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Joe Swenson

Reasons for Stressing Plates with Tapered Ribs.

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A lot has been going on since I've been away. :D

Spent several hours the other night watching Davide Sora's violin making videos on YouTube the other night.  Wonderful stuff!
Great way to learn refinements in techniques I had only guessed at in the past! :)

One of the first video's I watched was the one on tapering the ribs.  (Thanks for the translations of the text!)

On the instruments I have built so far I have done the dummy approach of a gradual taper from end block to neck block, not understanding the principle of tapering from the upper blocks to the neck block. So my instruments have no stress placed on the front of back plates.  Most observations on instruments with this taper taper is that it is exclusive to the front plate, while  back plate remains flat. 

In Davide's video he distributes the 2 mm taper on the violin to 0.5 mm on the back plate and 1.5 mm on the front plate.

I'm interested in applying a "proper" taper going forward and am interested in the reasoning behind the taper.  And also the reason for making the decision to taper both plates.  I mean, it makes sense if the reasoning behind the taper has to do with a desired change the  resonant response of each plates. Certainly such a stress would alter the way the plate vibrates shifting or perhaps deadening the some key body resonances. Perhaps this is a way to mute some troublesome resonances that lead to wolf tones? It must alter the tonal characteristics in a positive way otherwise this refinement would not have been made.  

Interested to hear your feedback on this.

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49 minutes ago, Joe Swenson said:

I'm interested in applying a "proper" taper going forward and am interested in the reasoning behind the taper.  And also the reason for making the decision to taper both plates.  I mean, it makes sense if the reasoning behind the taper has to do with a desired change the  resonant response of each plates. Certainly such a stress would alter the way the plate vibrates shifting or perhaps deadening the some key body resonances. Perhaps this is a way to mute some troublesome resonances that lead to wolf tones? It must alter the tonal characteristics in a positive way otherwise this refinement would not have been made.  

Interested to hear your feedback on this.

While I do taper my ribs around two millimeters between the lower and upper blocks, I have never run across a solid reason for doing so, aside from tradition. My taper is also on a flat plane on each rib surface, rather than having a bulge at the upper corner blocks.

It is certainly arguable that the upper rib surface should be convex, from end to end, since normal string forces will counteract that, and probably make it go away or even reverse over time. But what we normally find is that rib surfaces on old instrument have gone so wonky, that it probably doesn't matter.

As far as pre-stressing the top goes, wood is such a plastic material that I would expect such minor pre-stressing to disappear within a few years.

This isn't to take anything away from Sora's methods. He does what he does, and I do what I do, and I think we're both OK with that.

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I believe that is what David was discussing in the second paragraph.

Personally, I don't see any benefit to springing either top or back;  I make both top and bottom rib gluing surfaces a straight, flat plane.

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1 hour ago, David Burgess said:

While I do taper my ribs around two millimeters between the lower and upper blocks, I have never run across a solid reason for doing so, aside from tradition. My taper is also on a flat plane on each rib surface, rather than having a bulge at the upper corner blocks.

33 minutes ago, Bill Yacey said:

Personally, I don't see any benefit to springing either top or back;  I make both top and bottom rib gluing surfaces a straight, flat plane.

I can't think of any acoustic or structural reason to spring the plates, nor can I think of any reasons NOT to.

Since I make all of my corner blocks the same height to start with, it's easiest to put more taper between the upper corners and the upper block, so I do spring the plates, sortof like Sora.  The plates are pretty floppy  before they are glued to the ribs, so I don't worry about it one way or another.

 

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46 minutes ago, Don Noon said:

Since I make all of my corner blocks the same height to start with, it's easiest to put more taper between the upper corners and the upper block, so I do spring the plates, sortof like Sora. 

 

Since I have not yet discovered a viable and efficient method of making the blocks to a specific height from the get-go, I make them a bit high, and then plane them (along with the too-high ribs) down to final dimensions in one operation.

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I now taper the top like Sora only because @Roger Hargrave convinced me that this is the historically correct method. However, it is a bit of a meaningless distraction. The straight taper works well too and looks fine. I may switch back and no one would notice.

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4 hours ago, David Burgess said:

While I do taper my ribs around two millimeters between the lower and upper blocks, I have never run across a solid reason for doing so, aside from tradition. My taper is also on a flat plane on each rib surface, rather than having a bulge at the upper corner blocks.

It is certainly arguable that the upper rib surface should be convex, from end to end, since normal string forces will counteract that, and probably make it go away or even reverse over time. But what we normally find is that rib surfaces on old instrument have gone so wonky, that it probably doesn't matter.

As far as pre-stressing the top goes, wood is such a plastic material that I would expect such minor pre-stressing to disappear within a few years.

This isn't to take anything away from Sora's methods. He does what he does, and I do what I do, and I think we're both OK with that.

I'm not sure how the additional longitudinal warping of the top adds much to countering the forces placed on the top by the strings. It seems like the major player in that role is the normal arching structure of the top, locking down the perimeter with the rib garland also supported by the back.

I thought the same thing that after some time the initial stress placed on the top would dissipate. Perhaps it give the instrument a better initial sound quality which might take a non-tapered instrument some additional time to develop? 

It might be interesting to make a violin with uniform thickness.  Measure its tonal characteristics then remove the top and taper the ribs and replace the top to see how the additional stresses affect the tonality. Someone must have already done this. ;)

Thanks for you input David!

 

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2 hours ago, Don Noon said:

I can't think of any acoustic or structural reason to spring the plates, nor can I think of any reasons NOT to.

Since I make all of my corner blocks the same height to start with, it's easiest to put more taper between the upper corners and the upper block, so I do spring the plates, sortof like Sora.  The plates are pretty floppy  before they are glued to the ribs, so I don't worry about it one way or another.

 

Since this occurred later on in Stardivari instruments, there must have been some good reason for him to take this extra step.  Just sayin' :D

It seems that if you have tap tuned a shaped wooden asymmetric "bell" so that it rings nicely then add some longitudinal stress to the upper third of the bell you will undoubtedly be changing it's resonance characteristics.  I could see that this taper would have to be subtle to not overdo the effect.  Too much taper would likely suppress the ability of the "bell" to ring properly and kill the desired sound of the instrument.

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1 hour ago, Michael_Molnar said:

I now taper the top like Sora only because @Roger Hargrave convinced me that this is the historically correct method. However, it is a bit of a meaningless distraction. The straight taper works well too and looks fine. I may switch back and no one would notice.

So you noted no differences in tonality?  I love the sound on my second violin which has a straight taper. I can't help wonder how a slightly stressed top on the same instrument would sound.  It's modeled after Guarneri arching.  Did Guarneri instruments also follow this tapering method?

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22 minutes ago, Nick Allen said:

Anyone consider possibly it had something to do with baroque fingerboards?

Wouldn't it have been present in early Strad's as well then?

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56 minutes ago, Joe Swenson said:

So you noted no differences in tonality?  I love the sound on my second violin which has a straight taper. I can't help wonder how a slightly stressed top on the same instrument would sound.  It's modeled after Guarneri arching.  Did Guarneri instruments also follow this tapering method?

I observed no tone difference that I could attribute to a bent plate. Re-read Don's post above.

Hargrave was talking about Guarneri in particular. You can find that thread on MN. 

Edited by Michael_Molnar
Clarity

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49 minutes ago, Joe Swenson said:

Since this occurred later on in Stardivari instruments, there must have been some good reason for him to take this extra step.  Just sayin' :D

It seems that if you have tap tuned a shaped wooden asymmetric "bell" so that it rings nicely then add some longitudinal stress to the upper third of the bell you will undoubtedly be changing it's resonance characteristics.  I could see that this taper would have to be subtle to not overdo the effect.  Too much taper would likely suppress the ability of the "bell" to ring properly and kill the desired sound of the instrument.

On a violin, everything affects everything, even merely removing the top and re-gluing affects the sound, so I don't know how any meaningful conclusions tone-wise  could be arrived at between springing or non springing the plates.

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I think it is way difficult (realistically impossible?) to understand with statistical certainty whether the effects of this taper have acoustic or structural advantages, but the same is true to understand if not doing it is better. That said, I believe there are both structural (counteracting deformations) and acoustic (better responsiveness) advantages. But it's just an idea I made and I could be wrong, I have no reliable scientific evidence.  The only certainties in favor of this taper are the historical evidence (undoubtedly it was part of the ancient Cremonese system) and for the best aesthetic effect that results. However aesthetics is linked to personal taste so for some it may be irrelevant.  So the discussion could continue indefinitely without moving anyone from his positions, acquired on the basis of his results, his experience and his personal taste, which inevitably is based on sensations and impressions rather than scientific evidence. That's violin making, it's always been so and I don't think it can change, rely on your intuitions and hope to get it right.:)

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Even if I think Strad did it on top side (see the Reynier violin) I do it on the back side , where It make sens for me.

i make the taper round in the upper part of the ribs structure, having the back making tension on the upper block, counterbalancing the string tension and helping the neck projection to not drop down.

 

The Reynier:

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8 hours ago, Michael_Molnar said:

I observed no tone difference that I could attribute to a bent plate. Re-read Don's post above.

Hargrave was talking about Guarneri in particular. You can find that thread on MN. 

No, it’s in a Guarneri book but he is talking about Stradivari.

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Maybe the 2mm taper in the upper bout helped  to sight a line along the instrument between the corners. Lining up the nut and the corners to get the correct neck angle?

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For what it’s worth my own observation about cremonese instruments is that the plate that gets glued first is flat, and the one that gets glued second is tapered, so guitars, for example, where the belly is glued to the ribs before the back, have a flat surface for the belly and a tapered surface for the back, and a violin is the opposite.

If I’m not mistaken, I think Roger Hargrave’s explanation was that the taper had to do with the neck set, which was not 90 deg., but more like 87 (or something). Placing the tapered rib of the upper bout flat on the bench (with a spacer for the edge thickness) and fitting the neck heel to that angle before nailing sets the neck with that angle.  I’ve done it and it works.

To attach the neck of a guitar, you place the ribs and belly structure upside-down on the bench, with an overhanging tongue of spruce sticking out where the neck goes, and place the neck upside-down on the tongue ( with a spacer under the rest), and fit and nail the neck to the rib structure, so the neck is in the same plane as the belly.

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13 hours ago, Joe Swenson said:

I'm not sure how the additional longitudinal warping of the top adds much to countering the forces placed on the top by the strings.

 

Not on the top, but on the entire body of the instrument. Arching the top rib gluing surface may result in that surface ending up straight over time due to string tension forces and wood plasticity, rather than it becoming concave from end to end.

That's just a theory. By the 17th century, violin makers already had at least a couple-hundred years of older violins to learn from, and may not have wanted them to go banana-shaped. ;)

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1 hour ago, Kevin Kelly said:

For what it’s worth my own observation about cremonese instruments is that the plate that gets glued first is flat, and the one that gets glued second is tapered...

A very practical reason for this:  say you put a lot of spring into the back plate (assume it is glued on first).  What happens is that the garland gets sprung, since it is wimpier than the maple plate once the form is removed.  If you have cut out the plates while the garland is on the form, then the top plate won't match up any more.  And the end blocks will be pointing in wonky directions, meaning you have to true them up without the inner form being in place, which is more of a pain.

More and more, it looks to me like a practical and/or aesthetic solution to the idea that you want the ribs shorter at the neck.  And to me, it's a little less work and confusion to cut all the blocks the same height except for the neck block, and put all the taper in the upper bout.  

Any worries about stress and tone I think are total red herrings.

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Did anyone here try to curve the rib surface extreme enough to get some good tension on the top to see if there is a difference for the sound?

(or the more elegant solution would be to curve the underside of the top lengthwise. However thinking about arching deformation when glueing the plate on the ribs sounds like 'don't make stupid experiments.'.)

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21 minutes ago, Andreas Preuss said:

Did anyone here try to curve the rib surface extreme enough to get some good tension on the top to see if there is a difference for the sound?

For a "difference in the sound", you'd need to assemble an instrument without springing, test it acoustically, take it apart, shave down the ribs and endblock, re-assemble it, and test it again.  Definitely not something that would be quick and easy.

However, I did take and old top plate (with bass bar), clamped it down at the corners and end block, and measured how much deflection resulted from a 1-kg weight applied to the neck block area.  It was about 1 mm.  So we're not talking about large forces, compared to the forces applied by the strings.

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