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8 hours ago, David Beard said:

I am not talking about the resulting pitches, but about how the mass in question is roughly divided in parts by the standing waves.  These set up in some integer number of parts of the mass.  The divisions of the mass into standing waves will roughly correspond to 1/2 cycles of the mode frequency, except at open boundaries where it will be 1/4.

Where the q of the mode is high enough for there to be a corresponding natural resonance, then the standing wave pattern will correspond to a mutation of that mode's natural resonance wave pattern, but pushed to the driving frequency.   And, this corresponding mode will be a 'harmonic' of the resonance, either the fundamental or a partial.

We're wasting energy tangling over the language.

The interesting point is that resonances can support driving signals more broadly if the Q is not maximized.  (Q here is Q, and not just a stand in for dampening.)

 

Anyway, interesting to me.  If not interesting to others, fine.  No needed to talk about here in that case.

Actually I disagree strongly that it's a waste of time to refine definitions of technical words. Clarity and precision in language is necessary for clarity and precision of explanation.

While Its obvious that in a craft tradition it is a hands-on knowledge so words are superfluous, that's not the case when we are typing messages to each other!

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11 hours ago, bungling_amateur said:

Actually I disagree strongly that it's a waste of time to refine definitions of technical words. Clarity and precision in language is necessary for clarity and precision of explanation.

While Its obvious that in a craft tradition it is a hands-on knowledge so words are superfluous, that's not the case when we are typing messages to each other!

Alternate definition are part of pursuing new or variant ideas.  And, in such efforts, it's common enough to use variant definitions of language where the new or variant idea parallels the orthodoxy.

In math for example, 1+1 generally equalls 2.  But it turns out to be powerful, interesting, and even useful to explore variant math systems where addition is given a variant definition.

In some of those systems, 1+1 is defined to equal 0.  And, they still call the + opperation 'addition', even though it's been given a alternate definition.

This particular example of a consistent mathematical system turned out to be historically important also. It demonstrated why the long and convoluted efforts of logisticians in the mid 1900s to conclusively prove that 1+1=2 ultimately failed.  It failed because the proposition is false.  There are consistent and meaningful where it isn't true.

Careful use of language is valuable, but that encompasses stretching language conveniently to aid exploring parallel variants of more familiar common ideas.

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34 minutes ago, David Burgess said:

Aren't you reaching a bit? To me, a garbage man is still a garbage man, deserving no more or less respect than if he or she has been re-labeled as a "waste engineer".

I'm trying to open a discussion on a behavior of driven standing waves that is  closely related to natural resonances.

 

You're blocking any such discussion with general ad hominem and pointless entaglement over language.

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21 hours ago, Don Noon said:

I think David is saying "nope" to the apparent idea that strings, air columns, and structures vibrate similarly.  Structures in general do not have modes that are related in harmonic ways.  Definitely nope to that from me, too.

Even a super-simple rectangular beam does NOT have harmonically tuned modes

There are at least on exception to that: Tuned bells. 

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21 hours ago, David Beard said:

I am not talking about the resulting pitches, but about how the mass in question is roughly divided in parts by the standing waves.  These set up in some integer number of parts of the mass.  The divisions of the mass into standing waves will roughly correspond to 1/2 cycles of the mode frequency, except at open boundaries where it will be 1/4.

Where the q of the mode is high enough for there to be a corresponding natural resonance, then the standing wave pattern will correspond to a mutation of that mode's natural resonance wave pattern, but pushed to the driving frequency.   And, this corresponding mode will be a 'harmonic' of the resonance, either the fundamental or a partial.

We're wasting energy tangling over the language.

The interesting point is that resonances can support driving signals more broadly if the Q is not maximized.  (Q here is Q, and not just a stand in for dampening.)

 

Anyway, interesting to me.  If not interesting to others, fine.  No needed to talk about here in that case.

Your comments above is true for a membrane with no bending stiffness. In plates with bending stiffness the resonances does not follow a harmonic series like it does for membranes and strings. The waves in plates are said to be dispersive. That is: the bending wave speed is frequency dependant. In a curved plate also in plane stiffness comes into work. E.g mode 5 is about 50% in plane stiffness an the rest is bending. Less so e.g for mode 2.

For flat plates and strips, tap tones, dimensions and weight can be used for extracting material parameters. E.g. Youngs moduli, damping factors and density. All important parameters for acoustic performance.

Working like that with violin plates sort of does the same thing, although the material parameters are harder to extract that way. A well worked top plate tends to have some degree of harmonic relations between some tap tones. Maybe best for the feel than anything else. A violin plate is kind of a very open bell.

Such relations disappears in the assembled instrument. But it is likely to give more control than nothing.

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Also, if the imperfect elasticity of a medium causes the modes that divide the mass into parts to sound pitches that are not in tune ideal harmonics, still the naming of these isa question of semantics rather physics.

You could say they are 'not harmonics', or you could say they are 'distorted harmonics'.    The situation is not changed either way.  But, to me, 'distorted harmonics' reflects more of the physical facts of the situation.  And 'not harmonics' seems to push away from something actually true in the situation.  'Not ideal harmonics' would be more accurately communicative to me.

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17 minutes ago, Anders Buen said:

Your comments above is true for a membrane with no bending stiffness. In plates with bending stiffness the resonances does not follow a harmonic series like it does for membranes and strings. The waves in plates are said to be dispersive. That is: the bending wave speed is frequency dependant. In a curved plate also in plane stiffness comes into work. E.g mode 5 is about 50% in plane stiffness an the rest is bending. Less so e.g for mode 2.

For flat plates and strips, tap tones, dimensions and weight can be used for extracting material parameters. E.g. Youngs moduli, damping factors and density. All important parameters for acoustic performance.

Working like that with violin plates sort of does the same thing, although the material parameters are harder to extract that way. A well worked top plate tends to have some degree of harmonic relations between some tap tones. Maybe best for the feel than anything else. A violin plate is kind of a very open bell.

Such relations disappears in the assembled instrument. But it is likely to give more control than nothing.

Even with complications of stiffness, boundaries, and geometeic shape, I believe the standwave patterns that set up from a drive can be viewed as mutations from the simpler scenarios.

Also, a violin doesn't just set up standing waves on the plate as a diaphragm.  It will set up waves in all the most readily avaialble ways.  And that will include comparatively simple compression modes of the air mass inside the body, and 'swinging' modes of some masses of the body.

To me, it's more interesting to think closely about these dynamics of the final state of the instrument than to worry much about the easier to measure free plate modes.

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On 1/21/2021 at 12:04 PM, David Beard said:

With the back, wouldn't it make more sense to leave the center mass heavy, then attach to the sides, then tune the main resonance of the center mass?

 

On 1/22/2021 at 1:02 PM, David Beard said:

I'm not a tap tune person, so I haven't explored that yet.  But I am curious about that now.

My first guess is that when assembled the central back mass helps provide a resonance supporting the A string.  But, I'm just guessing.

Normally, I'm much more interested in thinking about the many diverse ways the instrument will move and twist when driven across the full range of frequencies.

But I am growing curious to understand which physical modes most directly support each open string.

I've not experimented yet, only considering the question.  First thoughts are that like candidates are 1) G: the pumping of the bass bar side of the top by the G foot of the bridge, 2) D: the mass of air inside the violin body as a whole, 3) A: the extra wood mass of the back center pumped by the post, 4) E: the upper treble wing of the bridge island torqued between the post and the E foot of the bridge.

These are just first guesses. I'd be shocked if they all turn out ti be correct. But I'm curious now.

However, I continue to believe that the breadth of a resonance resoonse in a violin is more  valuable than the the precise center pitch of the resonance.

That means I want to focus on lowering the Q of resonances as opposed to tuning them precisely.  And, in fact, clean pitch definition is a cofactor with higher Q, so I consider precise clean definition of resonance pitch to be harmful.

 

On 1/22/2021 at 2:30 PM, David Beard said:

In total, no.  Just as you say, each part participates in many modes.

However, each individual mode is that simple.  Each is a particular limited mass flexing in a single particular way as its fundamental, and then the mode also has harmonics.

And, when any standing wave sets up in response to a drive, it can be viewed as a natural mode pushed off its pitch center to follow the drive.

 

On 1/22/2021 at 7:45 PM, David Beard said:

When thinking about driven resonance I think we can generalize the notion by thinking about the physical division of the mass for the particular mode.  So, when a standing wave sets up in air mass and divides the mass the same way the 2nd partial of the natural resonance would, I think we can still talk about this as a harmonic, even if the drive has pushed the pitch to different value.

 

On 1/23/2021 at 9:19 AM, David Beard said:

The wording game doesn't matter to me.  

The point is that if a whole mass has a mode were it compresses or flex as a whole, it will also have related modes where it moves in halves, thirds, fourths, fifths, sixths, etc.

I'm happy calling that related family of modes 'harmonics', or 'zoomics', or whatever.   It's the underlying idea that matters.

 

On 1/23/2021 at 10:38 AM, David Beard said:

What part is nope?   Are you saying an air body that can be driven into a standing wave a one pitch can't normally also be driven into two standing waves at thw octave, and three at the ovtave and fifth?   Are you saying 'nope to that physical fact?

Or are you saying 'nope' that I don't care what you name the relationship between such modes of standing waves?

What are you saying 'nope' to?

 

22 hours ago, David Beard said:

I am not talking about the resulting pitches, but about how the mass in question is roughly divided in parts by the standing waves.  These set up in some integer number of parts of the mass.  The divisions of the mass into standing waves will roughly correspond to 1/2 cycles of the mode frequency, except at open boundaries where it will be 1/4.

Where the q of the mode is high enough for there to be a corresponding natural resonance, then the standing wave pattern will correspond to a mutation of that mode's natural resonance wave pattern, but pushed to the driving frequency.   And, this corresponding mode will be a 'harmonic' of the resonance, either the fundamental or a partial.

We're wasting energy tangling over the language.

The interesting point is that resonances can support driving signals more broadly if the Q is not maximized.  (Q here is Q, and not just a stand in for dampening.)

 

Anyway, interesting to me.  If not interesting to others, fine.  No needed to talk about here in that case.

This is important,

I find it rather nostalgic that no one seems to understand how one of these little boxes work.

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10 hours ago, Anders Buen said:

There are at least on exception to that: Tuned bells. 

Tuned bells have to be actively tuned, to force (some of) their different partials to approximate a harmonic series. And that is still not a totally exact science especially in the higher partials though great improvement shave been made in the past decades.

http://www.hibberts.co.uk/ is probably the best resource for understanding this.

I would say that violin plates are different from bells in two main ways, one being they are not circular cross-section so they don't have the rotational symmetry. The second way is that in practical use they are glued all round their edge to other bits of wood rather than hanging free to vibrate.

 

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2 hours ago, bungling_amateur said:

Tuned bells have to be actively tuned, to force (some of) their different partials to approximate a harmonic series. And that is still not a totally exact science especially in the higher partials though great improvement shave been made in the past decades.

http://www.hibberts.co.uk/ is probably the best resource for understanding this.

I would say that violin plates are different from bells in two main ways, one being they are not circular cross-section so they don't have the rotational symmetry. The second way is that in practical use they are glued all round their edge to other bits of wood rather than hanging free to vibrate.

 

I know this. Woodhouses article on the bell is very interesting.

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44 minutes ago, David Beard said:

Big difference, we strike a bell but drive a violin.

Also, bells are much stiffer both in materials and in geometry.

A violin is not a bell, nor a marimba.

Depends on what the perspective is. We all know what you say here that metal is different from wood etc. Still my point is valid. And you need to know a bit about the ortotropic properties of the wood to understand, I guess.

The shape of the bell matter, e.g if you want a major bell it will have an outward bump on the curve. I know because I received a patent application some 30 years ago on this while working at the official patent office in Norway.

Minor bells are those we know. They help them a lttle by tuning them by turning or drilling I guess. They get some help from the hum note.

There are wooden bells too, but they do not ring so loudly and long. Wood is also not so well suited because it changes with the climate.

The violin is struck every time the kink of Helmholz motion passes the bridge and finger or nut. 

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On 1/23/2021 at 10:01 AM, Anders Buen said:

Looks nice with those flames. The summer wood look very wide in the four corners. Does the grainlines look _! to the clueing surface or are they at an angle? The crossgrain bending stiffness drops as the angle is changed from 90 degrees to say 80 or less. 

The grainlines in the centre are also pretty wide. I do not know this wood, but I would probaly not go to thin with it. 

Maybe the mode 2 frequency can say something about the crossgrain stiffness?

Hi Anders, the wood is very well quartered for the most part.  The treble side is almost perfect, the lower bout on the bass side flips almost sideways right at the end; until the last 1/2 inch it is perpendicular. I don't think that edge is going to matter at all. I'm not worried about it, but then again, I don't worry about ANYTHING, so that doesn't mean much!  The wood is very stiff, and the arching is very strong.  The numbers on the poster were all pretty thin,  not for this model, this I just got from a calendar that was in The Strad from Hans Weisshaar violins.  The same model was used 2 times, and I like the way it looks.  The Maggini poster is much wider, and looks more like a small viola to me.  

Carving violins you don't notice cross grain stiffness as much.  The wood starts out stiff, and you carve stiffness into it. If you took 4mm thick slice of it, THEN you would notice cross grain thickness right away.  I was shocked when I could bend a 1/4" piece of redwood from the arch top I was making with absolute ease.  It came out just fine.  Now I don't go around pulling on the wings of the f holes or anything like that. 

I tune everything after, just by getting the tapping in sections even.  They are damped off, it isn't open ringing tones. I only use the open plate tuning as a measure of where the plate stands compared to others.   I think this kind of tuning is used more for tuning large soundboards like pianos, and harpsichords. Maybe it allows the top to move more like a sheet over the prescribed arch, the more even it is, the more free it is to move?  I don't know.  But it seems to work, even in blending a back in the c bouts from 5 mm thick to 2.5 mm thick.  You can do it on the outside without measuring.  This is the first time I ever fully completed the parts before putting them together.  I usually glue the plates on, and then put the purfling in, and cut the recurve, so I don't even know how they feel completely done. 

This one still feels pretty stiff.  The arch is a little under 18mm.  The back is only about 14, because that's all I had left, when I split what I had left after cutting two pieces for a guitar back and sides.

I just have to finish the neck and I can glue it up.  I'm going to do varnish it all first.  Try something different.  I like different. 

IMG_0257.thumb.jpeg.65155866d28211898e95719357682492.jpeg

 

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4 hours ago, David Beard said:

A violin is not a bell

A violin is essentially an untuned wooden bell to which we attach a bridge and strings.

If you want it to make a pleasing tone when you hit it with a hammer, then it needs to be tuned. ;)

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