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Anders Buen

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About Anders Buen

  • Birthday 06/03/1970

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    Oslo, Norway
  • Interests
    Violin-, Hardanger- fiddle-, room- and architectural acoustics.

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  1. the top, the back plate will usually have a more "circular" longitudinal arch. The stiffness in the two directions are more similar too, for a back plate.
  2. I think a circular long arch will give a weaker sounding violin. Crossgrain arch can be rater strong, because the wood is weaker in that direction. But not the longitudinal. I can't prove it here and now, though.
  3. The strings pull up and down an arch on "flat top" guitars. Easy to spot against the light. The arching of any wooden instrument, archtop guitars, violins, or the like, will have a time varying arch shape following the relative humidity variations of the indoor air. The free plates may warp visibly. The arch needs to be rather high before it has an effect on the modes. I have looked into this in relation to concrete floating floors where the drying process may cause the corners to rise while the concrete hardens. In a 5 x 5 m floor the central region needs to rise more than 20 cm (as far as I can remember) before it starts to affect the modes significantly. This is Soedel shell theory, probably known to Marty.
  4. I think arching is also a matter of stability over time for climate variations. The flatter arched instruments after Stradivari behaves better for humidity variation than than the older higher arched instruments. Personally I think this is more important for the development of the instruments than their sound, although old instrument arch and thin plates does sound a bit different from flatter thicker arched instruments.
  5. Otto Möckel seen to have a similar idea, to use stiff borders. I have been working on flat plates and their mode shapes related to their effective masses. The way the edges are fixed play a role. Eg clamped edges give a smaller first mode shape, but a lower effective mass than simply supported plates where the edges are free to «tilt» over the edge. The result is probaly a louder resonance. Bernahrd Richardson describes this in one of his later articles on the guitar, which do have almost flat plates. The above experience made me understand his idea on this. And I think your comment here support the same idea, although it is not described in acoustic terms. I think George Stoppani may have informatiuon on this as he do measure mode properties on violin plates on «pinned» edges, almost immobile. One shoould see effects from a stiffer edge region on these mode shapes.
  6. Letting the edges of the violin body touch the table, hard, may prevent them from vibrating naturally. Holding it as Don suggests is better, and more realistic. I would also let the mic have some free air around it, or use a very close to the table postion where all sound is reflected "+ 6 dB". Everything between close to surface mic and in free space may lead to interference or interaction with modes in the room, or both.
  7. Slabcut backs seem to give low B1+ mode frequencies. I think the low crossgrain stiffness of the top play a significant role in violin acoustics and performance. The arching should give smaller effects from the E-modules on the main mode frequencies than for a flat plate, at least so for mode 5. The crossgrain stiffness fall fast when the ring angle is off 90 degrees. And it is quite possible to get crossgrain stiffnesses lower than the general tangential stiffness of spruce may give alone. Of of the main reasons for not using slabcut spruce is the larger humidity creep and swell in the tangential direction. I think that may be the case for the maple backs too, although the differences probaly are smaller for maple than for spruce.
  8. The resonance frequencies are proprtional to the youngs modulus^1/2. - Thanks!
  9. No, but not far from. The tangential direction is about half the radial, while both are 5-13% ish of the longitudinal. So for all practical means, quite similar. The twisting modulus is also close to the radial modulus for spruce. Of course, there are variations from piece to piece. i think the bending stiffnes goes as the modulusˆ1/2 so the numers does not need to be very precise for practical assessments.
  10. Don is right, the youngs moduluses of spruce in radial and tangential direction are fairly similar.
  11. Work around it, if the bar otherwise is ok.
  12. Thought some of the wood nerds here maight find this article interesting:
  13. I have no idea. It will move naturally with the varying climate. That is the varying RH indoors, and in the flight cabin if that is the transport used.
  14. It may be worth trying a different chinrest. The Guarneri models attached over the tailpiece affect the B1+ mode to some extent, adding mass and thus reducing the amplitude of the B1+. The frequency may also move a bit. Then the wolf may move too I prefer light side mounted chinrests. Lighter strings also reduces the driving force, and thus wolf. Maybe mainly the G string or both G and D.
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