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ttonon

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Chatty concertinist

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  1. While on this topic, is there a consensus among makers which action is superior, if any, the hook or riveted? Thanks. Tom
  2. Paul, thanks for your helpful measurements. Alex, thanks for your detailed explanation. I calculate that the average spread in all of Paul's measurement to be 0.0059 inch, or +/- 0.003 inch. Can you estimate the average gap between tongue and slot that you get with your finished product? If I recall correctly, Dana once commented that his gaps are maximum about a half thousandths of an inch. Paul's measurements indicate that the slot inaccuracies don't follow the same trends among the different results, and that would perhaps make filing the tongue more tedious. I'm curious how you visualize the gap in order to see how your filing is going. I once used an optical comparator, which, on an overhead screen, displayed a very magnified version (10x) of whatever you placed on the table, which had a glass surface that was backlit. I'd think that such an apparatus could be very helpful for this kind of work. Regards, Tom
  3. As you know, you can verify an acceptable fit with your eyes, by looking at the gap between the tongue and slot through a bright light. But it's another issue to measure and provide quantitative data that others can evaluate. So, too bad you don't have a way to do that.
  4. Can you measure the slot width at 5 - 6 places with an inside Vernier caliper and tell me what the measurements are? I'm interested in this for my own projects. Thanks. Regards, Tom
  5. Lucayala, yes, I can now see that the blocks and reed plate are two different components. I don't mean to belabor this, but have you tried 3-D printing of tongue slots? Your statement doesn't acknowledge the tolerance that is present in all fabrication. For instance, what is the tolerance of variation WITHIN a given slot? It would be something like 4.97 +/- x1 for the AVERAGE width - an issue that you can overcome by your trial-and-error approach. But there will also be a tolerance on how much different parts of the the actual slot differ from the average, or something like 4.97 +/- x2. And also, the printing machine might change the "average" value over time. Maybe you understand all that, and I mention it only because you didn't. Regards, Tom
  6. Okay, but there are still outstanding unanswered questions. (Are you familiar with these standards?) From the pictures, I don't see the separate "Plate" assembly, consisting of many tongues mounted above slots carved in their own plate portion of the assemble, as with the traditional bandoneon. But I'll take your word for it. But again, how is the necessary accuracy accomplished? Regards, Tom
  7. Hi Pistachio, why do you say a "cold weld" forms between tongue and plate? Such does not occur between dissimilar metals, and most reeds have steel tongues and aluminum plates. I doubt even with brass tongues on brass plates cold welds occur because the mating surfaces probably cannot be cleaned well enough of the metal salts that form on them, but I could be mistaken. I also don't see how any such weld would affect performance, since riveting and screwing work so well.
  8. Lucayala, I looked at the information in the link and find it most interesting that the slots in which the tongue vibrates are formed directly in the accordion-style reed blocks. How is this done? Does the 3-D printer form only a rough slot, and afterwards there's a necessary filing step to make the final shape? It's my understanding that the tongue should fit within 0.001 inch on either side within the slot, and I'd be surprised if the 3-D printing process allows such accuracy. Does it? In addition, with all the slots being an integral part of the reed block, if you make filing errors in finishing the slot, there's no simple way to fix just that one slot. I realize that many bandoneons contain metal plates that have many slots, presenting the same kind of issue, and nevertheless, makers do go in that direction. I guess the bottom line is how well these 3-D printed instruments sound and play. Have you ever played one of them? Regards, Tom
  9. Lucalaya, you ask only about tongues, but the slot the tongue vibrates in and the metal plate in which the slot is made are also important. So are the leather valves. You might be interested in this website: https://www.harmonikas.cz/cz/sortiment#obsah This company makes bandoneon, accordion, and concertina reeds, and there are subtle differences among these kinds of reeds. On this website, you can obtain much information on the tongue geometry (length, thickness, width) for the various reeds in different pitch ranges. You might also benefit from knowing the formula that calculates the natural frequency of a vibrating cantilever, which is what the tongue is. This formula strictly applies to tongues vibrating in a vacuum with a cross section that is constant throughout their length. f = 0.1615*sqrt[E*h^2/(rho*L^4)] where the material properties of the tongue are E, or Young's Modulus, and rho, density. h is tongue thickness and L is tongue length. The actual vibration frequency of the tongue will be a little less than what you calculate above, because of air resistance and inertial loading. But you can use this to get an idea of say, the thickness and length that you need. Best regards, Tom www.bluesbox.biz
  10. Richard, It's a common misconception that work hardening a metal increases its Young's Modulus. It looks simply like, "Well, steel has a higher Young's Modulus than does brass and steel is harder than brass, so I guess if you make the hardness of brass up closer to that of steel, you will also make its Young's Modulus up closer to that of steel." The misconception arises because we are talking about two different mechanisms within the metal. One is elasticity and the other is plasticity. Young's Modulus is a feature of elasticity, and elasticity is possible only for small enough stresses. Such sufficiently small stresses involve only the intermolecular forces within the material. You can visualize them as tiny springs. That implies that only the chemical nature of the material participates in the observed elastic property. Once you stress the material so much as to cause plastic deformation, you involve other forces than just the intermolecular forces. Every metal has internal features that tend to resist deformation, such as grain boundaries, inclusions, and dislocations. With plastic movement, these features get "locked in" more than they were just before deformation, and subsequent deformation escalates the resistance to relative movement that these features provide. That explains the hardening, why it's harder to cause more deformation. But the intermolecular state is not changed appreciably by the deformation. That's probably because the total volume of the material occupied by the grain boundaries and other defects is very small compared to the total volume of the material. Thus, if the material is only slightly stressed again after the deformation, those tiny springs behave just as they did before deformation.
  11. I'll give my two cents from an acoustic point of view. The only material parameter governing the vibration of cantilevers is the ratio of Young's modulus to density. In other words, all materials having that same ratio will vibrate in identical ways. However, when we consider the acoustics of the air vibrations caused by those vibrations by the tongue of a free reed, there are other complications. Yet without anything else to go by, and to a first approximation, I'd look at this ratio in trying to guess what the acoustic properties will be for different materials. That ratio for 1095 spring steel, the usual material used for tongues, hard tempered flat brass, and phosphor bronze is 2.78E8, 1.43E8, and 1.42E8, in English units of ft^2/sec^2. And the corresponding ratios are 1.00, 0.51 and 0.51. We often hear that brass tongue instruments sound softer or more mellow than steel tongue instruments, and so we might conclude that lower values of the ratio Young's Modulus to density lead to softer sounding reeds. By this criterion, phosphor bronze tongues should have a sound similar to brass tongues. In the literature they state that phosphor bronze has resistance to fatigue, and my guess is that it's superior to brass in that regard. The conclusion is thus that phosphor bronze might very well be a good choice for tongue material. Concerning fatigue, we often hear that brass tongues tend to break, and ten years ago, I did an analysis that explained why that's so. I posted it on this site at https://www.concertina.net/forums/index.php?/topic/14533-why-do-brass-tongues-break/#comment-138648 It's a long post and only those hard core techs will be interested, but be my guest. Tom www.bluesbox.biz
  12. Lukasz, from my calculations, I see no possible resonance interference with the tongue vibration. This applies to both Helmholtz and quarter-wave tube resonance. I thus cannot make a suggestion here, only I'm still not clear on what the basic problem is. Are you saying that all the F3 reeds you put into the "bad" cavity show the same problem? Also, that when you put those same reeds into a different cavity but with the same dimensions of the "bad" cavity, there is no problem? Best regards, Tom
  13. Hi Lukasz, I just now heard your wav file and I agree, the 1st and 3rd sounds seem restricted, and the 2nd and 4th more open or free. In my experience, such a restricted sound occurs when the mounting of the reed - most often the geometry of the cavity - begins to acoustically interfere with tongue vibration. For instance, if the port is too small, or even if the leather valve isn't opening completely enough. Alternatively, there could be some defect in the construction of the reed, such as a burr, or other way to interfere with tongue vibration. Your guess that the problem lies in a restricted second partial seems to be borne out by the spectrum. In the bad note, that partial is about 13 dB below the fundamental, and in the good note, it's only about 5 dB below the fundamental. I'm not sure there's evidence in the spectrum for your claim that the energy of that second partial is fed into the higher partials, which from my experience would be an odd occurrence, knowing what I know about the conversion of pressure pulses to audible sound. We can notice that the bad note has also a greatly reduced 8th partial, compared to that of the good note, but I doubt that has anything to do with what we hear, since the pitch of that partial is about 22,000 Hz, far above our normal hearing range. However, your discovery of this reduced second partial may give us a clue. If you'd go through the trouble of presenting here all the exact 3-D dimensions of the cavity and the size of the port, I'd be glad to take a look at it, possibly finding an identification of the second partial frequency with some way the cavity could resonate. If it's a simple rectangular cavity, it should be easy to do. Best regards, Tom
  14. Hi Lukasz, Audacity enables the calculation of a frequency spectrum showing a rectilinear graph, with sound intensity on the vertical axis and frequency on the horizontal axis. I believe that such a representation is much more useful than the kind of spectrum you posted here. If you can't figure out how to get that graph on Audacity, let me know and I can perhaps lead you through it. More basically, I don't know what your "problem" is. Apparently there's a problem with the sound of two different F3 reeds when alternatively mounted in the same cavity. Is this correct? If so, could you please explain in detail the problem in the sound? Do you think you see the "problem" in the spectrum you posted? If so, please explain. In the "Bellows pressure and musical pitch" thread, if I recall, you thought that the poor sound was because of a pronounced harmonic and I suggested you do a spectrum analysis. Do you still think the problem is with a pronounced harmonic? If so, the kind of spectral graph I describe will be most useful. Regards, Tom Tonon www.bluesbox.biz
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