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Tap tone test , top plate


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1 hour ago, violins88 said:

David:

You are not using the term Q in the standard physics meaning. Sorry, you are just not. I could attach my own definition to oil, and I could say “oil and water are miscible.” In my head I would be consistent. But if I actually want to communicate with others, it won’t work. Again, sorry.

I agree that a long marimba bar rings for a longer time than a short one. But that is not Q. For measuring Q, you would compare the ringing time of a dry spruce one vs a wet spruce one.

The first part of this link is actually decipherable: 

https://www.giangrandi.ch/electronics/ringdownq/ringdownq.shtml

You link is good, even if focused on a limited example.

It contradicts none of the things I've asserted.

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5 hours ago, Don Noon said:

I wish I could explain everything, but I can't.  Yet.  Getting back to the fundamental issue:  there is no coherent hypothesis that I'm aware of that can explain the difference in spectral response observed over 30 years ago by Dunnwald in assembled violins (see below).  I am not going to believe in magic, but something odd appears to be going on to attenuate the range around 1kHz and above 4 kHz, yet remain strong between those ranges.  Whatever it is, I think it's complicated... and involves how wood properties change with age.  How this manifests itself in plate taptones is likely related and might help understand the effects, but a step removed from the real interest.

546390937_Dunnwaldplot.jpg.899e3c3f8dc17f0d2accbdbab9172490.jpg 

The problem with the first graph is that all those old Italian instruments have been substantially modified. From Vuillaume's time onward they were given a longer neck and much steeper neck angle.

This radically alters the sound, does it not?

 

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43 minutes ago, sospiri said:

The problem with the first graph is that all those old Italian instruments have been substantially modified. From Vuillaume's time onward they were given a longer neck and much steeper neck angle.

This radically alters the sound, does it not?

If the sound is modified by those modernizations, then they should be directly comparable to modern, since the necks and setups would be the same.

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3 hours ago, David Beard said:

Absolutely.  For physics, elastic means the material retruns energy.

When you strike maple or spruce, they store your energy input as flex, then return that energy with good efficiency.  That is elasticity.

If you strike the wood with something too hard, or in the wrong way, the wood dents.  That is 'plastic' deformation and wastes the energy.  Not what we want.

Rubber is different.  If you stretch rubber, it behaves elasticsally and returns the energy by pulling to stretch back.  But if you strike rubber to make sound, the material is quite dampening and wastes much of the energy.  That is not eleastic behavior.

So, for receiving and holding sound vibrations, maple and spruce wood are very elastic.  Rubber is much less so.

 

Rubber sheets are perfectly elastic and have very little damping but they are poor sound producers because they are not stiff enough.  Bending waves in the sheet can move a lot of air but are too short relative to sound waves so the sound produces is only very near the surface.  At longer listening distances the sound waves cancel each other and all you produce is warm air rather than sound.

Sometimes the use of "elasticity" and "elastic" words is confusing.  A highly elastic material stretches a lot with a given amount of force( like a rubber band).  A material with a high elastic modulus is stiff and stretches very little with a given amount of force (like a braided steel tail chord).  Elastic modulus is usually abbreviated  as E. 

Thus a highly elastic material has a low elastic modulus and can stretch a real lot like my underwear's elastic waist band.

 

 

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11 minutes ago, Marty Kasprzyk said:

Rubber sheets are perfectly elastic and have very little damping but they are poor sound producers because they are not stiff enough.  Bending waves in the sheet can move a lot of air but are too short relative to sound waves so the sound produces is only very near the surface.  At longer listening distances the sound waves cancel each other and all you produce is warm air rather than sound.

Sometimes the use of "elasticity" and "elastic" words is confusing.  A highly elastic material stretches a lot with a given amount of force( like a rubber band).  A material with a high elastic modulus is stiff and stretches very little with a given amount of force (like a braided steel tail chord).  Elastic modulus is usually abbreviated  as E. 

Thus a highly elastic material has a low elastic modulus and can stretch a real lot like my underwear's elastic waist band.

 

 

Thank you for this welcome injection of sanity. I was just about to install a set of violin ribs in my tighty whities.

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15 minutes ago, Marty Kasprzyk said:

Rubber sheets are perfectly elastic and have very little damping but they are poor sound producers because they are not stiff enough.  Bending waves in the sheet can move a lot of air but are too short relative to sound waves so the sound produces is only very near the surface.  At longer listening distances the sound waves cancel each other and all you produce is warm air rather than sound.

Sometimes the use of "elasticity" and "elastic" words is confusing.  A highly elastic material stretches a lot with a given amount of force( like a rubber band).  A material with a high elastic modulus is stiff and stretches very little with a given amount of force (like a braided steel tail chord).  Elastic modulus is usually abbreviated  as E. 

Thus a highly elastic material has a low elastic modulus and can stretch a real lot like my underwear's elastic waist band.

 

 

Thanks for the clarification!

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5 hours ago, Marty Kasprzyk said:

 ( ... )

As Anders Buen has pointed out before the damping from holding the violin by the player is much greater than these other sources of damping anyway.  I had a good violin player demonstrate how just changing his chin pressure affected the violin's sound. 

Maybe the damping of shoulder rest foam material might be more important than the internal damping of the violin's wood.  The newest running shoes have more bounce than earlier ones and running records are getting quicker.

Maestro Kasprzk, would you consider designing a should rest?

Maestro Buen is the K-pop band ( BTS ) of acoustics here; he is a superstar.

How should we design the shoulder rest? With some students, especially those with longer necks, we work through what I do, with no neck and and no shoulder rest. I occasionally work as a running back.

Is there a happy medium for those who play with shoulder rests? I am only half joking as I have made wooden shoulder rests with minimal padding. Not to encourage others ( our little secret... ) as there is quite a bit of money in higher- end shoulder rests. As instruments reach unobtanium limits, should not shoulder rests? I am just angry that I will spend a $1/2K usd on a shoulder rest for a student. I am happy with my Peter Mach ( better for shorter necks, not so stuck as Bon Musica players ) for weird stuff, thought the legs are not as secure as the Kun for some, which fade with age. 

How much a would a professional basketball player pay to increase their free throw percentage?  Though there is the much bigger picture of how we should play, there are some kids out there who would love a shoulder rest that allowed them to sound "open/ free" and still hit the epic 7+ position shifts of their pieces.

Maestro Obi Kasprzk, "you are, our only hope."  NOT kidding.

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On 5/17/2022 at 9:09 AM, Don Noon said:

There are several different measurements that define the properties of wood, and different makers will focus on different properties to decide for themselves what they think is important.

If the wood pieces are exactly the same dimensions, then the second piece would have a higher speed of sound divided by density... sometimes referred to as "radiation ratio" (RR) or "quality factor"... although "quality factor" can also mean RR divided by damping.  A higher RR is not always better, although abnormally low RR I think would tend to be relatively quiet.

>

If the two pieces are exactly the same dimensions then the second one with its higher tap pitch simply has a higher speed of sound c.  The radiation ratio RR is the speed of sound c divided by the density p:    RR= c/p.   So we have to also measure the density p of the two samples before we can determine which one has a higher radiation ratio. 

But I don't believe a high radiation ration is a good violin wood quality measurement anyway.

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3 hours ago, Marty Kasprzyk said:

Rubber sheets are perfectly elastic and have very little damping but they are poor sound producers because they are not stiff enough.  Bending waves in the sheet can move a lot of air but are too short relative to sound waves so the sound produces is only very near the surface.  At longer listening distances the sound waves cancel each other and all you produce is warm air rather than sound.

Sometimes the use of "elasticity" and "elastic" words is confusing.  A highly elastic material stretches a lot with a given amount of force( like a rubber band).  A material with a high elastic modulus is stiff and stretches very little with a given amount of force (like a braided steel tail chord).  Elastic modulus is usually abbreviated  as E. 

Thus a highly elastic material has a low elastic modulus and can stretch a real lot like my underwear's elastic waist band.

 

 

"Rubber sheets are perfectly elastic" Well according to my Uncle Chuck that's just not the case, they just ain't that perfect, account my cousins and all :rolleyes:

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3 hours ago, GoPractice said:

Maestro Kasprzk, would you consider designing a should rest?

Maestro Buen is the K-pop band ( BTS ) of acoustics here; he is a superstar.

How should we design the shoulder rest? With some students, especially those with longer necks, we work through what I do, with no neck and and no shoulder rest. I occasionally work as a running back.

Is there a happy medium for those who play with shoulder rests? I am only half joking as I have made wooden shoulder rests with minimal padding. Not to encourage others ( our little secret... ) as there is quite a bit of money in higher- end shoulder rests. As instruments reach unobtanium limits, should not shoulder rests? I am just angry that I will spend a $1/2K usd on a shoulder rest for a student. I am happy with my Peter Mach ( better for shorter necks, not so stuck as Bon Musica players ) for weird stuff, thought the legs are not as secure as the Kun for some, which fade with age. 

How much a would a professional basketball player pay to increase their free throw percentage?  Though there is the much bigger picture of how we should play, there are some kids out there who would love a shoulder rest that allowed them to sound "open/ free" and still hit the epic 7+ position shifts of their pieces.

Maestro Obi Kasprzk, "you are, our only hope."  NOT kidding.

Ole Bull Already did that....in 1879, I made my own version, it was ok

https://patents.google.com/patent/US217330?oq=Ole+Bull+chin+rest

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33 minutes ago, Marty Kasprzyk said:

If the two pieces are exactly the same dimensions then the second one with its higher tap pitch simply has a higher speed of sound c.  The radiation ratio RR is the speed of sound c divided by the density p:    RR= c/p.   So we have to also measure the density p of the two samples before we can determine which one has a higher radiation ratio. 

But I don't believe a high radiation ration is a good violin wood quality measurement anyway.

It seems to be better for plucked instruments but not good to have too much for bowed

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3 hours ago, GoPractice said:

Maestro Kasprzk, would you consider designing a should rest?

Maestro Buen is the K-pop band ( BTS ) of acoustics here; he is a superstar.

How should we design the shoulder rest? With some students, especially those with longer necks, we work through what I do, with no neck and and no shoulder rest. I occasionally work as a running back.

Is there a happy medium for those who play with shoulder rests? I am only half joking as I have made wooden shoulder rests with minimal padding. Not to encourage others ( our little secret... ) as there is quite a bit of money in higher- end shoulder rests. As instruments reach unobtanium limits, should not shoulder rests? I am just angry that I will spend a $1/2K usd on a shoulder rest for a student. I am happy with my Peter Mach ( better for shorter necks, not so stuck as Bon Musica players ) for weird stuff, thought the legs are not as secure as the Kun for some, which fade with age. 

How much a would a professional basketball player pay to increase their free throw percentage?  Though there is the much bigger picture of how we should play, there are some kids out there who would love a shoulder rest that allowed them to sound "open/ free" and still hit the epic 7+ position shifts of their pieces.

Maestro Obi Kasprzk, "you are, our only hope."  NOT kidding.

We have drifted away from the original question about wood quality.

I very much appreciate your heartfelt plea but I'm not interested in designing rinky-dink, ticky-tack (produces a short ring time?) shoulder rests which add weight and damping to the instrument and creates a fear of falling off only at the most appropriate times when lots of people are there to hear you play. This fear creates some tension which inhibits your expression of music.

I used to think a low height shoulder rest in combination with a high chin rest was the very best combination for basketball type players with their longer necks.  This lowers the height of the instrument on the shoulder so the right arm doesn't has to be raised very high for bowing which in turn reduces stresses on the right shoulder which in turn reduces repetitive stress injuries.

Football players with their short necks and thick shoulders don't need shoulder rests at all but these guys usually weren't violin players unless they wanted to be with the girls in the orchestra. 

But the basic problem is that the old traditional violin and violas have poor ergonomic designs which require shoulder rests. This happens because they have constant height ribs mating with the flat edges of arched plates so everything is easy to shape and can be glued together easily.

A much lighter total design uses a back plate having the shape that matches the shape of the player's shoulder and chest area having a widely variable rib height to completely eliminate the need for a separate shoulder rest ( I'm having some difficulties in finding friendly females to scan). This is difficult to build but I think it is better.

l'll show some photos in a day or two.

 

 

 

 

 

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15 hours ago, Marty Kasprzyk said:

If the two pieces are exactly the same dimensions then the second one with its higher tap pitch simply has a higher speed of sound c.  The radiation ratio RR is the speed of sound c divided by the density p:    RR= c/p.   So we have to also measure the density p of the two samples before we can determine which one has a higher radiation ratio. 

But I don't believe a high radiation ration is a good violin wood quality measurement anyway.

What about just c, the speed of sound?

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2 hours ago, Michael_Molnar said:

What about just c, the speed of sound?

That's what I think too--just c is a better quality index.  The RR derivation speed of sound c divided by density p, RR=c/p  was done for a flat plate and it is not valid for plates assembled into a box.

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1 hour ago, Marty Kasprzyk said:

...just c is a better quality index.  The RR derivation speed of sound c divided by density p, RR=c/p  was done for a flat plate and it is not valid for plates assembled into a box.

If the "box" has a flat plate, then RR applies as an indicator of how light you can make the plate for a desired frequency.

If the plates are curved, then C determines the "ring mode" frequency, where RR begins to apply above that frequency (where the plate breaks up into smaller antinodes, and bending begins to determine the physics).  Violin plates are curved in different directions and flatter in others, so it's a complicated mess.

C and RR both indicate something about what the wood will do in a violin plate... just different things.  The problem with high RR is that (due to math) it indicates low density... which is not always a good thing, for durability reasons.  There is also the issue that extremely high RR means you will have to work in an abnormal range of very light plates or very high bending frequencies, and abnormal is usually a bad thing.

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Elastic Energy

Elasticity

Plasticity

Stiffness

 

 

On 5/30/2022 at 2:57 PM, Marty Kasprzyk said:

Rubber sheets are perfectly elastic and have very little damping but they are poor sound producers because they are not stiff enough.  Bending waves in the sheet can move a lot of air but are too short relative to sound waves so the sound produces is only very near the surface.  At longer listening distances the sound waves cancel each other and all you produce is warm air rather than sound.

Sometimes the use of "elasticity" and "elastic" words is confusing.  A highly elastic material stretches a lot with a given amount of force( like a rubber band).  A material with a high elastic modulus is stiff and stretches very little with a given amount of force (like a braided steel tail chord).  Elastic modulus is usually abbreviated  as E. 

Thus a highly elastic material has a low elastic modulus and can stretch a real lot like my underwear's elastic waist band.

 

 

Ah!   I was ready to accept all this on face.   But you made me read more.

It's a little bit complicated, but very relevant to understanding violin materials.

Elasticity and elastic moduli are a little bit different things.  And, stiffiness is a different thing again.

Elasticity is the general property of restoring shape after a deformation.  And, this is central to sound or most any vibrating system, because elastic deformation stores energy.

Most of the vibrations we work with in violins involve the cycling of energy between storage in the kinetic energy of a moving mass and storage as elastic energy in a deformed or flexed mass.

Elasticity does not for physics mean pliant or stetchy, nor does it mean stiff.  It means the material restores it shape, and returns its elastic energy after deformation.   

The opposite of elastic is not stiff, but plastic.  This physics word means a material absorbs and does return a deforming energy, it stays deformed.  Good examples are tar and peanut butter.  These are the opposites of elastic materials.

To make matters more complicated, materials can have different elastic quailities for different kinds of deformation.  

Some materials are elastic under stretch or compression.  Examples are air, rubber, spruce, maple, and even steel. The speed of sound in materials is based on this kind of elasticity.

Notice that this elasticity is quite different than simple stiffness.  Air is very elastic because it very efficiently stores and returns the elastic energy from its deformation.  Steel is similar in elasticity, but vastly stiffer.

Other materials can also be elastic in various forms of axial deformation.  This includes spruce, maple, and steel, but not air, and not generally rubber.

This sort of axial deformation is very important for violin wood.  All the standing waves formed by the plates and body of a violin are cycling their energy between the moving mass of the wood, and flexing elastic deformation of the wood.

Elastic moduli are methods of quantifying the different kinds of elastic deformations of a material.   Elasticity itself is about a material's ability to restore shape and return deforming energy.  'Ideal Elasticity' means perfect return of shape and complete return of eneegy.  But most materials will break or plastically deform at some point.

In contrast, the elastic moduli essentially measure the stiffness encountered for the different deformations of an elastic material.  They do this mostly as a ratio of force to strain.  Higher moduli, stiffer elastic material.

Simple stiffness is another matter again.  Stiffness is the general resistance to deformation, not just to elastic deformation.  So, cold peanut butter can be stiffer than warm peanut butter.

Also, elasticity and the stiffness or moduli of elasticity are properties of the material itself.  But stiffness is a property of a specific piece of material. So thickness and shape come into play.

Similarly, resonances and therefore Q are not properties of materials but of specific pieces of material.  Shape and thickness come into play.

So, for example, the archings of a plate create areas of 'cupped' shapes.  Cupped shapes have no impact on material properties like elastic moduli, but they do increase stiffness locally through geometry, and such things do impact resonances.

 

Etc.

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2 hours ago, David Beard said:

Other materials can also be elastic in various forms of axial deformation.  This includes spruce, maple, and steel, but not air, and not generally rubber.

I still think rubber bands are elastic.

But back the original question about picking wood to use for violins the only material properties we need to measure are the speed of sound,  density and damping.  I don't know what is best and there are differing opinions but probably everybody will agree peanut butter but isn't good.

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1 hour ago, Marty Kasprzyk said:

I still think rubber bands are elastic.

But back the original question about picking wood to use for violins the only material properties we need to measure are the speed of sound,  density and damping.  I don't know what is best and there are differing opinions but probably everybody will agree peanut butter but isn't good.

Yes. Rubber bands are elastic for stretching.  And, if you ball them up, for compression.   Much more challenging to get elastic deflection from them.  They simply don't return that shape or energy.

Elasticity is the main reason spruce and maple are chosen.

Other than that, relatively low material dampening is good.

Maybe Don's bit about high radiation, I'm not sure.

Definitely Diaboli's thing about wood that is 'lively'.  Or 'talkative' when you tickle it.

Attractive wood with basically normal properties is good while we're at it.

After these basics for materials, I suspect shape is the real issue.

Mainly, avoid going out of your way to make specific high Q resonances (that means tap tones that are too clear or pitch defined).  Also, avoid putting resonances in simple interval relationships.  Keep them 'off' from one another.

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To answer the previous questions from @Don Noon, the recordings were made with the built in mic in an iPhone placed about 10-12 inches away from the center of the plate.  I was holding loosely near the edges of the plate on the corresponding nodal lines and tapping the center with a fingertip.  Here are some recordings of a couple of tops I made.  Both have bass bars.  
 

I don’t for a minute think that dead plates are good, but I’ve noticed that free plates on some of the better sounding classic instruments I’ve been able to see in pieces have a lot more think than ring.  They also feel incredibly lively when tapped, unlike the dead duds on some subpar old instruments. 

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14 hours ago, Don Noon said:

If the "box" has a flat plate, then RR applies as an indicator of how light you can make the plate for a desired frequency.

If the plates are curved, then C determines the "ring mode" frequency, where RR begins to apply above that frequency (where the plate breaks up into smaller antinodes, and bending begins to determine the physics).  Violin plates are curved in different directions and flatter in others, so it's a complicated mess.

C and RR both indicate something about what the wood will do in a violin plate... just different things.  The problem with high RR is that (due to math) it indicates low density... which is not always a good thing, for durability reasons.  There is also the issue that extremely high RR means you will have to work in an abnormal range of very light plates or very high bending frequencies, and abnormal is usually a bad thing.

And for those reasons I evaluate c and ρ separately.

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4 hours ago, Advocatus Diaboli said:

To answer the previous questions from @Don Noon, the recordings were made with the built in mic in an iPhone placed about 10-12 inches away from the center of the plate.  I was holding loosely near the edges of the plate on the corresponding nodal lines and tapping the center with a fingertip.  Here are some recordings of a couple of tops I made.  Both have bass bars.  
 

I don’t for a minute think that dead plates are good, but I’ve noticed that free plates on some of the better sounding classic instruments I’ve been able to see in pieces have a lot more think than ring.  They also feel incredibly lively when tapped, unlike the dead duds on some subpar old instruments. 

Good points, but can we quantify “liveliness”?

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5 hours ago, Advocatus Diaboli said:

the recordings were made with the built in mic in an iPhone placed about 10-12 inches away from the center of the plate.  I was holding loosely near the edges of the plate on the corresponding nodal lines and tapping the center with a fingertip.

Well, that's not the ideal way to get the mode frequencies to show up clearly, especially M2 where there are + and - antinodes close together near the middle of the plate which cancel each other out.  My plots (posted earlier) were recorded with a computer mic placed very close to the area of maximum mode amplitude, held at an exact nodal line, and excited with a 5g vinyl-tipped "hammer".  The best way I can think of to get a measurement that really doesn't matter.

Anyway, the new plates apparently have more "ring" to them, compared to the old ones, and the modal frequency peaks are more distinct.

1 hour ago, Michael_Molnar said:

but can we quantify “liveliness”?

I would expect so, with enough effort.  Basically it would be a measure of acoustic energy out divided by the vibration energy going in... as a function of frequency.  However, if there is a "gong" effect, where energy gets transferred to other modes, that might be more complicated.  https://www.youtube.com/watch?v=mL2r6E1E7sM

I have noticed that my most "lively" wedges of wood tend to be high RR and low damping, as physics would suggest... with long "ring" at the lowest frequencies too.  The tricky part is how something can have deadness at the lower frequencies, but lively elsewhere... as anecdotal evidence seems to suggest.

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