Jump to content
Maestronet Forums

Marty Kasprzyk

  • Posts

  • Joined

  • Last visited

Everything posted by Marty Kasprzyk

  1. Making the ribs higher to duplicate the original cavity volume may also restore some of the violin body's stiffness loss.
  2. I use the terms "cup up" or simply "u" and "cup down" or "n" to describe the direction of the plate's arch shape in the assembled violin. So it's easy to see why some of my ideas hold water while others don't.
  3. Most of the volume is enclosed by the rib structure and only a little is from the back plate's arched shape. I estimate flipping the back over so it is cup down will decrease the total cavity volume by about 10%. The A0 frequency is nearly proportional to the volume to the 0.25 power so the frequency increase is only about 2.4% therefore the A0 would increase only to about 277Hz. This is still in the range of typical good violins.
  4. I liked your linky windy levity.
  5. Flipping the back over is an interesting experiment. I'm not sure if cup downward for both plates nn is better than cup downward for the top and cup upward for the bottom nu so this might be a no-no. I agree the nu produces some twisting of the ribs but on the other hand nn produces some lengthwise stretching of the ribs. I don't know which is worse in wasting energy. The rib portions do produce some useful sound but only at high frequencies because their areas are so small. My last instrument is a large 362m violin which is powerful because of the higher tensions of its longer 343mm strings but it also sounds pretty good with viola strings on it. I screwed up and should have made it as a small 5 string viola with an added E string.
  6. If you want your narrower violin to sound like a typical one then the various plate mode frequencies should be similar. The plate mode frequencies are dependent upon the longitudinal direction stiffness and the cross direction stiffness which are in turn dependent upon the material's elastic modulus in these directions and their cross section shapes. Plate stiffness S is proportional to the inverse of the width w squared: S ~1/w^2. So your narrower plate is naturally much stiffer in cross bending than a normal violin width plate and your violin will have a much brighter sound than normal. One way of reducing the cross bending stiffness back to normal is to cut many parallel longitudinal grooves into a thick narrow plate. Another way is to glue on many parallel longitudinal thin braces (like small bass bars) onto a thin narrow plate so that the plates are stiff in the longitudinal direction but real flexible in the cross direction to give something like single faced corrugated cardboard.
  7. The Smithsonian recording using one of Mount's violins might be this one: https://folkways.si.edu/gilbert-ross/the-cradle-of-harmony-william-sidney-mounts-violin-and-fiddle-music/classical-historical-song/album/smithsonian My similar violas were very loud but they sounded too bright because my top and back plate arch heights were much too high which made the instrument too stiff. I suspect that Mount's instruments could have been very successful had he had the interest in promoting them more but his livelihood as a painter was a higher priority. A lot of inventions fail to be commercial successes because of a lack of sales/marketing skill and effort rather than because they didn't work. I also think it is sometimes a mistake to patent some ideas because it prevents others from using them. Therefore they are never widely adopted even though they might be superior to prior art.
  8. Do you want to use the standard violin 325mm string length and normal neck length or do you want something shorter?
  9. Does "Linky windy" mean what's the web site? https://www.youtube.com/channel/UCb8nC_6JQtlqal0-bVQZMeg Sam's presentation today will probably be listed in a few days.
  10. In order to get some sound post tension on the plates it is necessary to have the sound post longer than the distance between the parallel top and back plates. So you have to pull up on the f hole edge with some sort of hook to enable the sound post to be inserted.
  11. I try not to guess. Some things can be mathematically predicted. Attached is Colin Gough's paper on how the shell of a violin behaves using finite analysis and one of his drawings showing how the plate arching causes the violin body to bend. Also attached is a graph of the approximate change in width occurs when the top and back plates are pushed downward. From this I concluded that an instrument with flat plates should be louder than one with arched plates sonmy last 30 or so experimental violins and violas have all been made with flat tops. Unfortunately none of these have yet been double blind tested in comparison to Strad or DG instruments but VSA judges don't like them. As Don Noon often points out --anything that sounds different usually isn't liked. Arching stiffens a plate which increases the frequencies of its various vibration modes. I'm trying to do similar stiffening by adding various braces to the flat plates to get my instruments to sound similar to conventional ones but also louder. 1076234128_JASA2015Shellmodes(1).pdf
  12. That's correct. In a normal violin the "cup down" top plate spreads out (in plane motion) while the back plate "cup up" becomes narrower (like a bimetallic strip).This causes the entire body to bend downward when the soundpost pushes downward from the bridge's rocking motion. Everything of course is reversed when the bridge rocks the other way. This body bending vibration generates only a little sound because the body doesn't have any air volume change because the ribs move outward at the top while they move inward at the bottom. So this energy consumed by the bending the body is wasted by not producing any sound. The amount of spreading and narrowing of the plates is dependent upon their arch heights. I believe lower arched plates should be more efficient at producing sound than higher ones and this might be the reason why Stradivari and DG began to use lower arched plates. Making both the top and back plates cup downward eliminates this body bending and should be a more efficient sound producer.
  13. Mount's 'cradle-of-harmony' violin's influenced me to make some bent top and bent back violas like his. Attached is a photo of one of them which uses a spruce guitar plate which is easily bent to shape for the top. The back is two layers of thick curly maple veneer vacuum bag laminated to shape over a mold.
  14. I forgot to mention if your goal is to produce a light plate then its areas that don't show cracking can be thinned to reduce weight. Those areas that do show cracking should be made thicker. This used to be a common technique in mechanical design before finite element analysis could be done with computers.
  15. That's a good idea. A Google search for "brittle coating stress analysis" will give some insight. My impression from patents is they are similar to rosin violin varnish but with less plasticizer oils which makes them brittle.
  16. Here's the photos of the back shaped like a shoulder rest.
  17. Damned if I know. I was just trying to explain why things might have been done in the past. My small viola/big violin that I just completed has a flat Paulownia top plate with braces and a bent birch plywood back plate with braces both (bunch of Ps and Bs are hard to say) weighing only about 56g. But everything about it is different from traditional instruments so my results probably aren't useful to others.
  18. I fully agree some of the energy lost due to internal material damping which is the area of the hysteresis loop in the stress-strain curve. But it is a closed loop 0--not an open shape n. The unloaded wood sample goes back to its original shape it is fully elastic. There is no permanent plastic deformation. You bring up a good point. The stress-strain curves are often found with a tensile testing machine pulling or pushing a straight strip or bar--no air is being moved by the sample so there isn't any air damping. However knocking a wood violin plate does move air around (that's why we hear it) so it is not easy to determine the relative amounts of internal material damping in the wood and air damping. So going back to Arsalan's May 17 question regarding which of the two wood billets are better I would just make a violin back and ribs and try the two different tops on it to see what happens.
  19. Rubber balls are perfectly elastic. When bounced they always return to the same shape. But they do loose some energy due to sound and air friction damping so each successive bounce height is a little lower than the previous one. However I have had experiences of round rubber tires going flat on the bottom. All woods are perfectly elastic at tiny amount of vibration deformation during playing (measured in microns) so elasticity in not the reason why spruce and maple are preferred for violin plates over other woods. Spruce is used because it has a high speed of sound and a low density so it a top plate made from it can light and stiff and produce a lot of sound. Maple is used for the back plates for opposite reasons. Its relatively high density makes the plate heavy and a poor sound producer. So most of a violin's sound comes off of the top plate where it can usefully reach a distant audience while less sound is going off the back plate where it is wasted going into the player's body and back of the room. (This helps explain why violin players in an orchestra aways have the tops of their violins pointing forward towards the audience while the viola players point their tops towards the back.) A simple example is a back plate weighing 90g and a top plate weighing 60g gives a ratio of 1.5 which is about the ratio of the total amount of sound coming off the top to the total amount of sound coming off the back. Spruce and maple are probably the traditional violin materials because they were commonly available around northern Italy when the violin was first developed. Other regions in the world used other woods with similar properties they had available.
  20. I still think rubber bands are elastic. But back the original question about picking wood to use for violins the only material properties we need to measure are the speed of sound, density and damping. I don't know what is best and there are differing opinions but probably everybody will agree peanut butter but isn't good.
  21. That's what I think too--just c is a better quality index. The RR derivation speed of sound c divided by density p, RR=c/p was done for a flat plate and it is not valid for plates assembled into a box.
  22. We have drifted away from the original question about wood quality. I very much appreciate your heartfelt plea but I'm not interested in designing rinky-dink, ticky-tack (produces a short ring time?) shoulder rests which add weight and damping to the instrument and creates a fear of falling off only at the most appropriate times when lots of people are there to hear you play. This fear creates some tension which inhibits your expression of music. I used to think a low height shoulder rest in combination with a high chin rest was the very best combination for basketball type players with their longer necks. This lowers the height of the instrument on the shoulder so the right arm doesn't has to be raised very high for bowing which in turn reduces stresses on the right shoulder which in turn reduces repetitive stress injuries. Football players with their short necks and thick shoulders don't need shoulder rests at all but these guys usually weren't violin players unless they wanted to be with the girls in the orchestra. But the basic problem is that the old traditional violin and violas have poor ergonomic designs which require shoulder rests. This happens because they have constant height ribs mating with the flat edges of arched plates so everything is easy to shape and can be glued together easily. A much lighter total design uses a back plate having the shape that matches the shape of the player's shoulder and chest area having a widely variable rib height to completely eliminate the need for a separate shoulder rest ( I'm having some difficulties in finding friendly females to scan). This is difficult to build but I think it is better. l'll show some photos in a day or two.
  23. If the two pieces are exactly the same dimensions then the second one with its higher tap pitch simply has a higher speed of sound c. The radiation ratio RR is the speed of sound c divided by the density p: RR= c/p. So we have to also measure the density p of the two samples before we can determine which one has a higher radiation ratio. But I don't believe a high radiation ration is a good violin wood quality measurement anyway.
  24. Rubber sheets are perfectly elastic and have very little damping but they are poor sound producers because they are not stiff enough. Bending waves in the sheet can move a lot of air but are too short relative to sound waves so the sound produces is only very near the surface. At longer listening distances the sound waves cancel each other and all you produce is warm air rather than sound. Sometimes the use of "elasticity" and "elastic" words is confusing. A highly elastic material stretches a lot with a given amount of force( like a rubber band). A material with a high elastic modulus is stiff and stretches very little with a given amount of force (like a braided steel tail chord). Elastic modulus is usually abbreviated as E. Thus a highly elastic material has a low elastic modulus and can stretch a real lot like my underwear's elastic waist band.
  25. I'm starting to get confused. Isn't "thunk" just an uneducated past tense of "think"? I thunk the decay time for a sample vibration is dependent upon the total amount of damping that is present in the vibrating system. The total amount of damping is a sum of : the internal material damping in the wood, the amount of of air damping the sample produces, and the amount of damping in holding the sample. The amount of air damping in turn is a sum of the desired sound radiation damping and the amount of wasteful damping from ineffective heating of air. Both of these air dampings are dependent upon the size and shape of the sample and its material properties such as the various stiffnesses, density, and the above mentioned internal material damping. As Anders Buen has pointed out before the damping from holding the violin by the player is much greater than these other sources of damping anyway. I had a good violin player demonstrate how just changing his chin pressure affected the violin's sound. Maybe the damping of shoulder rest foam material might be more important than the internal damping of the violin's wood. The newest running shoes have more bounce than earlier ones and running records are getting quicker.
  • Create New...