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Violin #5 - Strad Body modes


Peter K-G

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Where is the modern powerful violin to match that :)

 

There might be a lot of them, all over.  I might have one on my bench right now.  We'll never really know, until we can get the Cannone into some shootouts... which doesn't look too likely.

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Busy day

 

Mold released and linings set, Back and rib garland roughly finished, too much glue as usual

 

post-37356-0-84179400-1368287832_thumb.jpg  post-37356-0-58514400-1368287866_thumb.jpg

 

Spring is coming humidity has been 30-40 % for 1,5 week

MC ~5%

 

Back before glued on the ribs

 

weight=99 g,

M2 = 175

M5 = 343

 

Coupling frequency on ribs 287 Hz (the other frequency 329)

weight = 165 g

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Because the back plate is under pressure flowing outwards from the sounding box due to the sound post. It is advisable to take all precautionary measures so that the back joint does not split open. On the top plate, cleats are unnecessary.

 

www.kreitpatrick.com

Internal cleats will not stop this....external ones would.

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Busy day

 

Mold released and linings set, Back and rib garland roughly finished, too much glue as usual

 

attachicon.gifMoldRelease.jpg  attachicon.gifBackRibs_RoughlyFinished.jpg

 

Spring is coming humidity has been 30-40 % for 1,5 week

MC ~5%

 

Back before glued on the ribs

 

weight=99 g,

M2 = 175

M5 = 343

 

Coupling frequency on ribs 287 Hz (the other frequency 329)

weight = 165 g

As long as you're collecting all these numbers you might also consider dividing the mode frequencies by the weight of the plate. This Hz/g gives some indication how effective your wood choice and plate shapes are.  For example, your back's mode 5 of 343Hz divided by your plate weight of 99g gives 3.46 Hz per gram. 

 

You can track this effectiveness number as you do your plate thinning. If you thin an area and this number goes down it might mean you picked the wrong area to thin. 

 

I don't know if this is helpful but its another amusement.

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 If you thin an area and this number goes down it might mean you picked the wrong area to thin. 

 

This is only true if the goal is to maximize the Hz/gram value of the free plate.  If you have some information that I don't, showing that maximizing this value for a given piece of wood does something beneficial for the sound of the completed instrument, please let us in on this research.

 

While it may be true that finding a higher Hz/gram value might be a good thing (if higher stiffness/weight is good) in a plate made to a consistent arching and graduation pattern, it does not follow that selectively thinning to mazimize the value in a given plate would have any similar benefit.

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This is only true if the goal is to maximize the Hz/gram value of the free plate.  If you have some information that I don't, showing that maximizing this value for a given piece of wood does something beneficial for the sound of the completed instrument, please let us in on this research.

 

While it may be true that finding a higher Hz/gram value might be a good thing (if higher stiffness/weight is good) in a plate made to a consistent arching and graduation pattern, it does not follow that selectively thinning to mazimize the value in a given plate would have any similar benefit.

I don't know the plate's mode 5 or 2 Hz/gram values for lots of great and poor sounding instruments so I can't say whether or not they're important. 

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As long as you're collecting all these numbers you might also consider dividing the mode frequencies by the weight of the plate. This Hz/g gives some indication how effective your wood choice and plate shapes are.  For example, your back's mode 5 of 343Hz divided by your plate weight of 99g gives 3.46 Hz per gram. 

 

You can track this effectiveness number as you do your plate thinning. If you thin an area and this number goes down it might mean you picked the wrong area to thin. 

 

I don't know if this is helpful but its another amusement.

 

Actually I did that Marty, this is from the top plate:

 

Top_tuning.JPG

 

with rounded edges it will be around 67,5 g (5,1 Hz/g)

 

This is very well described in the book, also how to ensure that it's stable/does not increase once the violin is finished and after year of use. The goal was to tune it to 5,3 Hz/g (65 g), but I didn't manage to tune the extrados/arch good enough for that.

 

The back plate was a nightmare due to tuning at 0% MC. I managed to fix it with help from Patrick. Got it down to 99 g from 110 g

 

Could you post your original tuning descriptions, I can't find them anymore. Before I read Patrick's book I use to follow them (The blue, red, white areas and where to tune)

 

Thanks

post-37356-0-96811700-1368339395_thumb.jpg

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Dividing the mode 5 frequency by the weight of the plate in the white before cutting the f-holes and before installing the bass bar is valid only:  a) at the moment when you finish the plate and  for a given moisture content in the wood. In no way does it indicate whether the choice of wood or distribution of the thicknesses is correct.

Example for PKG’s top plate:  347 Hz ¸ 68 g = 5.1 Hz/g at 6% MC.

When the moisture content in this same top plate rises to 12%, the frequency will be 329 Hz and the weight 71 g.   329 Hz ¸ 71 g = 4.6 Hz/g.

 

www.kreitpatrick.com

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Dividing the mode 5 frequency by the weight of the plate in the white before cutting the f-holes and before installing the bass bar is valid only:  a) at the moment when you finish the plate and  for a given moisture content in the wood. In no way does it indicate whether the choice of wood or distribution of the thicknesses is correct.


Example for PKG’s top plate:  347 Hz ¸ 68 g = 5.1 Hz/g at 6% MC.


When the moisture content in this same top plate rises to 12%, the frequency will be 329 Hz and the weight 71 g.   329 Hz ¸ 71 g = 4.6 Hz/g.


 


www.kreitpatrick.com

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Dividing the mode 5 frequency by the weight of the plate in the white before cutting the f-holes and before installing the bass bar is valid only:  a) at the moment when you finish the plate and  for a given moisture content in the wood. In no way does it indicate whether the choice of wood or distribution of the thicknesses is correct.

Example for PKG’s top plate:  347 Hz ¸ 68 g = 5.1 Hz/g at 6% MC.

When the moisture content in this same top plate rises to 12%, the frequency will be 329 Hz and the weight 71 g.   329 Hz ¸ 71 g = 4.6 Hz/g.

 

www.kreitpatrick.com

 

It only takes a few minutes to scrape a small area of a plate and to measure how its mode frequencies change during that step.  It is highly unlikely that the humidity can change that quickly.  So the frequency change amount and its up or down direction is due only to that scraping.

 

If you like doing this kind of work it makes sense to climate control your shop to give a constant humidity and temperature.

 

I have no idea what choice  of wood or thickness distribution is correct.  I don't even know what "correct" means.

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Actually I did that Marty, this is from the top plate:

 

attachicon.gifTop_tuning.JPG

 

with rounded edges it will be around 67,5 g (5,1 Hz/g)

 

This is very well described in the book, also how to ensure that it's stable/does not increase once the violin is finished and after year of use. The goal was to tune it to 5,3 Hz/g (65 g), but I didn't manage to tune the extrados/arch good enough for that.

 

The back plate was a nightmare due to tuning at 0% MC. I managed to fix it with help from Patrick. Got it down to 99 g from 110 g

 

Could you post your original tuning descriptions, I can't find them anymore. Before I read Patrick's book I use to follow them (The blue, red, white areas and where to tune)

 

Thanks

This is merely the overlay of the mode 2 node lines  and mode 5 node lines.  The basic idea is that if you thin within the node lines, the frequency goes down and if you thin outside of the node lines the frequency goes up.post-44223-0-77654600-1368376855_thumb.jpg

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A little late on this thread but really impressed at all the info being passed around. Lots of great references to hang onto.

This is exactly why I regraduated Violin #1-3. They didn't sound great anymore M5 had increased ~15 to 20 Hz on top plate and ~10 to 15 Hz on back.

I took my top plate back off my #1 violin the day after I finished it when I realized how much I disliked the tone. Lucky it was an easy regraduated fix in my case. Needed thinning in the wings of the lower bout mainly below the sound holes.

Rather than adding another quote from a few days ago, a question. If the top has good modes /tap tones, what other aspects are missing when you say if the violin sounds like crap when you are done then the tap tones don't matter.? It seems that the good tap tones at least tells you that your top and back should play nice together and make decent sounds when all glued up and varnished.

I now some on the forum find the discussion of tap tones rather annoying and irrelevant. How then do these makers know when to stop thinning the plates and what thicknesses to use and where. My guess is by feel and what the scraper sounds like in each area of the plates while thinning. That's something that I noted when graduating plates. Seems like tap tones are a quantitative guideline for the more intuitive process which comes after carving many tens of plates.

Joe

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I guess that most makers get a gut feeling by bending the plates in different directions. Other possibilities is Learning how to choose wood and suitable arching templates to that and a well known graduation schema and then wish for the best :)

 

The tuning methods that I have used lately is so sensitive that I can not see any other way to come even close to acheive what I want to do.

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I don't know how to track back plate coupling frequence on a finished violin, but you should match the top to the calculated free back plate M5 from that coupling frequency. or take the back of as well, if you dare :) The most important thing is to know the moister content % in the wood.

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