Light weight fiddle

[Roger Frankland]

Don, I am surprised to see so much variation in the tap frequency among expertly made fiddles, including the Strads. With all due respect, it makes me wonder if the data is flawed. I've found that my M5 measurements are repeatable to within a few hertz. However, I've also seen shifts of up to 50 hertz as a result of cutting f holes and barring. Perhaps there is also 10 to 15 hertz variation due to patching and repairs, I don't really know. And some more variation due to varnishing and final trim, although trimming the outside edges of a plate has very little effect on M5, whereas radii and center mass are all important.

If there really is this much variation in tap frequency among high quality fiddles then the builder rule to carefully set the tap tone is not a very good rule. Hmmm. What do you think about that?

[uncle duke]

Some pieces need that kind of analysis attention and some just ring so true that none may be necessary.  But I learned mostly from Don, Marty and Peter, so you can say I'm a follower of those guys.

[Roger Frankland]

Some pieces need that kind of analysis attention and some just ring so true that none may be necessary.  But I learned mostly from Don, Marty and Peter, so you can say I'm a follower of those guys.

So maybe you are right. If so, I got really lucky on my last build...which is currently getting varnished after testing it in the white.

[Don Noon]

If there really is this much variation in tap frequency among high quality fiddles then the builder rule to carefully set the tap tone is not a very good rule. Hmmm. What do you think about that?

 

I think that taptones (and weight) are convenient guides to get plate stiffness into an approximate zone.  Precision is pointless, for a number of reasons.

There are makers who do very good, consistent work who do not use taptones... they just flex the plate by hand to tell when it's thin enough.  How precise can that be? (correct answer = "not very, but good enough")

[Roger Frankland]

I think that taptones (and weight) are convenient guides to get plate stiffness into an approximate zone.  Precision is pointless, for a number of reasons.

There are makers who do very good, consistent work who do not use taptones... they just flex the plate by hand to tell when it's thin enough.  How precise can that be? (correct answer = "not very, but good enough")

I am getting a headache. I make 6 fiddles where I stretch the rules and they are junk. I make a 7th where I precisely follow the rules and it is glorious. Then I find out that the rules don't matter.....

[uncle duke]

Let's start with a 15.5 - 15.7 belly arch height on the next one.  Did you go back and change any bass bar heights after the mis-calculation episode?

[uncle duke]

More specifically, one of the traditional steps in plate carving is to tune them to an M5 of 350 hertz. (Ref: Strobel. "Violin Making, step by Step"). If one takes wood off from there M5 goes down and the resultant tuning gets skewed. I thought I could find a way around it but I failed. Now, 350 hertz is a religion for me, and that puts the brakes on major weight reduction. That being said, I think you must have a several graphs, Don, showing plate weight as a function of material properties ... presumably all carved to 350 hertz.

This may not help but other times you must know when to stop.  Marty had a colorful red, blue and green graphed out plate dagram.  He may of patterned that after something Curtin did.  On some plates the pattern/mode removal suggestion doesn't work like you'd think.  You can remove wood without noticeable changes.  Other times you will not believe the change that can be made following his method, I really saw one of my plates make a transformation for the better by scraping in certain mode areas to adjust sound without dsturbing the other mode.  It will catch your eye before your ears.  I made sure I was careful there.  The problem herein is that I was doing 6 violin builds at the same time.  I did not keep track of the plates that the graph worked on- no, I was in a hurry to get things together.  I can't remember if changes were noticable before f-hole cuts or after but I think it was before f holes.  It could of been the backs that were responding, I'm not sure.  Sorry for the confusion. 

[Roger Frankland]

Let's start with a 15.5 - 15.7 belly arch height on the next one.  Did you go back and change any bass bar heights after the mis-calculation episode?

Arch height - check

Bass bar height - adjusted until tap tone returned to 350 htz.

[Roger Frankland]

This may not help but other times you must know when to stop.  Marty had a colorful red, blue and green graphed out plate dagram.  He may of patterned that after something Curtin did.  On some plates the pattern/mode removal suggestion doesn't work like you'd think.  You can remove wood without noticeable changes.  Other times you will not believe the change that can be made following his method, I really saw one of my plates make a transformation for the better by scraping in certain mode areas to adjust sound without dsturbing the other mode.  It will catch your eye before your ears.  I made sure I was careful there.  The problem herein is that I was doing 6 violin builds at the same time.  I did not keep track of the plates that the graph worked on- no, I was in a hurry to get things together.  I can't remember if changes were noticable before f-hole cuts or after but I think it was before f holes.  It could of been the backs that were responding, I'm not sure.  Sorry for the confusion.

Good stuff, thanks. For the last year, I have been focused on getting the B1 + / - modes working right. On a scale of 10, they're a 10 to me. My theory is if one gets all the outside plate dimensions right first, M5 tap tuning works to compensate for different wood properties to achieve the desired stiffness to mass ratio and hence the proper fundamental body modes (Dons scattergram of M5s sort of blows my mind though). Matching a maple back to a spruce top probably adds color but I have not proven that (I know it works on other stringed instruments). I also believe that anything that can be done to reduce mass without effecting stiffness will help response and ringing because fundamentally mass acts as a damper.... Still haven't proven that either, but I hope to on my next build. Past that everything is way above my pay grade.... A good set of B1 modes takes care of the low end fiddle tones for me. The high end tones and unwanted harmonics are all the result of string vibrations which have to pass through the bridge and can best be controlled by bridge tuning.... Like whether you want a solo fiddle or just want to fit in with the group. I agree there are a bunch of tricks and secrets that help achieve all this and that is what makes it such an exciting art. Chapter 2 would be about setup, appearance, balance, and how to play double stops.

[Don Noon]

You might want to wrap your head in compression bandages...

 

Almost everything seems to work, although I think if you have B1+ over 570 Hz that might be too stiff, and below 510 Hz might be too wimpy.  That leaves a huge zone of being OK, and the actual goodness of the tone depends more on what happens above the B modes.

 

I don't put much attention into B mode frequencies, although I do look at shapes and amplitudes a bit.  The frequencies just seem to automatically come out within the OK range, and I depend on playing it to decide if it's too stiff or not.

 

[Roger Frankland]

You might want to wrap your head in compression bandages...

B frequencies.jpg

Almost everything seems to work, although I think if you have B1+ over 570 Hz that might be too stiff, and below 510 Hz might be too wimpy. That leaves a huge zone of being OK, and the actual goodness of the tone depends more on what happens above the B modes.

I don't put much attention into B mode frequencies, although I do look at shapes and amplitudes a bit. The frequencies just seem to automatically come out within the OK range, and I depend on playing it to decide if it's too stiff or not.

I actually like that graph.

[Roger Frankland]

You might want to wrap your head in compression bandages...

B frequencies.jpg

 

Almost everything seems to work, although I think if you have B1+ over 570 Hz that might be too stiff, and below 510 Hz might be too wimpy.  That leaves a huge zone of being OK, and the actual goodness of the tone depends more on what happens above the B modes.

 

I don't put much attention into B mode frequencies, although I do look at shapes and amplitudes a bit.  The frequencies just seem to automatically come out within the OK range, and I depend on playing it to decide if it's too stiff or not.

I was looking again at the Strad 3d videos of B1+ and B1- What I see are fundamental vibrations in the long axis of the fiddle - which makes sense realizing the frequencies involved. What I also see are large deflections at the edges of the fiddle. I realize that the deflections are very small, but the videos suggest that the fiddle ribs are bending perpendicular to their width. That is hard for me to believe understanding how stiff the ribs are in that axis. Could it be that is a measurement artifact? That the ribs don't move but the top does - close to the channel but not actually at the ribs. If so, that would explain why a thin channel has such a large effect on sound.

[Don Noon]

There's a file showing the isolated movement of the rib, and most of the movement looks like you'd expect from a squiggly piece of thin wood... twisting and bending, but not so much bending in the vertical plane.  You can still get plate edge deflections that way.

 

I also think there's some amount of artifacts too.  Plate index points might not really be near the edges, and just shown that way.  But still, the rib does move... quite a lot in the lower body modes, but not much once you get over 1 kHz or so.

[Roger Frankland]

There's a file showing the isolated movement of the rib, and most of the movement looks like you'd expect from a squiggly piece of thin wood... twisting and bending, but not so much bending in the vertical plane.  You can still get plate edge deflections that way.

 

I also think there's some amount of artifacts too.  Plate index points might not really be near the edges, and just shown that way.  But still, the rib does move... quite a lot in the lower body modes, but not much once you get over 1 kHz or so.

Thanks, that would explain it. My second thought is that it is a little hard for me to understand why there are two quite similar resonances, (B1 + and B1 - ), at close to the same frequency, in the closely coupled top and bottom plate system. I do realize that one resonance may be fueled by the heavy bottom plate, whereas the other by the lighter top plate. But if they were tightly coupled, it seems to me intuitively that only one resonance should exist. My thinking is reinforced by an early fiddle I built that displayed only one of the modes. Can you shed any light on that? Perhaps the truth is that it is not necessarily a tightly coupled system. Perhaps the truth is it happens all the time and I am just not thinking straight. But then, why just two, why not three sometimes?

[Don Noon]

The B modes are just the most obvious structural modes, but there are a few other low modes around that don't get much attention.  If you look at the Titian response plot, for example, there are not just 2 big clean peaks, but they have smaller peaks and dips superimposed on them, or nearby.  B- and B+ get the attention, though, and they are characterized by crossgrain flexing in one plate and longitudinal flexing in the opposite plate.  So you get a pair of them.  The other nearby modes are much weaker.

 

I have seen a few examples where there appears to be just one mode.  I expect the pair still exists, but one dominates in amplitude, and the frequencies might be close together so that no distinct pair of peaks appear (I measured an Amati that just had one peak, as well as a Strad).  I know Collin Gough has been studying these modes for a long time, and his knowledge is far beyond mine.

[Roger Frankland]

The B modes are just the most obvious structural modes, but there are a few other low modes around that don't get much attention.  If you look at the Titian response plot, for example, there are not just 2 big clean peaks, but they have smaller peaks and dips superimposed on them, or nearby.  B- and B+ get the attention, though, and they are characterized by crossgrain flexing in one plate and longitudinal flexing in the opposite plate.  So you get a pair of them.  The other nearby modes are much weaker.

 

I have seen a few examples where there appears to be just one mode.  I expect the pair still exists, but one dominates in amplitude, and the frequencies might be close together so that no distinct pair of peaks appear (I measured an Amati that just had one peak, as well as a Strad).  I know Collin Gough has been studying these modes for a long time, and his knowledge is far beyond mine.

 

again, thanks.  makes more sense now.

[Roger Frankland]

Now that I have gained all this new knowledge (thanks everyone), I am planning to try again. Slightly more restricted goal. A fiddle that really rings while maintaining traditional tone. A side result is that it will probably be somewhat lighter and louder! I think I can improve my odds of success by first carving up, comparing and carefully measuring some plates with different wood properties. So the question, folks, is what should I do differently to create a fiddle that rings twice as long as your average fiddle? By the way, electronic gadgetry and stone cathedrals are not options.

[Roger Frankland]

Oh. The headache has gone away!

[uncle duke]

 So the question, folks, is what should I do differently to create a fiddle that rings twice as long as your average fiddle?

 

The best bet may be the use of European tonewood.

[Roger Frankland]

The best bet may be the use of European tonewood.

Well I agree only if it entails actually going there and smelling the roses.

[Roger Frankland]

The best bet may be the use of European tonewood.

Well I agree only if it entails actually going there and smelling the roses.

[Roger Frankland]

As a result of some expert help, I am learning that tapping fiddles to discover their signature modes is very exacting... like just about everything else involving fiddles. Here is my improved measurement of B1 modes I made this morning while waiting for varnish to dry. Remember the old adage "measure twice, cut once"?

[uncle duke]

Is it normal for the E note to bottom out like that?

[Roger Frankland]

Is it normal for the E note to bottom out like that?

I don't know what is normal. Perhaps the dip is because the lower frequency B1+ resonance was very strong thus 'robbing' sound from the 600 htz region. There was less of a dip at other spots on the back where the B1 response was not so high. Bear in mind that these signature resonances are all wood resonances. There were no strings on the fiddle when I did the test.

[Roger Frankland]

When an arched plate vibrates (deflects downward and then upward) it has to expand and then contract horizontally.... Or buckle or compress. Think about all of the things that can happen and in what order. It might suggest, for example, that thinning a plate somewhere would only make it pop somewhere else. This is really really complicated in my mind, much more so than those 3d videos suggest (in all due respect).