Jump to content

ttonon

Members
  • Content Count

    271
  • Joined

  • Last visited

About ttonon

  • Rank
    Chatty concertinist

Contact Methods

  • Website URL
    http://www.bluesbox.biz
  • ICQ
    0

Profile Information

  • Gender
    Male
  • Interests
    Many
  • Location
    Princeton Junction, New Jersey, USA

Recent Profile Visitors

722 profile views
  1. 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
  2. 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
  3. 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
  4. 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?
  5. 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.
  6. 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
  7. 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
  8. 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
  9. 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
  10. Hi Dana, sorry for the delay. I'm glad to see your post because I actually suffered remorse for the possibility that I was too harsh in my last response. I do like to be direct with people because I no longer have the patients to worry about personal issues. To me the important thing is the subject matter and finding a way to explain it in the most direct way, which I agree can sometimes be toned down. So I apologize if I was lost in my own head. This surprises me because the major amount of energy addition to the vibration is during the downward movement of the tongue through the slot. With high draft angle, there's a lot more air flow between the edges of the tongue and the walls of the vent, lowering the pressure driving the motion. In fact, my model does predict that for straight sides, the thicker the shoe, the larger the vibration amplitude. I suppose it's possible that you might hear a louder volume for a lower vibration amplitude, and that's particularly intriguing. Understanding the vibration of the tongue is not the same as understanding the acoustic effect on our ears. So yes, I'm intrigued. Just how do you do that? Do you use a ball mill cutter? I can't see that you're cutting the sides with some kind of file or scraper, so maybe I really don't understand what you mean by a "belled" relief angle. I agree. Would you agree that the effect is a little like that of a thinner shoe (plate)? I didn't see in your description a possible effect of the sound produced by the air delivery system, when there's a powered blower. I know in my own set up there are interference resonances with the SOUND the blower makes, for whatever reason, the sound of the motor, it's fan, or in the air flow noise. It can be pretty complicated. Regards, Tom
  11. I recall an incident when I was experimenting with free reeds in my jig, with the reed isolated and freely exposed over a port through which airflow traveled downward. A friend came by with her toddler son to say hello, but she shortly had to leave after only a few minutes because she feared the sound was too loud and might damage her son's hearing. She was standing a few feet from the apparatus. I then realized how really loud the sound was and it became annoying, after which I reduced the driving pressure down from about 4 - 5 inches w.c., which I think we established here is not uncommon in normal playing. I wonder if she would've had the same fears if the reed was inside an instrument, with the same driving pressure. Dana, I'm not sure I understand what you mean by "bell," but if it means that the draft of the vent sides has a bell-like curve rather than straight-line angle, I'm very surprised, maybe even suspicious. There's no mechanism I can think of based on fluid mechanics that could explain such an effect to the extent that it would be noticeable or measurable, and so I'd have to question the measurements themselves. No offense, of course. Experimental physics isn't trivial, if we want to be certain about results that are accurate, reliable, and reproducible by others. This checks with my own experience. Before getting into a lot of detailed discussion, it's very common for both theoreticians and experimentalists to eliminate extraneous conditions. It would be silly, even impossible, to try to include all real world effects when trying to understand any given phenomenon. The wisdom here is in realizing the essential elements of the phenomenon. That's what makes a good researcher. What's the point in including the feature of open or closed bellows? The sensible approach is to first understand the essentials, then if worth it, try to include less essential aspects, especially if those aspects have their own explanation, as in the case of bellows volume? For the free reed, it can indeed be excited as it sits freely outside bellows and away from the traditional cavity geometries. You can excite its vibration without any effect of a cavity. So why not understand first that arrangement? You can then add other features. I'm not sure your conclusion that the size of the bellows is the reason your reeds didn't speak. But if you're right, the only theoretical explanation I have is that the bellows volume and port opening over which the reed is mounted form a Helmholtz resonator that has resonance near the reed fundamental frequency. Did you check that? That's my guess, but not seeing the complete geometry of the apparatus, I can't say for sure. I assure you that your experience can be explained by acoustic theory, and the underlying effect can be eliminated in an investigation on how the free reed vibration itself occurs, given tongue and vent geometries and a uniform, steady pressure difference across it. Really? But you could look at numerous papers in scientific journals that do just that. Of course, the investigative history of any given instrument gets more inclusive with time, and it's the early papers that will have the simplest investigations. Whether those simpler investigations are adequate can be judged by the effects included in subsequent papers. But with many woodwinds, it's not necessary to consider upwind effects for a basic understanding, and the inclusion of such effects are done sometimes more out of a luxurious curiosity, on a special case basis, by people who are paid to come up with new ideas. Progress in scientific investigation is aided by knowing what to include and what not to include. Many heroes in physics and engineering found just the right mix and their names are memorable. It takes real talent to realize what's important and what's not. Just because some feature of a real instrument can influence the sound of the instrument doesn't mean that the feature is essential and must be included for a basic understanding on how the instrument works. You first cleverly identify the essentials, figure out the results, then add in other "real" effects. With tongue vibration of the free reed, first understand how it works in isolation, without a cavity (or bellows), then add in more. Then move on to acoustics, and you can then deal with the acoustical effect of the cavity, which can be noticeable, but not largely. And concerning tongue vibration, we already know that the effect of the cavity and bellows is normally small, except in those instances when a resonance occurs, which in turn is also a well understood phenomenon. To me, the Western free reed is an enigma. On one hand, it's one of the simplest sound sources - just a vibrating cantilever involving little companionship with other vibrating systems - but on the other, just its vibration alone has withstood a complete-enough understanding. On one hand, its musical tone can be largely understood without bringing in its geometrical environment, on the other the details on how the acoustic sound is made solely by virtue of its own vibration is extremely complicated. The Asian free reeds are more complicated because in addition to what happens to the Western version, you do have a system coupled with a resonator. So to me, the complexity of the free reed, unlike other sound sources, is largely confined to itself, whereas with other sound sources, additional vibratory elements must be considered. But I think I know what you mean, and I can be more accommodating by noting that in some instruments there are some real world effects that must be included for a more-or-less complete understanding of its tone. The harmonica is a good example, and it's brethren to the concertina. Without understanding the acoustic effects of the musician's body parts, one cannot get a realistic understanding how harmonica tones come about in actual playing. It's again the wisdom of the investigator, knowing what to include and what not to include. But if all you want to understand how the harmonica reed vibrates subject to a steady pressure difference, you don't have to look upstream. There are some instruments that are borderline cases. Organ pipes are one. For a hundred years there were claims that the body of the pipe flexed to the degree that it affected the sound. But we're talking now about nearly imperceptible acoustic effects. It was only fairly recently that the issue was mostly settled. And then it was discovered that in some cases, because of construction details, the funnel shaped connection between the shallot (mouth) and the pipe could vibrate in acoustically noticeable ways. But that was exceptional. Then it was discovered that in some rare cases, the pipe walls could noticeably contribute to the tone. But that was happenstance, due to exceptional construction details. I don't recall the exact details, but while I'm at it, and concerning the issue of whether materials of construction affect musical tone, musical instruments cover the full spectrum, from stringed instruments in which materials are key to the tone, to woodwinds, where materials have very little affect on the tone, except some of the brass instruments that have large bells (the bells vibrate and affect the tone directly and sometimes indirectly by feedback to the musician's lip vibration), with organ pipes intermediate, involving uncommon occurrences. In many of these studies, simplified approaches are taken, with a focus on what your goal is (say mechanical vibration vs acoustical sound spectrum) and in some cases further study is needed to obtain a more comprehensive picture. You often see the titles of investigations with the format, "Investigation of the tone of the X, for the case of Y," where X is the instrument and Y is the added element. We might see in the future something like, "The vibration of the free reed, including the effect of a cavity." It depends on how accurately you want to understand the sound of the instrument. If the criterion is only to understand the vibration of the tongue, the issue is enormously simplified, as compared to a criterion to understand the perception of our ear/brain system. Moving on to the acoustical effect of the vibration is an added complication. The ear/brain system is phenomenally sensitive, and that raises a high bar for theoretical understanding. But acousticians have methods to deal with that. Right now, I'm working on the vibration problem of the tongue, a relatively simple aspect, and believe me, the lion's share of understanding can be gotten with the isolated reed. Such a solution can be incorporated into the acoustic issues, which can involve the effects of the cavity, as well as the bellows. If you want, you can also consider the acoustic effects of the wood structures, the end plates, the fact that the instrument is played on the lap of a human, the presence of a wall or corner behind the musician, the presence of the musician's hands in front of the end plates, the presence of other musicians in a room with furniture, wall hangings, the clothes the musician wears, the hearing response of the ear of the listener, and so on. At what point do you stop? Well, we all know the answer to that. Best regards, Tom
  12. Hi Chris, I think I found your post on bellows pressure, back in 2014, at Terry McGee also posted (I wrote in the English units): The conclusion I come to is that normal concertina bellows pressures are about the same as I expected for accordions. In light of the fact that a concertina player needs to supply only about a third of the muscle force to produce the same bellows pressure, that extra reserve is not utilized and it's the volume of the note that determines how hard the musician pumps. Rather obvious, I guess. Big box accordion players have to supply about three times the muscle power for the same volume as concertina players, and realizing that makes me wonder whether playing force is a factor in limiting the largest size of big box accordions If you also consider that big box accordion playing involves many chords, incorporating maybe 5 - 8 times the number of notes that concertina players use, accordion playing can be much more strenuous than concertina playing. This incidentally is the reason why big box accordions can be used to play good tango music, it can never produce the dynamics produced with the smaller bandoneon, the traditional tango instrument, especially when the bandonistos slam the instrument down on their knees. Best regards, Tom
  13. Hi Chris, so good to hear from you! Yes, something seems amiss and I guess it's back to the drawing board. A simpler experiment is to put a digital scale between one of your palms and the concertina and have someone read off the forces as you play steady notes. My guess is that the pressure calculation from bellows cross section and force should be pretty accurate, but that should also be checked. It should also be said that we need to use the same unit system, because far more disastrous results have occurred because of a mix up in unit system. I'll look for your post. There are differences in construction between accordion reeds mounted in the common way using a reed block and the traditional concertina method. With the accordion method, the reeds are situated with one end near the air hole (port) and the other end removed, at some angle not far from 90 degrees. The concertina method places the reeds flat (zero degrees). In my experience, the flat mounting produces louder tones, because some of the melodian-type accordions, such as the Louisianan Cajun type, place them flat, and I play both. The question is, do the accordion-reeded hybrid concertinas with reed blocks sound at lower volume than the traditional concertinas (for same pressure)? But I suspect any difference would be too small to explain these differences in normal playing pressure. Interesting comment about draft angles in accordion reeds. Best regards, Tom
  14. Very simple. Just highlight the text in my post that you want to quote and a little window will appear immediately with ""quote selection." Click on it. Here's more. Impedance is defined as oscillatory pressure divided by oscillatory velocity, and the definition is sometimes useful, sometimes not. Bellows pressure is not oscillatory, and it can be considered steady, or constant, for the purpose of examining its affects on tongue vibration. The slugs of air going in and out of a finger hole in a woodwind is caused by the wave motion inside the body of the instrument. This wave motion is characterized by standing waves - waves that are the additive result of forward and backward moving traveling waves - producing pressure and velocity oscillations that are a function of time, but not position (hence, "standing"). Thus a given finger hole, being at a fixed position ejects an air slug when the pressure just inside the hole, caused by the standing wave, rises (above atmospheric), and the motion there is periodic. This is entirely a wave phenomenon and you can define an impedance for the air oscillations in and out of the hole (with time average flow being zero). On the bottom of the vent in a free reed, there are pulses of air, but they are not caused by wave flow, but rather by the opening and closing of the tongue/vent valve. In order to understand the nature of this oscillatory flow, we need to look at the equations of fluid mechanics, coupled with the governing equation for the tongue vibration. The simplest equation for tongue vibration is the Euler-Bernoulli equation, which can also be called the tongue's wave equation. Once the motion of the air slugs passing through the vent is calculated by this approach, you can now define an impedance for that oscillatory air motion, the same way as for a finger hole. At this point, the oscillation does not care how it is produced. In fact, we can use that definition of impedance for the underside of the free reed to couple it to the equations governing the air vibration in the cavity, or for resonators. I was maybe too restrictive to say that impedance is not helpful here. My point is that it's not helpful in understanding how the pulses are formed and the effect of the reed geometry on those pulses. Once we understand those pulses, we can define their impedance in order to do further study. Trying to understand how those pulses are formed by invoking impedance can give the erroneous view that there is a sound wave passing through the vent and encountering a change of impedance because of the sudden area change. That's not what happens. But it does happen with the woodwind, when the forward traveling wave meets the end of the tube, or bell, and out to the atmosphere, where there is a large change of impedance. There, impedance is a very useful concept. The free reed is its own animal. Very unique when it comes to musical instrument sound sources. So you're not measuring bellows pressure generated by human muscle during playing, and my guess is that your judgement on the magnitude of driving pressure is made by the perceived volume you hear. I wonder. As I said, I measured the bellows pressure in an actual instrument, while playing. The bellows I used measured roughly 18 x 6 inches, inside measurement. Pushing on that "piston" with 20 lbs of force produces about 5 inches w.c. My guess is that accordion players could produce such a playing force, though that's probably around the highest. A concertina cross section is, my guess, around 6 x 6 inches, so that the same force produces three times the bellows pressure. I doubt concertina players push anywhere near 20 lbs, but these figures to me suggest that 4 inches is well below the capability for the instrument. All this may only prove that concertina players play for reasonable volume, and the difference from accordion players is interesting. But all in all, the free reed can sound extremely loud with your ear next to it, and that perception is quite different from what we get when it's being played inside an instrument by a musician wanting to be heard above other instruments in a session. It would certainly be an interesting experiment to fix an instrument with a pressure transducer and record the data during a session. That's surprising. Do you see higher or lower pitch with extended bellows? You're saying that the precision with which the tongue fits the vent doesn't make much difference? Intuitively, I would've guessed that a tighter fit would lead to more higher harmonics, but maybe they're just not noticeable. This is most interesting, because I'm in the process of extending my model to include the effect of a draft angle on the sides of the slot, as well as the effect of a gap in the fit between the tongue and the vent. Do you put the draft on all sides, including the tongue tip side? Of course, there, the tip naturally pulls away from a non-drafted side as it travels through the vent, and this can be calculated. But that effect is much smaller than that the draft angles you quote. Incidentally, I find that the smallest fitting gaps are a couple thousandths of an inch. Does that check with your fits? Except for the tip corners, which can go down to a thousandth. Interesting. You're saying that a draft angle increases volume, something that I'll look for in calculations. Confusion here. If "thinner reed sets" means thinner tongues, they might bend with more curvature than thicker tongues. Is that what you mean? The higher curvature would mean that the tips pull away more from the tip side wall, suggesting that they would need less draft than thicker tongues, and I agree. But your results seem counter intuitive, because as I mentioned above, tongue travel through the vent is prime time for which static bellows pressure can move the tongue. When you cause more leakage between the tongue and vent wall, that pressure effect decreases. Of course, some of the effects that happen during down-travel of the tongue through the vent are compensated for by up-travel a half cycle away. This is something I need to ponder. It's an interesting feature to explore. My experience with accordions is very limited, but I've never noticed any draft angle with accordion reeds. Maybe someone else here can add to that. Best regards, Tom
  15. Many thanks Dana for what you've done here: a plethora of information that will be of much help. To be sure, the notation f# 5 invokes the piano keyboard, so this reed has a fundamental vibration frequency of about 740 Hz, correct? What I understand is that this seems to be about the dividing line between reeds that have their tongues that most often travel through the shoe, and those above that do not, generally, but not absolutely. Since you make the vent for this f# reed slightly longer than the reed window (the hole in the wooden chamber wall), my guess is that you're not too concerned about the tongue hitting the wood during normal playing. Is that right? Yes, in my physical model, the time spent while the tongue moves through the vent is when the major portion of energy is transferred from bellows pressure to the vibration. With analogy, this is the moment the father pushes on the swing his boy is riding. There is a small contribution when a tongue exits through the vent, but still moving downward, due to the air jet passing through the vent and hitting the tongue. But that small contribution is then largely cancelled when the tongue comes back up, before again entering the vent. My explanation above about the jet addresses this. "Impedance" is not a good description of the underlying physics. Impedance is a useful concept for understanding the behavior of wave motion. Here, we're dealing with fluid mechanics, no waves. Yes. This sudden widening of the gap is what ends the (static and dynamic) bellows pressure force on the tongue. Without the vent, the action on the tongue from the bellows pressure is indirect. When the tongue is below the vent, the air jet caused by the bellows pressure acts on the tongue. And as I said, this aspect of energy transfer is both positive and negative, with nil net result. When the tongue is above the slot, there is nil direct influence from bellows pressure. There are small effects caused by air motion into the slot just before the tongue gets there. Have you measured bellows pressure directly? Years ago I attached a manometer to a full size accordion bellows and concluded that the larger pressures should be around 6". That's for those bellows with a push area much larger than concertina bellows. Aso, I didn't push with all my might, and I do know that some gorilla accordion players can be exceedingly loud. I thus concluded that concertina maximums should be around about twice that. Of course it depends on how strong the player is, and maybe the limiting pressures are determined by what happens to the reed. What are your thoughts on this? Do you think the reed can be damaged at such high pressures? What happens to the sound of your reeds when you push or pull on your bellows with all your might? I'm impressed with how low that is. If you recall, I came up with a theory on how to predict the minimum starting pressure for a reed and published it here a few years ago. I'll have to go back and look see that post. I'm very curious now, concerning pitch, or vibration frequency. Can I trouble you, or anyone else when you get a chance, to observe a real time reading on a pitch meter (tuner) to see how the pitch changes as you slowly increase bellows pressure (either plus or minus), from the very lowest pressures to the maximum pressure? Just qualitative results, such as "higher" or "lower" would be very interesting from a theoretica point of view. One complication here is the presence of the leather valve, which moves as pressure changes, and that might have an effect on pitch, so ideally there shouldn't be a valve. Yes, in my workshop, which currently is in disarray, I have an electric powered testing rig, with the reed mounted over a window. The electric blower can suck steady air through the reed, with the tongue vibration freely visible and accessible. The strobe is a nice touch. The "real world" data I'm after does NOT contain a chamber, or any confined space. I'm interested in the reed vibration by itself, without any other physical phenomenon going on. Once I understand this, I can formulate the case when the reed is mounted on a cavity, or resonator, which is an entirely different problem. I'm sure you'd agree that I cannot hope to analyze all real world effects, only to give an accurate-enough description. Best regards, Tom
×
×
  • Create New...