Is this arching wrong ?

[David Burgess]

25 minutes ago, reguz said:

 

 

 

There ya go! Your experiments clamped the violin at the soundpost position, which would render that point stationary, with everything else moving in relation to that. Unfortunately, that is not actually the way violins work or emit sound

"To a nail hammer, everything looks like a nail".

The extent to which you have allowed yourself to be consumed by self-seduction is beyond bizarre!

[Anders Buen]

Red laser, HeNe. Not a high tech table, but may still be on vibration insulators. Appears to be stone plate surface, but would be conveniant with a magnetic metal plate.

I am not impressed by the fixture, and kudos to David B for spotting the fixture point at the soundpost position. The imaging system may be outside of the picture. It is an electronic hologram patter, ESPI system, I guess. So there has to be a computer somewhere. If it is classic, then the pictures come off glass plates illuminated by a direct spread out beam and the reflection from the object. This might be the reason why the box appear to be blackened and possible to close.

It can also be a safety measure against the laser light.

Is this Molins system_

Edited December 14, 2023 by Anders Buen
Added a line on safety.

[Andreas Preuss]

2 hours ago, reguz said:

Working together with Staffan Borseman we got clear results so we learned what was possible to do

Would you mind to describe the ‘clear results’ a bit more? Did Mr. Borsemann say anything particular about the sound or the playability for the violin after the correction? 

[Dr. Mark]

5 hours ago, reguz said:

My reference is the sound post. This is not a frame. But you may explain what you see as a frame. I do not understand.

To be very brief - A Cartesian 3-dimensional coordinate frame consists of a point called the origin, three mutually perpendicular axes passing through the origin, and a scale.  It provides a consistent reference for measurements such as position, displacement, velocity, etc.  For motion measurements there's a fourth mutually perpendicular dimension -time -, that may be illustrated using video or multiple plots.

The terms 'frame of reference' and 'coordinate system' are often used synonymously in this context, as I do, although they are not strictly identical.  The general definition is beyond anything I want or need to go into here, so if you want to delve into it further a starting point is here: https://en.wikipedia.org/wiki/Frame_of_reference.  If you're familiar with vectors surely you're familiar with coordinate systems. 

A sound post is a 3-d object.  A portion may flex or otherwise expand or contract or move in some way with respect to other parts of itself.  Like other extended parts of the object being measured, for any measurements I can think of off-hand it's wholly unsuitable as a reference.

[uncle duke]

3 hours ago, David Burgess said:

There ya go! Your experiments clamped the violin at the soundpost position, which would render that point stationary, with everything else moving in relation to that. Unfortunately, that is not actually the way violins work or emit sound

"To a nail hammer, everything looks like a nail".

The extent to which you have allowed yourself to be consumed by self-seduction is beyond bizarre!

How long does it take to learn to put together equipment like what he uses for violin testing?

[Evan Smith]

8 hours ago, Dr. Mark said:

A sound post is a 3-d object.  A portion may flex or otherwise expand or contract or move in some way with respect to other parts of itself.  Like other extended parts of the object being measured, for any measurements I can think of off-hand it's wholly unsuitable as a reference.

Are you serious about this?

[Dr. Mark]

6 hours ago, Evan Smith said:

Are you serious about this?

Is your question serious?  Please say 'No'.

[Delabo]

14 hours ago, Dr. Mark said:

A sound post is a 3-d object.  A portion may flex or otherwise expand or contract or move in some way with respect to other parts of itself.  Like other extended parts of the object being measured, for any measurements I can think of off-hand it's wholly unsuitable as a reference.

If the sound post is not a stable reference point, then what part of a violin can be used as a datum, if any?

[Peter K-G]

7 minutes ago, Delabo said:

If the sound post is not a stable reference point, then what part of a violin can be used as a datum, if any?

Joseph Curtin Rig

 

[David Burgess]

4 minutes ago, Delabo said:

If the sound post is not a stable reference point, then what part of a violin can be used as a datum, if any?

I still prefer squishy support at the neck, and a little firmer support at the chinrest area, since this more accurately represents the way a violin is supported and moves when it is played.

My second choice would be support at the endblocks. These have enough mass attached (the neck and the chinrest) that there is much less motion and sound radiation involved, than in the more central portions of the violin.

There is also the option of suspending a violin on something like very compliant rubber bands. This would allow the violin to move more as if it was floating without attachments.

[Dr. Mark]

On 12/14/2023 at 8:54 AM, Delabo said:

If the sound post is not a stable reference point, then what part of a violin can be used as a datum, if any?

Well, before answering your question - assuming he's serious, Mr. Smith's questioning my assertion is fine - a lot of what I write is either unmitigated nonsense (which I try to correct when I notice it) or questionable (which I try not to present as an assertion).  It's just his question that's kind of pointless in that case, which is why I asked if his question was serious.

I see by Webster's that 'datum' can mean something used as a basis for calculating or measuring, so I take it this is what you mean.  I've only used the term in reference to a single measurement or bit of information so correct me if I misunderstand:

First, is the sound post a stable reference point?  I don't think anyone would deny that it's a cylindrical piece of wood with moduli of elasticity, so not rigid and fixed by friction to the belly and the back.  When we're talking about small displacements in a violin I think we want to stay away, as much as possible, from using an extended, deformable part of the instrument as a reference 'point', e.g. the origin of a coordinate frame, or just as bad, assume that it's rigid when the amplitudes of its motion may be on the order of the measurements we're trying to make.

I proposed a few different reference frames in different discussions when I thought appropriate - primarily those that might be used, or useful, for a theoretical discussion or finite element analysis.  Not necessarily practical - for example if we want to use the center of mass as an origin during an experiment it could be difficult to find and keep track of.  The easiest way I guess would be to balance the violin at a few points.  At each point draw a vertical (gravitationally, e.g. using a plumb bob) line through the point.  Where the lines intersect is the center of mass.  Not too easy to do with accuracy.  However for theoretical discussion of violin motion it may be just about ideal, and the question then is how to orient the axes.

I noticed in one of the diagrams posted here that the author appeared to use a line through the midpoint of the rib height at the center line as a reference axis.  That looked like a good choice for either an experiment or discussion so I thought I'd describe it - thinking out loud.  I won't repeat myself here.

I see above that people with more direct experience with actual experiments and playing conditions described some practical and relevant options.

[Delabo]

2 hours ago, Peter K-G said:

Joseph Curtin Rig

 

Interesting, thanks for that.

[Delabo]

2 hours ago, David Burgess said:

I still prefer squishy support at the neck, and a little firmer support at the chinrest area, since this more accurately represents the way a violin is supported and moves when it is played.

Seems logical.

[Delabo]

2 hours ago, Dr. Mark said:

I see by Webster's that 'datum' can mean something used as a basis for calculating or measuring, so I take it this is what you mean. 

Oops, I should have said "datum point", hope thats better?

[David Burgess]

11 minutes ago, Delabo said:

Seems logical.

While I am still occasionally afflicted by my logic demons, I am working hard to annihilate them, so I can better fit into, and interface with contemporary majority society.

[reguz]

18 hours ago, Dr. Mark said:

To be very brief - A Cartesian 3-dimensional coordinate frame consists of a point called the origin, three mutually perpendicular axes passing through the origin, and a scale.  It provides a consistent reference for measurements such as position, displacement, velocity, etc.  For motion measurements there's a fourth mutually perpendicular dimension -time -, that may be illustrated using video or multiple plots.

The terms 'frame of reference' and 'coordinate system' are often used synonymously in this context, as I do, although they are not strictly identical.  The general definition is beyond anything I want or need to go into here, so if you want to delve into it further a starting point is here: https://en.wikipedia.org/wiki/Frame_of_reference.  If you're familiar with vectors surely you're familiar with coordinate systems. 

A sound post is a 3-d object.  A portion may flex or otherwise expand or contract or move in some way with respect to other parts of itself.  Like other extended parts of the object being measured, for any measurements I can think of off-hand it's wholly unsuitable as a reference.

To answer your description briefly. I ask the question; have you applied what you describe and can you explain your results understandable for us violin makers who don't have math skills

[reguz]

17 hours ago, uncle duke said:

How long does it take to learn to put together equipment like what he uses for violin testing?

 

18 hours ago, Dr. Mark said:

To be very brief - A Cartesian 3-dimensional coordinate frame consists of a point called the origin, three mutually perpendicular axes passing through the origin, and a scale.  It provides a consistent reference for measurements such as position, displacement, velocity, etc.  For motion measurements there's a fourth mutually perpendicular dimension -time -, that may be illustrated using video or multiple plots.

The terms 'frame of reference' and 'coordinate system' are often used synonymously in this context, as I do, although they are not strictly identical.  The general definition is beyond anything I want or need to go into here, so if you want to delve into it further a starting point is here: https://en.wikipedia.org/wiki/Frame_of_reference.  If you're familiar with vectors surely you're familiar with coordinate systems. 

A sound post is a 3-d object.  A portion may flex or otherwise expand or contract or move in some way with respect to other parts of itself.  Like other extended parts of the object being measured, for any measurements I can think of off-hand it's wholly unsuitable as a reference.

Please Mark can you show briefly how you applay the math 3-D so we simple violin makers can understand.

[Spelman]

13 minutes ago, reguz said:

us violin makers

What do you mean by "us" kemosabe?

[reguz]

19 hours ago, Anders Buen said:

Red laser, HeNe. Not a high tech table, but may still be on vibration insulators. Appears to be stone plate surface, but would be conveniant with a magnetic metal plate.

I am not impressed by the fixture, and kudos to David B for spotting the fixture point at the soundpost position. The imaging system may be outside of the picture. It is an electronic hologram patter, ESPI system, I guess. So there has to be a computer somewhere. If it is classic, then the pictures come off glass plates illuminated by a direct spread out beam and the reflection from the object. This might be the reason why the box appear to be blackened and possible to close.

It can also be a safety measure against the laser light.

Is this Molins system_

Anders, The equipement is in a closed room made of concrete wall roof and floor on a marble table. The temperature is constant the humidity is constant. A camera make pictures that become handled in a computer.. Yes the red light is the only light. All this is done by experiented people at the LTH university. I do not know what the system is called. We did this 2007

[David Burgess]

19 minutes ago, reguz said:

can you explain your results understandable for us violin makers

 

11 minutes ago, reguz said:

Please Mark can you show briefly how you applay the math 3-D so we simple violin makers can understand.

What's this crap about "us violin makers", and "we violin makers", posted by someone who has never made a violin?

[reguz]

This is typicall a David answer. Hec read no papers just answer and come with bad replay. Read the dissartation papers and yoy will see who made the plates they used. They are on picture.

 

[David Burgess]

1 minute ago, reguz said:

This is typicall a David answer. Hec read no papers just answer and come with bad replay. Read the dissartation papers and yoy will see who made the plates they used. They are on picture.

 

Wrong again! I did read the papers, and understand that you furnished the plates. But have you ever made a violin?

[reguz]

46 minutes ago, David Burgess said:

Wrong again! I did read the papers, and understand that you furnished the plates. But have you ever made a violin?

YES

[David Burgess]

5 minutes ago, reguz said:

YES

Interesting! When asked previously, your response was that others have made violins incorporating your design ideas. So which is it? Have you ever, yourself, made a complete violin?

[Dr. Mark]

1 hour ago, reguz said:

have you applied what you describe

A bit.

1 hour ago, reguz said:

can you explain your results understandable for us violin makers

That depends on what results we're talking about.  If you mean some specific applications, then no, I can't talk about them at all.  I guess I can say that writing and applying algorithms for coordinate systems and transformations among them is an integral part of what I'm (still) paid to do.

1 hour ago, reguz said:

Please Mark can you show briefly how you applay the math 3-D so we simple violin makers can understand.

Sometimes it's just a matter of a lack of common language between two people involved in a discussion - there's a story about this in Genesis, but never mind.  Since some replies above indicate that a number of people are very familiar with the concepts then perhaps my very limited knowledge of foreign languages, requiring you to discuss the topic in English, is a roadblock to communication.  Since you clearly have a computer and internet access you may want to do a search on 'coordinate frames', 'reference frames' or similar terms in your native tongue to find a clearer explanation.  Once we're on the same page it may be easier to continue...