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Roger Hill

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Everything posted by Roger Hill

  1. In theory, yes. In practice, no. The problem is that you will not be able to hold the plate with a constant angle to the cutting tool. By this, i mean as follows: Draw a tangent to the plate edge, then (mentally) construct a perpendicular to the tangent at the point of tangency. To get a satisfactory groove, you must hold this line to lie perfectly along the line between the cutter and the contact point with the work stop. Neither you, nor I nor any other mortal is good enough to do that. Secondly, the slightest relaxation of downward pressure on the plate will result in the cutter lifting (and ruining) the plate as it zips off in some random direction through the plate. It will try to take your hand along for the ride. Of course, you must gingerly relax the downward pressure on the plate in order to smoothly move it along. A down shearing cutter may alleviate this, but by the time you come to this realization you will have ruined several plates. Now, others may tell you that after some practice it is possible. What I will tell you is that no two pieces of wood cut the same and that practice merely gives you enough overconfidence to go ahead and try it, thus ruining a good plate. Fair warning from the voice of vast experience.........
  2. "Other features affect velocity of different projected frequencies, i.e., different frequencies move at different speeds, adding "depth" [perception] at the listener's "ear"." Do you have a simple reference for this? I haven't encountered the notion that air should be dispersive over the range of frequencies of interest. Thanks.
  3. Hi Anders: Could you verify whether we are looking at the top from the inside or outside? Thanks,
  4. quickest and cheapest is a cookie baking sheet from a thrift store.
  5. and if it is successful I will always wonder why I didn't take up this hobby 30 years ago........ drop down to "GuarnerI Violin" http://fortcollins.craigslist.org/search/sss?query=violin
  6. From Langsather's website- ".The ideal frequency is 322 HZ.(Other frequencies that resonate with carbon are 300, 285, and 262 HZ)" Is he trying to say that just because wood has carbon in it, it should resonate like carbon? Certainly some tuning may have a positive affect on set ups, but some of this sounds like BS to me. Also, what part of the pegs am I supposed to carve off to adjust the tone? diameter ?(darn, won't fit the holes any more) head? It is from Dieter Ennemoser, read his site and decide for yourself. I think it is preposterous B.S. Check the prices of his spirit varnish. He has sold a lot of it to audiophools.......... http://www.ennemoser.com/c37theory.html
  7. one of these should do the trick...... http://www1.mscdirect.com/CGI/N2DRVSH?PACA...000000075232874
  8. "The thing I found most impressive was the video of him talking about the design of the ff-holes, and the animation showing the top vibration patterns" Tell me where to find this. Maybe I am a little dense.........
  9. Stradofear is not Michael Darnton. When I posted on the inhomogeneous catenary, Stradofear was open minded but reasonably skeptical. On the other forum, Michael Darnton was absolutely scathing in his comments about the inhomogeneous catenary. Try another guess, guys.
  10. is there any reason not to use a small area of silk reinforcement in the sound post areas of the plates?
  11. Nigel Harris makes some interesting comments on varnish/emulsion/particulates here: http://www.nzlistener.co.nz/issue/3484/art...vibrations.html Not endorsing it, just something from someone else aimed at a different audience.
  12. The cosmology that Hawking and Penrose study is testable by measurements (at least to a certain extent). I have yet to read of any verification of anything predicted by string theory, or for that matter, of any prediction of string theory that could be verified by a well designed experiment. I think string theory is an interesting (to some) excursion into mathematics and belongs in the math department a major universities, not the physics department. We are at least 30 years into it with no physically verifiable results.
  13. Lets not complicate this unduly. Einstein didn't accept quantum mechanics, for which he laid much of the basis, because he couldn't accept the statistical nature of its predictions. He was holding out for something causal and deterministic ("God does not play dice with the universe") We modern sophisticates know that quantum mechanics is correct because our computers and cellphones work, or at least our probabilistic minds perceive that they work, I'm not really sure which is (probably) true. Or perhaps it is only in the minds of string theorists that anything works. Fortunately, string theory can't predict anything that can be measured............. My own opinion is that theoretical physics is way off track and that anything that admits to alternate realities shouldn't be included under the topic heading "Physics"
  14. It will sound like hell at low frequencies i thik the impression was that it became weaker in the low register I think we are in agreement. Or am I missing something? BTW, add me to the list of your appreciative supporters. You really can't expect to get as much back as you put into a forum like this because many of us are here precisely because we know so little, and are hoping to pick up good info from those few like you who know so much. So please keep giving us your info and wisdom, it won't go unappreciated.
  15. Hi William: Remember, I am focused on strengthening the responses to the lowest frequencies, and trying to find a way to do meaningful frequency matching of front and back plates with static tests on the theory that the old masters had some means of doing that. Doing tests just on the top would not fit into what I am trying to learn, namely a way to maximize the vibrational amplitudes in the lowest frequencies of the response. I am studying mainly the breathing mode which has both the front and back vibrating at relatively large amplitudes and similar amplitudes for front and back as shown in the Schleske animations for the Helmholtz mode. The reason I say I "think" the resonance I am most interested in is the constrained plate mode is that at low frequencies, simply displacing the front and back simultaneously at the bridge/sound post and then releasing them will probably result in vibration at frequencies above the Helmholtz frequency. My working hypothesis is that the violin body is a driven oscillator for a portion of a cycle and then a free oscillator for the balance of the cycle, and that maximum low frequency vibration amplitudes will result if the front and back are trying to move together at the sound post location on each. If I am way off base, you can be the first to tell me. (I think I am being repetitious )
  16. Well, John, to paraphrase some character or another in "Alice in Wonderland", "Rebound Frequency" means whatever I want it to mean . I "think" the frequency I mean is the frequency you would measure by taking the free plates, constraining the edges and measuring the lowest resonance that occurs by exciting the plate at the bridge/sound post position. My intuition is simply telling me that if you deflect the plates at the bridge/sound post position, then release it, the plate will vibrate at some characteristic frequency and you would like for these to match for the top and back. Nothing more sophisticated than that, just gut level intuition which is certainly subject to error. If I am all wet, just tell me so and I will shut up Of course, I have never done such an experiment with a great violin, I have examined exactly one of them in my whole life, a del Gesu. I didn't even touch it out of respect for it's varnish.
  17. John: Let me try this another way. Suppose I take a great violin and glue a big lead blob to the back right under the sound post. I haven't changed any areas or thicknesses, except at the one tiny spot. It will sound like hell at low frequencies. The down bow will push the lead down allright but the back will not rebound as fast as the top would like to rebound due to the inertia of the lead. The increased mass means that the rebound frequencies of the plates, as measured with constrained edges, are radically different. The stiffness's of the plates remain the same. It may still sound just fine at high frequencies, where the back plays a lesser role due to it's greater mass. All I am suggesting is that with matched rebound frequencies, the body may respond in a single vibration mode, a breathing motion, and be a better low frequency radiator. (I understand that the edges are not perfectly constrained, and that that will have an effect) Oded: Someday I will learn not to trust my memory, it is too old to be reliable for anything I learned more recently than forty years ago Meant to say about 290 Hz, as shown at Schleske's site for that particular Strad. Stradofear: I have studied Schleske's site to the point of memorization of everything there except the Helmholtz frequency. What I am trying to get a handle on is a way to match rebound frequencies of top and back plates using static flexure tests. I hope I am making progress in my understanding, but won't know until I finish this first violin. (and then I suspect I will have only enough data to be be truly confused)
  18. Hi Oded: What I was trying to say is that as we pull sideways on the string(s), we exert a torque on the bridge that results in downward pressure on the treble side bridge foot. When the string slips, the treble bridge foot, top plate and bottom plate all rebound upward. Melvin: at the resonant frequencies, all that happens is that the amplitude increases rapidly relative to the amplitude off-resonance and there will be an increase in SPL radiated. John: You will not be losing any energy when the top and bottom want to go in different directions, but if you are looking at a particular mode of vibration, it seems to me that if you have the top and bottom arguing over which direction to move, higher order modes will be excited which lack the coherence of a single mode, and there will be a a concomitant loss of vibration amplitude and SPL. In other words, the top will try to move according to one vibration mode, the bottom according to another, not adding into a coherent single mode. Just a gut reaction, no elegant analysis to support. Also, I think the air mode is around 190 Hz.
  19. Thanks, John. I am most interested in what is going on at the low frequencies, quasi-static, i.e. the breathing mode rather than the ring mode. It seems to me that what is going on is as follows: As we pull on the bow (down bow) both the top and bottom are depressed until the bow slips. At that point, the top and bottom will behave as un-forced oscillators with an initial condition of a given deflection. In the absence of tension (we are in the slipping phase of slip-stick) the top and back both spring up, each trying to do so at their resonant frequency but constrained by the connection between them, the sound post held in place by string tension. If the resonant frequencies of the plates (not the Helmholtz frequency) are close, when the bow catches again the back and top will be headed in the same direction and the back and top will be working more or less in unison, a seemingly desirable condition. If the top and back frequencies are about the same, there is no energy lost to the top and back fighting with each other as to "which way to go". Please straighten me out if I am not visualizing this correctly. Thanks,
  20. Hi John: Would you mind giving us the frequencies and masses for both top and bottom plates for as few of your best violins? Also the type of spruce for the top and densities of spruce and maple if you have them? I would like to play with the numbers a bit. If this is propriety or too much trouble, no problem. Thanks,
  21. Hi Anders: We newbies would all benefit from your assessment of the research areas that are irrelevant. My own list begins with free plate tuning. Tell us more, please.
  22. You need a bench grinder, but not to sharpen your gouges. Use #1 is to shape scrapers, you want a fine grinding wheel, say 200 or so. Use #2 is to polish your gouges after sharpening them with the scary sharp system. You will need a felt wheel for this. If you are the least bit careful, you will never have to regrind an expensive gouge, chisel or plane blade. Here is everything you need for sharpening: thick glass plate or flat smooth tile, at least one square foot (Home Depot has them cheap) spray adhesive wet/dry paper from auto body shop supplier in 220, 400, 600, 800, 1000, 1200, 1500, 2000 grits (and finer if available) felt wheel for grinder stick of polishing rouge the above is all you need for the scary sharp system, well under $50 for a ten year supply. When I am roughing plates, I will touch the gouge to the polishing wheel every 15 minutes or so, makes a noticeable difference. I suggest you start learning to sharpen with a cheap 1/2" chisel from home depot before you touch your gouges and plane blades. It takes very little effort to learn how to do it. A search of this site and a Google search for "Scary Sharp" will provide you with all you will ever need to know, the secret is to just practice until you get it down. For scrapers you need a 10" smooth mill file, a burnisher (which can be the back of one of your gouges) and the scary sharp supplies above (sometimes). The most important lesson for scrapers is NOT to buy the commercial cabinet scrapers. The reason is that the steel is so hard that you will never get it sharp or be able to turn an edge on them. Instead, go to Office Depot and buy a 12" stainless steel ruler and take the cork off the back. Cut this into 2-3 scrapers and grind to shape. This steel is soft enough that you can get a good sharp edge and it is malleable enough that you can turn the edge. Took me six months of frustration with the scrapers sold at Woodcraft to learn this lesson. Do a search for posts by Oded Kishony on scraper sharpening for good advice, but basically he sharpens scrapers with a file after grinding then to shape. I do that but then smooth the beveled edge on the sandpaper and felt wheel before turning the edge. You may find that scrapers work better without turning the edge. Have fun!
  23. Don't spend your money on water stones. The "Scary Sharp" system is better, in that you do not have to worry with keeping stones flat, and much cheaper. Do a search here and you'll find lots about it.
  24. Hi Craig: I don't have the Sacconi book and unless prices change, I am unlikely ever to have it. However, there are a couple of things I have learned while studying arching/graduation. First, the centroid of the violin plan form is at the bridge position. Draw it out, work the numbers, and you will find that it is around 190+/- or so mm from the top. Secondly, if you take a top with uniform thickness, you will have the center of mass north of this position for the simple reason that relative to the planar area, there is a larger surface area, and hence mass, in the upper bout than in the lower bout. Now, FF holes and bass bar will also affect the CM as will the graduation. I think the biggest effect on where the current CM is relative to the original CM has to be in changed graduation and bass bars. It would be nice if someone like Jeff Loen would use his maps to compute a "relative" center of mass for violin tops he has measured. Now, tell me what you know about this. Thanks,
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