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ttonon

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  1. Hi Ragtimer, The phenomenon you experience is due to acoustic coupling between the reed and the air column that the reed is in acoustic communication with. This column includes the cavity, the tube, and the nasal/larynx/lung cavity of your own body. Thus, the reed is only part of an acoustic (vibrating) system with many parts. The opening of the system that the reed looks into requires a particular relationship between oscillatory pressure and air velocity; i.e., that relationship that the system – minus the reed - provides when air within it is set to vibrating. In acoustic terms, the reed sees an impedance when looking into the rest of the system. If this relationship (impedance) is not compatible with that which the reed requires in order to vibrate, the reed chokes; i.e., it will not vibrate. Thus, the reed and cavity are only part of a dynamically (acoustically) coupled system, and changing any part of this system may allow compatibility (vibration). What people usually do is what you have done yourself – change the dimensions of the cavity. In order that one cavity enable vibration for a variety of reed pitches, the safest thing to do is to simply make it large enough. In this case, pressure oscillations within the cavity become small enough so that they cannot interfere with the self-excitation mechanism that makes reed vibration possible. In other words, the reed can operate more or less independently; the large cavity isolates, or de-couples, the reed from the rest of the system. For more explanation on this type of coupling, and on many other issues regarding vibrating reeds, you can go to an article I wrote for PICA (Papers of the International Concertina Association), available for free on the web, at http://www.concertina.org/pica/ Best regards, Tom www.bluesbox.biz
  2. Hi Chris, I agree that (pressure) force goes up as the square of air velocity, but not always. This model is true for steady-state motion, when air is forced through an opening, forming a jet, and I think it can be useful when discussing reeds with sufficiently low pitches. For the higher pitches, however, unsteady effects come into play, and the model breaks down. A simple way to explain the underlying Physics is to imagine a spring situated vertically, with the bottom end attached to a table, and with a mass attached to the upper end. If you push down on the mass slowly enough, the force you feel is essentially the same as the force that the spring pushes against the mass. Now imagine your finger glued to the mass and oscillating up and down, remaining in contact with the mass. At low frequencies, your finger again feels essentially the spring force, but as you increase the vibration frequency, you begin to feel the inertia of the mass. You have now arrived into a regime of unsteady motion, where inertial forces (really, time derivatives) become important. At the highest frequencies, your finger will feel only the inertial force of the mass, because then, the spring force will be negligible. The last time I looked at this issue with regard to the free reed, and using rough calculations that incorporate typical geometries, I concluded that unsteady effects in the air motion will come into effect at frequencies above approximately a thousand Hertz. Of course there’s still a mean flow of air through the vent at these high frequencies, but “mean” flow is not then the same as “steady” flow, and I'm not prepared to speculate here on just how this mean flow at the high frequencies varies with pressure. Such a point may seem like too much of a complication for some, but it really should be included for a thorough understanding of reed behavior. For instance, because of this transition from steady (really, quasi-steady) to unsteady regimes, my guess is that the effect of belling that Dana refers to above would be more pronounced for the higher pitched reeds - again, those with pitches higher than roughly a thousand Hertz. For these reeds, the vibrating air, because of it's own inertial forces, probably follows the bell contour more completely than a quasi-steady jet of air would. Best regards, Tom www.bluesbox.biz
  3. Hi Larry, The section on free reeds is only about 3 pages, and I'm not sure of your interest, but if you'd like, I could copy the pages and send them to you. You can send me your address by email. Best regards, Tom
  4. In studying the free reed phenomenon, we need to distinguish between the motion of the reed tongue itself and the motion of the air, which is integral to, but separate from, the motion of the tongue. It’s easy to confuse them. The driving force for all motion arises from the excess (static) air pressure on the side of the reed where the tongue is placed on the shoe (plate). Let’s look at the tongue. Like all elastic bodies, the tongue can vibrate freely (as if plucked), and/or it could vibrate in forced oscillation, as when it produces a musical tone, being forced by air pressure. Vibrating freely, the tongue possesses natural modes, and as Dana points out, these modes are not harmonic (contrary to the vibration of flexible strings), and thus, are non musical. (As an aside, “harmonic” describes whole number ratios. In some vibrations, the overtones are precisely harmonic, and in others, they are clearly not harmonic.) With forced motion, the tongue will vibrate at the frequency of the exciting force. If the exciting force contains numerous frequencies, the tongue will vibrate at the same numerous frequencies, with varying amplitudes. This is basic Physics, and when we apply it to concertinas, the crux of the issue at hand becomes, What is the relative amplitudes of possible separate vibrations that make up the vibration of the reed tongue? I have an answer for this, but now, let’s look at the air. The air pressure force acting on the tongue is very complex, described by what I’ll call a step-function-like force. At the risk of belaboring this picture to some, I need to point out that, when the reed is inside the slot (vent), it experiences essentially the full static air pressure difference. When it exits the top side of the shoe (where the static pressure is positive), the pressure force acting on it rapidly drops to nil. When it comes back down, the pressure force rapidly increases again to the maximum, with the tongue again in the slot. There is a smaller change of pressure force as the tongue moves through the slot, as air leakage around it increases, causing more air velocity within the slot, and because of Bernoulli, the pressure force on it decreases. If the tongue exits the bottom of the slot (it may not), the pressure force again rapidly drops to nil. There are additional complications, such as the fact that, since the tongue sometimes moves upwind to the mean air stream and sometimes downstream, a dynamic pressure component is included. Also, when the tongue is near the opening in the slot, air velocity around it, because of Bernoulli, tends to change the pressure force in a slightly more gradual way. Some of these effects may be negligible compared to others, but in any event, one can see that the pressure force acting on the tongue is complex, not sinusoidal, and, if there are no non-harmonic parts to the tongue motion itself, this pressure force will be periodic (see note, below). It’s a well known fact that a periodic forcing function with rapid changes in time can be represented by a harmonic series of terms, with each term a sinusoid. As the quote from Benade that Dana posted says, the total function is non sinusoidal, but it’s made up of many sinusoids. This is basic, and it’s true for both the reed tongue and the air vibration. We can thus see right here that the musical tone we hear is a direct result of these pressure forces traveling as waves through air, and is complex, not sinusoidal, just like the originating source. This musical tone is made up of a series of harmonic terms, with large contributions from overtones. Many of us have seen these terms in spectral data of the emanating musical tone. There’s no question that the air contains vibrations with many frequencies, no doubt varying in relative amplitude as we compare different kinds of reeds in size, material (brass vs steel), cavity geometry, etc. A further conclusion is that the step-function-like pressure force will, in principle, produce tongue motion at many frequencies. Now we address the question at hand: What is the relative amplitude of these separate vibrations that make up tongue motion? For the answer, we look to experiment. The only published experiment that I’m aware of that treats specifically this issue is, “The Motion of Air Driven Free Reeds,” By Cottingham, Lilly, and Reed, at the Physics Department at Coe College, Cedar Rapids, IA. I have this paper in pdf form and would be glad to send it to anyone interested. In their experiment, the authors measured the actual motion of the tongue from a free reed organ by a variable impedance method, and then analyzed the motion. They present data for this at two driving pressures. In general, the higher the driving pressure, the less is the tongue motion sinusoidal (single frequency), but even in the worse case, with the higher than normal driving pressure, the departure from a sinusoid is very small. Figure 4 in this reference is a beautiful plot of the results for this case, which plots the spectrum of the Amplitude of tongue vibration. In this plot, the Amplitude of the second harmonic tongue motion is about a tenth of that from the fundamental; the third harmonic is about half of the second, and all others are less than about 1/100 of the fundamental. The first overtone of the tongue’s natural (free) modes can be seen on the plot at about 6.3 times the frequency of the fundamental, and it’s amplitude is about 1/1,000 that of the fundamental. In other words, even though the tongue is excited at many frequencies by the complex pressure force, it remains relatively insensitive to all frequencies except the fundamental. Apparantly, it’s stiffness is too much for the air pressure forces at these frequencies, most of which lie far away from the higher natural modes of vibration. It’s important to note here that Power scales as the square of the Amplitude. Thus, the second harmonic, being of one tenth the Amplitude of the fundamental, contains 1/100 the power of the fundamental. Thus, about 99 % of all the energy of reed vibration is contained in the fundamental mode. Incidentally, the power contained in the second mode beam vibration is on the order of E-6 times that of the fundamental. In the context of this thread, I thus maintain the conclusion I made in my previous post, that, if the reed tongue is capable of exciting wood members of a concertina to vibration, the resulting vibration will be essentially at the fundamental frequency, since relatively so little energy at other frequencies is available. One might argue that concertina reeds are different from harmonium reeds. Fine, if there’s not just speculation, but rather a real argument based on experimental evidence, or at least physical principles. Until something better comes along, the Cottingham paper, in my mind, takes precedence over speculation. Quotes from Dana’s Sept 3, 9:02 AM post: I agree with this, if the “modified sinusoid” of the “wave form” you mean is that of the oscillating air pressure in the musical tone. If you mean to describe the tongue motion in this way, I disagree and must ask for some substantiation, for it directly contradicts experimental evidence. I’ve read the Benade book you reference, and I’m not aware of any mention of free reeds, and a quick check now shows no mention in the index. In any event, here, and elsewhere, you seem to be mixing up the motion of the tongue itself with the wave form of the pressure oscillations. Without seeing a clear physical distinction between these, there will undoubtedly be confusion on this issue. For instance, unless I’m wrong, and please correct me if I am, I doubt that you have done an experiment that measured the actual tongue motion, and thus, I don’t understand how you’d be able to see the overtones of the tongue motion on your wave analyzer. On the other hand, if what you saw on your wave analyzer described air vibration, we are in agreement. Same here. It’s something like the squeak of a clarinet or sax reed. I don’t understand the relevance to free reeds. Heterodyne frequencies are produced by some sort of nonlinearity in the vibrating system. What source of nonlinearity do you envision with the free reed? Non harmonic overtones can be produced by linear systems. I understand our ears are nonlinear and produce heterodyne frequencies, but that’s also beside the point. I totally agree if you are referring to the air pressure wave form we hear. Although the evidence shows that all concertina reed tongue motion is essentially sinusoid, I could believe that slight departures might increase as the pitch of the reed drops. This is the statement that spurred on my post here. It’s helpful to see your qualification, and it indicates to me that you are open to suggestion on this issue, so I took the (considerable) time to do it. I hope it goes well in that direction and that you understand my reasons for it. Dana, I understand that, to one who isn't aware of experimental evidence to the contrary, it's reasonable to suppose that such asymmetry can possibly introduce significant nonsinusoidal behavior in tongue motion. I explain this mechanism myself in this post. It's a supposition, however, and experimental evidence indicates that, although correct in theory, the magnitudes involved are quite small. Again, if you're interested in the Cottingham results, I'll email it to you. Note: We know the tongue motion is essentially periodic, because it results in musical tone. Thus, any non harmonic (which also means non-periodic) contribution must be very small. Best regards, Tom
  5. Hi Johann, This appears to be an article on a computer procedure for the optimization of reed tongue profiles, and I don't see it's relevance to the quote of mine that you referenced. Is the issue you wish to address on overtones in reed tongue vibration? Does it deal with accordion reeds or organ reeds? Can you summarize this reference, please? Thanks. Best regards, Tom
  6. I’ve had a little more time to think on this topic and it occurred to me that, if the chief source of energy that imparts wood oscillation is the vibrating mass of the reed tongue, this fact would greatly simplify the picture. Big Idea: It’s a well-known fact that when you excite any acoustic system, no matter how many natural modes of vibration it contains, by forced vibrations at a single frequency, only that natural mode having the driving frequency will be excited. Refinement: With damping in the system, the response spreads from this single frequency to both smaller and larger frequencies, but this spread is small for lightly damped systems (such as vibrating wood). Caveat: We are assuming the systems are linear, which I think is valid, since I see no source for significant nonlinearity, which is a rather esoteric subject, not often encountered in acoustics. Let’s review first how the reed produces sound. An air stream excites the reed tongue to vibration in sinusoidal fashion, being chopped in the process. This chopping introduces rapidly changing pressure pulses in the air, resulting in a musical tone, complete with fundamental (reed tongue frequency) and higher harmonics (because of the physiological response of our ear/brains to the pressure pulses). The first conclusion is that any wood oscillation produced as a result of energy transfer directly from the vibrating reed tongue to the wood will impart wood vibration at (essentially) only the excitation frequency of the vibrating reed tongue. Some people might claim that overtones present in air vibration will also cause significant wood oscillation, at the frequency of respective overtones. I think this is highly unlikely, simply because I don’t see that much force/energy available. I haven’t proven my judgment here by any method - calculation or experiment. It’s just my gut feeling. On the other hand, I think it’s reasonable to at least assume that the energy of vibration of the reed tongue, however, is capable of causing sufficient oscillation in wood. One can reasonably estimate, for instance, the power associated with the vibrating tongue, and compare it to that associated with the acoustic waves in the air (even including the fundamental). It’s my guess that the former is vastly larger than the latter. Maybe some day I’ll have enough time to do this calculation. Also, some people might claim that the reed tongue motion is not sinusoidal, but rather contains overtones. This may be true for high blowing pressures, and even then, the motion in the higher modes is orders of magnitude less than that of the fundamental. It’s certainly not true for low to moderate blowing pressures. Assuming my hunches are correct, I conclude that all the discussion in this thread alluding to the complex arrangement of various natural modes of wooden members is irrelevant WITH REGARD TO FINDING A MECHANISM TO EXPLAIN THE OBSERVATION that wood material affects timbre. In other words, there seems to me not enough energy available to excite the many natural modes of the wooden parts. Only one mode will be excited, at the frequency of the vibrating reed tongue, because that is the only reasonably available source of excitation. So then, what explanation can there be for the complex alteration in timbre observed, which implies an alteration of the overtones in the musical tone? From this point, the only mechanism I can think of to explain the observation is the effect that wood oscillation has on the reed shoe (plate), and the consequent effect this motion has on the chopping of the air stream. To see this, one should imagine the tongue passing through the window (slot), but with the window also moving. With this combined motion, the relative motion between the reed tongue and the window is altered. Both the tongue and the window move with sinusoidal velocity, but most likely with different phase. The sum of two sinusoids with different phase is also a sinusoid of varying amplitude – maximum when the phase is zero and minimum when the phase is 180 degrees. But here, I see difficulties, when I compare the relative amplitudes involved. I can’t see that the window vibrates with much amplitude compared to the tongue, even when excited by the tongue. And so, this mechanism (effect of wood motion on the chopping of the air stream) starts to loose my interest. But let’s continue anyway, assuming that for some reason, the reed shoe (plate) vibration is appreciable. In this case, the relative velocity between the tongue and the shoe is still sinusoidal, as it is without wood motion, but with different amplitude, depending on the relative phase. Relative velocity between tongue and shoe translates to tone volume. From this analysis, then, the only result of this mechanism would be to possibly alter the volume of the musical tone, and the alteration would be different for different reeds, according to where they lie with respect to nodes and antinodes of wood vibration. So this mechanism seems not able to explain a change in timbre, just volume. At this point, I fail to see a mechanism for the reported results, and also feel that the mechanisms proposed in this thread are also not plausible explanations. Yes, I could be wrong, and would welcome anyone to find the error. I regard the conclusion that I make about the single-frequency excitation of wooden parts a firm conclusion, and it would be nice if anyone could substantiate, rather than simply assert, any claim that overtones in the musical tone can impart wood oscillations at natural frequencies that are the same as their respective exciting overtones. A suggestion here would be to calculate the pressure force on realistic wooden areas due to the pressure oscillations defining these overtones and estimate a resulting amplitude of wood oscillation. I haven’t time for it at present. Best regards, Tom
  7. [ As I think more on this, except for possibly organ pipes and brass bells, these examples may not apply to concertinas. The woodwind instruments with circular cross section are very rigid to the pressure pulses inside the instrument, and thus their bodies cannot flex much in operation. There are no asymmetric bending modes on the instrument. Wooden organ pipes, though, are often rectangular in cross section, with walls that might be susceptible to flexure, but perhaps the wall thickness is far beyond that which guarantees rigidity. I’m not sure about brass bells. Dana, your comment here is well taken, and I overlooked the reed tongue vibration itself, visualizing only the air vibration. Thanks for the suggestion. With this in mind, there may indeed be sufficient energy to cause large enough amplitudes of wood vibration in concertinas to affect musical tone, especially because of the generally flat nature of the pans and boards, and that concertinas belong in their own class, somewhere between body-resonance instruments and air column resonance instruments. The other point that came to me upon further reflection is that the density of the wood can possibly directly affect the amplitude of the natural modes of wood vibration. In my comments regarding bending modes in my earlier post, I focused only on natural frequencies, and overlooked how the amplitude of these vibrations might be influenced by wood density itself. More massive woods might vibrate less than lighter woods. Thus, I can see that there may be a plausible physical mechanism (or pieces of it) identified that might explain the observations of you and others. Of course, we are still speculating, but I can at least see a pathway for it. Thus, wood density, a factor that I already noted as a reasonable explanation in an earlier post, might work to vary the amplitude of vibration of various natural modes, and it’s reasonable to expect that some woods would vibrate with different amplitudes than others. It may be that the actual modes have different frequencies, but due the complexity of these, the specific modes may not be that important. In other words, any set of modes, with sufficient amplitude, might contribute to an identifiable timbre (within some limits governed by typical concertina construction practice). Thus, the energy of vibration of the reed tongue, the generally flat geometry, and the influence of wood density could all provide the parts for a plausible mechanism that would allow sufficient amplitude of wood vibration. There may be simple enough ways to theoretically evaluate and carry this conjecture further. I think the best experiment, though, would be to measure the amplitude of vibration of various wooden parts, and this would give many clues on how one can regard this conjecture. Chris, do you know the relative densities of Sycamore and Tasmanian Blackwood? If you have some pieces, maybe you can cut two identical pieces of each and accurately weigh them. The obvious question here is, can wood density be a single parameter in predicting how the material will affect tone? I doubt things could be that simple, and perhaps there’s enough evidence already around to answer this question. I present another suggestion at the end of this post. Dana, you have mentioned that you regard damping within the wood as an important mechanism for altering tone. Do you have an idea how the effect of damping might compare with some other consequence to vibrational modes in wooden members, such as, for example, movement of the reed shoe (plate) itself? In this regards, it’s interesting to note that the hardwoods exhibit less damping than the resonance woods, in general by about a factor of two. I’ll have to think more on why the lighter Bigleaf Maple produced for you a louder, raucous tone. Do you have any idea why the lighter material sound went in that direction, than in say, to a softer, more mellower tone? I’d like to offer here a recent observation that came out of my thinking on this topic. With regard to resonance woods, a well know acoustician who did much work on musical instruments, Schelleng, proposed (The Violin as a Circuit, JASA, 1968, Vol. 35, 326-338), in the making of violins and similar instruments, a parameter, rho/c, where rho is the material density and c the sound speed, as being of prime importance when changing materials of construction in a way that would keep acoustic performance the same. I offer this here only to communicate what I have read and have not tried to evaluate this approach. The idea is (taken from Fletcher and Rossing, 1998, The Physics of Musical Instruments), suppose we wish to replace a plate with density rho-1, sound speed c-1, Young’s Modulus E-1, and thickness h-1 with another plate made from different material with parameters rho-2, E-2, c-2and h-2 in such a way as to leave vibrational performance unaltered. In order that both plates have the same stiffness and inertia, there follows, for the material properties, rho-1/c-1 = rho-2/c-2, and for the thickness, E-1*h-1^3 = E-2*h-2^3. It’s interesting to note that Norway spruce, a choice resonance wood, has both rho/c and Q value (a measure of internal damping, the less damping, the higher the Q) near the top of the list of most all woods. A conclusion here perhaps is that woods with higher rho/c would perform better, at least when acting as they do within string type instruments. For concertinas, there may be different conclusions, particularly if something like reed shoe (plate) movement itself is important. In any event, this result is interesting to me, because, if one were concerned only with natural mode >frequencies<, one need only make the ratio E/rho (neglecting the effect of Poisson’s Ratio) the same, as I posted earlier. I think what Schelling’s proposal does is to bring in the added effect rho has on the amplitude of vibrations. I could be wrong on this, but it seems like a reasonable observation. Best regards, Tom
  8. Hi Chris, Was this “rasp” present throughout the musical range of the instrument? How was the tone changed? Did the first concertina (with Sycamore soundboard) then become raspy and the second concertina then sound sweet? As you know I’m skeptical that material alone could account for the change in sound. Some organ pipes are made of wood. The wood material does not directly affect the sound. The material that a flute is made of does not directly influence the sound of the flute. The material that a clarinet is made from does not directly influence the sound of the clarinet. The material that comprises the bell of a brass instrument does not directly influence the sound of the instrument (Within limits. Someone in Germany built a bell out of soft rubber, and there was a measurable effect, but this represents a change in material properties by more than a factor of 1000.) It is true, however, that different materials allow or produce different geometrical changes. With the flute or clarinet, for instance, a metal allows much finer detail and sharper corners around the tone holes than does wood. Such subtle changes can make a convincing change in tone. The above examples involve musical instruments that utilize a vibrating air column to generate sound, and this air column vibrates with relatively large amplitude throughout the instrument. With the concertina, sound is generated right at the reed tip, like a siren, engaging a small amount of air to vibrate at large amplitude before escaping the instrument. If the above instruments are not influenced directly by material of construction, why should the concertina be different? This is an old story with musical instruments. There have been many examples of people claiming to hear things that, in reality, are generated from within their own brains. The story with flutes went on for decades, until definitive experiments proved the above statement. The results of blindfold tests with different violins show that many "experts" are simply wrong about their ability to identify "pedigree" instruments among others. There are also many examples in the Hi Fi world, where, for instance, some people claimed silver plated speaker wire makes a difference, which is nonsense. I’m not suggesting that you’re in that category, because human experience is very vast. I realize you don’t expect me to believe what you believe based on your single experience, and I see no problem with our different views. I’m left right now only to ask you to be sure that some subtle, indirect effect isn't at play. Are you absolutely sure that, when you changed action boards, nothing else changed? For instance, could it be that one action board permitted the gaskets to fit much more tightly than did the other? Perhaps the screw patterns were different, allowing more rigid assembly with one action board? I suggest you try to think about all the factors that you definitely know influence musical tone and be sure that none of these enter into the action board exchange. I’m thinking, but so far cannot convince myself of a physical reason for it, and this could be due to my limited experience. I would very much like to hear the examples you and Dana note, but that's not easy to do, and so I'm confined to my theoretical perspective, which I admit, is limited. Perhaps, hopefully, someone will suggest a physical mechanism I can believe plausible. In the meantime, let’s keep talking. Best regards, Tom
  9. Hi Johann, Thanks for your comments. I may be mistaken, but you seem to require that theoretical calculations be accurate, and if they aren’t, they are of no practical use. For instance, The value of theoretical calculations is often more in the understanding they allow than in whether or not they are accurate. Sometimes all it takes is an adjustment, or a fudge factor, in order to account for difficult issues, but again, the real value in these calculations is in the way they illustrate the physical mechanisms at work, allowing us to extrapolate our knowledge to areas not covered by experiment. We then master a physical phenomenon, allowing us to possibly enhance its expression in what we build. In the paper, I do explain the sources of error I’m aware of. If you haven’t already, you might want to read the section “Complications” that lists some of these inaccuracies, but I’m sure you’re aware of these things. I think the greater value of the paper is in allowing an understanding how resonance in chambers becomes more likely for the higher pitched reeds, and how lower overtones of the musical tone become more susceptible to cavity resonance as the pitch increases. Such an understanding eliminates a lot of experimental investigation. Perhaps it would be worth sharing your experimental data with me, and we can look at the calculations together. I think you missed the main point of my last post, which was to evaluate a possible physical mechanism (wood resonance) that would explain the effect changing wood material in a concertina has on musical tone. I clearly did not say what you claim above. Do you have any comments on my reasoning, in the purpose of my post? I agree that the speed of sound varies with grain direction in wood. It’s interesting to first note that this fact is a direct result of the fact that the Young’s Modulus varies with grain direction, which again illustrates the general principle that the square root of the ratio of stiffness to density is, practically, the only material property that influences the natural frequencies of vibration. I say “practically” here because, in my previous post, I simplified things a little. With some vibrations, Poisson’s Ratio also comes into play, in a smaller way, and this ratio is pretty much the same among most construction materials. Also, please note, I’m NOT saying that this factor is the only material property that explains ALL acoustic effects. It’s interesting to note that Young’s Modulus in the longitudinal direction for most woods is from roughly 10 to 20 times larger than that across grain. One exception is Oak, with a ratio of about 2.5. For Spruce, choice material for the top plates of string instruments, it’s from 13 to 24. Since the density is the same in both directions, this means that the speed of sound will be greater along the grain by a factor about equal to the square root of this ratio say, about 3 to 5. This is one reason why the aspect ratio of bowed string instruments is approximately 3 – sound moves out to the edges more or less uniformly, enabling many mixed vibrational modes. An added complexity is that the sound speed varies more or less continuously with grain angle, achieving the above maximum and minimum at zero and ninety degrees. (Let me also mention that, for sound waves in wood, one uses the dynamic Young’s Modulus, which is about 10% greater than the static value, and it varies inversely with moisture content, but this is getting boring.) In any event, let’s speculate and suggest that this non-homogeneous property of wood might explain why different woods behave differently in a concertina. To explore this, I’d first like to ask Frank, Dana, Richard, Chris, and other builders if they orient the grain in preferred directions when building. If they don’t, I’d tend to think the effect isn’t important, since so little can get by these craftsmen :-) Without knowing this, I’d have to guess that there’d be little influence of grain orientation in the reed pan or action board of radial reed layouts (Wheatstone?). With parallel arrangement (Jefferies?), one might choose to orient either the long axis or the short axis of the cavities with a particular grain orientation. After building several concertinas and evaluating their musical tones, conclusions may be drawn. That’s a lot of work. Still in my guess mode, I don’t see much merit in this, and one good reason for my skepticism is that, with all the cavities attached to the reed plate, the resulting structure is much more rigid than the simple board, and so too with the action board, which often has another rigid plate attached (to guide the buttons). These additional members, I think would bury a 40 % change of sound speed with grain orientation. If we really want to know the answer to the question of the original post, a good experiment to do would be simply to measure the amplitude of wood vibration in the different wooden members. Knowing this number would surely spawn a lot of thinking. But I’m not inclined to do such an experiment until I’m more convinced, for whatever reason, wood material is important. You have me confused. Do you think wood material is important to musical tone in concertinas or not? Perhaps my memory fails me, but as I recall, didn’t you once make accordion reed cavities from balsa wood and found no noticeable effect? In any event, I appreciate your comments. Best regards, Tom
  10. Greetings, The design of reed cavities in concertinas is a topic of considerable interest here, and we we visit it often on this board. An article I wrote for PICA on reed cavity design and resonance is now available for free download at: http://www.concertina.org/pica/index.htm (Vol. 2, 2005). The article discusses many aspects of this subject, both qualitatively and quantitatively, presenting sample calculations and, I think, interesting conclusions. Enjoy. Best regards, Tom www.bluesbox.biz
  11. Hi Chris, Most all these factors are discussed in detail in an article I wrote for PICA II, now available for free download at: http://www.concertina.org/pica/index.htm (Vol 2, 2005). I'd be interested in any comments you might have. Best regards, Tom
  12. Hi Dana, Thanks for your explanations and descriptions of experiments you have done, and it’s this kind of work that keep us thinking. I refer especially to when you changed the material of the reed pan and action board wood from Bigleaf Maple to Rock Maple, keeping all dimensions the same. You appear quite sure that this change of material had a very noticeable effect on musical tone, and I find this result quite interesting, even surprising. I’d like to explore it a bit further from a theoretical point of view, and thinking about it from my own limited knowledge of acoustics, if it is indeed true that the tone was changed considerably, I see no physical reasoning for it. I agree with you that we can hypothesize many possible factors; however, on close scrutiny, I think most of these can be ruled out. For instance, you say: I’d like to note my own disagreement with this speculation for the following reasons. Johann can perhaps recall that I’ve already posted on the RMMS group that the only way material properties affect resonant frequencies in vibrating systems is through the ratio of stiffness to density, and even there, it’s the square root of this ratio that’s important. This is quite universal. If you look at the solutions for resonant frequencies (and relatedly, the speed of sound) in metal strings, columns of air, vibrating reeds, vibrating membranes, vibrating plates, etc., it’s this ratio by which material effects enter the expressions for modal frequencies – the fundamental and all overtones. I find it interesting that that such a complex thing as resonance can have such a simple statement associated with it, but I invite others to verify this simple fact. Thus, if we seek to understand the effect two different woods might have on the acoustical properties of a concertina – in so far as resonant behavior is concerned, and of course assuming all other factors (mainly geometrical) being the same, all we need to do is calculate this ratio for both woods, take the ratio of these calculations, then take the square root of that. The result will give us a good idea how resonance effects will shift in frequency. For solid materials, the stiffness property is its Young’s modulus. When we do the above calculation for all woods, we don’t find a very large departure from unity. For instance, of 18 hardwoods I have data for (Mark’s Mechanical Engineering Handbook), the largest ratio (for Basswood) divided by the smallest ratio (for Black Tupelo) yields (after the square root) 1.2. For 14 softwoods, the corresponding largest (Douglas Fir) and smallest (Eastern Hemlock) yields also 1.2. This, to me, indicates that resonant shifts of partials of the musical tones are confined to within about 20 %, for most all woods, and perhaps significantly less than that for the woods normally used in concertina construction. For a concrete example, let’s approximate the reed pan or action board of a concertina by a disk of Basswood of 6 inch diameter and 1/8 inch thick. For this example, the specific dimensions don’t matter, nor does it matter that, in reality, there are other components screwed and glued to these pieces. These complications will only change the numbers, and not the point I’m trying to make. For this idealized shape, the fundamental vibrational mode and first few overtones have the following frequencies, 150, 313, 514, 586, 897, etc. Notice that these frequencies are not in whole number ratios to each other. So, if we change the material for instance, to Black Tupelo, its natural frequencies will be changed to 125, 261, 428, 488, 747, etc. Thus, the natural frequencies are changed uniformly. From this, it’s true that a change of wood might cause a more favorable or less favorable match with the partials of a single note; however, given the fact that each musical note contains many overtones, which are whole number ratios to each other, it seems highly unlikely that such a uniform shift of unequally spaced natural frequencies of any wooden member of the instrument could alter the tone of many notes in the same way. I see a very complex shift of both more and less favorable matches. A claim that the concertina becomes generally “brighter” or “more mellow,” for instance, implies that many notes of the instrument are affected in the same way, which, to me, cannot be explained by such a mechanism. The one property of wood that I could see having the same effect on many notes is its density. As illustration, and I’m sure you are aware, Russian bayans are generally regarded as having a brighter tone than similar instruments built with Italian (accordion type) reeds, and it’s generally assumed that the reason for this has much to do with the fact that the bayan reed tongues are mounted on a monolithic plate (I believe, often Zinc). This plate, because of its greater mass, is able to remain more stationary than the Italian plates during tongue vibration, enabling sharper pressure pulses and thus more (numbers of significant) higher harmonics. As far as I know, this explanation is still in the realm of speculation, but it’s a kind of speculation that, to me, has a firm physical basis. On the other hand, until someone does the decisive experiment (if it hasn’t been done already), as far as I’m concerned, the theory could be disproven. In any event, at the present time, I wouldn’t really argue against this speculation that a change to more dense wood – everything else being the same – might possibly cause brighter tones. With this reasoning, a concertina with a Lead body might sound the brightest, but of course, this density solution could have rapidly diminishing returns as density increases. But even here, I would like to know more about the amplitude of vibration of the concertina wooden parts. If this amplitude at the reed mounting is, for instance, orders of magnitude less than the part of the tongue vibration that’s key to sound production, the range of wood densities available might for me rule out this possibility as an explanation. Perhaps Johann knows more on experimental work done on this issue. With regard to your experiment, I need to point out – and I think you will agree - that it wasn’t really controlled, in the sense that the two concertina versions are not available to be heard simultaneously. (Perhaps you made good quality recordings?) We all seem to agree that we haven’t language to speak precisely about tonal qualities, and you’re even talking about changes effected by switching one kind of Maple to another. How much does Young’s modulus and density change among the Maples? (I don’t have data for these.) I’m not claiming that your conclusions are incorrect, but if they are correct universally so, I see little physical basis for it, and I don’t think anyone here has identified a robust physical explanation, unless perhaps, the densities of these two woods are very different. In any event, it would be nice to have objective measures; e.g., the trace of an oscilloscope, or a frequency spectrum that we can try to translate to the subjective realm. Perhaps your memory of your subjective reaction is very good, but I think you’d agree that it’s in the realm of anecdotal reporting which is difficult to translate to another person without some tangible evidence. All I can do now is thank you for your report and file it away for future reference. It appears that you view wood resonance as destructive to the expression of partials. Yet, if you think wood resonance is a mechanism to alter timbre of the instrument, don’t you think that some of this energy would find its way into the air vibration associated with the musical tone? As you know, this is how sympathetic vibrations work in those instruments where sympathetic vibrations are known to be important; e.g., violins. Wood resonance in these latter instruments causes some damping, but in the main, provides a mechanism to amplify and shape musical tone – provided of course the impedance match between different parts of the instrument in the line of energy flow is in the right range. (With too much impedance, sound waves are reflected back and don’t get outside, and with too little impedance, too much energy is removed from the part upstream of the flow of energy.) This is a subtle point, but it appears to me there’s some contradiction in postulating that wood resonance is only dissipative, yet it is capable of changing the characteristic tone of the instrument to “raucus, loud but terribly harsh and coarse.” With regard to the pad hole, from my own investigations on resonance in cavities, if the cavity behaves as a Helmholtz resonator, it’s location is probably not that important with regard to resonance. If the cavity behaves as a quarter wave tube, it’s location is critical, with regard to its affect on resonance. Relatively simple calculations can be made to see what kind of resonance is or is not present in the cavity. These points and many others are dealt with in detail in an article I wrote in PICA, now available for free downloading at http://www.concertina.org/pica/index.htm (Vol. 2, for 2005). Thanks again for your comments and I look forward to more. Best regards, Tom
  13. Hi Chris, It’s nice to be back after a long absence. I tend to agree with Richard on this one. Let’s simplify, by saying that a concertina is comprised of 1) it’s reeds (plates, or carriers plus reed tongues) and 2) everything else, called “design.” Your experiment may actually prove that the design can be more important than the reeds, in so far as steady state tone goes. Included in the design, of course, is the material of the wood. So in order to resolve this, we should ask, what evidence is there for one to say that this design aspect is at all important? What wood materials were used in both concertinas? What differences were there in the other aspects of the design? Now, I can’t say wood material has no importance, but before I believe it does have a prime importance, I’d have to hear some kind of physical reasoning behind it, and in saying this, I’m only trying to push the discussion further. What possible physical mechanisms can be at play, in order to give weight to your belief? Are there direct acoustic factors, such as resonance, or perhaps there’s some kind of indirect effect, such as the possibility that different woods enable different dimensional relationships between the parts? The latter possibility occurs, for instance, in flute making; metal construction allows more precise hole geometries than does wood construction, producing audibly – and measureably - different results in the musical tone. Best regards, Tom
  14. Hi Bob. I recommend you listen more to modern diatonic harp players, led by Howard Levy. These people play all 12 chromatic tones with their ten hole harps, and with facility. The accidentals are achieved by bending, using techniques that are difficult to master. These techniques involve down bending, acheived by pulling the pitch downward with the help of the other reed in the chamber, and up bending, achieved by what they call "overblowing," which causes the reed tongue to function as an "opening reed," as opposed to their normal operation, which is as a "closing reed." With these guys and in certain types of music, some kind of bending is ubiquitous. I think, strictly speaking, what you refer to as vibrato is more properly called tremolo. This may have been discussed in this group before, but I believe vibrato is a quiver in pitch (frequency), and tremolo is a quiver in volume (bellows pressure). I'm not aware of anyone who has accomplished true vibrato with facility in the conventional squeezebox. Best regards, Tom
  15. It sounds like an interesting technique to achieve dynamics, though not usually encountered here in the west, as far as I know. Even bandoneon players, when playing tango, with extreme variations in volume, accomplish the attack by hitting the box against their knees, transferring the impulse to the bellows. Very effective, and gives one reason why no other kind of accordion could produce tango music like a bandoneon can. Your concern is justified, for the bend force is a critical choice, and will depend upon the kind of keyboard, music, and above all, the player. For Kenny, the force he chose for the bend was three pounds, and it took a couple prototypes before we got that right. Kenny also plays piano, so he plays really heavily. With lower bend forces, it's true, he was bending notes unwillingly, and it sounded like he was playing a broken accordion. With the proper force, however, this problem was solved, though even now, he tells me he could tolerate even more bend force. Thanks for the info. Best regards, Tom
  16. Which recording on the site are you referring to? Without knowing the answer to that, I can still venture that I don't think the size of the cabinet is crucial. There are many variables here, and in reference to one of the more important ones, I refer you to the article I wrote, entitled, "Reed Cavity Design and Resonance," in Papers of the International Concertina Association (PICA), Volume II, edited by Allan Atlas, available fro the Center for the Study of Free-Reed Instruments, City University of New York. I don't know what you mean by "double chamber;" however, none of the accordion recordings on my site makes use of a tone chamber (cassotto). Best regards, Tom www.bluesbox.biz
  17. I appreciate your comments, though see no advantage in a lever. Bending occurs only with the expressed intention of the player (when everything is working right ) Best, Tom
  18. Hi Jim. This is an interesting effect and doable, though as you indicate, it takes practice. With the two stage key-bend triggering I mentioned above, an up bend is accomplished by pushing the key to the maximum bend position with very little bellows pressure, then coordinating the application of pressure while backing off on the key, into the first stage. This effect was very intriguing to Kenny, who plays on the CD featured on my web site. He has since learned the technique, and it took practice. Another challenging effect that Kenny is perfecting is vibrato, which adds warmth to the musical tone in a way that cannot be achieved by the tremolo often employed by free reed musicians. Best, Tom
  19. I also think that the volume of the bending note might be less of an issue than theorized. For instance, because of the nature of the acoustic effect, for constant bellows pressure, the volume of the bending note tends to drop a bit, and I find that I want to press or pull a little harder on the bellows of my modified accordions while bending notes. Harmonica players deal with this all the time. When we consider the bending note as a new feature in the musical line, the listener may not care much whether its volume is exactly the same as the rest of the line. If there's any issue, it may be with regard to the volume of the notes that follow the bend, but again, this concern may be a bit exaggerated. There are technologies that I've explored that allow bending up, though I haven't yet incorporated any of these into a playable instrument. My guess was that down bending would be the simplest to start with. Perhaps, but I'll simply repeat that, when we consider the bending note to be a separate musical feature, the issue may become less important. Thanks for your experiments and comments. Kind regards, Tom
  20. I believe the specific point here is that it might be hard for a concertina player to properly regulate the force he uses on the buttons. For example, when he is pulling the bellows open, the hand strap is going to act as a lever that will increase the force he uses on the button which will increase the force he is using to play the note which could, under this system, lead to unintentional bending of the note. -- Bill I see what you mean. There are torques placed on the box that have to be counteracted by one's fingers, and I assume this would be true for both push and pull. I should explain first that pitch bending is activated by additional finger force in the second part of a two stage process. The first stage is accompanied by the normal playing force necessary to open the pallet, during a reasonable normal travel distance. There's a soft stop at the start of the second stage, so the player thus feels a definite boundary between playing and bending. The force necessary to overcome the soft stop, as well as the actual bending force during the bend, can be made to the spefications of the player. Hope is that there's a combination of these programmed features that allow a practical mechanism. I tend to think that one cannot predict ahead of time how practical this will be, especially when one considers the, as yet, unknown, ability of the player to adjust to such things. Building a prototype would be the only way to really explore this idea; however, I haven't found a suitable concertina player who's willing to work with me on evaluating such a prototype. Best regards, Tom www.bluesbox.biz
  21. I'm curious to know why you say this. Another concertina player mentioned to me that there might be a problem with such a trigger mechanism for the bending, because of possible adverse effects on bellows pressure. I myself don't play concertina, so I'm not one to say what's important here. How is the force to compress the bellows transmitted from one's hands? If it's through the tips of the fingers that are resting on unplayed keys, then there could be an issue. How much of an issue, I don't know, because the triggering force necessary for bending need not be much more than the force required to open a pallet. Thus, pushing a little harder on a key now and then may not be a big deal. Then of course for the pull, such an issue shouldn't really come into the picture, and I don't see it as a serious disadvantage to bend notes on the pull. This last point is of course more true for EC than for Anglo, since for the Anglo, not all notes are accessible on the pull. I'd appreciate hearing various viewpoints on this subject from experienced concertina players. Best regards, Tom www.bluesbox.biz
  22. Hi Richard, It may be just a case of terminology, but instead of "reamed," could you have meant "broached?" If reaming is done with a circular cutter, I can't see how you can ream the inside of the vent and still maintain sharp corners, but I may be assuming a too restrictive meaning for this term. Physically, how is the inside of the vent finished? How does the tool cut? Best regards, Tom
  23. Hi Clive, If you investigate this topic, I think you'll conclude that the free reed tongue vibrates only at its fundamental bending mode (with or without weighted tips), with next to nil contribution from higher modes, measurable if at all (by sensitive electronic instruments) only at higher than normal blowing pressures, and the same goes for twisting (torsional) modes. All these modes, by the way, are sinusoidal. If there were significant contributions from more than one mode, the result would be noise, since their frequencies are not, as a rule, close enough to integer multiples of each other. Thus, one cannot expect to encounter these modes in any instrument that produces acceptable musical tones. Best regards, Tom http://bluesbox.biz
  24. Hi Jim, Concerning Stephen’s original question, and having given my previous post, I think I can succinctly state my response as follows. Changing only the angles of cavity walls (parallel vs. non-parallel), without changing volume or other construction parameters, would have negligible effect on cavity response, when such response is that of a Helmholtz resonator. For quarter wave response, or any other response involving standing wave oscillation in the cavity, such a change at most alters the resonant frequency of the response, and I see no way that this change could always produce the same result on tone (e.g., a more brighter tone). These statements apply to any frequency of excitation, including reed fundamentals as well as reed overtones. In my response to Stephen’s question, I thus see no reason to bring in the various issues you refer to, which to me, would unnecessarily complicate my explanation and perhaps confuse people. These issues are of course interesting and I’m glad you mention them, but before I myself move off the main question, I’d like to be sure I made my simple point. I have done a detailed study of these broader issues and put them in a paper that is scheduled to appear in the PICA, Volume 2, which is organized by Allan Atlas. In this article, Allan has allowed me to present a detailed quantitative analysis of these issues, and I hope you and other concertina enthusiasts find it interesting. Best regards, Tom http://www.bluesbox.biz
  25. Hi Stephen, Your interesting question has many aspects to it, and I’ll try to provide a straightforward response, with more elaboration added on. I see no reason why, everything else being the same, parallel-sided instruments would produce, throughout the musical range of a given instrument, characteristically different timbre than non-parallel side instruments. I can see specific instances where such differences can exist, involving specific reeds, pitches and sizes, but even here, and from a theoretical point of view, any one geometry can produce brighter tones, for instance, than the other. When we speak of the effect chamber shapes, sizes, etc. have on musical tones, we are interested the interactions with sound waves over a wide frequency range, and all acoustic systems behave very differently at different frequencies. As I indicated in my previous post, a change of angle between facing walls of a cavity, without changing cavity volume, and everything else being the same, would have minimal acoustic effect on the sound for those frequencies whose wavelength is much larger than all cavity dimensions. In other words, the wave doesn’t see the details of the cavity; it only senses its capacitive effect, in conjunction with the inertial effect of the pallet hole. Such a change in angle would alter the frequency that excites the cavity as a quarter wave tube, which in turn could either cause resonance with some partial of the musical tone, or destroy resonance with some partial of the musical tone. In addition, the walls of the cavity are part of an acoustical system, involving also the other parts of the cavity, the reeds, the pallet hole, the pallet, the box, with baffling and tone chamber effects, etc. It’s difficult for me to see how changing one aspect of this system can always have the same effect on musical tone. If it is indeed true that parallel-sided instruments produce brighter tones, I suggest that we need to investigate further what other changes in the instrument accompany such parallel sides. For instance, are the pallet holes the same area, do the pallets move away from the hole the same amount, is there greater influence from baffling (or “cassoto”) effects within the body of the instrument, etc., and of course, are there significant differences in the way the reeds themselves are made, scaled, sized, etc.? Perhaps it’s true that brighter or softer sounds occur with parallel sides for certain pitch regions in a certain instrument, or for certain isolated pitches. Even here, I suggest we would again have to look at all the important acoustic features of the instrument and perhaps measure frequency spectrums at different locations within and outside the instrument in order to understand why. Even then, our study may be inconclusive, simply because of the complexity of the acoustics and the fact that we are dealing with subjective judgments on tone quality. I read through the comments by the Authors you cited. The statement (from Rich), “A lot of the honkiness has to do with the fact that the chambers HAVE parallel sides AND that this enables the reeds to be size-optimized for response.” is interesting, though I’m not sure what it means. I don’t think Rich intended this statement to explain his full understanding of the topic. But here, I can only ask, Has someone proven that the parallel sides are indeed the reason? But then, what does “size-optimized” mean? Perhaps the parallel sides enable another construction feature that also influences tone, and thus, the effect is only secondarily through the fact that the cavity walls are parallel? The complete statement (from Steve), “My reed chambers are all parallel, but there are differing views on that too. Steve Dickenson told me that it was simply a matter of construction method, depending on how you secured the reed pan while cutting the rebates for the chamber divisions. I think it improves the tone, but he reckons that Wheatstone's original calculations show that it is better to avoid parallel sides. Some larger Wheatstone English models have a mixture so maybe even Wheatstone himself was prepared to use parallel sides when it suited the layout of the instrument better," indicates that there is some disagreement on the effects of parallel/non-parallel layout. The statement, “Wheatstone’s original calculations show that it is better to avoid parallel sides,” doesn’t mean much to me, since I don’t know what kind of calculations these are and I don’t know what is meant by “better” in “better to avoid.” I think the main thrust of Dana’s article is to indicate how complicated sound production is in a concertina and that there are no simple blanket statements that can be made on what feature causes what sound. I tend to agree with this. To say that parallel/non-parallel sides have such-and-such effect on tone to me seems like a blanket statement. Perhaps it’s true, and if it is, I don’t understand the physics behind it. Thanks for asking such an interesting question, and although I don’t think I answered it very well, it has allowed me to think more on the topic. Best regards, Tom http://www.bluesbox.biz
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