ctanzio

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About ctanzio

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  1. To echo Don's observation: once the strings are tensioned, the frictional force on the ball joints combined with the very small movements of the plates would render the joints effectively rigid, so no different than a simple spruce post in that regard. Mass, vibrational modes, and the very slight offset at which the plate loads are applied to the post are the substantive difference between the Hamberger and a simple spruce post. Something to keep in mind: when a spruce post is slightly adjusted for position, it inherently necessitates a change in how much it stretches the plates apart, and how the ends interface with the plates. One cannot avoid this given the plate arching unless one painstakingly changes the end fit and post length to replicate the end fit and overall post load. But when these adjustable posts are moved, they essentially replicate the snug fit and post load of the previous position. Be careful that you are not comparing apples to oranges, so to speak, when conducting tests of spruce versus adjustable posts.
  2. Nice color. One way to think about a finish coat is as a protective coat to guard against wear and fading of the underlying colored varnish. Consider something that dries clear and hard in a thin coat and can be easily touched up and polished to a range of finishes, satin to gloss, to give yourself a lot of flexibility. If it provides some UV protection, that is a plus. You want a finish with a refractive index close to the colored varnish so maximize optical transparency. Although if the colored layer is very smooth, then a finish with a higher index can intensify the underlying colors. Rosin based oil varnishes and high quality shellacs can all be formulated to fit the above requirements. Like most things violin, you need to experiment with test samples first to figure out what works for you.
  3. Beautiful work. I love the scroll. Thanks for sharing.
  4. This stuff is about 75% solvents: ethanol and ethyl acetate. Although ethyl acetate occurs in small amounts in may foods and drinks, it is a highly volatile solvent and can induce a variety of adverse reactions in living creatures. In terms of French polish prep, the essential ingredients are the shellac and oil, in this case, linseed oil. There really is no reason not to use just ethanol as the solvent. Maybe 5% to 10% by weight of shellac to ethanol to replicate the formula. Linseed oil is slightly soluble in ethanol at room temperature. Start with an amount of high purity ethanol and weigh it. Then apportion about 5% of that weight of artist grade linseed oil. Add a little at a time and shake until no more will dissolve. Add your shellac and you are good to go. Typically what happens is the shellac dries very rapidly as the ethanol evaporates. The linseed oil remains liquid on the dried surface and is easily wiped off. Further applications of shellac compounds will make any remaining oil float to the top of the finish as the shellac hardens.
  5. Colin Gough's work is basically an impossible read for anyone without significant education and experience in physics and higher mathematics. However, a lot of those formulas can be simplified if one considers the constraints on violin geometry due to player requirements, and violin material due to tradition. For example, one finds that the core frequency of A0 (air mode) for violins, violas and cellos is mostly dictated by the length of the body. f(A0) ~= c/(4L) c = 343,000 mm/s L(4/4 violin) = 356mm, A0 = 241hz L(16in viola) = 406mm, A0 = 211hz L(4/4 cello) = 755mm, A0 = 114hz These base values are modified a bit by two main factors: the volume cavity and the area of the f-holes. Also, the flexibility of the plates play a factor but this is a complicated effect and can be harder to control. For a maker, changing the rib height or the bout widths can be used to adjust the A0 frequency. Bigger will lower the frequency. You can estimate the reductions as follows: If V1 is the volume of an existing model, then changing the volume to V2 will change the A0 frequency by a factor of: SquareRoot(V1/V2). Changing the f-hole area will increase the frequency. The effect is a little more involved but a similar estimate can be used: SquareRoot(A2/A1). Because plate mechanics are so complicated, it is not easy to extract simplified design rules for body modes like B1- using the theoretical equations in Gough's work.
  6. A0 and B1- are coupled by the way energy is input to the violin. The air in the cavity for the A0 mode needs to be "moved". This is done by the movement of the plates. The plates are moved by the bridge. So in effect, the energy input to the A0 mode is through the body modes, like B1-. If you excite A0 independently of the body by blowing across an f-hole, then the movement of the air will have a certain "shape" and "frequency". If you excite the B1- mode independently of the air mode by playing in a vacuum, then the movement of the body will have a certain "shape" and "frequency". When you play the violin in a normal atmosphere, the wo modes are now "coupled" as described above. You actually get two new modes, each of which is some combination of the independent A0 and B1- modes. The "shape" of each mode is some synchronized combination of independent air and body modes, as is the frequency of each new mode. If the modes are weakly coupled, then each of the new modes will strongly resemble one of the uncoupled modes. If the modes are strongly coupled, the new modes can look quite different than the original independent modes. Saying the "tail" of the B1- mode drives A0 is not an accurate way of looking at it. The mode shape of tail is no different than the mode shape at the peak. The difference is in the amplitude of the deformation. So for notes near A0 peak frequency, B1- contribution is not much, but what it is doing is being strongly amplified by A0. Similarly, at a note near the B1- peak, even though A0 may not be very resonant, it is offset by the larger volume of air B1- is moving.
  7. A mathematical "circuit" is created for the A0 effects and numerically simulated, i.e., as if there is no B1-. That is the "air" line in the diagram. A similar thing is done for the B1- effects. That is the "body" line. The two circuits are then coupled and the new circuit simulated. Because these are two complex, COUPLED motions acting simultaneously, there will be small time segments where the effects do cancel, and other time segments when they reinforce. For any driving frequency, the combined plot represents the TIME AVERAGE of these effects. Phase variations certainly enter into the results, especially at driving frequencies between the natural frequencies of the two modes, but the dominant effect is the rapid decrease in the amplitude of each mode that drives the sound output that is observed in the uncoupled results. It is not a simple case of "Oh, they are completely out of phase. That is why it drops off so rapidly."
  8. The width of the "skirt" about each peak, typically taken at -3dB from the peak, correlates directly with internal energy loss (damping) for that mode of vibration. The horizontal axis represents the frequency of the note relative to the natural frequency of the mode. So when the note frequency lines up with the mode natural frequency, the peak is the highest. The dip between A0 and B1- is mostly due to the note frequency being "far" from the natural frequency of either mode, rather than any significant cancelling of air motion between the two modes. In terms of the ability to generate raw acoustic power across the playing spectrum, you want a lot of natural modes crammed across the playing spectrum. In other words, figure out how to create more natural modes in that frequency range. Simply switching the position of the A0 and B1- modes might not do much in terms of power or tone, assuming one could figure out how to do such a thing without a significant redesign of the basic shape of the violin.
  9. If you make a violin out of infinitely stiff material so there is, in effect, no B1- mode, then A0 will have a certain frequency. If you put a typical violin in a vacuum so there is, in effect, no A0 mode, then B1- will have a certain frequency. Once you have a violin made out of regular material in an atmosphere, the modes become physically coupled to each other and their characteristic frequencies change based on that coupling. There is no inherent cancelling or reinforcing based strictly on observed frequency of vibration. Cancelling or reinforcing of air movement is a rather complicated function of the driving frequency (note being played) relative to the frequency of each mode and the internal sound damping of the air for the air mode and the wood for the body mode. When playing notes on the G string, I would expect the A0 mode to be moving most of the air for the lower harmonics and the B1- mode doing almost nothing. For the higher harmonics, the A0 would see very little excitement while the B1- would spring into action. For notes played on the A string, the reverse would be true.
  10. Typically the five lowest natural resonances of the violin (also called "modes") have a name because their shape is similar in all violins regardless of price or method of manufacture. The frequency of each of these modes across violins tend to cluster within the same range. These are called the signature modes. Shapes and frequencies of the higher modes tend to diverge across violins, so these are talked about in more general terms, like the "bridge hill" or the "4khz roll off". Recent resonance names tend to begin with an A or a B. A is the prefix for an "Air" mode. This represents how the air vibrates inside the body. B is for "Body" mode. This represents the motion of the parts of the violin. A0 is the lowest signature mode. It is a strong function of the volume of air inside the violin and (roughly) the length of the f-holes. It is sometimes called the Helmholtz resonance because if follows the principals of a Helmholtz resonator studied by a scientist of the same name. Blow gently across an f-hole and measure the frequency of the tone. It will be around 280hz. This mode radiates a lot of sound. B1- and B1+ are body modes as Anders describes above. B1- vibrates around 465hz, and B1+ around 550hz. These two modes are easily driven by the strings and also generate a lot of sound. The two other signature modes are called A1 and CBR. They do not project a lot of sound into a room for various reasons and people have different theories on the effect of each mode on violin performance. As one might suspect by previous posts, having the frequency of a signature mode focused on a specific value is no guarantee of an exceptional (or crappy) violin.
  11. A violin will vibrate dramatically at certain frequencies. These are called "natural" frequencies of the violin. Associated with each of these frequencies is a characteristic shape. Some look like the violin is bending about some line across the middle, others look like it is twisting about it length, and others are similar to a chest breathing, i.e., parts of the plates rise while others fall. Over time, letter designations were assigned to these shapes. B1+ and B1- are two prominent shapes. Although the frequencies at which these vibrate differ among violins, the shape of the vibrations are similar.
  12. Depends on how close the frequency of the played note is to the base frequency of the open string or one of its stronger overtones. Open strings will vibrate at the frequency of the played note. The further the frequency of the played note is from the natural frequency of the open the string, the less resonate the sympathetic vibration. This is easy to experience by playing etudes based on ring tones. The entire tune sounds gloriously resonate except for the B's, which sound good but are distinctly less resonate than the G, A, D and E. As you play notes more far afield from these 5 tones, the power of the sympathetic vibrations drops. Anything an afterlength may contribute to this is negligible for any sound the projects into a room. Another thing to consider is that it is not possible to get all four afterlengths set to an overtone of its respective open string without some contoured tailpiece that no one has ever created. It seems unlikely that setting a single afterlength to a magical number somehow becomes a panacea to tonal issues across all four strings.
  13. F#5, 740hz, is somewhat close to the fifth fundamental of the cello open D, 734hz. Not sure how tuning the afterlength to a fundamental of the open string helps when you are fingering notes on that string, since the afterlength will NOT be a fundamental of most of those notes. Changing the afterlength changes the effective stiffness of the vibrating bridge. It should not be a surprise that this can affect how the instrument sounds and responds to the bow.
  14. If you are just looking for the first few resonances, a simple scratch with the fingernail will do. Or drop it on a solid table top. To substantially change the bridge resonance, one must remove a lot of material to the point where the structural integrity will be compromised. To substantially change the bridge response amplitude, a much smaller amount of material in key places can be used. The main rocking resonance of a bridge is well beyond the fundamental frequency of most of the notes that can be played on a violin. This means that reasonable bridge tuning cannot do very much to change the core tone of most of the notes. The main bridge resonance does fall in the frequency range where the human ear is most sensitive. So by trimming the bridge in a way that increases (or decreases) the response amplitude, one can affect the perceived brilliance and loudness of the violin by affecting the higher frequency modes of the notes. Basically, if your violin sounds like cr@p, there isn't anything bridge tuning can do to fix that. But if you want a little more brilliance or loudness, think about removing material form the waist on up in a way that does not compromise the ability of the bridge to hold up the strings without warping.
  15. Washing methods for linseed oil are so numerous, and many so convoluted, that a sanity check is in order before you jump down a rabbit hole from which you might never escape. A well known maker of stringed instruments, and long-time member of this forum, Roger Hargrave, published a simple washing method that I have used and can recommend. "I always use artists’ quality cold pressed linseed oil. NEVER use oils that were not prepared for artist use." "I wash my oils twice. Although it takes time, the process is relatively easy. It is best to use glass containers because you can see what is happening. You need about three measures of water to one of oil. "Neither do you need to add sand or anything else. You just need clean water and oil together in a jar. Shake it up every day for a week and leave it for a week to settle; sometimes it goes quicker. Do not be tempted (as I was) to use an automatic mixer; it may cause emulsification. Once it has settled, Siphon off the good stuff leaving the crap in the water." "In a dark cupboard this washed oil and/or finished varnish, can be stored for many years." "It is important to have as little air as possible in the storage jar." The addition of sand, as in Andreas' post, and small amounts of alkaline powders to neutralize the acidic nature of the oil are things that are commonly done. But I just use Roger's method.