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ctanzio

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  1. A "mode of vibration" is a specific deformed shape of a structure that repeats with a specific frequency. A drum Batter, a banjo Head and a violin Belly all have multiple, independent vibration modes depending on geometry and boundary conditions. The technical use of the words "overtone" and "harmonic" in physics means one of a series of vibration modes that are each an integer multiple of a base mode frequency. The words are interchangeable and mean the same thing. For a violin string, it can be demonstrated, both theoretically and experimentally, that the vibration modes form a harmonic series (or overtone series if you prefer). In casual conversation, the word overtone is sometimes used to refer to any mode with a frequency higher than the lowest modal frequency of the structure. Not a problem. Just be sure to explain how you are using it and be aware of the confusion it might cause. In the response spectrum of a violin, I can notice mode peaks at spots that suggest the lowest body modes, CBR, B1- and B1+, might have additional modes that form a harmonic series. But the amplitudes drop off rapidly and probably are not worth worrying about. The lowest air mode, A0, is caused by Helmholtz resonance. I would not be surprised to find that the air vibration might exhibit harmonic modes, but I am not sure and have no interest in researching the matter. The A1 mode, which is a standing wave along the length of the violin cavity, does have overtones. Are they significant? >shrug< I do not understand the phrase "ensuring the entire assembly resonates as a unit" when referring to a violin. In the case of a drum, the Batten and Resonator are specifically tuned to match the air mode of the shell, or very close to it depending on the effect one is trying to achieve. In the case of the violin, I am unaware of anyone attempting to get a body mode that matches the air mode. And it they were, it would soon become meaningless as notes in the upper register of the violin are played. In terms of tap tones: a little internet investigation and Maestronet searches should reveal comparisons between million dollar Strads and violins of more modest achievements. Not much difference in tap tones, but a world of difference in performance.
  2. Yes. In the case of the drum, banging on it imparts energy across a broad, more or less continuous range of frequencies. Since the strongest resonance of the Batter and Resonant match that of the air mode, that is the note that sounds the loudest. In the case of the banjo, each note being played imparts energy in very specific way: a frequency spectrum that consists of a base frequency and its overtones (integer multiples of the base frequency), quite unlike the banging of a drum. Same for sounding a note on a violin. The sound you hear is the base and overtone spectrum of the vibrating string filtered by the natural modes of the banjo head/resonator and air cavity, just like a violin. In the case of a banjo, you can easily adjust the tension of the head. When you tighten it, you shift the natural mode frequencies into higher values, making it sound more "brilliant", but the relative shape of the response peaks remains roughly the same. For a violin, things like pre-tensioning the bass bar, using variable rib heights to tension the belly, and installing a tight sound post all do something similar, but the effects can probably be mimicked, more or less, by changes in arching and belly thickness. Which is probably why the above things are not commonly done, since they stress an already thin structure.
  3. Thank you for sharing your experience as a new maker. Some ramblings on your recent ramble... The Batter and Resonant heads mimic the function of the violin belly/back. Like the violin, they have a range of natural modes of vibration. The drum shell and its enclosed air has a fundamental mode of vibration, just like the air enclosed in a violin. Let's adopt a term used in the violin world and call it the Air Mode, sometimes referred to as A0. There are overtones that are, more or less, integer multiples of A0. Tuning a drum is mostly getting the frequency of the fundamental mode of the Batter and Resonant to match the frequency of the air mode. Slight adjustments away from this add the color to the tone of the drum as you mentioned. Basically, a drum need only amplify ONE note, the note corresponding to the Air mode. The extent to which it can amplify other Batter/Resonant modes will drop off rapidly the further the frequency of those modes are from the A0 frequency. In the case of the violin, it must be able to amplify notes across multiple octaves. The violin Air mode frequency is around C#4, in the first octave played on the violin. As note frequencies get further away from this, the amplification due to the air mode rapidly drops off. This is why the ability of the violin plates to resonate strongly over a range of frequencies is so important. The tap tone approach, that focuses on a few of the lowest resonances of the violin plate, seems to give inconsistent results because it does not directly address the need to resonate at higher frequencies. Arching certainly affects the resonate frequencies of the plates, but it also serves an important structural function: resist the bending load caused by the strings tugging on the scroll at one end, and the end pin on the other. A flat belly/back would probably result in some serious deformation as the strings are tensioned. An instrument with a mostly flat top, like the guitar, does not experience these large bending loads because the strings run mostly parallel to the top with little offset to create a bending load.
  4. Little Wing is a wonderful fusion of jazz, rock and blues riffs with varying tempos weaved in, which might explain why it has been covered by so many great rock guitarist like Eric Clapton and Stevie Ray Vaughn. It also has a compelling voice part. It would be interesting to hear a classical take on those riffs, but I can barely recognize the basic theme in the Nigel Kennedy performances. What I heard was an excuse to power up an electric violin and play a series of disconnected cadenzas that may or may not have been based on Hendrix's version. I can understand the concern of a sponsor of classical music performances. If Nigel Kennedy honestly feels like ClassicFM is violating some sacred principle of diversity, inclusion and equity in classical music, then I apologize for the implications of my post. In that case, he might want to take a sober listen to his performance, and then use a little human empathy to see if he can understand the position of the sponsor.
  5. Thanks for the info. I have tried making the ridge lines lighter by rubbing with fine compound to get a more "worn edge" look, but I could never get a look that I liked. Scraping to get a more pronounced accent, sort of like inking the ridges but in reverse, is a nice look. On your question about preferred viola size, speaking strictly as a casual viola player... My arm span from finger tip to finger tip is 5'11". I currently play a 15-1/2" viola which I can easily handle without a shoulder or chin rest. It has a pleasant, although somewhat quiet, overall tone, but the C string takes a lot of work to get it to sound. I have played a 15-3/4" viola which was also comfortable with a shoulder rest. If I found one whose bow response and tone I liked, I would use it. I did not like a 16" viola at all in first position. I had to contort my average sized hands to reach the notes. I guess if I played from higher positions I could make it work. But since my preferred instrument is the violin, I will leave such struggles to the professionals or those with outrageous finger spans.
  6. Nigel Kennedy has world-class technique and musicality. That makes him no different than any number of world-class players. Nigel Kennedy has a quirky stage presence going back at least 30 years. That sets him apart from most of the world-class players who prefer to make the music the star of the show. I admit I am no mind-reader, but the cynical side of me asks why would one think his outrage is anything more than a marketing ploy? The people paying the bill should have some say in what is played.
  7. Lovely. Interesting how the ridge lines (edges) come out lighter. Do you do something deliberate to get that effect, or is it just a natural outcome from the varnish and how you apply it?
  8. Pure potassium silicate in crystalline form is colorless. But when ground into a powder, it will appear white because the irregular surfaces of the powder grains will scatter light. But this silicate also has a refractive index of 1.5+, about the same as wood, linseed oil and resin based oil varnishes. So when these varnishes are applied to the white powder, it will stop scattering the light and the texture and color of the wood will reappear. If varnishes are penetrating into the wood after you applied this ground, then you most likely used too much oil and/or not enough silicate. You want just enough oil to make a very thick paste so you can evenly spread the thinnest of layers of the silicate onto the wood. Once it dries, it should be clear unless you did not use enough oil to cover all the powder grains. Besides the challenge of getting the right amount of oil to silicate powder, there is also the challenge of getting the grain size fine enough to penetrate the openings in the wood grain. Mineral ground that simply sits on the surface of the wood can have adhesion problems. Additional layers of varnish may fracture or peel off. A downside to this silicate is that it is highly soluble in water. Anything applied to wood that also reacts with water is asking for trouble in humid conditions. But it also supplies another option for applying it. Create a clear, near saturated solution of the silicate in water. Now gently dab the solution onto the wood and let it dry between additional coats. You can finish by gently rubbing the surface to get a uniform white coat. This will guarantee that the silicate will penetrate into the wood grain and thoroughly seal it. Now apply oil varnish as usual to restore the transparency. Be aware that water-based ground applied this way can cause the grain to swell in visually undesirable ways. The challenge with pumice as a mineral ground is that it is a mixture of different colored minerals. It is normally not transparent. So when applied to wood as a fine powder, you are essentially coloring the wood, which means grain detail can be obscured. If you can grind it into a very fine powder, and only apply enough to penetrate into the wood pores without sitting atop the wood itself, you can both seal the wood and perhaps introduce an interesting colored pattern into the wood.
  9. Speculations that taint reputations without some reasonable evidence to back the claims are best avoided or else the Fora itself becomes suspect. That said.... The Dark Reality Behind America’s Greatest Thrift Store Empire | by Alice Minium | Medium Just a starting point for inquiring minds. I would have thought they would simply hang the violin at the local thrift shop. But if one wanted to maximize profits on the sale of free goods, hard to argue with unsupervised auctions over the internet.
  10. The qualitative categories need to have some numerical scale associated with them, like bad=0, good=1, awesome=2, for a computer to generate a scaled output. There is also the question of the inputs. There would have to be a standard way to test each violin that would give you confidence that you are capturing the parameters you think might indicate a violin's performance. Moreover, you don't just play into a microphone and expect the computer to make some sort of sense of it. You would need to give it some way of assessing the sound capture, like breaking it down into a response spectrum and extracting stuff like response peaks, relative strength of the peaks, density of peaks per octave, and maybe a dozen other things I can think of off the top of my head that may or may not be relevant to the sound and playability of a violin. AI that reproduces human adaptability to problems that occur during certain tasks doesn't need a neural net. It is a bit of a different AI problem. Classic examples I worked on years ago from the infancy of AI is teaching a computer how to be a medical expert in blood diseases, or diagnose problems with a fleet of diesel locomotives. The computer programs can accept and organize knowledge from human experts in the form of data points (object, property, value), to assemble and traverse decision trees to guide further testing and assess possible treatments/repairs. They are known as "heuristic" AI algorithms because, in a very real sense, the computers can learn by observing, like humans. Modern versions of these programs now have sophisticated interfaces that let computers gather the data points and do further testing without human intervention, but they still require human experts to train them, or at least spell out clearly defined goals that are quantified in some way. I once had an airplane flight instructor teach one of these heuristic learning programs how to help an inexperienced pilot to land a plane. After a couple of hours of "talking" to the computer using a natural language text interface, he was amazed at just how good the program became at talking someone into landing a plane in real time. We never actually used the program to actually help someone to land a real plane, as it was just a proof-of-concept of the program. The point is one needs clearly defined inputs and goals, all quantifiable in someway, even if it is just probabilities.
  11. AI is a catchall term for any computer algorithm that mimics some aspect of human thinking. It need not be a neural network. The work presented in the Strad article was covered previously on this forum. Here is the thing with neural net algorithms: you have to "teach" the net by changing an input and telling it what it should predict. It then compares what it predicted to what it should have predicted and then adjusts the "weight" it places on its inputs. You have to do this for a lot of different inputs and be able to measure the actual "result" it should predict for each of these cases. Technically, the authors used a neural net to develop a multi-dimensional curve fit of geometry parameters to measured modes. There is nothing really "intelligent" about this approach. It is more a computationally efficient algorithm for handling many inputs, or a small number of inputs with a range of values, to predict a limited number of results. The real question is the following: Is there something one can quantitatively measure that is an indicator of superior violin performance, like tone, bow response and projection. From many threads on this forum, it does not seem like mode predictions will fulfill that requirement.
  12. I agree with your observations about the effect of damping on transient response and decay after lifting the bow. But this doesn't address the idea of low damping giving a louder or more ringing response. Here is something to keep in mind: linear damping is energy loss per cycle of vibration. The vibrating wood is converting a percentage of its energy into heat with each cycle. For a given amount of bow work, a low damped violin will build up sound output to a higher level than a high damped violin. And once the bow is lifted, a low damped violin will vibrate longer and louder than a high damped violin. I cannot comment on your anecdotal story about tapping a Strad. If someone likes the tone of a violin with high damping, they can always bow harder to get a louder sound.
  13. You open the top, tilt back the neck, add a strip of wood, glue the top back, and think a 1 degree change in string angle is more significant than the surgery you just performed on the violin? Can you see why people may be skeptical that you "only changed the string angle"?
  14. How did you change the string angle without changing the bridge height or bridge position? How did you excite the spectrum? Bowing across all the strings using gliss? Tapping the side of the bridge? For a 1 degree change in string angle, you got a rather significant change in dB output. How did you measure that? At a specific frequency from the plot?
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