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pt3

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  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!
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