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Top Weight/Forensic Lutherie


Knuckled Under
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I am a hobbiest/ multiple instrument builder.

I hope to complete my first from scratch fiddle after working through a kit a few years ago and improving my finishing techniques with my last few Ukes.

I will be working through the Strobel books but my question is about an old violin.

I acquired a few parts and throw-aways from a luthier friend to review and possibly work on refurbishing.

 

My question is one of the instruments I should be able to refurbish when I gain more skill.

It needs edge/purfling repair from a probable drop and has a few cracks that I have repaired/cleated.

 

The label says "M Lubowski 1911 San Francisco - redone from a Old French Violin".

The top weight with intrinsic bass bar weighs only 69 grams. 

The gradations seem to be appropriate for a well-made violin.

Is this secondary to further desiccation of the wood?

This seems too light as a goal for a new build?

 

Thank you for your consideration,

 

Knuckled Under

Austin, Texas

 

 

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  • 7 years later...

69g for a top plate with bar is perhaps a bit on the heavy side for a well-made violin, but might even be on the light side for a violin made with crappy (low stiffness/weight) wood.  This is a survey of plate weights without the bass bar or varnish (except for the factory regrads in the lower right, which have varnish).  Add ~4g for bass bar and 2g for varnish.

My data is the red squares, and there is additional data from other makers and some reference Cremonese instruments (presumably with varnish).

Without bass bar or varnish, figure your plate would be in the region of 63-65g on this chart.

1084328037_Plateweightsandtaptones150622.jpg.1a140554b07103a5deeffae43618130a.jpg

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On 10/26/2021 at 11:13 PM, Don Noon said:

69g for a top plate with bar is perhaps a bit on the heavy side for a well-made violin, but might even be on the light side for a violin made with crappy (low stiffness/weight) wood.  This is a survey of plate weights without the bass bar or varnish (except for the factory regrads in the lower right, which have varnish).  Add ~4g for bass bar and 2g for varnish.

My data is the red squares, and there is additional data from other makers and some reference Cremonese instruments (presumably with varnish).

Without bass bar or varnish, figure your plate would be in the region of 63-65g on this chart.

1084328037_Plateweightsandtaptones150622.jpg.1a140554b07103a5deeffae43618130a.jpg

With exception of the 1716 Strad the few Cremonese instruments it looks like

Taptone divided by weight equals approximately 4.9 (Plus minus 0.1)

 

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8 hours ago, Andreas Preuss said:

With exception of the 1716 Strad the few Cremonese instruments it looks like

Taptone divided by weight equals approximately 4.9 (Plus minus 0.1)

There are some other Cremonese (small black diamonds) on the plot that for some reason don't have labels on them.  I noticed that it looked like two parallel lines... one with high taptone/weight, and one lower.  At one time I plotted the information, and it looked like the higher taptone/weight data mostly were in the "golden era" instruments.  Coincidence?

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1 hour ago, scordatura said:

Hi Don. What do the squiggly grey lines represent?

Those are the path of weight reduction as I thinned the plates.  They generally follow parallel lines, so the wood you start with primarily determines where you can get to on the taptone/weight plot.  I theory, they should be parallel to the turquoise RR lines, but the RR lines are theory for flat plates, and arched shells behave a bit differently.

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Dropping in to suggest that graduation distribution is a whole lot more important than weight and should be part of any graduation discussion.

If you have the weight in the wrong places it doesn't matter how well you match the "right" weight being suggested above. If you think more in terms of distribution, you can use the weight distribution to reinforce desirable characteristics, subdue the undesirable, and gross weight can be much higher with the possibility of manipulating more aspects of tone and playability. If you stick to low weights you can't explore those options. More tools to work with.

As an example, I've seen plenty of semi-commercial tops in older instruments that are very thin all around the edge, very thick in the middle, a good weight, and don't work at all. 

Saying 68 grams without consideration of distribution is like setting the timer for cookies to bake in 15 minutes, but neglecting to set the temperature.

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8 hours ago, Michael Darnton said:

Dropping in to suggest that graduation distribution is a whole lot more important than weight and should be part of any graduation discussion.

If you have the weight in the wrong places it doesn't matter how well you match the "right" weight being suggested above. If you think more in terms of distribution, you can use the weight distribution to reinforce desirable characteristics, subdue the undesirable, and gross weight can be much higher with the possibility of manipulating more aspects of tone and playability. If you stick to low weights you can't explore those options. More tools to work with.

As an example, I've seen plenty of semi-commercial tops in older instruments that are very thin all around the edge, very thick in the middle, a good weight, and don't work at all. 

Saying 68 grams without consideration of distribution is like setting the timer for cookies to bake in 15 minutes, but neglecting to set the temperature.

 That's what I found too.   If you thin the entire surface of the plates the mode frequencies will drop but if you thin the plates only in certain areas the the mode frequencies can go up or down or even stay the same.  

One attached plot shows how a top plate's mode 2 and 5 frequencies changed as the plate was thinned on the inside surface in 250 small consecutive steps to gradually reduce the plate's weight to get it into the range of Old Italian tops.

Another plot using the same data shows how the mode frequency/plate weight ratio changed with each step with a general pattern of increasing ratios.

 

My mental health therapist has also seen some patterns.

 

Screen Shot 2021-10-31 at 8.14.21 PM.png

Screen Shot 2021-10-31 at 7.31.12 PM.png

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