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1 hour ago, Paul McClean said:

The bass bar is now fitted and measures 13mm high at the highest point.  

Weight 84g

Thickness is 2.5mm all over except for f holes where it is 2.8mm, soundpost area 3.1mm and edges 3.0mm.

Mode 1   76hz

Mode 2   154hz

Mode 5   341hz

Any thoughts on graduating further to reduce the weight?  What would be a reasonable thickness to target for wood of this density without going too far?  Target for tap tones?

What weight and what frequencies does your back have?

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46 minutes ago, Davide Sora said:

What weight and what frequencies does your back have?

The back plate is currently 120g. Roughly 2.8mm in upper and lower bouts graduated to 4.8mm in the centre so still meat left for final graduation.

Mode 1 106hz

Mode 2. 163hz

Mode. 5. 363hz

Thank you..

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13 hours ago, Paul McClean said:

The bass bar is now fitted and measures 13mm high at the highest point.  

Weight 84g

Thickness is 2.5mm all over except for f holes where it is 2.8mm, soundpost area 3.1mm and edges 3.0mm.

Mode 1   76hz

Mode 2   154hz

Mode 5   341hz

Any thoughts on graduating further to reduce the weight?  What would be a reasonable thickness to target for wood of this density without going too far?  Target for tap tones?

 

11 hours ago, Paul McClean said:

The back plate is currently 120g. Roughly 2.8mm in upper and lower bouts graduated to 4.8mm in the centre so still meat left for final graduation.

Mode 1 106hz

Mode 2. 163hz

Mode. 5. 363hz

Thank you..

Since the weight of the back is also quite high, I would consider reducing the thickness a bit to bring it to F natural (349/350 Hz) trying to lighten the left and right areas of the upper and lower bouts first to lose weight and increase mobility, then reduce thickness in the center if needed (If it's not already too thin).

Then (again to reduce the weight as much as possible) I would thin the top by initially bringing the 2.5 areas to 2.4, then eventually to 2.3 if necessary, in any case I would try to bring the note to E natural (329 Hz) and I would stop there without going further down. Perhaps I would bring the right and left areas of upper and lower bouts to 2.2 as well, but in any case without letting the note to drop below E natural.

These are suggestions given blindly, so take them for what they are, although that is probably what I would consider doing if I were in your condition, which is not the ideal one I would like to be in.:P

PS Please note that I have used notes as a primary indication and not (frequencies), which greatly elevates the prestige of a real Tap Tuners above a sterile scientific/numerical approach.:lol::lol:

 

 

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29 minutes ago, Davide Sora said:

 

Since the weight of the back is also quite high, I would consider reducing the thickness a bit to bring it to F natural (349/350 Hz) trying to lighten the left and right areas of the upper and lower bouts first to lose weight and increase mobility, then reduce thickness in the center if needed (If it's not already too thin).

Then (again to reduce the weight as much as possible) I would thin the top by initially bringing the 2.5 areas to 2.4, then eventually to 2.3 if necessary, in any case I would try to bring the note to E natural (329 Hz) and I would stop there without going further down. Perhaps I would bring the right and left areas of upper and lower bouts to 2.2 as well, but in any case without letting the note to drop below E natural.

These are suggestions given blindly, so take them for what they are, although that is probably what I would consider doing if I were in your condition, which is not the ideal one I would like to be in.:P

PS Please note that I have used notes as a primary indication and not (frequencies), which greatly elevates the prestige of a real Tap Tuners above a sterile scientific/numerical approach.:lol::lol:

 

 

Thanks David. Appreciate the advice.  I like the idea of reducing the weight with a target 'note' to aim for keeping the back a semitone above the front at mode 5.  I'll let you know how I get on in few days as I only have an hour or two in the evenings

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3 hours ago, Davide Sora said:

Please note that I have used notes as a primary indication and not (frequencies), which greatly elevates the prestige of a real Tap Tuners above a sterile scientific/numerical approach.:lol::lol:

Since I definitely don't use notes and look at frequencies but mostly ignore them, that greatly demotes the prestige of non-TapTuners well below scientific/numerical into the murky region of the unknown.:D

While I might disagree somewhat with Davide on the importance of taptones, I certainly wouldn't disagree with his advice to get rid of excess mass.  And I certainly can't disagree with his results (although I have never personally heard or played one of his instruments).

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I just finished a top with .45sg wood, Port Orford Cedar. It ended up at 66 grams, complete with bass bar.  It is thin, 2-2.5 in the bouts, 2.5 -maybe 3 in the middle. The edges are maybe 2.5.  It's a Maggini, but it is a different one than the poster I have, but the thicknesses on the poster are similar.  It is a little longer, but it isn't any wider. It is 366mm long, but the stop is 195.  I don't tune with tap tones, I get the inside arch where I want it, and get the outside to be even when tapping it in sections that are blocked off with my fingers.  It usually gets it fairly even, but your ears can play tricks on you.  The tap tone is between e and f on my guitar; so abut 340 or so.

I would thin that belly down. I've seen many posters with 2mm and under on them.  See how much the bridge area pushes down under gentle pressure.  That is probably what gives you the "bow feel" that they were talking about.  If it isn't moving much at all, with a bass bar what will it do?  

Yes, I KNOW POC is not a violin tone wood, but it sure looks cool. And it carves really well. When roughing the smell can be quite strong. I'm tanning it now, and the color in the photo is off.  It is way darker, and like a greyed yellow. I never could get ANY color on bellies with UV.  Now I use water in a jar full of cherry chips, and water with wood ashes.  Now I can get something.  Sun, or 4 20w black lights alone do nothing for me ever.

The back is 99 grams, dare I say that it is wicked looking Padauk? The tap tone on that never was very high, so it is about D# on the guitar, or 312. It seems like the low mode of backs is usually higher than bellies, but the back is low F and the belly is F, (87/92).  Like I said, the back never was high. The thick point is about 4.8, high on the c bout; that's what the poster said.  The rest goes down to 2-3mm. Again, that's what the poster said.  It isn't that dense of a wood.  .65 sg.  It has large pores.

Then again, I know nothing, so it is just my experience.

 

IMG_0255.jpeg.e49ccaec70f3a051626139b5cec98166.jpeg

 

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19 hours ago, Don Noon said:

Since I definitely don't use notes and look at frequencies but mostly ignore them, that greatly demotes the prestige of non-TapTuners well below scientific/numerical into the murky region of the unknown.:D

While I might disagree somewhat with Davide on the importance of taptones, I certainly wouldn't disagree with his advice to get rid of excess mass.  And I certainly can't disagree with his results (although I have never personally heard or played one of his instruments).

In reality I don't give all this importance to tap tones, real "tap tuners" are much more obsessed with targets and mode shapes. I'm happy when I can stay within certain frequency and weight limits (for example if the various data of the plates coincided with those of some of my violins that I remember were particularly appreciated by players, gives me the feeling of being on a good track), but I'm always ready to ignore them by evaluating other aspects, when it is the case.

I think we all move in the same murky region, but some manage to avoid hitting hidden obstacles more than others, even if maybe just for luck or if you prefer to call it intuition:P

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14 hours ago, 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?

But specifically, tune to what?

I confess that I also take the tap tones of the back + ribs assembly, but if anything, then I try to understand if there are connections with the top and eventually I act on that, not on the back.

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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.

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13 minutes ago, David Beard said:

 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.

I don’t think it’s as simple as this part does this, and another part something different, it’s all interconnected.
For centuries people have been looking for the magic buttons, yet with all the amassed knowledge they still seem to elude us.

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1 hour ago, Wood Butcher said:

I don’t think it’s as simple as this part does this, and another part something different, it’s all interconnected.
For centuries people have been looking for the magic buttons, yet with all the amassed knowledge they still seem to elude us.

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.

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2 hours ago, 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.

...

Nowadays you can study lots of research that may enlighten your view on modes of the finished violin: Schleske, Strad 3d, Stoppani, Borman etc.

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4 hours ago, David Beard said:

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.

As the wonderful Sam Cooke sang: i don't claim to be an "A" student. But surely the modes are the modes? And they don't have harmonics?

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10 minutes ago, Bodacious Cowboy said:

As the wonderful Sam Cooke sang: i don't claim to be an "A" student. But I think the modes are the modes. They don't have harmonics.

Yes.  My wording is bad.  Each mode is just a mode, even though each will be in family of harmonics that use different divisions of the same mass and the use the same flex.

Thanks for the clarification.

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24 minutes ago, David Beard said:

Each mode is just a mode, even though each will be in family of harmonics that use different divisions of the same mass and the use the same flex.

"Harmonics" implies some kind of multiple in frequency between modes.  For a string driven in the Helmholtz mode by a bow, yes.  For a general structure, no... the modes are all over the place and not particularly "harmonic".

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21 minutes ago, Don Noon said:

"Harmonics" implies some kind of multiple in frequency between modes.  For a string driven in the Helmholtz mode by a bow, yes.  For a general structure, no... the modes are all over the place and not particularly "harmonic".

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.

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6 hours ago, 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.

Bell people are quite particular about this; it's considered a basic error to talk about the harmonics of a bell; they call them "partials", and would say that they should only be called "harmonics" when they (nearly) follow a harmonic progression 1:2:3:4:5... like in a string or air column.

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On 1/21/2021 at 9:49 PM, Ken_N said:

I just finished a top with .45sg wood, Port Orford Cedar. It ended up at 66 grams, complete with bass bar.  It is thin, 2-2.5 in the bouts, 2.5 -maybe 3 in the middle. The edges are maybe 2.5.  It's a Maggini, but it is a different one than the poster I have, but the thicknesses on the poster are similar.  It is a little longer, but it isn't any wider. It is 366mm long, but the stop is 195.  I don't tune with tap tones, I get the inside arch where I want it, and get the outside to be even when tapping it in sections that are blocked off with my fingers.  It usually gets it fairly even, but your ears can play tricks on you.  The tap tone is between e and f on my guitar; so abut 340 or so.

I would thin that belly down. I've seen many posters with 2mm and under on them.  See how much the bridge area pushes down under gentle pressure. 

IMG_0255.jpeg.e49ccaec70f3a051626139b5cec98166.jpeg

 

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?

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I've made quite a few instruments with both unusually narrow and wide-grained tops and/or backs, and don't think it's terribly important for sound. While grain width may sometimes have something to do with the mass or stiffness, it often does not.

Same with bridges.

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7 hours ago, bungling_amateur said:

Bell people are quite particular about this; it's considered a basic error to talk about the harmonics of a bell; they call them "partials", and would say that they should only be called "harmonics" when they (nearly) follow a harmonic progression 1:2:3:4:5... like in a string or air column.

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.

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34 minutes ago, 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.

 

Nope. But I can understand how this could be an attractive theory, since it can work reasonably well for things like wind columns, and the theoretical "ideal string".

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51 minutes ago, David Burgess said:

Nope. But I can understand how this could be an attractive theory, since it can work reasonably well for things like wind columns, and the theoretical "ideal string".

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?

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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

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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.

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