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Anders Buen

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Everything posted by Anders Buen

  1. In general the edge thickness correlates with the average thickness of violin plates. However, the edges tend to become thinner by wear and one can of course choose to keep them thick or thin at will. I do not have much experience in doing edge work on assembled bodies. But I understand that this may give changes to the body modes. I guess George Stoppani is an expert on this and his pinning of the plates before assembly may give a situation somewhat similar to the assembled violin. I think he has said that the central tinning does most. The talks VSA have run are on Youtube. One of these are with George.
  2. Ok. Mode 2 har the highest amplitude at the ends of the plate where it is flattest. I think that tilted ring angles or a higher angle cut may do something of the same, weakening the crossgrain bending stiffness.
  3. I do have a fairly large dataset of free top plates from my own practice and other sources I have come across in searches or have received for analysis. Not all have arch height given, but a fairly lage amount does. There is no clear correlation in my data between the archeight and any of the free plate frequencies, and thus not mode 2 either. However, there are numerous other factors that are clear, like the mass, the thickness and the crossgrain soundspeed. There seem to be an influence on mode 5from the arch-height, and thus it is possible that the ratio between these modes may be influenced by the arching height. I know Jim Woodhouse has said that there is about 50% stretch and 50% bending energy in mode 5.
  4. The perimeter thickness of the free plates are quite influencial on the free plate mode frequencies. This is a region where fine old insturments do see wear and the edges are doubled when necessary. I would believe the restorers would try to keep the wood as thick and original as possible, and would fill inn missing or worn wood until a given limit. I do not know if the doubling of the wood does make it stiffer than the original wood all way through. If the perimeter thickness did become thinner the tap tones wouild go down somewhat. According to George Stoppani who play with pinned edges plates, the centre thicknesses are more inportant for the pinned plates than it is for the free plates, where the perimeter seem to count more. The «Sacconi plateu» used in the end of the plates pushes up the mode 2 a little in comparison to a plate graduated also closer to the end blocks form the side.
  5. I once regraduated a cheap cornerless violin and it got a weak B1+. I added a coin to the block regions and it improved. I added corner blocks and it behaved more normal with a balance between the B1- and the B1+ Static force does not give any effect on the sound, beyond the possible small changes to the arch shape, which does influence the sound.
  6. Sure, there are more going on. There is at least longitudinal bending of the back as well. And the vibration shape is different for the top plate in the B1- mode as the activity is highest at the bridge, while it is in the ends for fre free plate mode 2. I do have a better tool for nonlinear regression now that might give more answers than just one major in statistical tests. May coma back to that later. I found a better prediction poower from using mode 2 of the free top than mode 5. Regarding the backs I use the backs on the ribs when I take out the modes. A practice better suited to regrad projects or if you build using half made back and rib assemblies as I have, as well as my grandpa. Faster, but less control. Still the mode 5 and 2 is there, but the ribs push up mode 2 and reduces mode 5 frequencies somewhat. Can be used for regression too, but will be more difficult to use for bask plate makers, if anyone would use it., anyway :-)
  7. I agree that the amplitudes are important too. Jersus A Morals experiemnts in the mid 80ties combining varying stiffness backs, tops and ribs, may be a source to look up. He measured the amplitudes at the bridge top. In his studies the amplitudes of the signature modes went down a little with increased thickness of the ribs. About 1 dB per 100% increase in thickness, if I understand the data correctly. The article on htat work can be downloaded here:https://www.speech.kth.se/prod/publications/files/qpsr/1984/1984_25_1_001-029.pdf
  8. Rodgers and Andersons article can be downloaded here, in case you want to read, see the referred fiugres and references: https://stacks.stanford.edu/file/druid:xh244qv7083/CAS_xh244qv7083.pdf You get the whole journal issue at about 25 MB size, takes a few seconds on my high speed line. The article starts on page 13.
  9. One way to try to figure out the answer to that question is by using FEA on a violin box model. Oliver Rodgers and Pamela Anderson wrote an article in the CAS Journal Nov 2001 based on their calculations. They write: Earlier work on free plates had indicated that only three of the stiffness properties of wood are important in adjusting the vibrating frequencies of plates [10 ]. These are stiffness along the grain, cross grain stiffness, and shear stiffness in the plane defined by these directions. The most sensitive characteristic was revealed to be the ratio of the cross grain stiffness to that along the grain. Calculations were made of the first eighteen frequencies (up to about Figure 5. Deflections of top at 1336 Hz (viewed from inside violin). Note sidewise deflections of bassbar and bridge. Note also that these deflections are in opposite directions. 1400 Hz) when the ratio of cross grain stiffness to along grain stiffness of the spruce (top and bassbar) was increased by 21%. All frequencies were increased by about 1.5% to 2.0% except for one at about 1150 Hz (corresponding to the 1120 Hz configuration; fig. 2b) that stood out with an increase of 3%. A similar calculation of the effect of across direction stiffness ratio reduction of 29% produced similar results, -2.5 to -3.0% except for a -6% decrease in the 1150 Hz mode. The 1120 Hz mode in the base run clearly is more strongly influenced by cross grain stiffness variations since all its nodal lines run along the grain. Calculations of the effects of changing shear stiffness gave similar results. Only one mode, in this case at around 1270Hz, seems to be affected more than others when the shear stiffness was changed, presumably because the deflection patterns of that mode were moresensitive to shear deformations. They got rather small effects, ecept for the mid frequency range. In my statistics playing around it seems as mode 2 and the B1- follow each other closer than e.g. the mode 5 of the top and B1-. I would believe that a top with weak crossgrain stiffness, e.g. with grain lines going at an angle different from 90 degrees to the gluing surface would tend to have a lower B1- frequency. Experience also tell that a slab cut back tends to give a lower B1+ frequency possibly also because the crossgrin stiffness of the back then is lower. The same is likely to happen if the back plate is thin, I believe. The nodal lines in the back plate goes like )( for the B1+ and like that for the top in B1-.
  10. The most important effect on the crossgrain stiffness, except for the grain angle, is the thickness of the plate. The arch has a rather limited effect on the free plate mode 2 frequency. More on mode 5. However, for the assembled violin body the arch may be more important, as that is a true shell construction.
  11. Crossgrain stiffness of spruce and wood in general is very depedent on the grain angle. It drops fairly fast with increasing angle. So squaring up the wood makes the plate as stiff as that piece of wood can be, crossgrain. In my statistics work it seems like the crossgrain stiffness is more significant than the along grain stiffness. At least when it comes to predicting the B1- frequency. Mode 2, )(, seems to be a better predictor than the other three typical modes, #1, or #5. Mode 2 is mainly crossgrain bending.
  12. He used to have this on his website. http://www.fiddleheadstrings.com/fiddleheadstrings_web_revised_dec17_010.htm
  13. Oliver Rodgers and Molin et al idependantly developed measurement procedures for assembled symmetric top and back plate blanks for extraction of three of the elastic moduli and density, of course, based on FEA calculations during the early 90ties, I believe. Rodgers made graphs and a program for the purpose. Molin et al made graphs for the purpose. Later Tom King made an Excel sheet based on Rodgers work Both methodes were presented in the CASJ, (Catgut Acoustical Society Journal) which is open access now.
  14. This kind of data was what I originally was looking for. So thanks for that! Are the weight gain for the entire violin or just the plates?
  15. An update on the statistical modeling on free violin plates. Now I have run some multivariate regression which seems to work pretty well for the top plate data, a larger set than for the back plates. The input for the top plate modes are weight, average thickness, in some cases the density, the crossgrain soundspeed C|_, and for the highest mode (#7) also the Davis impedance, Z is used. The archeight given by the highest arch height does not enter the models, somewhat to a surprise. For the back the formulas are a bit more simple. Nonlinear regression does work for very narrow values of the input data, but just outside that, the predictions becomes non natural, even negative in some cases. Clear signs of a too small data set, especially for the more un-usual modes to note. The back plate data size also suffer from not having my n= 92 ish data points in there, as I record the tap tones for the backs on the maple, ribs and the neck in place. In spite of this, the predictions are not far from the former sets based on weight or average thicknesses alone, except for #7 in the back plate where the data and model rely heavily on Schelskes thinning experiment in 14 steps. The back plate mode 7 has very high frequencies in that study. The back plate mode 5 prediction is also probably a bit weak, only 52% of the variation in the set is explained by the used model. The prediction is lower in frequency than I would have expected. However, not far from the other simpler models. The nonlinear modelled point in Möckels data end up in the lower quadrant as well for the Strads with a slightly higher mode 5 frequency for the top. The data points up to #6 still lie close to the top = back line, just barely lower indicating a slightly stiffer back than the top for this example. The other data inputs are shown in the first graph. For the top the explained variation is from 81-95%. For the back plate the explained variation is from 52% up to 97%. However, it remains to be seen if the models behave natural in all natural input regions.
  16. I think every now an then a violin can have a harsh note, even a fine one. Maybe the better violins have fewer of these. I think it is really hard to pin a harsh note down to a given building trait. But if you find one and a violin without a harshnes, or even better, a harsh note and a non harsh one of the same violin, those could be investigated further in comparisons. The best situation would be a harsh note and a good none next to each other. It is possible to make a fiddle with no recurve to sound deep and great. Nothing harsh. Arching is in my opinion less important than graduation and wood. We know a higher arch supress the lows and give an apparent boost in the highs. High and or bad archs give instruments that behave more suceptible to changes in the relative humidity.
  17. If the instrument is stolen, and the player knows, it may sound harsh.. :-)
  18. Lets say there is a twisting mode or so in a fingerboard neck lying close to a body mode. Slight chnges of fingerboard length or thickness may give an effect on that particular mode. I think there are examples shown in my article. Or at least shared here on MN while I conducted the change from violin to Hardangerfiddle in steps. Inlcuding steps of cutting the fingerboard. I have bought e few custom made dragon hardanger fiddles from China. There is a dip in the B1+ mode and I tried to hollow out the somewhat large heads, and the dip was still there. I know the dip is related to the neck-fingerboard system in some form (also shared here on MN), but that operation did not make much change to the dip nor playability. It was some time between the before and after test, though. In general I think the longer and heavier HF nack gives a lower B1+ mode frequency, although HF in general have thinner backs. Also a possible reason. It is hard, I think, to generalize on this matter. As it is with chinrests as well, I think. It is even harder to percept the changes by playing than to measure a change using high resolution instrumentation. However, I do believe violinists can spot these changes better than a fiddler as they can and my stay longer on each note at a given frequency.
  19. Thanks for being interested! It is a while ago I did these experiments. I do have the strings lying somewhere. I think they are sort of synthetic core strings, not much different from Dominants. They are not of the steel core ones. They are less easy to play, but probably louder. The test instrument is of "high grade", thickish as del Gesu but the wood is likely to be stronger. A rather stiff fiddle. I have not tested the different Chinese strings in detail. Maybe a thing to look into. The larger number of violins tested against hardanger fiddles are mainly with mittel Domintants.
  20. The most compressed version on this is a poster from the 2013 Stockhom Musical Acoustics Conference: https://www.researchgate.net/publication/339587232_Buen_SMAC-242_Poster_A3 The article governing it: https://www.researchgate.net/publication/325392479_THE_ACOUSTICS_OF_THE_HARDANGER_FIDDLE A more recent presentation, also including some speculations on the string effect, theoretically: https://www.researchgate.net/publication/351283853_Some_aspects_of_the_acoustics_of_the_Hardangerfiddle There is a later article as well governing this presentation. However, it is very similar to the one from 2013. If you prefer to hear me talk on a slightly shorter version of the above slides (nothing on the string theory, due to time constraints) i have the presentation from the Baltic Nordic Acoustical Meeting 2021, which was a video conference due to te pandemic: https://www.youtube.com/watch?v=YVY7MsN3lZ8&ab_channel=AndersBuen
  21. The Hardangerfiddle is kind of baroque. Gut strings, traditionally, and played at a higher pitch. Shorter and lighter strings makes it sound a little weaker than a violin with Dominants mittel. Still the sound is more intense. The bridge is also different with long legs, chelloish kind of. A baroque bridge would also influence the sound spectrum, and I guess the violins were played at lower pitch. Please correct me if i’m wrong. The pitch varied with the region and instruments there, like flutes, or maybe the church organ. I am sorry that the baroque violin and fiddles are not studied more in the VSA and in general. I think this limits the insights and makes the violin acoustics subject less interesting than it could have been.
  22. Maybe pure sound, and not necessarily loud, may be weak-ish fundamentals on the e-string first position and getting support from the bridge/body hill region instead. Maybe also a sharper dropoff at the very highs. I do not have full control over the bridge body model. But higher damping there can play a role, as well as lower damping of the bridge. In vibration insulation theory, a mass spring system with a dashpot damper (viscous damping) give a stronger filtering above the resonance than does a higher damped system. The response around the resonance will be stronger for the less dqmped system than the more damped one. So a low damped bridge body system may give a clearer bridge/body «formant».
  23. The lowest graph is the interior impedance. What goes out of the instrument in the open end is the part that does not become reflected. The wavefront in a woodwind instrument or a trumpet is a «flutter» going beck and forth in the conical tube, amplified or sustained by the lips or the beating reed. If the impedence is high in the tube, less enters the room behind he tube. With a cone, less becomes reflected and more enters the room. Brass instruments have a high frequency effect you may hear in angry elephants, even sportscars or japanese street racers with long pipes as a «brassy» sound. A trumpet eg, playing loud may sound more brassy, perceived as being louder. The brassiness thing is nonlinear, caused by a sharpeing of the wavefront inside the instrument which leads to higher output of higher frequencies.
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