Soundpost facts?

[BarryD]

To take one more step down this path if you add 130 + 195 + 325m/m??? How do you get to a scale length of 330??

[Brad Dorsey]

"To take one more step down this path if you add 130 + 195 + 325m/m??? How do you get to a scale length of 330??"

The scale length can be 130 because the bridge doesn't stand vertically -- it leans a little towards the tailpiece.

[Darren Molnar]

It's easy to go mad worrying about the numbers, I've been relieving myself of that burden, lately, a little bit. because:

If you measure the 195 with a ruler over the arch, it's longer than with the calipers. If you measure the 195 before any final finishing of the edgework, however slight, the 195 goes lower down the plate.

The neck set, and string height affect the final string length, be it 326,327,328, or somewhere around there.

If you measure the 130, parallel to the f-board, its shorter than if you measure a straight line from the plate edge to the f-board end.

If you move the bridge north or south a bit to find the magical sweet spot, ratios and measurements get thrown off.

Higher bridge, lower bridge, etc.

the profile of you're bridge moves the string length shorter or longer, depending on how you make it.

You're ruler, may be different than my ruler, I don't think all my rulers are exactly the same, either.

The more I think of it, the more I wonder if this is a part of the " the book says so " syndrome

Let you're experience guide you, learn by getting even more experience, always listen to other ideas, and find one that works for you, and is flexible.

And don't mention it to most players, or anyone who can only understand absolutes. If they are confident that you as a maker understands the extreme importance of exact measurements, then, as if by magic, the set up is " perfect "

[Jacob]

Good points Darryl.

Just to make your post a bit easier to comprehend in some places:

"You're" = "you are"

"Your" = "belonging to you"

I'm sorry if that comes over as being a pain in the a$$, but for non-English speakers like me, deciphering unusual syntax or grammar can be a brain-cracker at times

[catnip]

To take one more step down this path if you add 130 + 195 + 325m/m??? How do you get to a scale length of 330??

If you use the pythagroean theorem: (stop length)^2 + (bridge height)^2 then take the square root you will get an answer very close to 327 then if you lean the bridge back a bit you will be in the acceptable range 327-330 mm.

[Darren Molnar]

Thank you Jacob, I am getting too lazy with my english writing. I'm currently blaming that on spending my days " baby talking " to my four month old. Which I hope I can milk for another year or two.

[Craig Tucker]

Thanks all.

I really appreciate the link, which addresses my questions directly.

Still - there is a question (in my mind) about how the original bridge line WAS determined... especially if you take into account the fact that most plate work (i.e. repair work) is done varnished, with the bass bar on, and the ff holes cut - which is why I originally asked the question about where exactly, would the C of G be with regard to the bridge line, when the plate is in the formative stage without a bass bar or ff holes?

I waffle between the idea that Sacconi might have been thinking that the Cremonese used this method and this geometry initially, and didn't necessarily bother to explain that the C of G would not match where the bridge line was in the finished (or perhaps even re-thicknessed) plate...

There is no way for those of us who have no access to the originals, to determine these things empirically, and even more so because even if we can see the instruments in question, we will most likely not see them with the belly off, nor be able to further inquire with some sort of experimental method.

And, I find it a bit odd that this point was so adamantly mentioned by Saconni, and yet, is rarely if ever questioned by modern makers - plus, I am currently attempting to re-make my molds based on Strad and a del Gesu posters.

So - some of the original questions I had regarding the bridge position and ff hole placement are resurfacing again, including the question of possibly obtaining a geometrically correct bridge placement.

Am I correct in thinking that Mr. Darnton points out in the link that most Italian plates we get to observe, when complete with bass bar and ff holes, have the excess of mass showing up in the upper half of the plate? Can any one else who HAS observed many fine old (Italian) violins with the belly off, verify that this is the case?

[Roger Hill]

Hi Craig:

I don't have the Sacconi book and unless prices change, I am unlikely ever to have it. However, there are a couple of things I have learned while studying arching/graduation. First, the centroid of the violin plan form is at the bridge position. Draw it out, work the numbers, and you will find that it is around 190+/- or so mm from the top. Secondly, if you take a top with uniform thickness, you will have the center of mass north of this position for the simple reason that relative to the planar area, there is a larger surface area, and hence mass, in the upper bout than in the lower bout. Now, FF holes and bass bar will also affect the CM as will the graduation. I think the biggest effect on where the current CM is relative to the original CM has to be in changed graduation and bass bars. It would be nice if someone like Jeff Loen would use his maps to compute a "relative" center of mass for violin tops he has measured. Now, tell me what you know about this. Thanks,

[PFrank]

Hi Craig:

I don't have the Sacconi book and unless prices change, I am unlikely ever to have it. However, there are a couple of things I have learned while studying arching/graduation. First, the centroid of the violin plan form is at the bridge position. Draw it out, work the numbers, and you will find that it is around 190+/- or so mm from the top. Secondly, if you take a top with uniform thickness, you will have the center of mass north of this position for the simple reason that relative to the planar area, there is a larger surface area, and hence mass, in the upper bout than in the lower bout. Now, FF holes and bass bar will also affect the CM as will the graduation. I think the biggest effect on where the current CM is relative to the original CM has to be in changed graduation and bass bars. It would be nice if someone like Jeff Loen would use his maps to compute a "relative" center of mass for violin tops he has measured. Now, tell me what you know about this. Thanks,

I'm going to just throw this out there. I find your discussion very interesting but way over my head as I am not a maker and know little about the subject. Earlier I posted a photo of my violin with the oddly placed F holes. This discussion reminded me of a Chapter in the Hill book which I read this summer. I scanned the diagram from the book and superimposed cicles over the arcs as drawn. Note where the upper arc's intersect the F's and where the lower arc's center falls. Maybe this is obvious to all of you but does the placement of the bridge and the post owe more to geometry than to physics? Please pardon my ignorance.

[Chris Knowlton]

When one says to position the sound post Xmm down and Xmm outside the bridge, what part of the bridge is being referenced?

Chris

[Andres Sender]

PFrank--Geometry was probably the primary language in which the early Cremonese makers thought about design, and physics is (among other things) a way to describe the results they got through their empirical testing and refinement of their designs. So it's all interrelated.