ctanzio

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About ctanzio

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  1. ctanzio

    Cooking shellac

    There are many color-fast, highly transparent alcohol based dyes that can be used to tint shellac. At one time, water based dyes were more color fast than the alcohol ones, but I am not sure if that is still the case. Most of these water dyes will mix with alcohol due to the miscibility of water and alcohol. You can then add the water/alcohol mixture to the shellac. Some testing is needed to make sure the dried shellac is not adversely affected by the water content. The finish can become cloudy. I have had some success with brown water based dyes using the above method, but now I just use alcohol tints. Shellac, when heated past a modest temperature, will decompose and "burn" into a opaque brownish black, glassy-like substance. I've never been able to add color by heating without destroying its usefulness as a varnish. One other thing. Currently I prefer coloring the wood, then use amber and clear shellac without added tint as the varnish to add depth and protection to the finish. Coloring wood before applying varnish is a topic that has many posts in this forum.
  2. ctanzio

    About violin bridge tuning

    I hold the feet flush against the top of a table and let the bridge project beyond the edge. I then draw a bow across one of the sides while recording with a free spectrum app on my phone. Instant mode frequencies.
  3. ctanzio

    About violin bridge tuning

    Given "the usual" position of a bass bar, it would be unusual NOT to have the left leg sitting over the bar if you select a bridge where the outer distance between the feet is equal to the distance between the upper f-hole eyes. Have you had many occasions where the bar was placed so far inward from the f-hole that a bridge foot width selected based on the distance between the eyes would not sit over the bass bar?
  4. ctanzio

    About violin bridge tuning

    The dimensions on that drawing seem "standard". I would note the following... Unless the bridge is of very high-quality (meaning hard maple with high elastic constant), then keep the top thickness closer to 1.6mm than 1.3mm and be careful not to overly thin the bridge body. An overly thin lip on a soft bridge can introduce various challenges to tuning the strings. You might have to fix the grooves with a hardening treatment to avoid problems with a thin lip. A bridge with weak resistance to bending along the length of the violin can cause unusual tonal issues. I cannot say if the tonal changes are good or bad, but they do seem unstable in that the sound changes can suddenly occur. It seems to affect the A and E strings more than the G and D strings. For the heart, kidneys and area between the feet, my suggestion is modestly carve them any way you want to appeal to your sense of art. I have never been able to reliably quantify a change in tone, power or responsiveness by "tuning" these areas unless I removed so much material that the bridge looked ugly and began to deform in undesirable ways under the string load. IMO, the thickness of the bridge, roughly starting at the bottom of the heart and moving up to the lip, seems to be the only dimension worth changing to get a meaningful tuning effect. Your drawing shows an overall linear slope to the thickness profile. Some makers make it more rounded in order to keep more mass in the lower 2/3rds to resist bending, and less mass in the upper 1/3rd to make the bridge more responsive to the strings. The overall width of the bridge measured from the outer edges of the feet might be worth adjusting. I have not found a hard and fast rule that applies to all violins. I measure the shortest distance between the upper eyes and make sure the feet do not extend beyond that width. This is mostly a structural consideration to avoid loading the top plate in such a way that might introduce a crack along the grain to the treble-side eye.
  5. As a standard matter of scientific inquiry, the burden of proof is on the one making the positive affirmation. If there is no good evidence for Antonio shipping his in-the-white fiddles to the local furniture finishing shop, then the best we can say is "We do not know." I want to point out that there are some very high-quality commercial products that work fine on violins, both oil and spirit based. Make a list of properties you want from the varnish, and go test. The main advantages of a high quality varnish from a well-established commercial firm are consistency of finish and resistance to aging effects. Here is my list of properties in roughly order of importance: Clarity Color Color Permanence Thinness of Stable Coat Hardness Leveling Structural Aging (Resistance to humidity, heat and light) Of the list, I would not compromise on the first four. The fifth item, hardness, is a finishing and wear issue. But many times one can select another product as a clear overcoat to make up for deficiencies in a base coat that hits the first four tick marks. Leveling depends on the effect you are trying to achieve. Some like the texture of the wood to show through. Others prefer a smooth coat. Structural aging is almost never a problem with a high quality product. Modern companies tend to extensively test the aging properties of their varnish and paint products targeting the high-end market.
  6. ctanzio

    About violin bridge tuning

    In general, I have found that if you carve enough of the bridge away to actually hear a change in tone, then you have compromised the structural integrity of the bridge. Obviously from some of the posts made so far, others think otherwise. Find a reliable reference for the standard dimensions of a bridge. Adjust modestly for artistic effect. So basically what Melvin said.
  7. Thanks for the references. The A0 frequency range on that plot seems rather high for a 4/4 violin. Was it based on measurements of full sized violins?
  8. Making the f-hole area larger by increasing the width will tend to increase the A0 frequency, but the effect might not be easy to measure in a typical violin unless you really make them much wider. At that point you might run into other effects that will cause a different behavior. It will also decrease the power of the violin for notes played in first position. The circumferential length seems to be the main influencing factor for the f-holes on A0 frequency and power. Keep the f-hole widths as narrow as possible, but not so small that the air flow through the opening begins to choke due to turbulent flow. There is a lot of theoretical and experimental work needed to optimize fluid flow through a slot like an f-hole, but for the violin we have the advantage of centuries of practical experiments. If I wanted to experiment with a larger f-hole, I would look into copying something from a good sounding Guarneri, since they tend to have longer f-holes than Strads and still meet the tonal and power requirements of top players. I have no answer for the question on using different lengths for the two f-holes. Try it and see as an old professor used to tell me. I suspect the resulting violin would look a bit odd, to put it kindly, and so would never gain any traction with players regardless of any advantages you might be able to claim. Regarding the observation that the A0 frequency is proportional to (1/V)^0.25, I would like to see a reference to the study. A classic Helmholtz resonator has a theoretically derived and experimentally verified frequency that varies as (1/V)^0.5. Tests performed on multiple violins and then doing a curve fit to volume versus frequency plots tend to have exponents slightly bigger than 0.5. This can be partially accounted for by uncertainty in the measured volume of the air cavity. But this is a detail that is not really relevant to the discussion. Whichever accurately describes violin behavior, it remains that increasing the volume decreases the A0 frequency.
  9. I do not quite understand what you are asking. Are you asking what happens when you change the width of the f-hole but keep the length the same? In effect, increase the area of the f-hole without changing its overall length?
  10. A0 resonance is a strong function of the length of the classically shaped f-hole. When lengthening the f-hole, two measurable effects occur: 1. The resonant frequency increases, and 2. The power efficiency of the radiated sound near the resonant frequency increases. For the first effect, I agree with Don Noon that the A0 frequency in relation to the other main modes is probably more important than the actual value of A0. Remember that a fundamental mode actually vibrates at the frequency of the note being played, not at its resonant frequency. The further the note frequency is from the resonant frequency, the less that mode contributes to the power of the note. So if the resonant frequencies of nearby modes are too far apart, then notes played between the mode resonate frequencies will sound weak. But if the resonant frequencies of two modes are close together, then notes played near those frequencies might sound too booming. For the second effect, the perceived power increase would be mostly for notes played in first position, G through A strings. By the time one gets to the E string, the note frequencies are far enough removed from the A0 resonance frequency to have less of an effect on the power of the notes than other modes. Violins made during the Amati period tend to have f-holes in the 65mm to 75mm length range. Stradivari violins tend to have f-holes tightly clustered in the 70mm to 75mm length. Guarneri violins have a wider range of f-hole lengths but, on average, push the lengths to well over 75mm. The A0 frequencies steadily increased over those times, as well as the perceived power of the instruments for lower notes. For the mathematically minded, two equations are available to get an idea on what to vary to experiment with different values of A0. First, compute a sound hole factor as follows: F = S x L / V S is a sound hole shape factor which you can ignore for just thinking about small changes to a classic f-hole shape. L is the circumferential length of the f-hole. V is the air volume of the interior of the violin. The A0 resonant frequency is related to the square root of F: f ~ sqrt(F) The power of notes played near A0 is related to F squared: P ~ F x F For anyone thinking about radically changing the f-hole shape to dramatically increase the power, there are limits based on air flow velocities and the thickness of the top plate at the f-hole in relation to the f-hole length. F-holes became narrow and long because the air flow through the middle of the opening detracted from projected power. If the f-hole is made too narrow, then air flow along the edges will shift into the turbulent range and power efficiency will suddenly drop off. If the f-hole is made too long, then certain physical effects that can be ignored for a typical violin will become important and alter the behavior.
  11. ctanzio

    24mm fingerboard projection. Highly arched!

    I believe 15mm is considered "average", 20mm would be considered "high" and 13mm would be "low".
  12. ctanzio

    24mm fingerboard projection. Highly arched!

    If you set the neck to get a 27mm projection regardless of arch height, then you have compromise on some other geometry, like the over stand, neck angle or string angle. Assuming the neck stop, body stop and body length are within a mm or two of a standard 4/4 violin, then you need to select a combination of TWO parameters from a set of various other dimensions, like: over stand, neck angle, fingerboard projection, string angle over the bridge, bridge height. I can probably think of a few others that can be added to that list. I recall a post by Roger Hargrave where he said things like the neck stop length, neck angle and bridge height evolved to current values mostly for insuring that the player can comfortably finger and bow the strings. So, for example, if you pick one of the two parameters to be neck angle "standard practice", then adjusting the over stand to get a 27mm fingerboard projection will work just fine. Or if you use a common over stand as a target value, and shim the finger board to get a target fingerboard projection, it is geometrically equivalent to correcting the neck angle to a "standard" value. If you never had the need to develop a full command of geometry, it is easy to be fooled into thinking ALL the various dimensions on a violin drawing can be varied independently.
  13. ctanzio

    24mm fingerboard projection. Highly arched!

    The drawing does show the fingerboard projection. That projection is not an independently variable parameter. For example, if one follows "standard practice" for the location of the bridge and the nut, the angle of the strings over the bridge, and the clearance between the strings and the end of the fingerboard, then the fingerboard projection is automatically set and will vary according to the height of the arching. One could start with a fingerboard projection in mind and vary the neck angle to keep the string angle and string clearance within "standard practice". There are other design options. The usefulness of a fingerboard projection measurement is that it is easy to do and can suggest a potential problem, like a sunken top that has altered the neck angle. I wonder how many makers actually design to a specific fingerboard projection. My impression is that the set the stop length, neck angle and over stand to get a desired string angle with the proper string clearance. The fingerboard projection ends up where ever it is going to end up.
  14. ctanzio

    Anyone have any surplus Gemini soundpost Setters??

    You can see these setters in action on youtube. A metal channel is attached to a bent, hollow tube. A stiff string is threaded through the tube to form a loop across the channel. The sound post is inserted into the loop. A tug on the string where it comes out on top of the tube makes the loop hold the post securely against the channel. Insert the sound post. Release the string and remove the setter. A classic setter, or one of the newer setters with a spring-like clip work as well and probably a little bit faster with slightly less hassle. I've gotten so used to the spring clip setters that I can insert a post in a matter of seconds.
  15. ctanzio

    Tap Tone or Plate Tuning Equipment

    It captures the Q of the entire violin, string and body. For sine burst into the bridge, one supposes the bridge would need to be supported by the strings, so the damping of the strings would still come into play. I would need to think a bit about whether or not the results would be different between the two tests. The point of any of this really depends on what the OP is trying to accomplish. If one is trying to judge the effect of wood treatments or construction techniques on the Q of the body, then some burst sine input into an unstrung violin might be the way to go. Q values are frequently frequency dependent, so that adds an extra complication into figuring out what any of this means.