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ttonon

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About ttonon

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    Chatty concertinist

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    http://www.bluesbox.biz
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    Princeton Junction, New Jersey, USA

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  1. ttonon

    Push vs Pull - why?

    Hi Ted, yes, we can distinguish between average pressure on the reed and pressure difference across reed. Let's stick with practical numbers. A typical pressure difference is about 5 inches Water Column, so for that same pressure difference, the push reed experiences 5 inches WC higher average pressure than the draw reed (2.5 + 2.5 in WC). I fail to see though how that is significant concerning the playing of the reed. One atmosphere is about 14.7 psi absolute, or about 408 in WC, and so the average pressure difference is only 5/408 = 0.0122 parts in atmospheric pressure. How can that slight average pressure affect the operation of our friend the free reed? The only way I see is through density, but still, only a 1.2% difference in density is very small. If you're curious enough, you can try to discern such an effect of density by playing your concertina at sea level and compare the sound to playing at about 500 feet above sea level. Keeping the temperature the same, that will correspond to about a 1.2% difference in atmospheric density.
  2. ttonon

    Push vs Pull - why?

    Ha! I invented such an animal and got a patent for it just for fun, and of course there was no revolution. Bi-directionality is only a small part of the many issues involved in making such basic changes to an old hand-crafted technology. I'd rather not bring up this issue again, but you relative new comers can do a search for old threads on this issue.
  3. ttonon

    Push vs Pull - why?

    Hi Ted, I don't think we can look to Physics to help solve this riddle in the way you say. From a physics point of view, the push and pull are entirely symmetric. The reed cannot tell whether the pressure difference it experiences is either a push or pull. Neither can the bellows. A bellows can collapse from too much vacuum, but it can also blow outwards because of too much compression. I do agree that we can probably exert more force on the bellows with a push, mainly because of the way our muscles and skeleton are constructed. I'm sure an anatomist can provide solid reasoning, but simply, the push is accomplished by some arm muscles and chest muscles, whereas the pull is accomplished by different arm muscles and back muscles. Perhaps the main difference lies in stronger chest muscles than back muscles. Best regards, Tom www.bluesbox.biz
  4. ttonon

    CASTING REED FRAMES

    Thanks Dave, interesting process, looks like fun. In your first photos, it looks like you don't use runners, or passages to direct the molten metal to more than one area, and to let out air. Interesting that you don't have a problem with getting air out of the way with the gravity feed. Regards, Tom
  5. ttonon

    maintenance for brass reeds

    This is incorrect. The air flow velocity is a function of only bellows pressure, not flow area. The Bernoulli Equation, V = (2*Pb/Rho)^0.5, shows it, with V velocity, Pb bellows pressure, Rho air density. Physically, it means that specific potential energy (pressure) converts to specific kinetic energy (V^2), intrinsic properties of the fluid, nothing to do with geometry. Remarkably simple. Best regards, Tom
  6. ttonon

    maintenance for brass reeds

    Hi Dave, I understand. You illustrate the difference between "hand-made" and "machine-made," and I don't mean those labels in the way used by Italian and Chech reed makers, but in the more general sense. Before my questioning, I looked at it from an industrial perspective, but you have many more variables available "at hand," treating the fabrication more like an art. Your cost is time, but hopefully artisan work such as yours can continue to be something people are willing to pay for, of course because of the superior result. Thanks for the detailed info. Best regards, Tom
  7. ttonon

    maintenance for brass reeds

    Hi Dave, thanks for the descriptions. Why do you cold work it? I understand that brass usually comes in annealed, half hard, and full hard, sometimes with quarter hard increments, depending on how much cold working the material has in manufacturing. To me, the manufacturer did a useful thing to provide material with definite properties that are probably uniform and consistent. What's the advantage of doing your own work on it? Can you make a full hard material stronger by cold work? Won't it start producing cracks? Why buy a grade less than full hard? Beating implies hammering, which suggests a rather crude method. I suppose that if you have your own precision roller, you can avoid that, though still, why not use material with strict specs? Best regards, Tom
  8. ttonon

    FREE REED PHYSICS - 3

    Johann, I've mentioned it several times in this forum that James Cottingham has done extensive experimental investigation of free reeds. You can see a list of his publications at: https://www.researchgate.net/scientific-contributions/58932239_James_P_Cottingham Jim is joined by many others on these investigations, both theoretical and experimental, and I think you would be interested in the many details and the precision with which this research is done, using the scientific method, and proceeding far beyond anything we have discussed here. We often lead ourselves in circles, and unfortunately don't include the deep insights uncovered in the literature. This forum interests me mainly because of the interesting information provided by makers and doers and the resulting personal contacts. It still can't come close to an adequate stage to present all the knowledge about free reeds currently available. Best regards, Tom
  9. ttonon

    FREE REED PHYSICS - 3

    Johann, yes, our hearing response comes into it and it's entirely possible you hear more of the highest steel frequencies than I do. I know my hearing is compromised, thanks to my time as a carpenter and the circular and radial arm saws. Tom
  10. ttonon

    FREE REED PHYSICS - 3

    Okay, I misunderstood what you mean by "on top." I thought you meant "above." But the important thing is what I described, the titanium dominance of the 5th harmonic can very easily make the titanium sound brighter than steel. Do you agree? Best regards, Tom
  11. ttonon

    FREE REED PHYSICS - 3

    Hi Johann, don't you mean with the red line on top? I can see that you simply reversed the colors for steel and titanium, and now, titanium is red. Before, the red line in the 5th didn't show, so this is a better choice for color. But I think this indeed explains why titanium to me sounds brighter than steel. It's that fifth harmonic, which dominates all except the first, by at least a factor of 50 in amplitude. It's often very difficult to make guesses about how different spectrums will sound unless there's clear dominance among enough harmonic amplitudes, but in this case, and you may not agree, if I saw that spectrum, I'd be confident to guess that titanium would sound brighter. Best regards, Tom
  12. ttonon

    CASTING REED FRAMES

    Hi Dave, thanks for the interesting pictures and info. What's the reason to take that sand out of the slot, is it so that metal flows more easily to fill all portions? I assume you then have to remove the metal hymen. I'd opt to see pics of the freshly molded piece. Do you have an idea of the surface roughness, particularly on the sides of the slot? Best regards, Tom
  13. ttonon

    FREE REED PHYSICS - 3

    Hi Johann, you're right that the picture shows a tapered tongue, and I don't see much filing, so I'd guess that the tongue thickness is constant (no profiling) and that guesses about modal frequencies are probably reasonable. I apologize for not looking at that picture more closely. The biggest question I have about the spectral data is the prominence of the 5th harmonic. Since there's no red color on the bump - or at the base of the bump - I assume that particular harmonic shape is duplicated by steel and titanium, since all other harmonics show a dark color whenever the values for steel and titanium overlap. I think you'd agree that this puts into question the accuracy of that harmonic measurement, because it's unlikely that both steel and titanium would have an identical 5th harmonic response. It's probably caused by an artifact somewhere in the recording. Perhaps a resonance in the microphone? Do you have a copy of the frequency response for your microphone? Maybe it's in the electronic circuit or some feedback to the microphone common to both metals. But it's very curious that it occurs precisely at the 5th harmonic. If we truly hear that harmonic, for any reason, and it's not something hidden in the electronics, you'd agree that such a large harmonic could dominate the sound of both reeds. If that's the case, a hearing test would be invalid. The art of experimentation is an art; it's usual very difficult to obtain good data, and as you know, bad data is worse than no data. In my previous post, I forgot to point out that the first harmonic in my plots dominate the others by only a couple/three orders of magnitude - for the higher pressures, only one. Johann's data, and with other measurements I've seen, it dominates by about four - excluding the spurious 5th harmonic. This is a huge difference in relative amplitude, and perhaps lends more credence to my hypothesis, that higher harmonics from the reed displacement can perhaps contribute to the overall sound. Best regards, Tom
  14. ttonon

    FREE REED PHYSICS - 3

    I should clarify. When I hypothesized that higher harmonics in the first mode vibration of the tongue might translate to musical tone, I didn't mean to imply that the musical tone would be the result of only those harmonics. Harmonics associated with sudden changes in pressures and velocities of air motion due to the vibration are indeed a major cause for what we hear, as acoustic models and experiments verify. My hypothesis is based on the fact that different materials seem to sound differently to many listeners, and if that's the case, how else can they be heard? In more detail, it's possible tongue motion harmonics do not directly contribute, but only indirectly, as for instance if the minute motion of the harmonics superimposed on the main sinusoidal motion first affect the chopping of air flow through the slot. So rather than sound emanating directly from the quivering surface of the tongue (which is my hypothesis), that quivering mostly affects the time dependence of the chopping phenomenon, which is really what we do hear. However, whether indirect or direct, these higher harmonics need only make a contribution to the sound, enough so that we can discern it in the musical timbre. For anyone who claims that these tongue harmonics do not affect the musical tone, I ask by what mechanism can different materials affect the sound? I mean between two metals that can be fashioned into geometries having equal levels of preciseness. So Dana, I never disagreed with Benade's explanation, and I'm assuming here his explanation has to do with the mainstream idea that pressure wave harmonics are associated with chopping airflow. My hypothesis simply adds to it, in the growing comprehension of how complicated Nature really is. As an aside, I'm curious whether Benade attempted any explanation for how different materials can be distinguished. When I chastised Johann for spreading false concepts, I didn't mention that higher harmonics of the acoustic reed sound can be coupled to the air in the cavity, affecting the harmonics, and thinking back on it, that may be all he was referring to. But this is a very weak form of coupling, and it's far different from the "acoustic coupling to an air column" usually referred to with such terminology. Dana, I appreciate your explanation of the practical issues involved with different tongue materials and find it fascinating. The scope of any theoretical contribution I can make to the issue is very small, and it's the maker who carries the real burden. In fact, I wouldn't object to anyone describing my suggestion as a flippant remark from a theoretician. Can you please explain further what you mean by "equally stiff at the designated pitch." I recall you explaining that you used a scale to measure spring force of tongues. Do you use that in this process? Again, can you please elaborate? I do hear a difference between Johann's steel and titanium tongues, and to me surprisingly the titanium sounds brighter. This is emphasized while wearing headphones, as Johann suggests. There is a definite preponderance of the higher frequencies from titanium, and I notice that the steel first sounds much more "mellow," until about 2.5 seconds (where you can actually see a slight increase of amplitude on the graphics) higher frequencies ensue, but don't seem to dominate as much as with titanium. I agree that my perception seems to contradict what the frequency spectrum suggests. As interesting as Johann's data is, it cannot be decisive. Important information is left out. Most importantly, what kind of a microphone was used, where was it placed in relation to the reeds, is that relationship the same for both, was the same microphone used for both, what is the pressure level, what are the thicknesses and lengths of the tongues, what is the width and is it constant with tongue length, is there any profiling, etc. All these can have important influences. I'm struck by the very large 5th harmonic. In my experience, it seems exceptional. I notice that around the 6th harmonic, there's a blip that might suggest a slight contribution from the second bending mode of the beam. There's also a blip around the 16th and 17th harmonic, suggesting a third bending mode, however, we can't say for sure because we don't know if the geometry conforms to that of a simple constant area cantilever, for which such conclusions can be made. Additional blips might be contributions to torsional modes, though that's not too likely, but if pressures are high enough, maybe so. Then we have to wonder about the quality of the recording equipment and the software used to calculate the Fourier coefficients. It's clear that theoretically, experimentally, and practically, a full understanding of tongue material would require considerable effort. Best regards, Tom
  15. Greetings again. Here we compare steel to a titanium/tantalum alloy, Ti/Ta 70/30 Beta, which is used in surgical equipment and prosthetics. It interests me, not so much to propose it as tongue material, but because the tantalum increases the density well above the neat material. The modulus is only a third of that for steel, but its density is a little above that for steel, resulting in a modulus-to-density ratio about 0.3 that of steel. We can compare these results to those comparing Titanium to steel and find that the higher harmonic amplitudes in comparison to steel are very much less in the Ti/Ta alloy. The behavior with increasing bellows pressure shows the harmonic amplitudes making up the difference – just what happens in the Titanium/steel comparison; however, since the higher harmonics of the alloy start with such low values, they don’t catch up to those of steel nearly as quickly or as completely as in the case of the neat material. Comparing these plots with the plots for brass/steel, we see an enormous difference. If we can discern an audible difference in timbre between brass and steel, according to these plots, and if our basic assumptions are correct, there should be an enormous difference in timbre between either Ti or its Ti/Ta alloy and either brass or steel. Another interesting outcome in the case of the alloy is that I couldn’t get a convergence with a solution for bellows pressure less than about 2.2 inch w.c. On the other hand, solutions continue further on for the higher bellows pressure than they do for steel and other materials. This might indicate a material that may not be able to play at very low bellows pressures, but may perform better than other materials at the highest bellows pressures. The last plot in these calculations show that the trend of increasing harmonic amplitude with bellows pressure continues for even the highest bellows pressures, for those above solutions for steel become impossible. We can make such plots for most any feasible tongue material, though at some point, the usefulness tapers off, at least if we are in search of a practical tongue material. The theoretical interest continues, as a way of getting a good intuitive feel for the effect of material properties on musical tone. At this point, I think we need wait for experimentalists to compare information they have from work already accomplished or from new work. There might be other materials I'd like to do calculations on, such as glass, and other geometric factors, such as tongue thickness and plate thickness. A docx file showing these plots are at: https://app.box.com/folder/79305691686 Best regards, Tom
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