Light weight fiddle

[Roger Frankland]

Bridge tapping ...

[Roger Frankland]

One more time..

[Don Noon]

For hand-held, uncalibrated impact response, it's highly operator-dependent.  I have probably done it enough to get reasonably consistent results, but comparing results between different hitters is problematic.

 

But, trying to make something out of your plot, it looks like the main modes are incredibly low, with B1+ being the 485 peak.  Yet the "bridge hill" is very strong and broad.  If I had taken this spectrum, I would guess it would be from an extremely bright viola.

[Roger Frankland]

Hmm. I now have the worlds lightest viola!

I am a real novice with tap testing but, here goes, I absolutely agree that B1 +/ - are low.

Cause: I chased the belly M5 through the build and as Peter, in an earlier post, indicated would happen, it turned into M1- . He suggested 430 to 460 htz. I measured 433 - 435! I believe Don is also correct that B1+ is around 485. Cause for low values: belly was carved past optimal thickness ( M5 after cutting f holes was 261 hertz )!

Effect: ???

[Don Noon]

Effect: ???

 

A violin with some unusual characteristics.  Only the player can tell if the effect is good or not.

[Roger Frankland]

Well my goal is to sound like Alasdaire Fraser but somehow I don't think I'll make it with this fiddle ....

[Roger Frankland]

while waiting for varnish to dry I did some more testing to verify the drop off of the A string harmonics in final assembly.

a string harmonics.doc

[Roger Frankland]

I was checking around the e side c bout on one of my fiddles, looking for interactions and I found that stopping the f hole wing tip from vibrating reduced the harshness. Looking at the bowed spectrum, the A5 harmonic of the bowed open A rose 5-6 db and several peaks above 2000 hertz dropped out. A5 is 880 hertz, right in the valley. Well anyhow, it was interesting to me how a low frequency resonance can be sacrificed by a high frequency one.

[Roger Frankland]

Well what is done is done.

Tone - best I've done. Thanks for the help everyone.

Playability - I need to practice more.

Looks - Not good. I do not recommend aspen backs.

Weight - 322.5 grams ready to play.

I have definitely solved the problem of a tubby, bassy sound when going light. This fiddle has the most even sound across the strings of any that I've made! As a consequence, I really believe there is a sweet spot for a 300 gram fiddle, just have to find it! Whether all the overtones are where they should be is above my pay grade, but there are no glaring problems, wolves or rattles. Everything I build improves over the first year - linseed oil ground and oil varnish and many adjustments. I also have that psychological problem that everything I make sounds better after 15 minutes of playing. I plan to let this rest for a while and then find a pro to play it.

[Roger Frankland]

Weight 322.5 grams

Belly 60

Back 60

Sides 34

Neck / fingerboard 98

Accessories 70

.

[Don Noon]

I'm glad it turned out OK.  Hope you had some fun with it; it has been interesting to see it come together.

[Roger Frankland]

I have received some really killer spruce from Simeon Chambers. Clear with perfectly even grain, .325 SG and stiffness of E= 10000 MPa. onward to my next project. I have edited my first post to summarize my work to date. Anybody know how to delete meaningless posts which don't add to the story or do I have to write a book when I'm done.

[Roger Frankland]

I'm still fussing over high frequency response "problems" .... Like at 600 hertz and higher. Nothing really makes sense to me.

I mean we are talking about wavelengths measured in meters...

I wonder if sound through "wood" varies with frequency. My only reference is water. There the high frequencies get attenuated a little faster, I think. But I'll bet we are still talking meters or maybe kilometers.

And then we have terminations and interfaces to consider. But they are all wood! I think all they might do is rattle if they are not good...

The other thing is geometry and resonance. On one side we have this lovely bass bar, on the other, a tall post.... But now we are talking millimeters.

I realize the physics is impossible, but isn't there something we know for sure? Or some things we should rule out? The sound coming off the back of my fiddle is a lot different than the sound coming off the front.

[Don Noon]

I realize the physics is impossible, but isn't there something we know for sure?

 

Although I haven't tried it, for sure a violin made of 5mm thick lead will not make much sound.  Some of the more oddball theories in the "secrets of Strad" thread I'm also sure are bogus, although there are some who believe otherwise.

 

As for what works, and how it works... you have just begun to scratch the surface of how complex it all is.  I too have been mostly concerned about the higher frequencies for the last few years, and have nothing of great certainty to say about it.

[Roger Frankland]

Well tap tones are out and stiffness over mass is in! Now how to measure it.

Theory 327: Every point on a sounding surface should stay within it's elastic limits when vibrating. Any movements beyond that point will lead to distorted sound. This is especially important at higher frequencies where the human ear is most sensitive. This is why old singers don't sound so good but old fiddles do. And why Steinway pianos sound so good .... Tight joints, select spruce, curved, graduated, preloaded sound boards.

Theory 328: volume is inversely proportional to mass to some power. Mass acts to damp vibrations. This is most easily seem when adding a mute to a bridge. Higher frequencies are very susceptible to this effect. Theory 328 works in conjunction with theory 327.

Theory 329: Good overtones called harmonics are vital to a pleasing sound. A sound without overtones lacks punch. The reason for the development of harmonics is not understood but it maybe due to discontinuities in a sounding surface. Theory 329 works in opposition to theory 327.

Theory 330: a pretty, light, and sensually shaped violin will sound better because it appeals to the senses. This effect is independent of theories 327, 328, and 329.

[Roger Frankland]

What to do. I've started carving my next set of plates and I'm trying to decide when to stop carving. I've decided to go thicker on both the front and back plates which is tantamount to giving up on my light weight goal. Here is how I got to this decision.

My last fiddle, number 5 in this project, had a 60 gram front and back, very high but round arching, plates on the thin side of spec. In spite of the careful and high arching, the signature modes are all low as measured using the 4 step impact test sequence outlined by D. Noon on the Schmidt web site.

A0 = 245 to 247 hertz

B1- = 337 to 339 hertz

B1+ = 424 to 431 hertz

CRB = 385 hertz

Conclusion: 1. The only thing I am sure of is that A0 is low because of the additional air volume created by the high arching. This could probably be compensated for with lower rib heights and unknown effects. 2. I am totally unsure whether the low signature modes lead to a tonal problem. This fiddle has a very even response across the scale but lacks punch a especially at the high end. But I need to do something.

[Roger Frankland]

My fiddle was hissing and very sensitive to rosin buildup, so I decided to attack the bridge. The way I went about it was maybe a little unique. I cut out a sliver of wood and attached it to the back edge of the bridge with sticky back tape. Too much. So I cut off a little wood and reattached it. By trial and error I was able to tune the bridge where I wanted it ... Just to the point of hissing extinction...

Well, the sliver of wood is still on the bridge. I suppose I could glue it in place or make another bridge to my new "spec".

[curious1]

What to do. I've started carving my next set of plates and I'm trying to decide when to stop carving. I've decided to go thicker on both the front and back plates which is tantamount to giving up on my light weight goal. Here is how I got to this decision.

My last fiddle, number 5 in this project, had a 60 gram front and back, very high but round arching, plates on the thin side of spec. In spite of the careful and high arching, the signature modes are all low as measured using the 4 step impact test sequence outlined by D. Noon on the Schmidt web site.

A0 = 245 to 247 hertz

B1- = 337 to 339 hertz

B1+ = 424 to 431 hertz

CRB = 385 hertz

image.jpg

Conclusion: 1. The only thing I am sure of is that A0 is low because of the additional air volume created by the high arching. This could probably be compensated for with lower rib heights and unknown effects. 2. I am totally unsure whether the low signature modes lead to a tonal problem. This fiddle has a very even response across the scale but lacks punch a especially at the high end. But I need to do something.

If you didn't tell it was a violin I'd swear it was a viola.

[Don Noon]

If you didn't tell it was a violin I'd swear it was a viola.

All except for the CBR mode, which is a bit high for a viola, I think.

 

I don't think the low A0 is due to the volume so much, but more likely due to the very flexible plates.

[Roger Frankland]

All except for the CBR mode, which is a bit high for a viola, I think.

 

I don't think the low A0 is due to the volume so much, but more likely due to the very flexible plates.

I think you are right. I estimate the high arching led to a 5% increase in volume! That is not enough to account for the change in frequency assuming frequency is inversely proportional to the square root of the volume.

[Roger Frankland]

I finished carving a new maple back plate. This time I followed the rules and the arching and graduations are where they are supposed to be. Unfortunately M5 ended up low, at 299 hertz.

Because I'm hoping the back will contribute to achieving a swirling extended sound in the finished instrument, I decided to measure Q. I am getting much better at this measurement. But I measured only 5.2 cycles to the 50% point which calculates to a Q of 23.7 +/- 4.

Because the value seems low, I measured an old discarded very light "wooly" back and it's Q measures 60% higher! This is very perplexing. The new back sounds better to my ear, probably because it rings cleaner and higher. I have no idea what will work better.

[Roger Frankland]

Theory 331: A very pleasing effect can occur when the fiddle acts like a minor echo chamber and slight but controlled echos of the played tones are created as a result of sounds bouncing around for a little while before they are readmitted from the instrument. Our sophisticated spectrum analyzes are not capable of detecting this effect, but our ears can - which, in the case of the player, are close by.

[Don Noon]

While I do agree that there can be a built-in reverb effect, I disagree with the source.  It is unlikely that the sound will be "bouncing around" inside the instrument, but rather the energy is stored up in other vibrating things... plate modes, open strings, tailpiece, etc., and it takes some time to dissipate this stored energy as sound.  If you're looking for this effect with a spectrum analyzer, that's probably the wrong tool to use, which is why you don't see it.  But I believe it can be found by examining a time trace of the signal.

[Roger Frankland]

Yes, the fiddle box is seemingly too small to be an echo chamber in the audio range.

First, I should make sure it was not a "near" string phenomena that I was hearing. I was playing a particularly "live" fiddle and it sounded like it had a subtle vibrato over a broad frequency range. I was doing a side by side test but I suppose the live fiddle could have been interacting more strongly with the room acoustics .... that, in itself, would be interesting.

I also like the stored energy idea but I'm thinking the energy would have to be released in intervals. If the resonance was near a bowed frequency, could a beat frequency be established? Sort of like a melodic wolf note. This seems somewhat tenuous.

How do I do a time trace analysis? Now I agree. This is getting much more complicated.

[Don Noon]

I also like the stored energy idea but I'm thinking the energy would have to be released in intervals. If the resonance was near a bowed frequency, could a beat frequency be established? Sort of like a melodic wolf note. This seems somewhat tenuous.

How do I do a time trace analysis? Now I agree. This is getting much more complicated.

 

The violin body is forced by the string to vibrate at the string's frequencies... the body does not just start ringing at whatever frequency it wants to.  So, no... there will not be a melodic wolf note.  Even with wolf notes, the body is still forced to follow the string frequency... but it complains about it by wiggling the bridge in an undesirable phase so the bow/string dynamics get messed up.

 

There's usually way too much going on at once to tell anything from bowed amplitude vs. time.  The little I have done in that area was by using a sine pulse input to the bridge via a voice coil driver, and then looking at the build-up and decay of the response.  Nothing to report of any significance... just that some notes ring longer than others.