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About hrobert

  • Birthday 04/08/1958

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    lynchburg tn

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  1. I don't have a window in my workshop either; unless you count the window in the door going out into the messy garage (my wife would kill me in my sleep if I posted that). How 'bout a view from front of shop back toward house? Not current but its a heck of a nice photo anyway!
  2. I recently bought an old violin that had a Strad facsimile label (1721). Instead of an "A Cross S" in a circle it has a circle with what appears to be a harp and rays spreading out from it. Anyone seen one like this?
  3. CSMP is 'continuous system modeling program' or some such anagram; the last copy of it I had was on IBM cards if that gives you an idea why I said I was showing my age. As far as the sound post issue; I'm wondering if going beyond the conventional wisdom that the sound post is a support and pivot point for the belly to flex off of; what if we look at the notion that on a secondary level, when properly fitted, it acts as an acoustic coupling between the plates? This would at least suggest a possible explanation for the drastic change in tonal quality you guys are seeing in your sound post loose/tight experiments. Too loose and it doesn't 'couple'...too tight and it compresses deadening its own acoustic properties. Just a thought... The position of the sound post also has some interesting implications vis-a-vis the inflection point/s. We know correct positioning is critical to getting an optimized sound. These are just a couple of the types of variables I was referring to as a very complex 3d system.
  4. I think the point we're coming to is having to admit that we're trying to apply simple 1 & 2d models to an INCREDIBLY complex 3-dimensional system. I realize I'm showing my age; but has anyone ever run a 3d model thru something like CSMP? It seems this would give us a chance to actually do an optimization based on the type of post tension experiments JM described.
  5. It can also result from a bridge that is shaped assymetrically.
  6. I agree about the midranges. I just was thinking that with a flatter section in both directions you would get that benefit even more. I'm not familiar with the Sloan Strad ; what's the date?
  7. John Masters said; "I don't see how static stress changes eigenvalues and I don't think anyone has discussed it or shed any kind of light on it. What is the mechanism? " Straw man!!! I never said static stress changed eigen values...WHAT I SAID is that stiffness effects BOTH static stress and natural frequencies/eigen values. As far the point that Stradivari's instruments seem to show an increased response in 2k+ frequency range, to my thinking only serves to reinforce my point about the flatter archings...in a higher arched/stiffer instrument that band of resonance would be in a higher frequency range, perhaps even outside the band of frequencies that a violin reproduces efficiently. Thus the Amati's etc have that clear silvery tone but don't have the DEPTH a Strad does.
  8. I remember a quote about one early 20th century dealer who "asked himself not what is this, but what can we sell it as." I look at some of these ebay auctions and say to myself; "if this was what they say it is, why is it $200???
  9. Let me say first, I too am a professional engineer and I think what you're doing is great. Its your experiment, set it up however you want. I did the early part of my career doing this acoustic vibration stuff ( on turbojets ) but I'm admittedly fairly new to the science's application to stringed instruments. So here goes... If the inflection point is indeed the point of max bending, and again you guys that are working with this may have tweeked on this ages ago, but it seems this would be the lynchpin to understanding why Stradivari's flatter arches sound better than Amati or Stainer's higher arches. His spread out the area of inflection to be a wider band of high bending, rather than a tightly centralized inflection band which would be expected to make for a stiffer plate. So, the same loading or excitation of the plate results in greater vibratory deflection and thus a stronger pressure wave etc.
  10. Another thing about the Deft fill. I learned this doing guitar finish repairs. ( sorry I used the "G" word; but that's my background) Try this on something you can afford to experiment on. This works on Nitro-based laquers. Apply a little less than it appears you need then add a TINY touch of acetone. It will make the nitro flow right out without as much lap-over.
  11. Thanks, I liked the looks too. Think cracks will be O.K. As far as the rather bizarre "leg-pulling"...don't see the humor let alone the POINT. I was just looking for info. Turns out the jokes on Drac...I bought this for 60 bucks at auction. I wonder if he'd like to bet that 20 g's that I don't make a profit?
  12. If you figure out how to do the "laser like precision" thing let us all know how you do it. Also, weird side note; If you apply Deft in a cold environment (35-40 degrees) the more volatile parts evaporate first and the less volatile later leaving a surface that's permanently somewhat soft. I guess we could approximate Stradivari's soft varnish that way.
  13. Never dealt with this guy...but, the Ebay distance thing sword cuts both ways. I've gotten a couple of real steals on there because the photos were so lousy the violins LOOKED like Chinese junk.
  14. I gotta agree; I've got violins I bought at thrift stores I wouldn't trade for 3 of these things.
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