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Don Noon

Taptones Revisited

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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

 

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47 minutes ago, Don Noon said:

I am tempted to dispense entirely with taptones, and just go with wood properties, plate weights, arching, and graduation patterns. 

Oh goody. This helps justify my wilful ignorance of the subject.

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I appreciate it, Don. Thanks as always for sharing your data and analysis. As for wood properties, weights, arching, and grads, I'm guessing that's the information that was available to the Ancients (although their wood properties info was probably more qualitative than quantitative) and the seemed to do pretty well with it. 

 

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Yep, it seems that taptones are more related to the properties of the free plates than to the final result (sound) for which they are a red herring. But I still don't consider them completely useless during working, I think they give a more intuitive and immediate idea of wood properties for those who are not too inclined to formulas and calculations. The problem is when people consider them the holy grail, which is known, they will never find it.:)

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After discussing this with Don and now seeing Davide's post, I concur. M5 will be a guide, not an end result. We can rule out the extremes, nevertheless.

I am using a new arching and hope it will produce a better violin. Time will tell.

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24 minutes ago, Davide Sora said:

Yep, it seems that taptones are more related to the properties of the free plates than to the final result (sound) for which they are a red herring. But I still don't consider them completely useless during working, I think they give a more intuitive and immediate idea of wood properties for those who are not too inclined to formulas and calculations. The problem is when people consider them the holy grail, which is known, they will never find it.:)

I pretty much have a similar feeling. I track Impedance by means of Evans number (mass, #2 and #5) and I find it a reasonable indication of stiffness of plates, following Stoppani's approach. I also have found a good correspondance between the impedance and sound emission in the low register. It's also a good idea to track modes and weight when working with different archings and models to spot the effect of these on plate thickness. Btw thanks don for sharing.

Have you tried with A0 frequency (with sounpost and strings on)?

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For those wondering, the r^2 value in Don's plots is called the Coefficient of Determination.

Roughly speaking, it represent the fraction of the data that "fits" the straight line.

A value of zero (0%)means none of the data can be reasonably explained by a straight line fit.

A value of 1 (100%) means all of the data  can be explained by a straight line fit.

A value of 0.7 (70%) or higher usually means there is probably some strong physical dependence between the x and y data. In this case, between the M5 frequency the B+/- frequency.

Given that the highest value in Don's data is 0.067 (6.7%), and most are under 0.02 (2%), one can reasonably rule out a simple relationship between M5 and B modes.

There are computer models that show how the frequency of free plate modes evolve into assembled violin modes, but they account for a wide range of interactions, including rib, post and back interactions as well as stiffness, density and damping.

My professional experience with material properties and structures under dynamic loadings suggests Don is probably correct in focusing on wood properties, plate weights, arching, and graduation patterns. Find a range of values which yield "good" results and incorporate that into one's construction process.

 

 

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Another reason why I use modal analysis it the difficulties I have in separating m5 to the adjacenr modes. It would be very difficult for me to go blind and spot the correct m5. Quite often I see "place trading" between 5 and adjacent modes.

When I used to tap and listen quite often I was not sure about #5.

Now with a couple of hammer hit you can have the first 7-10 modes in a matter of seconds, and track them when finalyzing thicknesses.

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4 minutes ago, francesco piasentini said:

Another reason why I use modal analysis it the difficulties I have in separating m5 to the adjacenr modes. It would be very difficult for me to go blind and spot the correct m5. Quite often I see "place trading" between 5 and adjacent modes.

When I used to tap and listen quite often I was not sure about #5.

Now with a couple of hammer hit you can have the first 7-10 modes in a matter of seconds, and track them when finalyzing thicknesses.

One of the advantages of the old fashioned signal generator-speaker- glitter testing of plate modes is that the glitter showed the node lines of the vibration modes.

So it is easy to see if you were getting modes 1, 2, and 5 if the node line shapes were normal.  A hammer impact test doesn't identify what mode goes with what frequency.  You could go further and do a modal analysis using accerometers or laser scanners.   But I'm not sure its important anyway.  Just knowing  how the first 7-10 mode frequencies change with plate thinning might be good enough.

I agree that the Evans type impedance calculations using mode 2 and 5 are very helpful because they involve the plate's moving (effective) mass too.  Unfortunately each vibration mode has its own amount of effective mass.  I expect that George Stoppani's work with modal analysis and plate tuning will eventually help us.

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2 hours ago, sospiri said:

Oh goody. This helps justify my wilful ignorance of the subject.

I'd rather ignore things on the basis of knowing.

1 hour ago, Davide Sora said:

The problem is when people consider them the holy grail, which is known, they will never find it.:)

Trying to find the holy grail of taptones (or any other formula) is even a huge step removed from trying to find the holy grail of violin tone.

I am reminded of the Cannone and the ex-Jackson Strad, which are so completely different in arching, graduations, and tone as to be from different universes, and I can't imagine taptones and mode shapes being anywhere near each other... yet they are both considered to be extremely good.  So I don't see any holy grail, but a bunch of pretty good grails.  And for bluegrass fiddles (which interest me), there's a whole set of pretty good mugs and pitchers (they don't use grails).

26 minutes ago, francesco piasentini said:

Would you mind Don to plot for each plate/violin:

x-axis: weight divided per #5

y-axis: A0, B1+ as measured with the microphone

Sorry, I have already put more time into this dead end than I should... I have instruments to build.

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2 hours ago, Don Noon said:

I am reminded of the Cannone and the ex-Jackson Strad, which are so completely different in arching, graduations, and tone as to be from different universes, and I can't imagine taptones and mode shapes being anywhere near each other... yet they are both considered to be extremely good. . .

Because the static behavior you are measuring is nearly totally irrelevant compared with the importance of the dynamic behavior that no one effectively measures, which is virtually all that the player experiences and the audience hears?

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4 hours ago, Michael Darnton said:

Because the static behavior you are measuring is nearly totally irrelevant compared with the importance of the dynamic behavior that no one effectively measures, which is virtually all that the player experiences and the audience hears?

Don is ahead of you. He told me this exactly in an earlier email.

I am grateful that Don let me look over his shoulder. His data reinforced my intuition that we were doing the wrong analysis because I wasn’t seeing repeatable results.  His data graphically show that. However, the big issue according to Don is how to do this dynamically with reliable feedback and controls. I now let the players and audience do the evaluations.

BTW, all is not lost. Don has convinced me how important arching and wood are. There is a family of arching systems that gives nice results. And wood processing works too.

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Thanks Don for showing us your data, it is a lot of effort and much appreciated. The interesting thing from your graphs are the differences in Rvalues when the bass bar is added to the plate. To me this strengthens the theory that one cannot rely on the taptones alone, everytime something is added or removed the modal relationships will change. The almost horizontal slopes of linearity is another good sign not to rely too much on this stuff.

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5 hours ago, Michael_Molnar said:

There is a family of arching systems that gives nice results.

Can we please hear more about this? It is such an intriguing statement, yet it seems difficult (for me, at this point) to get much clarity about it.

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Tap tones might be useful to know the limits or at which frequency you must stop thinning down before you ruin the plate. 

I started wondering if we are not looking into the wrong parameter of tap tones which is the frequency. I suspect that it is more useful to look into the 'sound quality' of tap tones: damping and overtones (if there are any).

Otherwise I noted that top plates with lacking cross stiffness are problematic for a good sound production. (Maybe a wrong subjective impression).

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54 minutes ago, Andreas Preuss said:

I started wondering if we are not looking into the wrong parameter of tap tones which is the frequency. I suspect that it is more useful to look into the 'sound quality' of tap tones: damping and overtones (if there are any).

I've sat at the bench watching some top maker/restorers doing things like taking down a bassbar to its final height and shape, and was amazed at how the sound generated from tapping would evolve from a dull thud to a clear bell-like ringing, sometimes almost suddenly. 

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12 hours ago, Don Noon said:

Sorry, I have already put more time into this dead end than I should... I have instruments to build.

Me too I have a limited amount of time. And also I would prefer not to invest this limited time in making bad sounding violin. If something can help me in this way, I would rather invest time on it before making violins. And I would test my hypothesis with each instrument.

Graphs shows no correlation, but that don't tell us that measuring M5 is useless. Each point belongs to instrument with different archings, outlines, wood, wood treatment. You could make a similar graph between density and CBR and conclude that measuring density is not important.

List of questions is endless, just one: What's the initial hypothesis you want to prove or demolish with your scatter plots?

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1 hour ago, Andreas Preuss said:

I started wondering if we are not looking into the wrong parameter of tap tones which is the frequency. I suspect that it is more useful to look into the 'sound quality' of tap tones: damping and overtones (if there are any).

I was thinking the same just before I turned on my computer this morning.  I got drawn into tap tones fairly recently and could see how you can get drawn into chasing numbers while forgetting the most significant tool, the Mk 1 earhole. I am a structural engineer, so am attracted to numbers, but also know their limitations.

That's not to say it isn't interesting to try and understand what's happening.

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10 hours ago, Andreas Preuss said:

Tap tones might be useful to know the limits or at which frequency you must stop thinning down before you ruin the plate. 

I started wondering if we are not looking into the wrong parameter of tap tones which is the frequency. I suspect that it is more useful to look into the 'sound quality' of tap tones: damping and overtones (if there are any).

Otherwise I noted that top plates with lacking cross stiffness are problematic for a good sound production. (Maybe a wrong subjective impression).

I take all the parameters into consideration, just to make sure you don't just take the wrong one:)

What do you consider as "lacking cross stiffness"? Maybe a M2 frequency too low?

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9 hours ago, Michael Appleman said:

I've sat at the bench watching some top maker/restorers doing things like taking down a bassbar to its final height and shape, and was amazed at how the sound generated from tapping would evolve from a dull thud to a clear bell-like ringing, sometimes almost suddenly. 

Clear, ringing free-plate modes (which all involve flapping at the edges) do not logically imply clear, ringing tone of the assembled instrument, where most of the modes don't move much at the edges.  That's not to say that a top maker couldn't discover some trial-and-error connection between the free plate and final result... but I remain a skeptic about most of these things.

9 hours ago, francesco piasentini said:

List of questions is endless, just one: What's the initial hypothesis you want to prove or demolish with your scatter plots?

The main intent is not to demolish anything, but show some results for others to draw their own conclusions.  However, for me this is pretty convincing that there's not much point in trying to provide a prescription for plate modes in order to obtain specific signature mode frequencies, with the follow-on conclusion (from other data) that specific signature mode frequencies are not a holy grail.

I suppose it's mostly further proof that it's complicated. :)

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10 hours ago, Andreas Preuss said:

Tap tones might be useful to know the limits or at which frequency you must stop thinning down before you ruin the plate. 

A plate is ruined if the wood or the arching are wrong.  If it's too thin, it's not "ruined"... it's now a bluegrass fiddle.

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22 hours ago, Michael Darnton said:

Because the static behavior you are measuring is nearly totally irrelevant compared with the importance of the dynamic behavior that no one effectively measures, which is virtually all that the player experiences and the audience hears?

 

17 hours ago, Michael_Molnar said:

Don is ahead of you. He told me this exactly in an earlier email.

I am grateful that Don let me look over his shoulder. His data reinforced my intuition that we were doing the wrong analysis because I wasn’t seeing repeatable results.  His data graphically show that. However, the big issue according to Don is how to do this dynamically with reliable feedback and controls. I now let the players and audience do the evaluations.

BTW, all is not lost. Don has convinced me how important arching and wood are. There is a family of arching systems that gives nice results. And wood processing works too.

My response to Darnton referred to the timing of his post with Don's email. Nothing more.

We all know that Darnton and other prominent makers, have advocated for years the importance of dynamic feedback from playing a violin.

Nevertheless, Don showed us the incontrovertible scientific evidence.

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12 hours ago, Ethan Ford Heath said:

Can we please hear more about this? It is such an intriguing statement, yet it seems difficult (for me, at this point) to get much clarity about it.

Go down the list of just the prominent Cremonese makers for starters. 

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