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About Johnmasters

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  • Birthday 05/08/1944

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    Physics of violins
    Finite element analysis for eigenmodes, stresses, whatnot

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  1. Chin up. Ignore that it may have been refinished. For what you paid, it is hardly a loss if you like the sound and can play it. If you take lessons, you will soon pay over $400 total for them. Any loss from the revarnishing can be ignored. It is not "ruined," it is your functional violin. Enjoy it.
  2. I find that upside-down carbon paper works great. Before gluing, I clean off any black stuff that might have waxes etc in it. (I use xylene which I know many are afraid to use. Perhaps acetone would be fine.)
  3. If it is super hard and tough, It may be dogwood. I have some dogwood in sizable pieces and it looks somewhat like this. I have never tried to make anything from it. If it IS dogwood, I believe it would be very stable and polish up nicely.
  4. I notice that you do not indicate farenheit or centigrade degrees. Be sure you know the difference. The 250C is higher than 250F.
  5. Maybe it depends on the plumber's plumbing.
  6. Doesn't it seem reasonable, that if amount of hair in the ribbon is critical, one should ask whether one wants the ribbon at the point of transition away from pure elastic ?
  7. Brilliant double talk !! Just shove it back to them, they deserve it !!
  8. About "school" practices ... isn't it likely that many times a maker would have his own good idea for something, or were they all a bunch of robotic morons? (Who worked for starvation wages.)
  9. Yes, and a happy Thanksgiving to all from me also. But..... WHO is it that you say discovered the western world? Some of those people also say we CIVILIZED the natives that we found here. Ths seems unfair... The indigenous cultures here had their faults, but no worse than we with the nuclear weapons and corrupt governments.
  10. There must be a material to convert the vibrational energy to heat. Such as the rubber plug in the wolf note supressor. Vibration is not "absorbed." It must be dissipated into another form of energy such as heat (your conservation of energy.) Or into some vibration of the finberboard. Any kind of conversion that does not just throw away the vibrational energy. (Your conservation of Energy) Friction forces make conservation of momentum difficult to discuss.
  11. That is true, and I was thinking of the high-frequency noise that you speak about. These are what I suggested had a higher phase velocity. There is another possible thing to think about... damping of acoustical waves depends on frequency... It would be true even if these higher frequency components did not travel faster than the entire tone (wave packet.) I found a differential equaition here. It is the second equation, but it would take me a month to plow through it.......... Maybe Don can at least tell us if attenuation increases with frequency. That would also explain your example.
  12. And I think that the leading edge (in time) of the wave packet would be more affected. The initial bang should not see a "ramped" volume because these faster contributions will have passed and been damped out or at least much weaker than the peak of the pulse. But yes, I see your point and will do a calculation with your numbers for a non-shock wave such as a violin note. 100 Hz is certainly a low frequency, and I don't know what to say. I have no idea of what constant would be. At 30 meters, how far ahead of a 3000Hz wave would be a 7000 Hz wave? And would their separation then be at the level of a half wave of so? I choose 3000Hz as it is approximately the upper level for useful music hearing (for me at least) Do you have any ideas involving acousical dispersion , or do you think it is not something to consider? Also, your example of an explosion still does not seem to be a good example using your numbers.
  13. But you cannot really hear the late-arriving overtones. Your ears may saturate. But more importantly, I am not sure if a simple fourrier consideration would be right for a shock wave. Fourrier series suggest a linear superposition of components. This would not apply for a shock wave which compresses the working medium. Considering a Fourrier integral for a linear superposition is pretty basic, and I do not see how you can find it to not be relevant unless you reject the notion of phase velocity varying much in the listening situation. It WILL occurr, the question is by how much. And if you do not see any dispersion at all in a wave packet, then why don't all violins sound the same at a distance vs close up?
  14. I have added a new topic that suggests a possible physics view involving the difference of phase velocity and group velocity in any wave phenomenon. That is, the examples where the phase velocities of the components of a signal travel at different speeds in a medium. This is called "Dispersion."
  15. A possible explanation for why some "soft" violins carry well. The physicists and engineers here can comment... a signal of finite length (in time) can be considered as a summation of single-freqency components. (More exactly, a Fourrier integral of retarded components) These components all travel at slightly different speeds. The effect is more prominent in optical waves in, for example, glass. This is what allows a prism to split white light into its component colors. The fact that this was first seen in optics is likely responsible for the term "Dispersion" although it is not confined to waves in glass. AIR IS A DISPERSIVE MEDIUM FOR ACOUSTICAL WAVES ALSO. Air is almost certainly less dispersive for acoustical waves than is the case for optical waves in glass. But it exists. A wave packet will spread in time... this causes a smearing of the signal in time (distance traveled). It would be dependent on the bandwidth of the components of the wave packet. The two central ideas are phase velocity (velocities of the single-frequency components) and group velocity, the average velocity of the entire packet. The wider the band-width of the packet, the worse the dispersion. I have seen some statements that perhaps a sharp rolloff of response in a violin at about 7k or less is a good thing. This would lessen the dispersion of any wave packet signal. Also, under the ear, the violin might sound less loud. I consulted an engineer friend in California, and indeed, "phase lag" causes a difficulty in broad-band amplifiers. I believe it all goes back to considering the Fourrier integral for the signal and then taking the time representation of a signal heard at a distance. With too much band-width, the signal gets smeared over time. The higher frequency components are lost to the ear. And perhaps that is why a violin that "carries" well sounds a bit soft under the ear. (The player may unconsciously diminish his efforts because of the sensation of loudness under the ear.) Comments?