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Everything posted by ttonon

  1. Hi Frank, interesting point, and I want to make sure what's going on here, in detail. I think the depth of folds and the number of folds are independent parameters. Correct? It also makes sense to me that a shallow fold will require more force to open than a wider fold, simply because the part of the fold that flexes assumes a greater part of the fold material, resulting in less of a "lever distance" available to the musician, who must then exert more force. In addition, since the force required to bend individual folds is in series with all the other forces associated with the other folds in the bellows, the total force is equal to only one of the forces. Thus the total force to pull the bellows is only about equal to the force required to open only one of the folds. This applies to the force required to close the bellows, if the equilibrium position of the bellows is in an open position. Is that about how you'd sum it up? Thanks. Tom www.bluesbox.biz
  2. You might also try the new household bleaches formulated with hydrogen peroxide, which is also used in medicine. Better yet, buy H2O2 at the drug store, which I believe is stronger than the residential products. Another suggestion is Oxalic Acid, an organic acid that is often used to whiten materials, as an alternative to Chlorine bleach. I'm particularly cautious about Chlorine bleach because of it's tendency to combine with the ever-present hydrocarbons, resulting Chlorohydrocarbons compounds, many of which are proven carcinogens. So unless you're adequately protected, I'd shy away from Chlorine. So why do municipalities chlorinate public water systems? Exactly! Tom www.bluesbox.biz
  3. Hi Chris, I think you're right. I went to the site of a bandoneon restorer at https://www.alma-bandoneon.de/en/ and asked him the question. His response is below. Sorry for getting us all off on a crazy tangent of mine. It seems bandoneon makers have some unique ways to treat the leather valves. On the effect of tongue offset, what he says checks with the practices in accordions and concertinas. Hi Tom, thank you very much for your interest in my work. Your question relates to a topic in restoration where musicians and restorers split into two camps and which is much discussed. Technically, you have to keep in mind that at the time the bandoneons were made, leather was the only suitable material .The leather was relatively thin and very flexible, so that it could give way quickly when the reed swung and just as quickly folded back when playing in the other direction or the reed came to rest. However, over the years, leather will dry out and curl up towards the skin side (which is what you observed). Attempts have often been made to prevent or remedy this by making slight cuts in the surface of the leather. It is normal for the lamellas to stick out slightly from the reedplate, but rolled up lamellas cause unpleasant background noises and detuning. In addition, they also lead to a deterioration in the sound response and higher air consumption. When you look inside a bandoneon, you can only see the leather lamellas, which are opposite the reeds that you play in opening direction. In tango, the bandoneon is mainly played pulling, so that these leathers bend outwards more often. The lamellas inside are mostly much more flat ; ) Modern lamellas are usually made from a combination of leather and a thin plastic sheet. The leather lies on the reed plate and ensures a warmer tone and the foil bends the leather back into its position. Valves made of full plastic, as often used in the accordion, are not very popular with the bandoneon. They amplify the upper sound frequencies and the sound is "falsified“. Choke of the reeds in severe staccato has a different cause and depends on how the reeds are bent (adjusted) towards the reed plates. The rule here is that the less the tongues are bent, the easier it is for them to respond. However, this also means that they no longer work at high air pressure. Conversely, tongues that are bent up very far still respond well at high pressure, but consume more air and are insensitive. Lot of the old school bandoneon players are very conservative and swear on the original, 90-110 years old leathers, even if they are not perfect any more. Whether new or old lamellas is a matter of taste. However, rolled up valves prevent the instrument from functioning properly. The perfect adjustment of the reeds, voicing and choose of the right leather lamellas and tuning is the most difficult part in my job. Kind regards, Christoph
  4. Interesting because I'd predict the opposite. My guess is that setting the reeds to low offset would increase their tendency to choke under large pressure amplitudes imposed at the opening of the key. Aren't large offsets the way to accommodate such high driving pressures?
  5. Hi Dana, concerning valves and their idiosyncrasies (and I may have posted this before somewhere on this site) but there seems to be a completely different approach among bandoneon makers than there are here among concertina and accordion makers. But first a short story. I went to a Tango music performance played by an excellent bandoneon player from Argentina and an excellent piano player from Uruguay. Afterward, I talked to the bandoneon player about his instrument and he graciously offered to open it up and show me the workings. I immediately noticed that the leather valves were mostly all curled up away from the reed tongues. He cautioned me not to touch them because they are supposed to be like that, though he didn't know why, and I'm wondering if anyone here can make a guess on it. The only explanation I can think of is because of the nature the way the bandoneon is played in tango music. Every bandoneon musician I see playing tango sits with the heavy instrument on the lap, or with possible exception, stands, but now with the instrument resting on a pole to the ground. I also notice that bandoneon bellows have a wooden frame about an inch wide mounted at their center, and I often wondered why. For those who know tango music, especially traditional music, there are tremendous dynamics, with sudden explosions of sound when the instrument is dropped, then suddenly stopped by its underneath structure that supports the center piece of the bellows, with the two ends still pushing downward, causing a huge vacuum inside the bellows. My guess is that the curled up reeds prevent some of the high vacuum pressure from occurring inside the bellows by allowing some excess air flow through non-sounding reeds. This prevents too a vacuum pressure that would tend to choke the reeds that are intended to voice. If those reeds weren't so leaky in the first moments, perhaps the playing reeds would choke and not play at the right time. So we want maximum dynamics in volume, but don't want to choke the reeds. Regardless, I think it an interesting variation on the ideas discussed here.
  6. LIttle John, sorry for the long delay, but I just noticed your post. I think the answer to your puzzle is the fact that the beating reeds make use of an acoustic resonator, which forces the vibration of the reed itself. Typically, the natural frequency of vibration of the reeds in beating reeds is much higher than the frequencies of the musical tones. This is why you sometimes hear the squeaks when a beginner plays for instance the clarinet or sax. You're probably hearing that high frequency from the sole reed vibration, no air column vibration. Thus the pressure pulses from the standing waves in the resonator determine the vibration of the reed, and those pulses occur at 1/f seconds, where f is the fundamental frequency of the musical note, which if you calculate is on the order of milliseconds. As I explained, the vibrational start of the free reed has entirely different physics, leading to those relatively long start transients.
  7. RAc when you bend a wire having a circular cross section, the tighter the bend, the higher will be the compressive stresses in the side that is crimped and the higher will be the tension stresses on the opposite side, which is extended. The maximum tensile and compressive stresses developed in bending depends upon the ratio of the wire diameter to the bend (coil) diameter. The higher this ratio, the higher the stresses. You can understand this intuitively by drawing a little picture of the coil and note that the geometry is defined by two lengths, and that the scale of the whole drawing is determined only by the ratio of those lengths. Thus, the scale of your picture is defined only by that ratio, and all combinations of wire and coil diameters that have the same ratio can be superimposed on each other by manipulating the magnification (scale) of the drawing. Incidentally, this is the same situation with the bending of a beam. Said simply, the only thing the material knows or "feels" about its physical state is defined by that ratio of diameters, and this explains why thicker wire diameters have more stress for the same bend radiuses. Another suggestion I'd make is with the terminology, which can cause confusion. Broadly, there are "extension" springs and "compression springs. Using "tension springs" to describe "extension springs" confuses the fact that there is tension in both extension springs and compression springs. It's impossible to impart bending stresses in a wire without inducing both tension and compression stress. I apologize for being so exacting with all this terminology. That's just what I do. I find that many people get confused by either not fully understanding the terminology they use, or they confuse others by not using the best definitions in their explanations. Regards, Tom www.bluesbox.biz
  8. HI Little John, you raise an interesting question that I hadn't considered, and my first response will be to rely on the differences in the mechanisms by which the two musical tones are produced. Let's first look at both cases starting with the time the tongue starts to hit the plane defined by the top surface of the underlying plate. The beating reed hits the plate, and the free reed enters the slot. When the beating reed shuts off airflow, a rarefaction (reduced pressure) wave passes down the pipe, the resonator, at the speed of sound, hits the open end and is reflected from there as a positive pressure wave that returns to the reed, opening it, which immediately allows a puff of air on top of that returning pressure pulse, which then travels to the open end and returns as a rarefaction. The latter hits the reed, but keeps it closed, bounces back, still as a rarefaction, up to the open end, reflects as a positive pulse that travels back to open the reed. I said all that in order to state the complete cycle, but the important thing is that the opening and closing of the reed is determined by the pressure pulses in the resonator, not because of the natural vibration of the reed itself, which for beating reeds is far above the pitch of the resonator. What do we conclude from this? Mainly that the time to establish a full cycle of reed vibration is basically the period of oscillation of the musical tone. This time is largest with the longest pipes, having frequencies less than a 100 Hz, or on the order of ten milliseconds. That's the very largest. For smaller pipes, we are talking about periods much less than ten milliseconds. This is a rough analysis, but I think it gives an educated guess on why organ builders conclude that the free reed is much slower to start, having transient times many tens of milliseconds. For the free reed, much of the start transient occurs even after the tongue starts entering the slot, so we really don't have to bother with the complexities of vortex induced vibration. Many studies have been done that prove this out. I believe the reason lies in the fact that relatively very little additional energy can be incorporated into vibration amplitude during those starting times. In fact, most of the swing cycle of the free reed is symmetric, in that just as much energy is put into the vibration as is taken out - except for a tiny moment in time when the tongue enters the slot from the top, where there is a net energy addition. The situation is too complex to discuss here, but to say it simply, the beating reed organ pipe has much larger energy available for the start transient. The column of air within it is the primary vibrating element and the vibratory mechanism is more suitable for such energy levels. That's why brass instruments can be so loud. Regards, Tom
  9. I may as well have fun with this, but first, I'm assuming that by "rounded edge" you mean that the very thin side of the tongue is not a flat plane at right angles to the upper and lower surfaces, but rather it has a curved, convex shape . I base my comment on that picture. I tend to agree with Chris that such a feature should not affect the sound too much. But as usual, we can devise other possibilities in special instances. Such as the start transient and the amount of pressure needed to start vibration. Since the quiescent tongue offset is sometimes comparable to the tongue thickness, a rounded edge can conceivably require more pressure to start, simply because the bottom surface of the tongue enters the slot first, and if the edge is square (not rounded), less pressure would be needed than the pressure required to immerse the center portion. That suggests a rounded edge may require higher starting pressure. But even that's a guess because, in the case of the rounded edge, the larger air gap the bottom edge may still provide the proper conditions to start vibration. The start of vibration itself is a dynamic issue, involving the shedding of vortices moments before the actual start. The vortex shedding causes the tongue to vibrate at first with very low amplitude, low enough so that the tip doesn't enter the slot. This is a phenomenon in architecture called vortex induced vibration of cantilevers. With tongue vibration, eventually the amplitude becomes large enough for the tip to enter the slot, at which point the common mechanism for self induced vibration takes over with a rapid buildup to steady state. The whole event may take tens to a hundred or so miliseconds, and by musical instrument standards, this is a long transient start time. In fact, it's so long that organ builders didn't want to use free reed pipes in their organs. But in recent times they have become more forgiving. So one sees how picayune we must be in order to understand some seemingly simple things about this amazing sound source. Concerning the sound of reeds played at normal volumes, I'd reason that a rounded edge shouldn't have much affect, simply because the tongue thickness, say 0.010 inch, is much much smaller than the amplitude of vibration of the tip portion of the tongue. Whether that 0.010 inch contains a rounded feature shouldn't make any difference. I base this guess on the fact that the harmonics in the acoustic sound are a result of the aerodynamic forces acting throughout the cycle of vibration. Thus, the whole period of motion produces these harmonics, and tongue thickness itself is a minor dimension compared to the relative amplitudes and surface areas contributing to the total motion. But I could be wrong. We can again get a bit picayune here and wonder about very soft sounds, when the vibration amplitudes aren't as large. But I'll not go there. One suggestion would be to take one step at a time. Make two identical reeds, one with rounded edge and the other without, install them and play them. If you're energetic, make three sets at different pitch ranges. I think it would be foolish to make a whole reed set in order to check out such questionable advantages. Concerning fatigue of tongue materials and simply speaking, metals have what are called "endurance limits," meaning they break after a sufficient number of times in cyclic motion. The number of maximum cycle times decreases the higher the stress experienced. If we forget about internal residual stresses and stress inducing features and defects, most steel reeds last indefinitely because the stress levels in concertina playing are low enough, except sometimes for the very longest tongues. In this regard, some here may be interested in a long discussion on endurance issues we had on this site eight years ago: https://www.concertina.net/forums/index.php?/topic/14533-why-do-brass-tongues-break/ Regards, Tom www.bluesbox.biz
  10. John, again I'm not making myself clear. So I'll try again. When I say harmonic I mean harmonic, which is a mathematical term indicating whole number ratios. When I say harmonics, I'm not referring to the bending modes of the cantilever, which are not harmonic. As you probably know, the second bending mode has a frequency roughly 6.2 that of the first bending mode. The statement, "I take the clang tone to be the first bending harmonic" is erroneous. The clang tone is the second mode vibration, with it's fundamental roughly 6.2 times the frequency of the first mode fundamental, which is the usual one we observe. Each mode has it's own fundamental. "This spectrum shows nine integer harmonics of the fundamental in addition to the clang tone." This is correct. The "nine integer harmonics" are the same harmonics I refer to. They are not modes of vibration, but harmonics within the first mode vibration, as the caption says. Again, they are harmonics in time, you cannot see them with a strobe, which shows only the geometrical shape in space, and these harmonics do not change that shape. Again, the best way to understand them is to picture the vibration as "jerky" in time, not a smooth sinusoidal motion at the fundamental frequency. These harmonics vibrate at higher frequencies than the smooth sinusoidal motion. - gasp - Regards, Tom
  11. Hi Dana, I had a hunch that I wasn't getting my point across. I'll try again. We agree that the cantilever vibrates in different bending modes, and that its first (transverse, or bending) mode is the one that dominates in the free reed. Now, with that mode, there are also harmonic frequencies in time. The fundamental of those harmonics is the chief vibration we observe; i.e., that's the sinusoidal motion (in time) that causes the chopping of the air stream. However, there are also higher harmonics in that time vibration. As I said, it's best to describe this as a kind of jerkiness in the motion. There's no way that you could distinguish these bending harmonics from the acoustic harmonics you hear. That's why you couldn't measure them. I attach an article from Acoustics Today that explains this very well, with pictures. The article explains how a tuning fork vibrates in myriad ways, but since the tuning fork is basically two cantilevers attached together, you can interpret much of this to understand how the free reed tongue vibrates. The only difference is because the tuning fork is struck and then it vibrates freely, without the continuous forcing that an air driven free reed experiences. The strike of the tuning fork excites all kinds of modes and harmonics, but in the transient free vibration following that, the higher modes and vibration harmonics dampen quicker than the first mode and its fundamental sinusoidal character. That's why you get such a pure tone, with little "quality." The air driven free reed vibrates with a steady periodic motion, long after start transients have damped out, but the aerodynamic forces exciting it are not sinusoidal. They have essentially step functions in time, yet they are still periodic. This non sinusoidal forcing function will excite not only the fundamental sinusoidal excitation of the first vibration mode, but higher harmonics of that fundamental. Also, in many cases, but perhaps not all, even the second bending mode may also be excited by these aerodynamic forces, and this mode can be sometimes measured for all but the lowest bellows pressures. In fact, during the start transient of the free reed, torsional modes can also be excited. Although it's a common practice, we have no physical reason to oversimplify the vibratory motion of the free reed. Read the attached article. It's very interesting. In particular, look at Figure 3c. The-Tuning-Fork-An-Amazing-Acoustics-Apparatus-Daniel-A.-Russell.pdf
  12. Hi Dana, I know we discussed this before, but now I'm confused. "Air driven reeds produce a completely different set of actual harmonics in the 1,2,3,4 etc.X the fundamental." Are you talking about harmonics in the acoustic pressure wave form that we hear, or harmonics in the time dependency of the mechanical tongue vibration as a bar, within it's first transverse mode of cantilever vibration? "In my experience, air driven reed waveforms are only slightly sawtooth..." Again, are you talking about the acoustic pressure waveform that we hear, or the mechanical vibration of the tongue? There are entirely two different kinds of vibrations, or waveforms going on here, one is the mechanical vibration of the tongue, and the other is the vibration of the air medium, or the acoustic vibrations in the air, what we hear. Likewise, there are two ways the tongue vibrates, one is according to what are called "vibrational modes"; i.e., whether transverse (bending) or torsional (twisting), and the other is the "jerkiness" in the vibration, within each particular mode (e.g., first, second, etc. bending and first, second, etc. twisting). So there are many vibrational modes, and within each mode, there are many ways the motion can be jerky in time. The complexities in the ways this simple little thing can vibrate is often beyond the comprehension of most people. Regards, Tom
  13. Hi Alex, if that confuses you, let me confuse you further by a similar plot made by a different investigator, James Cottingham, one of the pioneers in experimental investigation of free reed physics. The figure caption explains the set up and notice the similarity between Ricot's measurement for pressure above the reed and this one: two humps roughly in the same place, with one hump significantly larger than the other. Notice also the complex pressure waveform in the cavity below the reed. That's all I want to point out here. In my view, the Western free reed can rank as the most difficult to understand musical instrument sound source, at least from a physical point of view. As usual, this doesn't stop some from holding convictions on unscientific pet theories about how it works. All this can only stir up lively discussion, which is good, but there's also a cautionary note there for one to be not so certain about his or her suppositions until hard scientific data becomes available. Regards, Tom
  14. A picture is worth much speculation and many posts. The attached plot shows the pressure upstream of a vibrating free reed, with time on the Abscissa. The reference is: "Aerodynamic excitation and sound production of blown-closed free reeds without acoustic coupling: The example of the accordion reed" Denis Ricot, Laboratoire de Me´canique des Fluides et d’Acoustique, UMR CNRS 5509, Ecole Centrale de Lyon, France; Rene´ Causse´ and Nicolas Misdariis Institut de Recherche et Coordination Acoustique/Musique, UMR CNRS 9912, 1 place Igor Stravinsky 75004 Paris, France The dotted line denotes the time the tongue opens, passing flush to the top of the reed plate as it moves away from the plate, and the dashed line denotes the time the tongue comes back down, closing the slot. You may notice that there are two pressure pulses, though they are very different in magnitude and shape. As some have mentioned here, the ear/brain system is extremely sophisticated and has no trouble interpreting these pulses as different; i.e., there is only one periodic time associated with this wave form. I'm delighted by the interest shown here on free reed physics, and this thread is an illustration that all we humans need to each learn individually everything that other humans have likewise learned. Although it's true that a very large number of such topics have been discussed on Concertina.net, and I presume the record is there for the searching, I understand that the thrill of such discussions of discovery through live discussion is irresistible. In particular, Dana, Chris, Richard Morse, myself, and others participated in discussions of these topics in great detail, going back at least 17 years. Not all of it is accurate, since just like here, it takes a while before correct understanding can be achieved, but there's much knowledge to be gleaned from those discussions. I can't hope to present all the information available in the scientific papers to this thread, because of it's wide range of concepts. I will mention one detail that has not been discussed here, and that is the fact that, although the vibrating tongue vibrates mainly in it's first bending mode, the second mode vibration can often be measured, and more importantly, this first mode vibration itself involves overtones that are whole number ratios; aka harmonics. Said in another way, the first bending mode, which consists of a node at the anchor point, with maximum amplitude at the tip, also contains harmonics that are unique to the tongue material and other parameters of the system. This harmonic spectrum causes the tongue to move - as a whole - in a jerky motion in time, all the while maintaining the same x-dependency of the first mode transverse cantilever vibration. Mathematically, that's because the x-dependency (tongue shape) and the time dependency (harmonics) are separable. It's my hunch that these harmonics in tongue vibration contain the clue to why a tongue of one material, say steel, will produce a different sound than a tongue of say brass. If not for these harmonics, why would the sound be any different? Regards, Tom www.bluesbox.biz
  15. Hi Wunks. I don't know the manufacturing process for these tines, but I'm pretty sure they are hardened steel. It's curious why they provide such excellent material for musical triangles. I have one, made by Larry Miller, a Cajun accordion maker in LA, and it's a perfect musical triangle because it does NOT have a dominating pitch, at least for playing Cajun music. Thus, it can provide a wonderful percussive effect, regardless of the key of the song being played. In contrast, many other musical triangles that are used in orchestras produce a boring "sinusoidal" acoustic sound, which lacks overtones, is very thin, and too well defined in frequency to be a very interesting percussive instrument. But of course they have their niche. I don't know why these recycled farming tools produce such fine musical instruments. I can only speculate. In any event, there's no reason to expect that a material suitable for one musical application will also be suitable to another application. As Dana points out, it would be extremely difficult to grind down these tines to the cantilever shapes needed for the free reed. It's really not worth thinking about, because the standard blue tempered 1095 "Swedish" spring steel is such a perfect candidate. Unless of course, you're interested in other materials because of the peculiar musical tones they might produce when fashioned into free reed tongues. Best regards, Tom www.bluesbox.biz
  16. Steve, maybe you want to explain a little more because the maker's website seems to be offering a brand new machine for less than you're asking. Please explain why you're selling it and how the model you're selling differs from the models that are being offered for less money. Thanks. Regards, Tom www.bluesbox.biz
  17. Hi Steven, thanks for pointing out the difference in terminology, which I wasn't aware of. I found a video comparing the sound of a harmonium to that of an American reed organ, for those interested: In addition, Wikipedia gives the following distinctions: > Reed organs are operated either with pressure or with suction bellows. Pressure bellows permit a wider range to modify the volume, depending on whether the pedaling of the bellows is faster or slower. In North America and the United Kingdom, a reed organ with pressure bellows is referred to as a harmonium, whereas in continental Europe, any reed organ is called a harmonium regardless of whether it has pressure or suction bellows. As reed organs with pressure bellows were more difficult to produce and therefore more expensive, North American and British reed organs and melodeons generally use suction bellows and operate on vacuum.< Lest some people get the wrong idea, it should be mentioned that the reed itself doesn't know what is positive pressure or vacuum. What does matter is the direction of airflow through the reed and whether the mounting cavity is either upstream or downstream of the reed. Unfortunately I couldn't find which is which in the descriptions given, indicating that the writers don't have a detailed interest in acoustics. Best regards, Tom
  18. This seems even more interesting to me, and I never heard of or considered such a twist. You see, I think the sound of the free reed is boring, because of its perfect partials. By "perfect partials," I mean that all overtones are harmonics. "Harmonics" is a mathematical term that means multiples of two. Thus, any overtone of the free reed are perfect multiples (or divisor) of two with any other. The only "fly in the ointment" here are so-called transients and some cases of very loud playing situations that excite either torsional or higher vibration modes, which in general are not multiples of two of the fundamental tone. But the "steady" sustained tone of concertina reeds produce perfect harmonics, and there are no other musical instruments that have perfect partials that I can recall at the moment, except the bowed string instruments. The basic reason for that is the fact that all those other instruments are transient sounds, or if sustained as in the woodwinds, nonlinearities in the sound source - a vibrating air column - cause non-harmonicity. In fact, I believe the phenomenon is an advantage for string orchestras, because I don't think the eerie blending of the many violins playing in the string section would be possible without it. Well, with all that background, I say our little reed friends sound boring because of this perfect-harmonic feature, in a similar way as a pure sinusoidal tone (as from a tuning fork) is boring. In addition, when more than one note is sounding, the overtones of the separate notes mesh, and we lose the identity of separate notes and the complexity of timbre - a kind of "clash" or "noise" - that say a piano or two saxophones produce. So introduce the twist. Is it possible to excite a torsional tongue vibration mode with the twist, so that such a mode would be continually excited, along with the main bending vibration mode? For this to occur predictably, it may be necessary to make the tongues wider. Dana recently told me that he has had experience with some extra-wide tongues, with unpleasant tonal results. But I'm not so sure the idea cannot be improved on, especially since the frequency of the torsional mode can be a design parameter, and some torsional pitches might blend very well, adding interesting complexities to the timbre. Here also let me suggest that the hump in the harmonium reed in the picture might be a way to force - and insure - the first vibration bending mode of the tongue. The only other bending mode I've seen in Fourier spectrums is the second, which for a constant cross-section cantilever, is around 6.2 times the frequency of the first mode. The second mode has a node about a third of the way from the tip of the tongue. It may be that putting the hump there, insures that a localized pressure force acts there during the swing cycle, and that would make excitation of the second mode very unlikely. Such an arrangement might be necessary for very long tongues. I believe it's very unlikely to excite the second mode of a short tongue, or if it's excited, we wouldn't be able to hear it, because of its high frequency. But for very long tongues, my guess is that the hump is perhaps necessary, if for instance harmonium makers wanted only very soft sounds, as during church service. Interesting in that I never thought of this "hump" explanation before, until I saw the twist idea. But now, of course, the question is, why did harmonium makers put in the twist? If we want to hold onto the idea that harmonium makers wanted softer sounds, do their tongue geometries have sufficiently small width-to-length ratios so as to rule out torsional modes, and thus the twist is just a convenient and quick way to make a starting offset? If tongue geometries are such that torsional modes are indeed excited, my explanation above for the hump would seem to be wrong. At this point of course, we'd have to talk to a harmonium worker that knows his business, though where can you find such a person? Best regards, and stay safe, Tom www.bluesbox.biz
  19. For those interested, I'm not sure how many of you are aware that harmonium manufacturers have their own standards about "best practice." Here's a drawing of one of their free reeds. I'm under the impression that the curious bend is rather typical. Can anyone here venture as to its advantages?
  20. Hi Don, pump performances are given by their "pump characteristic curve," which all have a characteristic shape shown in the attached figure. You see that at zero flow (cut off), they produce maximum pressure. That's because the power output is almost constant, equal to the product of pressure difference times flow rate. As one increases, the other decreases. That's a rough guide. Even at zero flow, the pump is still putting out power, only it's all going into dissipation and heating the fluid. For a single reed, the air flow rate is extremely small, down around 10E-5 cfm. Take that as zero. Thus any fan you hook up to the reed will produce it's maximum pressure. Even if you powered more that one reed, or more than a few reeds, it will still be essentially zero, compared to the capacity of most any of the types of fans commercially available. Bottom line is, yes, in general, the flow rate through from a fan will determine the pressure output, but in your case, the change in pressure for different size vents or number of vents is negligible. Best regards, Tom PS I did forget to advise to look for surplus or used equipment. Many years ago, there was a huge supply of all kinds of fans and blowers for a fraction of full price cost. I know that market dried up quite a bit, and I suspect a lot of it now goes overseas, like so much equipment that industries here in the States needed; that is, until so many of those industries went kaput. But still, it's worth a look.
  21. Hi Don, the key specification is exit pressure, not volume flow (cfm). None of the axial fans you link to can push air with enough force in order to develop the pressure you need. For tuning, you'd like at least a couple inches of water pressure, and those axial fans can deliver only tenths of that. You need a centrifugal blower, or a regenerative blower for tuning. If you want to power the reed with a full range of possible bellows pressure, get one that has a spec for maximum exit pressure (at zero flow) of at least, say 6 inches W.C.. The axial fans you link to do not even have a spec for exit pressure. So look at blowers with a spec that specifically tells you what maximum pressure they can deliver. If you want an elaborate setup, you can install plumbing from pvc pipes and two three-way ball valves, which will allow you to supply air flow in two directions, if you're tuning accordion style reeds that have two tongues, one for each air flow direction. And you might also look into a speed controller, like what Dana uses. Best of luck, Tom
  22. Yeah, well, I think I might have to retract that statement. I knew I was sticking my neck out by saying it because I never verified it myself and I hate saying things that seem like common knowledge without my own direct verification or without documentation. So I did look into this issue and found some things that may be of interest to some here. We want to compare the total energy input to the total sound energy output. Power input to the process is the result of our muscle power, and of course we can measure that by measuring our force on the bellows and multiplying it by the speed at which the bellows closes or opens. We don't have to do quite that, because that power is very closely equal to the product of the force the bellows pressure exerts on the airflow through a slot (consider only one sounding reed) times the velocity of that airflow. The bellows pressure force is equal to the bellows pressure times the area of (slot) flow. Bellows pressure is easy to know, but what is the slot flow area and the air velocity through the slot? The fact that there's a vibrating tongue obstructing air flow through the slot adds complexity, but we can simplify things considerably, first by saying the actual air flow area is about half the slot area and second by taking the average air flow velocity, which, thanks to Mr. Bernoulli, is easy to calculate. That air flow velocity in fact accurately represents the power input available to the vibration (power input without vibration). Here's our reasoning: bellows pressure forces the motion, exciting tongue vibration, which leads to acoustic power output and dissipation, or heat. In turn, of course, the acoustic power output is also dissipated. Of course, acoustic power output is generated in conjunction with tongue vibration and does not result at a time after vibration, but all these details don't prevent us from getting a good estimate of the power input. Separating the mechanical energy of tongue vibration from acoustic energy would be extremely difficult if you'd want to do that with a complete analytical understanding of the entire phenomenon. But there are easier ways than that, so stay tuned. The product of bellows pressure, slot area, and airflow velocity is very simple, and for a bellows pressure of 6 inches WC, slot dimension of 2 by 0.1875 (using only half that), I get about 1.5 milliwatts of input power. What's the total acoustic power output? A simple estimate is to consider how loud the reed sounds when you're a certain distance away, converting that to acoustic power intensity, then multiplying that by the area of a sphere of that distance. Here again, we make rough estimates. If you go to the web and find typical sound levels produced by various sound sources, you learn that conversational speech is about 60 decibels at one meter and a vacuum cleaner is about 70 dB at one meter. Let’s assume we have a particularly muscular concertina player who’s an extrovert and take 70 dB at one meter. This gives a total of 0.13 milliwatts, or about 1/10 the input power calculated above. So it looks like my statement above can be accurate, but bear in mind the simplifications we made. We are definitely in the realm of order-of-magnitude reasoning. I thus would not be surprised if in some cases, say for different pitched reeds, that statement may not be too accurate. I come away from this thinking, “Okay, that’s a rough rule of thumb, but…” Best, Tom
  23. Do you have a speed-controlled DC motor on the blower? That's a good feature. I should change to that. Right now, I'm using a "Windjammer" regenerative blower, which is one-speed AC, but it's capable of 18 inched WC, and I need it because of all the valves and small diameter tubes in the system. Neither do I; I haven't studied it carefully, though I have an inkling from other researchers. If you recall, several years ago, I posted a link to a paper by Ricot, et al, in France, where they did analysis of the acoustic sound field produced by an accordion reed. The results look good, with good agreement with measurement, so I assume the mechanisms they uncovered can give us a good idea about how the sound is produced. It's quite mathematical, as acousticians often are. I believe there are intuitive explanations yet to be discovered. You're right in pointing out that the tongue vibration is not the same as the sound. As I mentioned, I'm focused now on the vibration, and I hope the understanding of it can help in understanding the sound. Ricot didn't solve the vibration problem, merely substituted the actual tongue vibration for a simple valve. Perhaps a strict vibration analysis such as mine can contribute towards a better understanding of the sound. It's an interesting hypothesis. I can't say for sure. Certainly the bellows pressure fixes the maximum energy available for all aspects of the motion: both tongue vibration and acoustic sound field. Bear in mind, the acoustic energy is a small fraction of the total energy of the vibration, so a subtle change in energy transfer from the vibration to the sound field might produce a lot of sound. I'm not sure I agree, simply because higher bellows pressure makes more energy available for the sound field. So more bellows pressure, more energy available for sound; thus, higher volume. I believe you can always force more air through. The higher the bellows pressure, the higher the air flow rate through the vent. But I agree that there appears to be a maximum amplitude the tongue could vibrate at, and if that's really true, it's a clue to how the whole mechanism works. The mechanism for that still puzzles me, though it must have something to do with the dissipation that must grow in relative importance to the vibration. Very good point, and I sometimes lose sight of it. You're focusing on volume and I'm looking at vibration. Not the same. I don't think the mechanism for energy transfer to sound is very efficient, if you define efficiency as sound energy out divided by muscle energy in. It would be interesting to compare it to the efficiencies of other instruments. Nice talking, Tom
  24. Dana, I forgot to ask, do you put a belled draft angle on all of the vent (slot) sides, or only on some of them? Thanks. Regards, Tom
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