Jack Devereux

Basic Acoustics Resource

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52 minutes ago, Marty Kasprzyk said:

The side view cross section view of the Huberman shows that the sag in the middle portion of the longitudinal arch makes that portion nearly horizontal.  This may or may not be detrimental to the violin's sound character.

The attached paper gives some evidence that a long horizontal arch produces a "bridge hill" increase in sound output at about 2.5kHz which is often found with good violins and absent in poorer ones.

Perhaps this creep deformation was actually good and maybe it's a mistake to prevent it by making the center portion of the top plates thick.

vibsys_2016-ch19.pdf

I make no arguments about the sound but only point out that if we want a piece of wood to hold the shape we give to it we should be cognizant of the materials limitations.

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15 minutes ago, Don Noon said:

Young's modulus is what is related to the material.  Section modulus is something related to beam cross-sections, for calculating bending stiffness (by combining it with the Young's modulus of the material).

There's the modulus of the material... highly direction dependent, but a property of the material alone.  When it is cut into funny shapes, the shape and anisotropic material properties will definitely cause wide swings in the "effective modulus" of the remaining material.   Looking at the cross arch, if you have a 45-degree slope in the arch, it would locally be something like 10% of the modulus of the flat part... assuming normal quartered spruce.

If I take the cross section of the arch and combine it with the Young's modulus is that a section modulus?

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48 minutes ago, curious1 said:

I make no arguments about the sound but only point out that if we want a piece of wood to hold the shape we give to it we should be cognizant of the materials limitations.

Yes but you should specify what time period you want to hold the shape.  If at least 300 years is a reasonable then the Huberman thickness, arch and wood all apparently work well.  

If you want yours to last even longer then I agree it's a good idea to make them thicker.

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39 minutes ago, Michael_Molnar said:

The fly in the ointment with all this is that we cannot evaluate and select wood before it is purchased. Are there sellers who permit this, say, at a show?

Why not, in the end you're the one who pays, and the customer is always right.:)

The real problem is the time needed to do so, when you stand in front of a big pile of wood.

This is why it is important to learn not go far wrong choosing at glance.

 

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49 minutes ago, Marty Kasprzyk said:

Yes but you should specify what time period you want to hold the shape.  If at least 300 years is a reasonable then the Huberman thickness, arch and wood all apparently work well.  

If you want yours to last even longer then I agree it's a good idea to make them thicker.

I guess, if you count a breast patch and arch reshaping 'holding its shape'.

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8 minutes ago, Davide Sora said:

Why not, in the end you're the one who pays, and the customer is always right.:)

The real problem is the time needed to do so, when you stand in front of a big pile of wood.

 
This is why it is important to learn not go far wrong choosing at glance.

 

Or develop techniques that allow you to sort wood quickly.

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1 hour ago, curious1 said:

If I take the cross section of the arch and combine it with the Young's modulus is that a section modulus?

Not quite.  Section modulus is the geometry of the cross-section that helps determine bending stiffness.  Young's modulus of the material is the other part that determines bending stiffness.  Both together determine the absolute bending stiffness.

42 minutes ago, Michael_Molnar said:

The fly in the ointment with all this is that we cannot evaluate and select wood before it is purchased. Are there sellers who permit this, say, at a show?

I don't think they would stop you from doing that, unless you want to dunk their wood in a bucket of water to measure density.  The real annoyance is not just the time, but the equipment you  need to bring in to measure things, and perhaps the disapproving stares.  Going by appearance and feel, from reputable vendors usually has been OK for me.  Picking thru the bargain bin has usually been less OK.  

 

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1 minute ago, curious1 said:

Or develop techniques that allow you to sort wood quickly.

For example? Always interested in system to cut down the time spent in choosing wood, I am becoming more and more lazy with time passing and wood accumulating on the shelves....

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25 minutes ago, Davide Sora said:
 

For example? Always interested in system to cut down the time spent in choosing wood, I am becoming more and more lazy with time passing and wood accumulating on the shelves....

Some makers run their fingers across a spruce billet listening to the rustling sound, but isn't the pitch affected by the geometry of the billet?

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1 minute ago, Michael_Molnar said:

Some makers run their fingers across a spruce billet listening to the rustling sound, but isn't the pitch affected by the geometry of the billet?

They look for a liveliness and quickness of the response, dimension doesn't matter.

Styrofoam has one of the better response in this sense and is always taken as an example to explain the sensation.

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1 hour ago, Davide Sora said:
 

For example? Always interested in system to cut down the time spent in choosing wood, I am becoming more and more lazy with time passing and wood accumulating on the shelves....

I guess it all depends on your perspective of precision. Personally I don't need to know exactly what something is but only approximately what it is. I follow the Goldilocks Rule. Is it hot, medium, or cold?

My initial pass in the wood yard is all visual. Is the grain straight, is the split good, do. I like how it looks. The second sorting is more technical.

With an iPhone, metric rule, and pocket calculator you can measure the speed of sound in under 30 seconds. In the lumber yard you can divide the wood into low, medium , and high speed of sound quite quickly.

the same goes for density. If the wood is fairly uniformly cut you can get low, med, high very quickly.

 

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Once I get the wood back in the workshop and it is time to make fiddles then I get very exacting but I'll know that all the wood is in the ranges that I prefer.

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On 9/6/2017 at 2:22 PM, Jack Devereux said:

I feel like I'm beginning to have enough grasp of tool skills to kinda make a decent, repeatable box to a set of specs, and am now trying to be more systematic about documenting both the things I can control (arching, graduations, bar shape, whatever else), and the qualities of the wood I'm using. 

I hear all these terms and concepts about wood density, modes, speed of sound, all that jazz thrown around that I don't really understand, and would like to learn about this stuff, if only for note taking purposes. Is there a website, book or something else that breaks these basic violin making acoustics concepts down? I've searched and can't seem to find anything that seems definitive. 

Thanks!

 

 

I recommend the following fairly recent books:

 Michael F. Ashby, “Materials Selection in Mechanical Design, 4th edition”, 2011, Elsevier

 This book shows why various materials are chosen for different applications and how the materials are compared.  I gives an easy to understand explanation of physical properties (strength, stiffness etc. we often discuss for violins) and how they are used.

 

Neville H. fletcher, Thomas D. Rossing, “The Physics of Musical Instruments, 2nd edition”, 1998, Springer

 The first part of the book gives a background of vibration mechanics and mathematics.  The remainder portions describe how different classes (wind, percussion, string etc) of instruments function.

 

 Thomas D. Rossing, editor, “The Science of String Instruments”, 2010, Springer

 Chapter 13 on violins was written by Joseph Curtin and T. Rossing and it gives a good overview on how violins function.

 

 Eric J. Heller, “Why You hear What You Hear, an experimental approach to sound, music, and psychoacoustics”, 2013 Princeton University Press

 This is a really great book for describing how sound is produced and heard without using hardly any mathematics.  It has a chapter on the violin but everything else seems interesting too.

 

 For articles I suggest:  (which is attached I hope)

 Colin E. Gough, “Violin Acoustics”, Acoustics Today, summer 2016 volume 12, issue 2,  Acoustical Society of America

 Besides giving an excellent description of how violins work it gives many references if you want to further your reading.

Gough.pdf

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17 hours ago, curious1 said:

I guess, if you count a breast patch and arch reshaping 'holding its shape'.

A lot of things (racing: sailboats, bicycles, cars) which are supposed to move quickly are built to be as light as possible and they're often at the hairy edge of falling apart.  A high failure risk is acceptable if it gives you a competitive advantage.

Other things (buildings, dams, bridges) which are supposed to just stand there forever can be made more massive and have to be extremely reliable.

Both of these cases can benefit from very good structural engineering and they just differ in the probability of failure that is acceptable and cost.

So student violins are appropriately heavy and can withstand some abuse and while solo violins are lighter and often need bandages. If an old violin doesn't have all kinds of repairs it probably doesn't sound very good or it hasn't been used much.

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55 minutes ago, Marty Kasprzyk said:

 

I recommend the following fairly recent books:

 Michael F. Ashby, “Materials Selection in Mechanical Design, 4th edition”, 2011, Elsevier

 This book shows why various materials are chosen for different applications and how the materials are compared.  I gives an easy to understand explanation of physical properties (strength, stiffness etc. we often discuss for violins) and how they are used.

 

Neville H. fletcher, Thomas D. Rossing, “The Physics of Musical Instruments, 2nd edition”, 1998, Springer

 The first part of the book gives a background of vibration mechanics and mathematics.  The remainder portions describe how different classes (wind, percussion, string etc) of instruments function.

 

 Thomas D. Rossing, editor, “The Science of String Instruments”, 2010, Springer

 Chapter 13 on violins was written by Joseph Curtin and T. Rossing and it gives a good overview on how violins function.

 

 Eric J. Heller, “Why You hear What You Hear, an experimental approach to sound, music, and psychoacoustics”, 2013 Princeton University Press

 This is a really great book for describing how sound is produced and heard without using hardly any mathematics.  It has a chapter on the violin but everything else seems interesting too.

 

 For articles I suggest:  (which is attached I hope)

 Colin E. Gough, “Violin Acoustics”, Acoustics Today, summer 2016 volume 12, issue 2,  Acoustical Society of America

 Besides giving an excellent description of how violins work it gives many references if you want to further your reading.

 

Gough.pdf

:)  thanks Marty

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25 minutes ago, Marty Kasprzyk said:

A lot of things (racing: sailboats, bicycles, cars) which are supposed to move quickly are built to be as light as possible and they're often at the hairy edge of falling apart.  A high failure risk is acceptable if it gives you a competitive advantage.

Other things (buildings, dams, bridges) which are supposed to just stand there forever can be made more massive and have to be extremely reliable.

Both of these cases can benefit from very good structural engineering and they just differ in the probability of failure that is acceptable and cost.

So student violins are appropriately heavy and can withstand some abuse and while solo violins are lighter and often need bandages. If an old violin doesn't have all kinds of repairs it probably doesn't sound very good or it hasn't been used much.

Without being too contentious there are few premises that I would challenge here.

First, the Gibson has clearly fallen over the edge of failure and that is why it required a patch and probably now may only be at the edge of failure and function better.

Secondly, I don't hold that if it's lighter it's better. My singular example would be the Canon Guarneri del Gesu. At 444g it is  grossly overbuilt yet it was considered by Paganini, arguably the greatest violinist of all time, as the greatest violin.

 

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2 hours ago, Marty Kasprzyk said:

 

I recommend the following fairly recent books:

 Michael F. Ashby, “Materials Selection in Mechanical Design, 4th edition”, 2011, Elsevier

 This book shows why various materials are chosen for different applications and how the materials are compared.  I gives an easy to understand explanation of physical properties (strength, stiffness etc. we often discuss for violins) and how they are used.

 

Neville H. fletcher, Thomas D. Rossing, “The Physics of Musical Instruments, 2nd edition”, 1998, Springer

 The first part of the book gives a background of vibration mechanics and mathematics.  The remainder portions describe how different classes (wind, percussion, string etc) of instruments function.

 

 Thomas D. Rossing, editor, “The Science of String Instruments”, 2010, Springer

 Chapter 13 on violins was written by Joseph Curtin and T. Rossing and it gives a good overview on how violins function.

 

 Eric J. Heller, “Why You hear What You Hear, an experimental approach to sound, music, and psychoacoustics”, 2013 Princeton University Press

 This is a really great book for describing how sound is produced and heard without using hardly any mathematics.  It has a chapter on the violin but everything else seems interesting too.

 

 For articles I suggest:  (which is attached I hope)

 Colin E. Gough, “Violin Acoustics”, Acoustics Today, summer 2016 volume 12, issue 2,  Acoustical Society of America

 Besides giving an excellent description of how violins work it gives many references if you want to further your reading.

 

Gough.pdf

These are all good sources, but from the perspective of someone who teaches this stuff, I'd say that Heller's book is by far the most suitable for someone with limited background knowledge.

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19 hours ago, curious1 said:

With an iPhone, metric rule, and pocket calculator you can measure the speed of sound in under 30 seconds. In the lumber yard you can divide the wood into low, medium , and high speed of sound quite quickly.

the same goes for density. If the wood is fairly uniformly cut you can get low, med, high very quickly.

 

Did this once and was very exciting until I started to measure density at home. I had a lot of tops 6200 -6500 m/s but because of the strong correlation with density It is important to get the density too. 2/3 of my pile had 0,50 - 0,56 d. won't make that mistake again. My friends had better luck without the Ipad

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On 9/11/2017 at 10:51 PM, curious1 said:

 

Antonio Stradivari Huberman/Gibson 1713

Top density .35g/cc calculated by Steven Sirr based on CT scans. (If speed of sound does roughly follow density, the density of spruce is between .3g/cc-.5g/cc and the speed of sound 4800-6000m/s. Based on density it should be ~5200-5400m/s ?. It's modulus based on my formula 5200m/s^2 x .35g/cc = 9,464,000-10,200,000).

This violin fits into my criteria for low stiffness, low density, and thin graduations. Not withstanding it's fame it's arching has clearly collapsed and is being held up in part by the bell patch in the central area (my guess would also be that their was some arch correction when the violin was restored in the mid 1980s.

 

Haven't many (most?) Strads needed to have their arching "corrected" at some point?  Or do you think that many of Strad's fiddles were originally made with a double-hump camelback arching on the top?

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2 hours ago, David Burgess said:

Haven't many (most?) Strads needed to have their arching "corrected" at some point?  Or do you think that many of Strad's fiddles were originally made with a double-hump camelback arching on the top?

Yes, many Stradivari have had arching correction as have many fine bows. We expect some movement in wood under stress and I would not categorize it necessarily as a failure. I would say a breast patch is indicative of a structural failure though. In the Huberman case I would say the thinness of graduation (whether that is original or not is hard to say) lead to arch deformation. 

 

PS I don't think Stradivari made double hump camel back top arches.

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