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pt3

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Everything posted by pt3

  1. Primed varnish is a kind of oil varnish diluted in turpentine, used to enhance the depth of reflection of the wood. Could anyone tell me what's the ratio (by weight or by volume) between the oil varnish and the turpentine. It is said that the diluted varnish in turpentine is very weak, no residue will left on the wood surface. Prime oil is prepared with turpentine and several drops of linseed oil. I want to know the rough quantity relationship between the two ingredients. Both have the same functions ,which is better?
  2. please to read: guyharrison/blog/?p=295
  3. I am making a viola and want to know the knowledge of viola bridge tuning. On the violin we tune its bridge frequency to 3000 Hz to improve violin's high frequency response as J. Curtin pointed. How about the bridge on a viola with body length of 41.5 cm?
  4. M. Hutchins recommended that Mode M2 frequency should be tuned to a frequency = 1/2 M5 frequency (the so-called octave tuning). In a recent paper it is said that Mode 2 frequency can be constantly negative with regard to octave (in case the transverse sound velocity is lower) during the thicknessing. however, it must be no lower than 25 Hz below its octave upon completion. In my case, 357/2 = 178 Hz, 178 - 25 = 153 Hz the measured M2 freq. is now 157 Hz. I worry about how to keep M2 frequeny not less than 153 Hz, when thining the central region of the back plate and at the same time attaining my goal frequency of M5, 357 Hz.
  5. The weight of this back plate is now 114.8 g. so further thicknessing to reduce the weight seems to be necessary, but I hope not to reduce M2 frequency (reducing the thickness of the central region of the plate will lower M2 frequency far more than M5 frequency).
  6. I am now thicknessing the back plate and meet with a problem as follows: Lower bout thichness has already reached 2 mm, upper bout 1.8 mm, and central part 4.5 mm. using software Audacity, I have measured that Mode 5 frequency = 379 Hz, Mode 2 freq. = 157 Hz. My goal frequency for this back is 357Hz. so 20 Hz must be lowered, and I want that Mode 2 frequency to be kept as high as possible. What should I do to further this thicknessing process? The upper and lower bouts seem too thin already. and thin the central and intermediate parts will further lower M2 frequency.
  7. Hutchins proposed her famous "Tri-bi Octave tuning" method in the 1960s, namely, in graduating the violin plates trying to keep the frequencies in mode 5, 2 and 1 of the top plate in an octave relationship, and for the back just mode 5 and 2. I have tried to achieve this goal, and have found it is quite difficult. When the plates are thicker, (so higher resonance frequencies), this is easier, e.g., when M5 = 375Hz, I got M2 = 185Hz (top plate), with a weight of 84 grams. I continued to thin the plate according to Hutchins' graduation scheme, this octave relationship could not be met. I wonder whether this "octave tuning" is really beneficial. Most of famous old violins do not have this octave relationship. Furthermore, Schleske pointed in his paper that no correlation between the resonance frequencies of free plates and the frequency characteristics of an assembled violin.
  8. Thanks a lot! I'm planning to use the software "Audacity" to generate sine wave signal from the computer and feed the signal to the external small sound boxes with power amplifier specially made for computer use (2 boxes, each with 3 loudspeakers one of which is of medium frequency, I think this one is suitable for mode M5 and the larger base speaker may be for determining mode 2 and mode 1), for instance, 20 watts output. Is that OK?
  9. I want to know the appropriate audio output power for making Chladni patterns (mode 5 and 2)of a violin. Thanks!
  10. pt3

    Pumice and Tripoli

    Thanks a lot! I remember that in your ground coating system you have used the diluted Marciana varnish, 2 coats, followed by gelatin sizing, and then the pumice-varnish paste. What's the purposes of using the diluted varnish and gelatine solution? For the purpose of easthetics (highliting the flames on the back plate) or used as sealers? But pumice-varnish paste itself is a good sealer, is it nacessary to use other sealers in advance?
  11. Fine pumice powder or tripoli can be used for preparing the ground, which is the better?
  12. Could you tell me the concentration of copal in its turpentine solution (e.g., how many grams of copal in 100 cc turpentine) you use as a sealer?
  13. I am making an experiment on varnishing. I made the varnish according to Marciana Recipe. The steps for the first coating is as follows: 1) Sun tanning 2) Applying thin varnish diluted with turpentine about 1:5 by volume, light brown in colour 3) Sun tanning The result is shown in the attached photo. I am quite satisfied with its dichroic effect. The wood is from Northeast China, veery very cheap. I don't know whether it is detrimental to the acoustic properties of the plate. Of course, the thin varnish was totally absorbed by the wood. Mr. Don Noon: Could you tell me what resin in turpentine do you use for this purpose? Thanks!
  14. You have said that the first coating may be a thin solution of resin in turpentine. Could you kindly tell me what resin and what ratio of the rasin to turpentine (I mean how many grams of the resin in 100 cc turpentine)? I will follow your advice. I agree with you that thin varnish diluted in turpentine will do the same, but which one is better, thin solution of resin in turpentine or thin varnish diluted in turpentine? What about thin solution of dragon blood in alcohol? Dragon blood produced in China is quite transparent.
  15. Mr. Don Noon, I remember that you have recommended using sandarac as a sealer. Could you tell me the ratio of sandarac to alcohol? Is it better than shellac for this purpose? Thanks!
  16. Thank you very much for your valuable guidance! I have a further question: What's the difference between using this kind of varnish and using linseed oil for this purpose?
  17. Thanks a lot! The varnish I use is Marciana according to an old Italian Recipe, which consists of colophony, mastic and linseed oil. The ratio of oil to uncooked resins is 1:1 by weight. I intend to use turpentine to dilute the varnish and want to get your directions of the proper ratio of solvent (turpentine) to varnish.
  18. Thank you both for your immediate replies! So, using dilute spirit varnish may be a better alternative. I want to know the degree of duluteness, i.e., how much seedlac should be added to 100 c.c. of alcohol. Another alternative is gelatine plus alum. The concentration of gelatine solution is generally 2 ~ 3%, but how much alum should be added to this gelatine solution (e.g., 100 c.c.)with such concentration. It is said that alum is used as a hardener and makes the sealer not so hygroscopic as vernice bianca.
  19. It is said that oil varnish diluted in turpentine can be used as a sealer, originally I use Vernice Bianca (white varnish), but it is hygroscopic, so I want to make a try. What is the proper proportion (by volume) of the varnish and turpentine? I use Marciana varnish. But I am worried about that the penetration of the diluted varnish into the wood maybe too deep and harmful to sound quality.
  20. pt3

    Prime Oil

    I have read an article that says: Applying the wood surface with Marciana varnish diluted in turpentine will make the wood more reflexive. Could anyone tell me the appropriate ratio of the varnish and the turpenyine (volume ratio) Thanks
  21. There are 2 Master Grades: "Master fine" and "Master". The difference of them is the spacing of grain lines (annual rings), the former has denser grain lines with a spacing of up to 1 mm, while the latter 1 ~ 2 mm between grain lines. From the viewpoint of violin making, namely, the tone quality, which one is better, "Master fine" or "Master"? I have bought several violin tops, split extra quality, from Tonewood s.r.o. Slovakia, and have found their supplies are not satisfactory. The top blanks they supplied deviate greatly from radial cut, and grain lines near the bark side are very very tight, about 16 lines/cm (the spacing gradually to 1 mm and 2 mm on the other edge, and the blank is not wide enough to cut off those unsatisfactory parts. Are there any negative effects of the spruce plate with such too tight grain lines?
  22. Patrick Kreit, a French violin maker, has published a book, titled "The Sound of Stradivari". It is said that the resonant frequencies and frequency spacings of an assembled violin can be tuned to desired values by using his method step by step so as to raise its tone quality to its maximum potentiality. The price of this book is 285 euro. Has anyone read this book? I want to know whether it is worth reading and buying.
  23. Thanks a lot for your reply! You said that you always put max thickness same distance north of A than stop is south of mid plate A. Do you mean that the max thickness is located at a point north of A with the same distance of BA (B -- the stop)? If so, this is point C. Another question: Is there any difference for the location of max. thickness of the top plate and back plate ?
  24. I want to know the both, if their respective locations for max. arching heights are different. But according to Sacconi's data they are approximately the same.
  25. Could you kindly attach Part 2 of this Review on the forum. Many thanks!
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