutes ago, martin swan said:

OK this is helping a lot.

But for B to balance out, either the back has to stretch and the table contract, or both have to stay the same.

Doesn't the soundpost modify all that potential movement in arching? It's really not possible for the back to stretch (ie. the arching to flatten) without the table arching travelling up. 

The force diagram tells what the forces have to be, and then you have to figure out what those forces are doing to the structure.  With the top under compression and back in tension, the arching will tend to bow outward for the top and flatten for the back..... but ONLY FOR THE SEGMENT FROM THE NECK BLOCK TO THE BRIDGE AND SOUNDPOST.  There everything changes, and you need to make new force diagrams to account for the vertical forces of the string over the bridge, and how it gets through the top and soundpost.  More complicated.

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8 minutes ago, martin swan said:

I'm sure I haven't set as many soundposts as you, but I'm well over a thousand. On violins they all without exception get tighter under string tension. 

5 minutes ago, Jerry Pasewicz said:

Absolutely the overwhelming majority of the cases, no doubt.  But, if one that sounds incredible, gets looser, then it makes me wonder.  And when you see it, you will now wonder as well.:ph34r:  I am not saying it is good or bad, I do not know.  But, if it can be a variable, I would like to explore it.

From unstrung to under tension, I can't imagine a post getting looser. 

If you're talking about tightness or looseness changing over time... that's a totally different story involving relative creep of the top and back arching, among other things.

 

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4 minutes ago, Don Noon said:

The force diagram tells what the forces have to be, and then you have to figure out what those forces are doing to the structure.  With the top under compression and back in tension, the arching will tend to bow outward for the top and flatten for the back..... but ONLY FOR THE SEGMENT FROM THE NECK BLOCK TO THE BRIDGE AND SOUNDPOST.  There everything changes, and you need to make new force diagrams to account for the vertical forces of the string over the bridge, and how it gets through the top and soundpost.  More complicated.

Understood - and of course we see a lot of lightly built old violins with arching deformations that are different either side of the bridge.

On the other hand, it's quite incredible just how many 300 year old violins have front and back archings which appear to match, to be fluid, and to show no signs of longitudinal mess-up. So I would conclude that on average these forces are well balanced - torque is resisted, and stress in one place taken up in another. 

I think we mess with that stuff at our peril. And to some extent, trying to isolate and work up small parts of it are inimical to the nature of a violin.

Everything has to be seen all at once.

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6 minutes ago, Don Noon said:

From unstrung to under tension, I can't imagine a post getting looser. 

If you're talking about tightness or looseness changing over time... that's a totally different story involving relative creep of the top and back arching, among other things.

 

I can only go with what I have seen and made notes about.

 

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