Marty Kasprzyk

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About Marty Kasprzyk

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  • Birthday 06/02/1945

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    Olcott, NY, USA
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    Wine making, gardening, dog training,

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  1. Thanks. This is a serious question for makers and players and I'll address it in a few days. But I make lot's of mistakes so I worry about leading people astray. Doug Martin has been an inspiration to me and he said: "I love it when my most cherished beliefs are proven wrong."
  2. The wood's speed of sound c in turn is equal to the square root of its elastic modulus E divided by its density p which can be rearranged. c= (E/p)^0.5 C^2 = E/p E = pc^2 The elastic modulus E for the first wood is equal to its density times its speed of sound c squared (I'll drop all the zeros and units): E = 0.417(5)^2 = 10.4 The elastic modulus E for the second wood is E = 0.375(6)^2 = 13.5 These examples show that the second wood has both a lower density and a higher elastic modulus which causes it to have a higher speed of sound. It was desired that both plates have the same mode frequencies f. The better 16 RR wood with its lower density can also be made thinner which will further reduce the plate's weight compared to the 12 RR wood. We saw earlier that the frequency f is proportional to the square root of the plate stiffness S/plate mass m ratio f ~(S/m)^0.5 We saw before that the plate's stiffness S is proportional to its elastic modulus E times its thickness t cubed: S~Et^3 The plate's mass m is proportional to its density p times its thickness t: m ~pt f ~ (S/m)^0.5 f~ (Et^3/pt)^0.5 f~ t(E/p)^0.5 Recall that the wood's speed of sound c is equal to the square root of its elastic modulus E divided by its density p: c = (E/p)^0.5 Thus the various mode resonance frequencies f of a plate is simply equal to its thickness t times its speed of sound c times some constant b: f= btc A plate made from our 12RR wood with a speed if sound c of 5km, thickness of 3mm and the constant b is 30: f = (30)(3)(5) = 450Hz resonance frequency for some particular mode. A second plate made from our better 16RR with a speed of sound c of 6km can be made with a thinner thickness t to achieve the same mode frequency of 450Hz: t = f/bc = 450/[(30)(6)] = 2.5mm So our better 16RR wood can be made only 2.5mm thick instead of 3.0mm thick for our poorer 12RR wood and still achieve the same mode resonance frequency. (As a side note it should be mentioned that this is one downfall of the "plate tuning" concept where any wood can achieve the same mode frequencies therefore the violins can have the same sound character. This is true however a better RR wood can achieve a greater sound output as we will see next.) The stiffness S of the plate is proportional to the elastic modulus E of the wood times thickness t cubed so the stiffness S of our 12RR wood is: S ~(10.4)(3.0)^3 ~ 280.8 The mass of our 12RR wood plate is proportional to its density p times thickness t: m ~(0.417)(3.0) ~ 1.251 The impedance i of the plate is equal to the square root of its stiffness S times its mass m, i = (Sm)^0.5 so the impedance i of our 12RR wood plate is: i ~ [(280.8)(1.251)]^0.5 ~ 18.7 Likewise our other plate made with the better 16RR wood has a stiffness S : S ~ (13.5)(2.5)^3 ~ 210.8 and the mass m of the plate made with better 16RR wood is proportional to its density p times its thickness t: m ~ (0.375)(2.5) ~ 0.938 The impedance i of our 16RR wood is: i ~ [(210.8)(2.5)]^0.5 ~ 14.1 Admittance a is equal to the reciprocal of impedance i so the ratio of the admittances of the plate made with the 16RR wood to the one made with 12RR wood is 18.7/14.1 = 1.33 Going back again to Benade's graph we see that this 1.33 admittance ratio should give us about 2dB increase in sound output. So going from lousy 12RR wood to great 16RR wood gives you just a small improvement in sound output. So finally my advice to makers is to forget about all this shit and just make your plates to weigh about 65g with reasonable wood like Don said.
  3. The dark stripes look like pores filled with dark stain to me.
  4. I was afraid somebody would ask. Normally I do this all quickly in my head (just kidding). In the Schelleng reference I mentioned earlier he states that impedance i is equal to the square root of the product of stiffness S and mass m: i= (Sm)^0.5 Stiffness S of a plate is proportional to the thickness t cubed times the elastic modulus E : S = Et^3 mass is proportional to the thickness t times the density p: m = tp so substituting in the above impedance equation we get the impedance equal to the plate thickness t squared times the square root of the product of elastic modulus E times the density p: i = (Et^3tp)^0.5 = t^2 (Ep)^0.5 in the first example I gave the wood was kept the same so the elastic modulus E and the density were constant. The thickness t was reduced by 10% to achieve the 10% weight reduction that Don was curious about so the new impedance i is proportional to the new thickness (0.9t) squared: i ~ (0.9t)^2 ~ 0.81t^2 admittance a (how easy it is to move) is the reciprocal of impedance i (how hard it is to move) = a = 1/i the ratio of the admittance a of the thinned plate to the original plate is therefore: a new/a old = t^2/0.81t^2 = 1/0.81 = 1.23 So the thinned plate with 10% less weight has 1.23 times higher admittance than with the original thickness and their admittance ratio is 1.23. I've assumed (could be a mistake here) that a vibration peak amplitude of a vibrating system is proportional to the admittance of the system therefore thinning also increases the amplitude ratio by the same 1.23 ratio. But Don asked about decibel change and whether or not we would notice it. So it is necessary to convert the above 1.23 ratio into a decibel change. Rather than doing the log math I just picked off the dB change from a graph in Arthur H. Benade's book "Fundamentals of Musical Acoustics", second revised edition, 1990, Dover Publications. This graph on page 227 is attached and I hope the copyright police won't notice. In the second example I gave I considered a 10% reduction in weight achieved by using the same thickness plate but with a 10% lower density wood. We know the wood's elastic modulus E is generally directly dependent upon density p times some constant b: E = bp if we ignore all the constants and substitute this in the above equation for stiffness S we find that the stiffness of the plate is proportional to its density p times its thickness t cubed S = pt^3 substituting this stiffness S into the earlier impedance i equation gives: i = t^3 (Ep)^0.5 = t^3(pp)^0.5 = t^3p again the admittance a equals the reciprocal of impedance i, a= 1/i Since the thickness t didn't change the ratio of admittances a from using lower density p wood is just the ratio of their densities: p/0.9p = 1/0.9 + 1.11 and again reading off of Benade's graph for a 1.1 ratio of amplitudes gives an increase of about 0.5dB. So after all this work all I get is a lousy T shirt saying 0.5dB. The third example used woods with different radiation ratios RR of 12 and 16 and the plate thicknesses were adjusted to give the same mode frequencies. The radiation ratio RR equals the wood's speed of sound c divided by its density: RR = c/p The wood's speed of sound c in turn is equal to the square root of its elastic modulus E divided by its density p which can be rearranged. c= (E/p)^0.5 C^2 = E/p E = pc^2 so the elastic modulus E is politically correct squared. to be continued...
  5. The answer seems to be dependent upon how you make the plates lighter. Here's three examples: If you substitute the wood with one having a 10% lower density and keep the thickness the same there would be about a 0.5dB gain. I doubt it would be noticeable. If you just make the plate 10% thinner to reduce its weight by that much there would be about 1.5dB gain. I do think this would be noticed but the reduced thickness would greatly reduce the plate's stiffness (because of the thickness cubed) and the various mode frequencies would drop. The instrument would sound a little louder but also less bright. If you wanted to keep the same sound character you could increase the sound output by using a wood with a higher radiation ratio (RR= speed of sound/density). Let's compare two different RR woods. The first one is a rather poor wood with speed of sound of 5000m/sec, density of 0.417g/cc giving a poor RR value of only 12. The second wood has an impressive speed of sound of 6000m/sec, a lower density of 0.375g/cc giving a very good RR value of 16. Notice that the second wood has a 10% lower density than the first like in the first example. However it has a high speed of sound which allows it to be also made thinner. So the plate made with great wood would be about 25% lighter and would produce about 2dB increase which is very helpful. But this is comparing really poor wood with really good wood. One unit of RR increase gives only approximately 0.5 db more output. This doesn't seem that big an inprovement but maybe the difference between good violins and great (loud and bright) violins isn't very big either.
  6. I think your statement about instrument choking is really important. A prominent Julliard teacher mentioned that soloists appear to be poised and relaxed when they perform but actually sometimes they're quite nervous and they worry about screwing up anything that might give them a bad review. Nervous itself causes bowing errors. If they have an instrument that has a real high high maximum bow force it prevents choking and rough sounding notes. Playing it takes a lot of work (bow force times bow stroke length). So an instrument with thick plates has a lot of resistance needing a lot of bow pressure, is less apt to choke. This gives the player less to worry about, thus reduces nervousness, improves confidence and makes the music is better. So an instrument that is hard to play is sometimes actually easier to play than that one easy to play.
  7. An advantage of using a high radiation ratio RR (speed of sound /density, c/p) wood over using a wood with a lower RR is that it allows the plate to be made thinner thus lighter for the same mode frequencies. The lower moving plate weight makes the instrument louder. A high RR can be achieved by having various combinations speed of sound and density and often a wood with an especially low density will tend to have a high RR. So from an acoustic output point of view a thin plate made from low density wood is good. Unfortunately the strength (fracture strength or creep resistance) of wood is generally proportional to density so a plate made with low density wood is weaker than one made from high density wood. The bending strength of plate is also proportional to its thickness cubed so a thinner low density wood plate (great for sound output) is relatively very weak. Cracks and/or deformation will quickly occur. So there is a trade off between acoustic output and instrument life dependent upon your wood and thickness choices. This is not a new observation. John Schelleng, in his landmark 1962 paper "The Violin as Circuit" (1) showed the derivation of the radiation ratio criteria for picking wood and he stressed the benefits of picking a high RR wood. However he also said: "Strength of wood is another appears that a different wood parameter, strength/cp measures the upper limit of sound pressure produced" where strength is the bending, shear, tension strength across the grain, etc." Perhaps we should be picking our top plate wood on the basis of cross grain bending strength/cp to avoid cracks which seem to be so common in old instruments. Maybe we should also think about how long we wish our instruments to last. 1. The Journal of the Acoustic Society of America, Vol. 35, No. 3, 326-338, March 1963, Reprinted in CASJ Vol. 4, No. 3 [series ll], May 2001 Can you imagine the fine print on the bottom of a soloist concert program saying: "So and So sold their Strand, paid off his/her student loans, house mortgage, car loans, and all the credit cards and is now using instruments made by __ __ . They're especially loud you can easily hear them and only cost just a few thousand dollars so he throws them away (often into the audiences) and buys a new one every year and doesn't carry any insurance on them and doesn't worry all the time about theft or forgetting them in taxis. The reduced stress and anxiety has greatly improved the quality of his life and it carries through with a care-free spirt for performing which we hope you enjoy tonight."
  8. High arches increase stiffness which increases all the various mode's frequencies. On the other hand I would rather have high arches than flat feet if there wasn't a draft going on.
  9. Why use low-density high RR wood in the first place? If you're stuck with it I suggest using lower arches.
  10. Instead of tape, try a dab of chip dip.
  11. You might enjoy John McLennan's thesis (attached). "A Baroque violin was initially made. It was then incrementally converted to a Romantic (modern) setup by replacing the short neck with a longer, more slender neck and adding a longer ebony fingerboard, a heavier bassbar and soundpost. This increased the total mass from 386 to 440 g. Several different Baroque and modern configurations, with baroque and modern style bows, were used for acoustical measurements and playing tests with professional violinists." McLennanThesisComplete.pdf
  12. How many violas do you have? Ideally you should have enough to get through several days without power.
  13. It's a violin not a viola.
  14. Accurately duplicating the geometry of great instruments is not very helpful for getting great results unless their wood properties are also closely duplicated. I value multiple duplicity.
  15. The shape of the violin (size, length to width proportion, arch heights etc.) evolved in consideration of the woods available (spruce and maple) of certain properties (speed of sound in length and cross directions, density, damping etc) . I believe it is highly unlikely that other woods with different properties would work equally as well or better with the same geometry. It would most likely turn out worse. Simple material substitution usually doesn't work well. But different wood such as Ponderosa pine might work out quite well for a geometry found suitable for it. It will take a lot trial and error experiments and/or analytical effort. On the other hand, violas made from different woods but of equal weights have the same BTU heating value.