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Don Noon

Taptones Revisited

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2 hours ago, Don Noon said:

Blam! Blam! Blam! Blam! - Four more shotgun blasts... at least, with my data.

1822300098_M2correlations.jpg.fcb609b13737da24eefea2045dff339c.jpg

The best correlation in my data set is with B1+ and M5 of the back, and even that is mostly noise (and if you plot enough stuff, eventually you will find a plot that has better correlation, just from random chance):

1014925391_B1vsM5back.jpg.23b633f27805d53a5bfe67f351b9f484.jpg

More or less matches my data, back grads tend to be at least somewhat similar, whereas tops are easily confounded by bass bar.  As an example, I've done a bunch of experiments around bass bars (on cellos) and found that I can cut down a bass bar (moving m5 from 188 down to 165 - both still quite high) and B1- only moved from 175 to 174Hz - I have other tops ranging in M5 from 136Hz all the way up to the 188Hz that land with a B1- of 174-176Hz.  Where the stiffness and mass is matters quite a bit especially on the top.

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On 2/11/2020 at 12:44 PM, Don Noon said:

I hesitate to dredge up this controversial topic, but recently in discussions of taptones with Mike Molnar, I got around to looking at the data from all of the violins I have built so far.  M5 of the top seems to be the most popular thing to use, so I'm only showing that.  The others are similar... i.e. shotgun blast random points.  Note that if you clip off the extreme outlier points, any small trendline slope pretty much disappears, and you have a flat line with tons of scatter.  A few of the high outliers are small-body violins, where you naturally will get higher taptones and higher B modes, and voila:  a slope to the trendline.

There is a perfectly valid argument that M5 might be correlated with things other than signature B modes... like resistance to the bow, responsiveness, or some other non-quantifiable characteristic.  Good luck trying to make that kind of correlation... although you could make non-mathematical conclusions by trial-and-error, I suppose.

I am tempted to dispense entirely with taptones, and just go with wood properties, plate weights, arching, and graduation patterns.  However, it's so quick and easy to take taptone data, I'll likely keep up the tradition.  

Oh... and since there isn't any great proof that particular B modes are more desirable than others, that adds another layer of uselessness to this whole thing :)

2050968952_TaptoneM5andBmodes.jpg.5b62970b765a879ddf8c4dcb6273b1ea.jpg

 

In order to compare data from different plates, the mechanical properties of the wood should be considered. In fact, I can't see any reasonable ground supporting the idea that the corpus mode frequencies should relate linearly with the free plate mode frequencies, for structures made with materials of varying properties.  

Using my data I have found good correlation (r^2 around 0.9)  between B1+ and M5 taptone frequency of the back plate, and B1-  and M5 taptone frequency of the top plate, when plate's M5 taptone frequency AND corpus mode frequency are both multiplied by the plate's respective 'Radiation Ratio' ( the ratio between the sound speed and density).

It is indeed possible to put together a mathematical model to predict B1+ and B1-. Even a simple model like mine can give us interesting insights on violin construction and the role of the materials.  I have done this years ago, and I use it routinely in my workshop.

 

 

 

 

 

 

Edited by Rafael Sando
edited to correct a mistake

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On 2/13/2020 at 10:00 AM, Jeffrey Holmes said:

I assume you're referring to the  longer than average post approval delays the previous two weeks?  Careful what you ask for.  I was on a rare and needed vacation with little to no internet coverage.  Someone in admin was covering for me.

The delays don't bother me any.  The more time that is sometimes needed to get to me sort of improves my memory.  It's like, yeah, I do remember typing that the other day.  And then shortly afterwards it's thoughts like what the heck did I type that for? 

Usually when you don't adhere to your known times of responding/checking moderator approval needed posts I'm assuming the best - you're out gathering work for yourself or making arrangements to do so.  It's just when you're not around days at a time is what gets me wondering what's wrong - is he dying, sick, over in England bringing back violins to work on,  none of my business really but when one has been on the approval needed firstly since 2016 he gets to figure out some stuff.  I haven't figured out if there's three computers used by yourself but I do know there are two. Or one p.c and one phone. 

Ever since the Tecumseh traversing bit everyday that you're experiencing these days I've quit paying attention to what you've been doing.  I mean no harm sir.   

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In order to take material properties into account, I plotted  B1- * RR against free top M5 frequency * RR , and B1+ corpus mode frequency * RR against free back plate M5 frequency * RR, RR being the Radiation Ratio for top and back plates respectively.

After calculating the regression parameters  I ended up with expressions relating B1 and  M5 frequencies , with RR as a parameter.

I modelled the free plate's M5 frequency as  equal to k*RR*m  where m is the plate's mass and k a constant that should be calculated separately for maple backs, spruce tops with soundholes cut and without  soundholes (  I prefer to model the top plate M5 with soundholes cut ).

This simple empirical model gives reasonably good estimates for B1+ and B1+. But it is also gives interesting insights about the complicated relationships between  the  mechanical properties we consider using as targets. For instance, if we choose B1 corpus signature modes as targets,  the resulting plate impedances and stiffnesses will depend on the properties of the wood . For a given B1, the higher the RR the higher the plate impedance and stiffness.

Any thoughts welcome.

 

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There is a question whether the frequencies of the various "signature" vibration modes relate to violin quality.  

It is my belief that the amplitudes of these much more important.

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There is an error in all plots - they assume that you know M5, but you don't.

But even if that error would be corrected. Correlation of 1, can only be achieved if all parameters are controlled

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On 2/19/2020 at 10:01 PM, uncle duke said:

Ever since the Tecumseh traversing bit everyday that you're experiencing these days I've quit paying attention to what you've been doing.  I mean no harm sir.   

That's a little sad. The Tecumseh Harley dealership is the nearest that my wife and I can rent Harleys from. We have been through there many times, and always thought Tecumseh was a pretty cool town, whether riding our own Harleys, riding rented Harleys, or just going to visit Jeffery.

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1 hour ago, Marty Kasprzyk said:

There is a question whether the frequencies of the various "signature" vibration modes relate to violin quality.  

It is my belief that the amplitudes of these much more important.

While I agree that signature mode amplitudes are much more important than their frequencies, I rather think that the amplitudes of all those bazillion modes above the signature modes are even more important... and even more impossible to figure out.

You don't have to look very hard to find horrible violins with "perfect" signature mode frequencies, and great violins with "abnormal" signature mode frequencies... so I'm not very concerned with the whole frequency issue and how taptones correlate (or don't) to the body modes.

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9 hours ago, Don Noon said:

While I agree that signature mode amplitudes are much more important than their frequencies, I rather think that the amplitudes of all those bazillion modes above the signature modes are even more important... and even more impossible to figure out.

You don't have to look very hard to find horrible violins with "perfect" signature mode frequencies, and great violins with "abnormal" signature mode frequencies... so I'm not very concerned with the whole frequency issue and how taptones correlate (or don't) to the body modes.

I agree with Don and Marty. It is silly expecting to reproduce the acoustics of a great violin by emulating a couple of its “signature” body mode frequencies, unless, of course, one also emulates a lot of other things such as the wood properties, model, measurements, ageing, finish and so on.
However, not understanding how a potentially useful tool works is not a good reason to discard it.
Tap tones and body resonances can be easily assessed, controlled and documented - before, during and after the instrument construction. Understanding how they relate to the basic parameters of construction, (particularly material properties) can be very helpful for the maker who needs a strategy to decide what to do in order to build consistent instruments or optimize the not so great ones. Or just make the best use of the available materials and patterns.

By the way, isn’t the "whole frequency issue" related to plate vibration amplitudes and effective masses via wood properties, measurements and so on?

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On 2/21/2020 at 9:45 AM, David Burgess said:

That's a little sad. The Tecumseh Harley dealership is the nearest that my wife and I can rent Harleys from. We have been through there many times, and always thought Tecumseh was a pretty cool town, whether riding our own Harleys, riding rented Harleys, or just going to visit Jeffery.

What's sad?  Surely you wouldn't want me to be keeping being a pest in regards to following Jeffrey's every move would you?  That's called being a predator or something like that.

There's a caption in the old Petherick manual that states any high level restorer of the violin is not to be bothered in any way, so I always keep that in mind when replying here.  

We used to have a golden eagle here in Kansas named Tecumseh - if he's still alive these days he's ancient.

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15 hours ago, Rafael Sando said:

However, not understanding how a potentially useful tool works is not a good reason to discard it.
Tap tones and body resonances can be easily assessed, controlled and documented - before, during and after the instrument construction.


By the way, isn’t the "whole frequency issue" related to plate vibration amplitudes and effective masses via wood properties, measurements and so on?

I don't discard taptones and body mode frequencies... I still document everything.  However, after a decade of trying to figure out how this "potentially useful tool" works, I am not finding that it matters a whole hell of a lot, and other tools (caliper, scale) are probably sufficient.

Yes, frequencies are tangled up with everything else... amplitudes, wood properties, arching, etc... but my main point is that taptones and signature modes are almost ALWAYS looked at and discussed as a stand-alone factors... which I think is missing the majority of what really matters.

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14 hours ago, uncle duke said:

What's sad?  Surely you wouldn't want me to be keeping being a pest in regards to following Jeffrey's every move would you?  That's called being a predator or something like that.

There's a caption in the old Petherick manual that states any high level restorer of the violin is not to be bothered in any way, g here. 

Your opinions, experiences and approaches and mine, might be a little different. ;)

 

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The frequency of any mode is equal to the square root of its stiffness divided by its mass.  So a heavy stiff plate or assembled violin can have identical mode  frequencies as a lighter less stiff one.  But the lighter one will play much differently than the heavier one (wolf notes, minimum bow force, loudness, etc.).

These playability issues relate to the impedance (resistance to movement) which is simply the mode frequency times the body's moving mass.  So if you are taking the trouble of measuring the various plate or violin mode frequencies I encourage you to also weigh your plates and assembled violin bodies (before and after the neck and fingerboard are assembled and also calculate the impedances.

Like Don said, record these things.  Maybe a pattern will emerge of things you like to duplicate.

 

I think I've said the above things over and over again:  reminds me of the movie "Groundhog day".   The  Super Bowl Jeep commercial with Bill Murray was one of the funniest things I've ever seen.

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29 minutes ago, Marty Kasprzyk said:

These playability issues relate to the impedance (resistance to movement) which is simply the mode frequency times the body's moving mass.  

Since it's impedance at the bridge that's important, it's critical to know location of the bridge feet relative to the nodes/antinodes of the particular mode you're trying to examine.  Although mass and frequency are a lot more than nothing, it's not enough to know what's really happening, and could be misleading.

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4 hours ago, David Burgess said:

No problem. I am quite willing to accommodate those who got up on the wrong side of the bed, one day or another, and also those who have a stellar track records.

Which would you prefer that I place more emphasis on?

First, put yourself first and then decide do I dance with the ones who brought me or do I look another way like I'm only as good as my weakest link.  Rereading what I just typed seems like a different wording of what you just typed.

More emphasis placed on eh?  Beings how your still an early riser looking for something interesting to read before breakfast time these days, if it were me, and I felt a comment or two to start the day off is the way to go before starting work, I would.  Weather a colleague of yourself or someone like the early morning trollers or wanna be fiddle forgers shouldn't matter much. 

Just remember some have personal or mental problems before they show up here at Maestronet.  This place can be a place of escape for some.  I look forward every morning most days just to see what's new and if it just happens to be you just trying to pique someones interest when they're not quite ready is fine with me too.  It can only make them better people if they'll let it. :)  I like reading it all good or not so good.     

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The only reason for making thin arched top plates of spruce wood is to reduce weight to increase the sound output.

If hitting target mode frequencies were the only thing important you could make flat, thick plates from maple.  You could save a lot of work.

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A scientist, an artist and a building contractor walked into a bar and saw a violin sitting On the corner stool.

the scientist said "boy I bet I know what makes her tick, I bet I can get her number'

the artist said, "no,no, she's all mine, she'll be leaving with me"

then the building contractor walked up and said "ha, step aside gentlemen, I'll show you how to handle a lady like that"

just then, a violin maker walked in and put his arm around "her" and they started to walk out the door together, 'she" looked back and said;

"you guys would never understand, he's the only man for me, he's the only one who never tries to "figure me out" I don't care if he doesn't understand everything about me, all I know is that when he holds me, I know that he loves me more than anyone else ever could"

THE END.

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9 hours ago, Marty Kasprzyk said:

The only reason for making thin arched top plates of spruce wood is to reduce weight to increase the sound output.

Arching also shapes the tone by attenuating certain frequency ranges and enhancing others.

9 hours ago, jezzupe said:

A scientist, an artist and a building contractor...

There's no need to stick to only one profession.  A violinmaker/scientist/artist/builder combining all skills as appropriate I think could do pretty well.

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When I hear how arching determines stiffness, I recall the story about how Henry Ford silenced his “Tin Lizzie”, the Model T, that rattled loudly scaring farm animals. Ford’s design team discovered the importance of bends and folds in metal panels which silenced the rattling. Now, look closely at the f-hole arching of a Cremonese violin.  Do you see the new Model A?  ;)

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22 hours ago, Marty Kasprzyk said:

 

The frequency of any mode is equal to the square root of its stiffness divided by its mass.  So a heavy stiff plate or assembled violin can have identical mode  frequencies as a lighter less stiff one.  But the lighter one will play much differently than the heavier one (wolf notes, minimum bow force, loudness, etc.).

 

This is true for free plates only. Given two free plates with identical ring mode frequencies, the heavier will be stiffer and will also have higher impedance.

For the assembled instrument things seem to be different.
According to my model (derived from data), given two assembled instruments with identical B1- and B1+ corpus mode frequencies, the stiffer (the one made with woods with higher RR) will be lighter.
For this stiffer instrument, both top and back plates will be stiffer and lighter. The ring mode frequency of the plates will be higher. So, in terms of impedance  (I mean free, before assembling)  they won't differ too much from those belonging to the heavier instrument.

Edited by Rafael Sando

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18 hours ago, Marty Kasprzyk said:

The only reason for making thin arched top plates of spruce wood is to reduce weight to increase the sound output.

If hitting target mode frequencies were the only thing important you could make flat, thick plates from maple.  You could save a lot of work.

Be it natural or cultural, an advantage of design by evolution is that it follows what emerges as successful, rather than what was expected to be effective.  Further, the evaluation of what changes are effective or not tends to be holistic.  So the all the components of an evolved solution tend to function on multiple levels.

When looking from the outside, it's not so obviously correct to say that 'The only purpose of x is A.'

 

 

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I went to concert last night featuring the group "Time For Three"  (two violins and a bass) which was accompanied by our Buffalo Philharmonic Orchestra. I loved it.  Years ago our BPO concert master Nicci Chooi was briefly a member of the group and for one tune he joined the group.  TF3 Violin player Charles Yang and Nicci alternated back and forth playing the same music and it was a great opportunity to compare their two violins.

Nicci used to play a 1729 DG and a 1700 Strad violin on loan which he had to give up and after a lengthly search he purchased a 2016 Joseph Curtin violin. I haven't been able to find out what Charles Yang was playing but it was good too.

I was seated far back in our Kleinhans music hall and I couldn't see any difference in their violin's corner points.

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14 hours ago, Don Noon said:

Arching also shapes the tone by attenuating certain frequency ranges and enhancing others.

There's no need to stick to only one profession.  A violinmaker/scientist/artist/builder combining all skills as appropriate I think could do pretty well.

Oh I know Don, I like to think that anyone who makes instruments is kinda a combination of all three to some extent. Regardless, as good of scientist as you are, and as important to the field of violin acoustic science as you have been {probably one of the most important in a long time} I still think you have the potential to be better at violin making than any of the above mentioned and that I hate to see you spend too much time on something that is going to slow the rate of speed of your production. 

I mean I'm quite sure your aware of your free time and what time you can dedicate to whatever it is you do, but really out of anyone I can think of, your the guy who should be hiring on an apprentice who you can do a data dump on and get your rough work done for you so you can produce more. I have a feeling with you "build it and they will come" will apply.  

That is assuming the Corona virus doesn't kill everyone and the economy off.

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11 hours ago, Michael_Molnar said:

When I hear how arching determines stiffness, I recall the story about how Henry Ford silenced his “Tin Lizzie”, the Model T, that rattled loudly scaring farm animals. Ford’s design team discovered the importance of bends and folds in metal panels which silenced the rattling. Now, look closely at the f-hole arching of a Cremonese violin.  Do you see the new Model A?  ;)

[Examines one of her "Strad pattern" Markies] 

No, but I can see foreshadowings of the Volkswagen.  :ph34r::lol:

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On 2/21/2020 at 8:57 AM, Rafael Sando said:

In order to take material properties into account, I plotted  B1- * RR against free top M5 frequency * RR , and B1+ corpus mode frequency * RR against free back plate M5 frequency * RR, RR being the Radiation Ratio for top and back plates respectively.

After calculating the regression parameters  I ended up with expressions relating B1 and  M5 frequencies , with RR as a parameter.

I modelled the free plate's M5 frequency as  equal to k*RR*m  where m is the plate's mass and k a constant that should be calculated separately for maple backs, spruce tops with soundholes cut and without  soundholes (  I prefer to model the top plate M5 with soundholes cut ).

This simple empirical model gives reasonably good estimates for B1+ and B1+. But it is also gives interesting insights about the complicated relationships between  the  mechanical properties we consider using as targets. For instance, if we choose B1 corpus signature modes as targets,  the resulting plate impedances and stiffnesses will depend on the properties of the wood . For a given B1, the higher the RR the higher the plate impedance and stiffness.

Any thoughts welcome.

 

If you plot (B1-)*(RRt) against (M5t)*(RRt)   the slope of the plotted line is equal to the ratio (B1-)*(RRt) /  (M5t)*(RRt).

The RRt term above and the RRt below in the slope equation cancel so the ratio simply becomes B1-/M5t.  It seems reasonable that there is a correlation between the violin body's mode B1- frequency  and the top plate's mode 5 frequency.  Multiplying everything by the radiation ratio of the top  RRt doesn't give any additional insight.

Likewise for the body's B1+ mode frequency vs. the back's mode 5 frequency correlation.

 

The radiation ratio RR  is equal to the woods speed of sound c divided by its density p :  RR= c/p

I can be shown that for a given mode frequency a wood with a high radiation ratio will give a lower impedance than a wood with a lower RR for a uniform thickness flat plate of a certain size.  Using a high RR wood (good wood) will increase the sound output at a given mode frequency for a flat plate.

However as the plates become arched and then finally assembled as a hollow box the RR = c/p is no longer valid and probably some other relationship better describes wood quality.  

I suspect that the best wood is what ever wood the very best violins were made from.   I doubt it was wood with the highest radiation ratio.

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