francesco piasentini

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About francesco piasentini

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  1. At least in US you have a supplier. Here in EU didn't found any.
  2. hard to find in Europe. Only way to have something similar is to harvest silver fir resin (oxidized)
  3. Before comparing any B modes with plate fee modes, you should be aware that spotting a B1-+ mode is not easy with a microphone. A1 is quite often coupled with B1-, I can't say why since I just started using these tools and only recently manage to get reasonable results. From here to say if these results are useful, I will spend the rest of my carrier. But I like it. I enjoy it and it fullfill my innner's child curiosity. :-) So B1+- may be a mess, and #5 is the easier to confound with other modes. So you could turn comparing pears to apples. Let's make an example. A violin of mine, body with soundpost (no neck). In green you have the input admittance (measured at g bridge foot), in red the internal sound pressure measured with an electret capsule close to the back at halfway. Red curve is something similar to external sound pressure, it measures air moving (not vibration). Let's see it and compare it with the agreen dmittance curve (what the bridge feels under its g foot). Everything is is averaged using an instrumented impact hammer. -A0: higher in the red curve, but quite present in vibration. Helmotz mode is strongly coupled with the structure. A0 varies a lot with the dynamic stiffness/weight of the structure. -CBR: invisible (for that spot inside the violin) in the sound curve, but well present in vibration. Everything moves but does not sound so much -B1-: coupled with A1 (second air mode, logitudinal dipole??), in this case the sound peak is splitted, but quite often it's a single peak. SPeculation on B1- position without modal analysis are risky. I have to thank George for building a software that allows maker to discriminate modes. See the little dimple in the green curve and imagine you can get a very different mode shape from that kind of stuff. -B1+: a good correspondance between air and vibration And, Yes, it takes a lot of doing for doing those games during building.
  4. And, perhaps even more important, before that we have to decide which material and which outline/archings use! :-D It's a nightmare, but at least this experiment showed that thick and thin stands out. Everything in the average/normal/standard impedance/thickness gets more confused. I don't think the impedance as the new holy grail, but at least is something more realistic than any speculation about single free plate or body modes.
  5. An interesting approach was used during the Bilbao project. Here you have examples of impedance according to Evan Davis formula made during that project: https://www.bele.es/en/making-tops-backs/ Higher impedance (at given archings and with wood with similar features) scored worst in listening tests.
  6. Regarding the relation between free plate modes and body modes, a nice analysis was performed by Colin Gough. Google "colin gough fem free plates" and find nice pictures on how modes move from free plates to body modes changing rib's thickness in his FEM model. Enough to assess that it's a very complicated subject. But tracking M5 is indeed very helpful. Not to reach a specific target, but as a tool for assessing material properties (stiffness) at a given arching shape. I don't know what a bluegrass fiddle is. Is it something like a small viola-sound? Boomy and wolfy?
  7. Me too I have a limited amount of time. And also I would prefer not to invest this limited time in making bad sounding violin. If something can help me in this way, I would rather invest time on it before making violins. And I would test my hypothesis with each instrument. Graphs shows no correlation, but that don't tell us that measuring M5 is useless. Each point belongs to instrument with different archings, outlines, wood, wood treatment. You could make a similar graph between density and CBR and conclude that measuring density is not important. List of questions is endless, just one: What's the initial hypothesis you want to prove or demolish with your scatter plots?
  8. Would you mind Don to plot for each plate/violin: x-axis: weight divided per #5 y-axis: A0, B1+ as measured with the microphone
  9. Another reason why I use modal analysis it the difficulties I have in separating m5 to the adjacenr modes. It would be very difficult for me to go blind and spot the correct m5. Quite often I see "place trading" between 5 and adjacent modes. When I used to tap and listen quite often I was not sure about #5. Now with a couple of hammer hit you can have the first 7-10 modes in a matter of seconds, and track them when finalyzing thicknesses.
  10. I pretty much have a similar feeling. I track Impedance by means of Evans number (mass, #2 and #5) and I find it a reasonable indication of stiffness of plates, following Stoppani's approach. I also have found a good correspondance between the impedance and sound emission in the low register. It's also a good idea to track modes and weight when working with different archings and models to spot the effect of these on plate thickness. Btw thanks don for sharing. Have you tried with A0 frequency (with sounpost and strings on)?
  11. "CBD oil" may use hempseed or olive oil as excipients. The latter not exactly the best siccative oil I know. It's also in SCHILBACH catalogue: https://www.shop-schilbach.net/epages/79837849.sf/de_DE/?ObjectPath=/Shops/79837849/Categories/Gesundheit Even if it's not necessarily a varnish ingredient, may be helpful to the maker's mood, reducing the "varnish curing ansiety syndrome". A double-blind test against a placebo is necessary in order to prove it. I'll update you soon about it.
  12. Thanks MIchael, I like it too. You are right about the darkness/intesity, but this is not necessarily a problem. I'm going to cook it a bit more. I have a very limited experience in cooking resins. I noticed that after adding the oil the color fade a bit more than the expected. My chip test violin (from Romania). Over the back a couple of layer over of this varnish over a couple of layers of Joe's dark amber varnish (one clear and one with a bit of Robbia pigments from Fantuzzi):
  13. The resin after cooking (a few days): VID_20190904_092259.mp4 The varnish 4:1 resin/oil and same volume of warm turpentine.
  14. I cooked some spruce resin I harvested and some ordinary Kremer pale colophony (Pinus Pinaster). Spruce gave better red hue, even without any kind of iron in it. I used a pyrex becker for there tests. And I want to experiment different stages of the same species's resin: fresh, oxidized, etc..