ctanzio

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About ctanzio

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  1. I no longer have a cat. I tried using the dog, but he saw what happened to the cat and stays out of the workshop.
  2. This is a great thread and really shows MN at its best: basic, critical skills being shared by people with years of experience. I used to use the hair method until I sliced off a substantial strip of skin while distracted. >ouch< A piece of scrap wood now serves the same purpose. If the chisel cuts as described by Nathan, it is sharp enough.
  3. Yep. Your #4 should have been my #1. >grin<
  4. Radiation ratio (RR) is a concept to maximize the average displacement of a thin, flat, infinite isotropic board for a given "modal density". That is a lot of assumptions which may or may not be relevant to the violin. There are at least three effects that can render the rule "maximize the radiation ratio", irrelevant. 1. RR is a factor in the average modal density of a plate. Because damping in spruce plates varies significantly with frequency, changes in mode frequencies can result in higher overall damping which can offset the theoretical increase in plate displacement. 2. RR is a factor in the interaction of the plate with the strings. This interaction can be modeled using the concept of "impedance". A large difference between the impedance of the string and plate, and the violin is unresponsive to the bow. If they match too closely, one may loose the ability to color the tone. 3. RR is a factor in the interaction of the plate with the air which can also be modeled using impedance. It does not help to increase the average displacement of the plate if a significant portion of the sound energy is not efficiently propagated outward from the violin. If the goal is to maximize average plate displacement, one would want to maximize 1/(C x D xH^2), where C is the sound speed, D is the volume density, and H is the plate thickness. The problem here is that as C and H are made smaller, the structural integrity of the plate becomes compromised by the string forces. If the goal is to maximize responsiveness of the violin to the bow, then one must find an "ideal" impedance, Z = C x D, that allows quick response without killing the ability to create tonal variations. If the goal is to maximize the transmission of the violin energy out to the audience, then matching the impedance, Z = C x D, to the impedance of air becomes the major concern. Here is the challenge of modern science: it can objectively determine what is "good" only after we know what "good" looks (or sounds) like.
  5. I thought we were talking about computers and AI. A neural net based program, without the aid of opening game playbooks, end game databases or any sort of human heuristic rules, can go from rank beginner to beating Grand Masters in a matter of hours by simply playing games against itself. The famous Alpha Zero program uses the word Zero in its title because that is how much human input it had into developing its play strategy.
  6. There is a considerable difference between AI that learns chess and AI that could learn "violin arching". Chess has well defined rules and unambiguous goals: checkmate or stalemate. Once the rules and goals are in place, you have a few different AI approaches to "solving" the problem. For violin arching, what exactly are the rules and goals? Without that, no amount of data fed to an AI program will get you anything. It will just stare blankly at your violins. >grin< The great thing about science is that it can objectively evaluate any problem, but only after the rules and goals are defined. And for things like violin arching, that can be very subjective.
  7. Not sure why you chose the entire population of a country. If one is not exposed to the virus, it is highly unlikely one would die from the virus. >grin<
  8. According to the CDC, since 2010, the number of people who get the flu EACH YEAR in the United States measures in the tens of millions. The number of people in the U.S. who die EACH YEAR from flu-induced complications measures in the tens of thousands. The death rate is more or less around 0.1%. Now that the medical profession has more information on the cause and treatment of the corona virus, the death rate for that virus has dropped to under 1%. Wash your hands. Do not suck on your fingers. Get a flu shot.
  9. ctanzio

    Wolf Tones

    Two of the strongest modes in a violin are the A0 (air mode) and the B1+ (a corpus mode that is also strongly linked to fingerboard vibration). When you play a node close to the frequencies of these modes, the vibration of the string and bridge may not be strong enough to consistently drive these natural modes at the string frequency. The result is the chatter or howling associated with a "wolf tone", or in more mild cases an ugly, raspy sound. It just so happens these frequencies are around C4 on the G string and C5 on the A string or higher up the G string. Adjusting the sound post also shifts the location of the plate node points. This can strengthen or weaken the ability of the string and bridge to drive strong modes to the played note frequency. But a more successful strategy seems to be to add a dampener tuned to the natural frequency of the strong violin mode. Your other issues are most likely due to other causes. Frequently, especially in the case of the violin, it is wrong to assume there is one cause to all the tonal problems. This seems to lead to the notion that one need only find that single, magical sound post location to solve all the instrument's ills.
  10. ctanzio

    Wolf Tones

    What is your definition of a "wolf tone"?
  11. I am partial to reddish brown varnish. I like the restrained use of shading. There seems to be a tendency to go overboard on antiquing. Thanks for sharing.
  12. Weigh the current bridge and cut a new one that is a bit heavier. Resonance is usually considered a good thing. Does it really make the violin sound bad, or are you objecting to it simply because it is different that your other violin?
  13. Wood exhibits a phenomenon known as creep deformation. Something as innocuous as normal humidity cycling can induce enough local stress to cause the two halves of the plate to "creep" in opposite directions if the grain is not oriented in the same direction on both plates. From the pictures, it appears as if the grain is diverging significantly along the area that separated. It is frequently possible to recover some of the creep by stressing the joint in the opposite direction of separation. If it is going to occur, most of the creep recovery will occur within 1 to 5 days of constant stress. Raising the local humidity will also aid in the creep recovery, but as Jacob mentioned, considerable caution must be exercised. I would suggest using Jacob's method to clamp the joint closed, first without glue, and let it sit like that for a few days. It might help to hang it in your bathroom so it gets a bit of humidity cycling whenever you take a shower. Unclamp it and see if the joint separation as gotten smaller.
  14. 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.
  15. Yet another demonstration that with professional playing skills and plenty of vibrato, even a bowling ball can sound decent.