ttonon
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Posts posted by ttonon
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I never knew that! So, it's not like resting a tuning fork on a guitar body to get it to resonate more loudly? Have you ever noticed a reed increasing in volume when you set it down on a piece of wood while it's vibrating?
You might be able to observe that effect if you actuate a reed by plucking it, but that's not how a reed operates when it's being played.
You may be able to convince yourself of this by biting down on the corner of a harmonica as you blow through the first hole-- the sound doesn't get particularly louder or softer, and the harmonica doesn't vibrate your teeth like a tuning fork would.
Ransome, I think there’s a complication here worth mentioning. A free reed mounted properly in its wood slot will sound much differently than the same reed sounding while not being mounted, or mounted very loosely. When the reed is not mounted securely, the frame of the reed vibrates with much more amplitude than it does when it is mounted securely, and this vibration affects sound. Poorly mounted reeds will even sometimes buzz against their mounting.
The reason for the different sound is that the relative motion between the vibrating tongue and the frame slot can be significantly different between the two cases, and this difference shows up particularly as a difference in relative velocity. If the motion of the frame in the unsupported case is dominated by the fundamental mode, as I’d guess, there can also be a possible difference in phase between the fundamental of the emanating sound and the rest of its partials, though I’m speculating here. But most importantly, the relative velocity amplitude will definitely affect the volume of the tone, with some probable effect on timbre, depending on how poorly the reed is mounted. Buzzing (and air leaks) will of course add considerable complication to the resulting sound.
Although the free reed does not rely on the motion of a soundboard, as with string instruments, there’s still a relationship between the sound produced, the mounting, and the woodwork. The crux is how much the frame of the reed does actually move, even when the reed is securely mounted. Depending on the mass of the vibrating tongue, which depends on the pitch of the reed, and the geometry, density, and rigidity of the supporting woodwork, there may be significant frame vibration, which can be theoretically transmitted through the supporting wood structures, and consequently radiated by sound to the air, if the associated geometries, masses, and rigidity are suitable. I’m talking about very small effects here, though I wouldn’t go so far as to say that there is absolutely no contribution to sound by the woodwork for all reeds at all playing volumes, without doing the proper experiments, which I haven’t.
Regards,
Tom
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So if I want be able to adjust the balance between the 2 mic's can I make one of the resisters variable with a mid range value about the same as the fixed resister on the other line?
Yes, although you should be careful to keep the potentiometer and hook up wires small so that they don't become too much of an antenna that would pick up hum. Use the smallest pot, with the shortest hookup leads. In addition, any wires that you use for signal voltages anywhere that are longer than an inch or so should be the center conductor of coax cable, with the shield of the cable grounded on one end only. Small diameter coax is available. Shield grounding is the same for the coax cord that you will use for connection to the amp: ground only one end of the shield. Put the Y joiner at the far end of this (stereo) cord, just before the amp: there's no need for two long cords. With this set up, it may be more convenient to mount two pots on the instrument, one for each mic, because the Y will be mounted far away, where the amp is.
And the battery for the electrets goes in series in the output, does it, or do I have to have a separate power supply on the instrument side of each resister?
I don't understand. The Y itself is passive - no battery necessary. The standard electret mic hookup diagram shows a battery connected to a current limiting resistor, about 2200 Ohms, with the other end of the resistor split off to the hot wire for the mic and the isolation capacitor, about 1 uF. The other end of the capacitor is the signal wire for that mic, which can go to a pot, about 10k Ohm, and the same battery can be used for both mics. Does that make sense?
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The mixer come power supply is £40 from Microvox; buy that and make the mics myself seemed like the winning answer until I found someone who used to make them himself because he was so outraged at the price. 'Used to' sadly.
Dirge, I'm not sure I understand your reason for getting a mixer, but if it's only to combine the signals from two microphones so that the combined result can be plugged into an amp, you can very easily make a passive mixer, in a Y configuration, with the two input cables depicted by the top of the Y and the output is depicted by the bottom of the Y. The low side (often ground) of each cable at the top are combined directly to the low side at the bottom, and the two high sides (hots) at the top are each connected to the high side of the bottom, each through a resistor. The resistors allow each signal to perform independently of the other, providing a kind of "squash" so voltages can move independently. The two resistors should be the same value and are not very critical. I'd suggest values anywhere between one thousand and ten thousands Ohms. You can mount all this in a small aluminum box, with all three cables hooked in, or you can install three jacks in the box, allowing you to plug the cables into the box.
Tom
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Dirge, if you decide to go with an electret mic, you will find they have very good audio quality, with minimum cost. I would suggest the Panasonic WM 61A, obtainable at Digikey, for less than two dollars each. You can access a data sheet here, which gives their frequency response as well as a suggested hook up circuit. I would also recommend an external mic setup, much like Stefan recommends, with one mic for each side of the instrument. A stereo cord can then take the signal to an amplifier. If you decide to use a battery pack on the instrument instead of phantom power, you need only one or two AAA batteries, and you can use a 1/8" stereo plug/jack on the instrument side, with a standard 1/4" phono plug on the amplifier side of the cord, which will plug into the standard "high impedance" input of your amplifier.
Best regards,
Tom
www.bluesbox.biz
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I suppose this is a concertina player playing for concertina minded folk, but as far as Tango goes, I think the performance can be greatly improved by adding the accent, or snap, that Tango music is famous for. The entirely legato sound of this performance lacks the tango rhythm, retaining only its melody, and thus, falls short in that way. I don't think Tango dancers would like to dance to it. It doesn't feel like a Tango.
All this is a bit surprising to me because the concertina is such a light and mobile instrument, which should allow at least some of the sharp accents present in Tango dynamics. When Tango is played on the bandoneon, the traditional Tango instrument, the musician achieves many of the accents in volume by ramming the instrument down onto the thigh. I can't see why such effect cannot also be achieved with the concertina. As a caution, I do mention that there may be some limitations how dynamic concertina reed response can be, at least when comparing it to that of a bandoneon. They might choke. Bandoneon reed valves are purposely curved away from the tongue, I think, in order to allow such extreme dynamics.Best regards,
Tom
www.bluesbox.biz
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Adrian, I think you controlled bellows pressure quite well in the recordings you made. If you compare the traces in Figure 1 of the .doc file I attached above, it's obvious that the the inboard reeds have a much lower amplitude (volume) than the other reeds, and the most obvious guess why this is so probably has something to do with the doubly long aperture length. I'm assuming that the inboard notes you played do not have the chamfered aperture you show a picture of. As I mentioned to Mark, it's difficult to theoretically explain how such a long aperture would affect sound spectrum, but the effect on sound volume is intuitively easier for me to make guesses about. Thus, the apertures in your pictures were perhaps chamfered as an effort to increase sound volume.
Tom
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That is now.
Tom
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Hi Adrian, in the .doc attachment, Figure 1 shows the raw data traces of the sound files you provided, but with all traces organized so that each “Without” trace is followed immediately by its corresponding “With” trace. I think you’d agree that the amplitude (volume) of the middle note in each case – the notes made by the cavity you experimented with – does not show appreciable alteration by the insertion of Blu-tac. In fact, the last note shows that the “With” sound has lower volume than the “Without” trace, but I don’t think it’s very significant. It’s thus interesting to me that, although you feel your modification improves the sound of the two notes (both push and pull), such improvement does not show up as an increased volume.
But your sound files I think do belie a significant change in sound due to the cavity modification. The .wav attachment is a sound file extracted unmodified from yours, containing just the two notes made by the cavity in question, with the “Without” trace followed immediately by the “With” trace, for both push and pull, for both playings of the notes. I think making both sounds immediately next to each other might make comparison easier, and to me, the second sound, which is from the “With” file, reliably has a more treble sound to it, a sound some might describe as “more bright.”
Taking the Fast Fourier Transform of these sounds gives you the frequency spectrums shown in Figures 2 and 3 of the .doc attachment, comparing the notes before and after cavity modification. In Figure 2, which is for the C#3 note, the x’s (with modification) show a spectrum that has reduced low-end partials (frequency range up to about 2,000 Hz), and increased upper partials, from about 2,500 to 6.000 Hz. The frequency range about 6,000 to 8,000 Hz shows an interesting reversal, but for the highest end of the spectrum, the modified chamber again shows larger amplitudes. For me, this comparison is adequate evidence for a more trebly sound, as my subjective hearing concludes. I have no explanation for the 6,000 to 8,000 Hz spectrum, but more on that later.
In Figure 3, which is for the G3 note, the x’s do not show much drop in overtone amplitude at the lowest end, but do show the increased amplitudes in the range 2,000 – 6,000 Hz shown by those for the C#3 note. The range 6,000 to 8,000 Hz shows the same counter trend. The highest end of this spectrum does not appear to show much difference between the modified and unmodified sounds. But I think the comparison in the region 2,500 to 6,000 Hz provides a reasonable verification of the more trebly sound that I hear for the sound with the modified cavity. Such is reasonable simply because of the SPL amplitudes themselves, which our hearing emphasizes more in the 1,000 Hz area, and are also vastly numerically larger than the amplitudes further up the spectrum. Remember, we are dealing with a log scale. Further, one’s hearing at the highest frequencies can often be diminishing, and so they contribute less to the sound, especially for one in my age category.
Okay, I’m convinced that your modification does change the sound of the note, and not really it’s playing amplitude. Providing a clear physical explanation for this is very difficult and beyond anything I can do here. It is true that your modification will most likely modify the resonance characteristics of the cavity/aperture system, and I would definitely expect it to change the amplitudes of at least some overtones, but an explaination why it would modify so many overtones would take a good deal of theoretical investigation, once having obtained accurate dimensions of the geometries involved.
Mark, thanks for bringing my attention to this thread. (For some reason, my notification feature was turned off.) Concerning your query about the effect of the aperture, the situation is a bit more complex. I myself, and probably professional acousticians, can apply only the simplest and basic concepts in trying to understand how the free reed makes the peculiar sounds it does, without a serious research effort. My approach is to apply the well-understood models of resonators: Helmholtz, quarter-wave, half-wave, etc. and try to draw conclusions. Thus, if you’re applying the Helmholtz resonator model, you would consider the aperture in conjunction with the cavity volume, and perhaps also the aperture created by the reed slot itself. If you invoke a quarter wave model, you look at key linear dimensions in the cavity and in the aperture, taken separately.
For instance, the peculiar response enjoyed by the 6,000 to 8,000 Hz range in the above frequency spectrums indicates that the cavity volume did not affect whatever it is that is causing this. One possibility is perhaps that the aperture is behaving as a half-wave resonator for these overtones.Note: I'm editing out an incorrect interpretation here. In this frequency range, it appears that the Blu-tac lump does effectively eliminate much of the enhanced overtones, for both notes. Perhaps there is some kind of half wave effect of the aperture coupled with the cavity volume that is eliminated when the cavity volume is changed.
Before even the simplest models can be applied, as described here, one would have to first make accurate measurements of the relevant geometries, then apply some clever detective work, starting with the simplest and building from there.
Best regards,
Tom
www.bluesbox.biz
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Thanks Jody. A plaintive, wailing kind of song, with much expression. I like the bluesy solo near the end. Also, I like your arrangement of "Give the Fiddler a Dram," and the interesting photos.
Best regards,
Tom
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In the members section, when viewing a member's profile, there's an option on the menu to view that member's "posts," but the list given is of only the most recent posts. Is there a way to view all the posts made by that member, displayed in a single list? Thanks.
Tom
www.bluesbox.biz
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I have used Mammoth Ivory to make replacement buttons . I do have quite a lot of 'off-cuts' of Mammoth tusk left over from my day job so if any one needs a few pieces to copy Ivory buttons I might be able to help out.
Geoff, I'm very curious. Is "mammoth ivory" truly from mammoths (or mastodons), the prehistoric animals, or might they really be elephant tusks, with a disguised name, because of international laws clamping down on poaching? It's puzzling to me how remains of prehistoric animals could be apparently so available. What are the origins of the materials you have, and what prices are you aware of?
Regards,
Tom
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Hi Geoff,
I understand your concern for the average concertina user, who like the user of most other mechanical contraptions, is much less interested in understanding their functioning parts than he/she is in keeping the contraptions in a trouble-free, usable condition. I think you are also probably correct in assuming that the original poster is likewise adverse to experimentation, on the belief that the workings inside the box are far more complicated than anything he/she would ever want to deal with, with a risk for damage on top of it. I thus agree that your advice is entirely reasonable to the vast majority of situations conjured up in this forum, and in particular, to the original poster, with well deserves admonitions and caution.
But I also think you would agree that the forum here does contain a fringe element of people who are genuinely curious enough and willing to take on some risk and effort for experimentation, which often provides an essential path to understanding, in an area of personal interest. I’m sure you yourself would be in this fringe. And in truth, not knowing anything else about the original poster, I think there may be a small, though still unlikely, chance that he/she is also in this fringe. With such people in mind, I do think my comment starting with “It would be an interesting experiment…” does add something to the forum. What’s more, I’m sure you understand all this, and my question to you was more as a gentle chide, in representation of that fringe, where sometimes occurs very interesting activity and discussion, which I’m sure you would not want to discourage.
Best regards,
Tom
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It is wise not to experiment unless there is an actual problem.
Geoffry, is that always the case, or might it depend upon your objectives?
Tom
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Don, sometimes there’s a conflicting resonance between high pitched reeds and their associated air chambers, and such conflict chokes the reed, preventing it from speaking. A slight air leak in the chamber will destroy this resonance, and the small gap provided by the short valve may serve this purpose, because the leak will occur when you try playing the other reed in the chamber. But of course, none of this may apply to your case, and so it would be an interesting experiment for you to re-seat the valve, assuming it is long enough, and see if the other reed in that chamber chokes when you try to play it.
Best regards,
Tom
www.bluesbox.biz
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Tom,
My reading of the gouging was it is a crude method of tightening the clearance at the tip. Mind you, I say crude but it is only in appearance as it might have worked very well.
Chris
Chris, it reminds me of the high output piccolo reed (HOPV) invented a couple decades ago, as a way to increase the volume of the highest pitch reeds on accordions, so that they can compete better with other reeds. According to an Italian reed maker that I talked to, it was effective, although it seems like the concept never made it into commercial use. Photo is attached.
Regards,
Tom
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Here's 2 pictures of the reeds I received. 2 sets of 30 reeds.
Now just need to find the time to do something with them
In the picture of the single reed, it looks like the brass reed carrier is gouged out near the free end of the reed tongue. Does that gouge stop before the slot, leaving a thin brass surface that is not gouged very near the slot edge and still contiguous with the top surface of the brass? Can anyone explain the purpose of this gouge? Do many of the reeds have this gouge?
Regards,
Tom
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Hi Chris, the differences in playing volume that you mentioned would have nil affect on the normalized sound spectrum, which I plotted. As I mentioned, normalization cancels out volume differences. The only possibility left is whether such volume differences could appreciably alter the spectrum, and I seriously doubt that, for the steady tones you recorded.
I am confident the recordings reflect what I hear in the flesh.
Hmmm… might we define here the concepts of flesh hearing and electronic hearing?
Best regards,
Tom
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From a scientific standpoint, I think you've hit on the weak spot of the test.
Hi cj, I don't think so. I mentioned in my second post:
I also should have added that the volume of your playing of the notes, as measured in the sound file, is very much the same for all notes, and since our hearing responds in some kind of logarithmic fashion, that part of the experiment was fairly well controlled.
Assuming Chris oriented the instrument in the same way with respect to the microphone, there are only two variables left in the way you play it: choice of notes and bellows pressure, and from visual observation of the sound file, it looks like he did this well. A professional classical pianist once told me that there are ways you could press on the piano keys that will impart more effect to the note than simply the strength of the blow on the strings, alluding to some kind of after touch effect, but of course, he could offer no physical mechanism for it. When it comes to musical perception, some people get religion.
Best regards,
Tom
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It seems to me that you identified the fundamental and then plotted the spectral amplitudes at the exact harmonics of this frequency.
I'm under the impression that inharmonicities between the upper partials are an important part of an instrument's timbre.
I don't expect that it invalidates any of the conclusions that have been drawn so far, but is there the possibility your plots
don't reflect the maximal values of the peaks, since they may be slightly offset from their ideal frequencies?
I'd also believe it if someone could confirm that free-reeds have particlarily harmonic overtones, which would be consistent
with my understanding of how the sound is produced, but I'm not 100% about this.
Hi Dave, you ask good questions, and they can help fix some basic ideas. Part of my answer to your questions appears at the end of my previous post, so check that out. Here, I add that sustained musical tones, whether from a free reed instrument or a woodwind, horn, etc., must be made of periodically occurring pressure pulses. The tone generator of the free reed is a vibrating bar, which vibrates periodically, at its fundamental. There are sometimes contributions from the next higher mode, vibrating at about 6.3 times the fundamental (not an integer multiple), but not at normal playing volumes, and even then, very little. You would have to look very hard to see evidence of this mode in the sound spectra. As for people who claim they can hear it, well, let's simply continue. Thus the pressure pulses from the reed occur strictly periodically, which means that all overtones must be a multiple ratio of the fundamental, otherwise they could not repeat their periodic cycle in unison, and when the fundamental does, resulting in noise, or perhaps, a sound akin to a bell. The same applies to woodwinds and to the sustained notes of a violin. Now, I would like to introduce a bit of noise into the sound of the free reed, because its harmonicity restricts the expression of individual notes, when played along with others.
The inharmonicity and tonality you involves musical instruments that operate in a transient, as in struck or plucked instruments, such as the piano string. There is of course a transient when the free reed starts speaking, which involves more than one mode of bar vibration, but this lasts only milliseconds.
The overtones I show in the plots are indeed the maximums that occur in the musical tone. Your question is a very good one, because the peaks of these overtones are very sharp, and if you don’t pick their amplitude at precisely the right frequency, the amplitude you calculate will be very far off. I was particularly concerned about this, and in order to satisfy my own mind, I had to delve into just how Audacity works. With this program, they allow you to export the data, but I found that inadequate. I used the highest resolution in calculating the Fast Fourier Transform, which gave me a data point at about every 2.6 Hz of frequency. But if you use only the discreet values from the exported data, you could miss the peaks by as much as 2.6/2 = 1.3 Hz. I thought that would introduce too much error, as remarkable as that may sound, and here I found a saving feature of Audacity. When you use the graphed data, moving a cursor over the spectral plot, onto an overtone, the program curve fits the discreet data points and calculates the peak, spitting out the corresponding frequency at which it occurs. There is of course some error in that a curve fit is a mathematical device, but this error is quite small and acceptable. So my procedure was the opposite of what you suspected: I (Audacity) found the overtone peak first, then got the frequency at which it occurred.
Thus, I can assure you that what you see are true peaks, as can be reasonably measured/calculated. In addition - and here's the final confirmation - I calculated the ratio of overtone-to-fundamental frequency for all the notes, and provide the data for you in the attached file. It’s remarkable how accurately these ratios are indeed whole number ratios, and thus, they very strongly indicate that the values shown in my plots are indeed the true overtone peaks. They also confirm my statements, above, and the precision of the Audacity program.
Best regards,
Tom
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Hi Chris, first let me add a comment to my original post, which I was headed to the computer for, but you had already posted. Last night, I was too weary to put all this in. Concerning the technical setup, I should’ve mentioned that, since you are conducting a controlled experiment, using the same microphone in as much the same way as you can, the requirements on the microphone become much less stringent. I do think this is a worthwhile experiment. I also should have added that the volume of your playing of the notes, as measured in the sound file, is very much the same for all notes, and since our hearing responds in some kind of logarithmic fashion, that part of the experiment was fairly well controlled. The tuning of these notes, by the way, is very good, though that information doesn’t show on the charts I posted. I tried to post the Excel spreadsheet I used, but the site doesn't allow uploading that kind of file. Go figure.
The debate on how much end plate material affects sound reminds me of the one debating how much flute body materials also affect sound. For many years, in the past, this was an intense debate, though my understanding now is that, among the people who study this both experimentally and theoretically, there’s no discernable difference due to the materials themselves. (I don’t however think the debate has entirely ended, and I doubt it will be.) There can, however, be significant tonal differences because of the different geometries that come about in construction. For instance, metal wall thicknesses can be much thinner, and so the length of side penetrations can differ. I haven’t examined endplates in detail, with measurements, concerning what differences there are in metal and wood construction, but my own current belief is that any tonal differences that do exist are due to the different ways they are made. Think about it. Imagine a wood end plate with the same exact geometry as a metal one. Can you think of any possible way the sound would be different? I can’t. We can of course throw out ideas, leading theoreticians to scramble for explanations. For instance, you are left now with the acoustic affect of the surface itself, wood being porous, and metal being acoustically smooth. Such a difference can show up only as reflected sound waves, and only those sound waves with wavelengths as small as the pore size of the wood would be affected, leading us to conclude that only ultrasonic frequencies would be affected. There’s also a possibility that reflected sound energy would cause more vibration in one material than another. Without analyzing this, my guess is that the sound pressure levels would be too small, but I could be wrong.
I do, however, consider the possibility that you agree with all that, and that, in essence you are wondering just what differences in geometry would lead to the often claimed tonal differences. This is an interesting question. In order to answer this, one would have to start simply by making detailed measurements, and then go about the horrendous analysis. Considering the many different open hole geometries, such measurements might seem too difficult, but such features can be approximated by simplifications, such as total open area ratio, etc. But then you might have to consider effects such as unsymmetrical placement of the open hole pattern, the effect of the musicians hand, blocking some of the holes, etc., and so, the scramble continues.
Since we are allowed to volunteer our own subjective impressions, mine are that such a debate is a bit of a waste of time, or perhaps only nerdy. As can be seen from the experiment, people, en masse, can often bark up the wrong tree, when convictions rule over facts. I do accept that in a specific instance or so, a given person can actually discern an acoustic difference, but my first guess is that there’s also significant difference in geometry, but more likely, there are other features of the instrument that are really the source for the difference. You have done here a practical experiment with an effort for control, though, as I think you realize, it probably won’t end the debate.
When I first listened to your sound file, I did have the impression that the first sound of the first note was marginally brighter than the second sound, and the spectrum seems to verify that. But honestly, the difference, to me, was useless, in practical, musical terms, yet the spectrum does show a decided difference in response at the higher partials. Are we to take this to mean that the spectral approach may be more sensitive than my hearing preference? People can think about this, and maybe an interesting outcome of your experiment is to evaluate how sensitive the Fourier approach really is.
re-reading your post I realise this sentence encapsulates a thought I was trying to formulate. Bright sounds suggest high partials, but could they be a relationship between lower partials.
No, I think from all we know about acoustics and the workings of our own hearing, which cannot violate laws of physics, bright sounds will be the result of the degree to which higher harmonics contribute to the total sound, especially in relationship to the lower harmonics. I can’t see a way that a bright sound would arise because of some kind of interlacing of frequencies over the entire spectrum.
What about partials a third apart which are disproportionately loud?
There are no such things as partials a third apart, over the entire spectrum, but only in a happenstance way. Partials (greater than the fundamental) are also called overtones. With a steady tone of the free reed, overtones are harmonics, which means they are exact whole number ratios of the fundamental. Thus, it’s possible that a harmonic has a “third” relationship to some harmonic that appears at a lower frequency, but this is very seldom, making up a very small portion of the entire spectrum. You might alter your inquiry by wondering if odd harmonics, or every third harmonic, etc. might be the source. For odd harmonics, we have the example of the clarinet, which does emphasize odd harmonics, and we know the characteristic sound of that instrument. For these other kinds of speculations on the spectrum, if the suggested response occurs over the entire range, without predominantly affecting higher partials, it shouldn’t affect the brightness. Now of course the descriptor “bright” is a subjective concept, and I think here we are beginning to deconstruct it. But that’s okay, I’d still make the claim that a brighter sound has more higher partials contribution to the spectrum than a less bright sound.
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Hi Chris, thanks for the data for an interesting experiment. Apart from exploring the consequences of different materials used for endplates, this experiment can perhaps also evaluate the widely held concept that “brighter” sounds are associated with higher harmonics in the frequency spectrum.
I thus plotted the frequency spectrum of each of the notes you played, using the open source free software Audacity, which is a marvelous accomplishment by generous individuals. For those interested, I attached a Word.doc file with the results. There’s a graph for each of the six notes, plotting the normalized response level vs frequency, showing the peak overtones. The dark markers are for the first sound of each note (A), and the red markers are for the second sound (
. I’d be glad to furnish more explanation for anyone so interested.But having a frequency spectra of the wave forms is only a starting point, because one must still resort to subjective convictions on how to evaluate them. There’s of course a possibility that two spectra can show large enough differences so that one can confidently decide for instance that one spectrum has a larger contribution from upper harmonics than another. We can also, of course, resort to mathematical algorithms as a way to attempt a more objective evaluation, but in the end, it’s my feeling that subjective decisions will have to be made.
With all that said, going by these frequency spectra and assuming the sound files are an accurate representation of the true audio sound, my guess is that the first sound for Note 1 and the first sound for Note 5 should sound directly “brighter” to the human ear, if indeed higher harmonics are the determining factor in how “bright” the sound is to our ears. For these notes, markers A have a decidedly larger response than markers B, at the high end of the spectrum. Such a conclusion is marginally the same for notes 3 and 4. The story with the other notes, for me, is not as clear. Concerning my ear response, yes, I can convince myself that I hear in the files what the frequency spectrum is suggesting, but only really for Notes 1 and 5.
If I might make some general comments, the higher pitch notes (4, 5, and 6) have a low frequency artifact, easily discernible as an annoying buzz, and I believe this is due to the compression of the sound file, to MP3 format. This buzz does interfere with my audio evaluation. I suggest for such experiments that high-resolution sound files (e.g., wav) be used. Also, it may be better to make mono recordings, instead of stereo, because there can be unnecessary complicating factors when two microphones are used instead of one.
Perhaps most importantly, the response of the microphone and amplifying circuit is part of what we hear (and do calculations with). I assume you did not use a calibrated microphone/amplifier system, and of the two, it’s most likely that the microphone would be the weaker link, and certainly also, cheap computer speakers add their own problems. For instance, if the response of the microphone is weaker for the higher frequencies, we will then not hear, or measure, in the sound files, the true response, and the contribution from the high frequencies may not appear as large as they really are, when you hear the instrument in the room. Thus, such unfortunate outcome would invalidate such an experiment. In other words, without knowing the frequency response of the microphone you used, we really can’t say for sure how accurate the sound files are. I find that some electret mic cartridges have flat response – which is what you want - over the entire human ear response range. And they are in general no more expensive than others. Such microphone elements are available from electronics stores such as Digikey for only a couple/three dollars each, and their frequency response can be viewed online, before purchase.
Best regards,
Tom
www.bluesbox.biz
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Hi Chris,
The problem is every "fast" reed can be played softly, at which point it would move as a "slow" reed and if speed is the major creator of difference in sound then that difference should be apparent when a steel reed is played quietly. Is it?
I think your point is valid, and it indicates some of the complexities here; however, if we find that two reeds of different materials but of the SAME length, pitch, and bellows pressure have different speeds (presumably because of different amplitudes) there may be differences in sound spectrum as a consequence. Thus, speed by itself is meaningless, but speed in a context where other parameters are held constant may provide clues.
The ones that I have here have a approx 30 degree twist to the reed about halfway along. This would certainly interfere with partial creation.
I’m not sure what you mean by “interfere with partial creation,” but I’ll guess that you conclude that the harmonium reed sounds less bright because of the bend in its tongue. Is this according to your experience? If so, it might be an interesting clue on how the beast works. Some simple experimentation could answer this question. If on the other hand, your statement results from a belief that such a shape simply cannot produce many partials, then I must ask for the evidence for it.
Having seen the Cottingham graph and the other pressure changes you mention, the "wiggles", very interesting, and what could produce those? My first thought…
In this graph, I have trouble making sense out of the phase difference between the tongue displacement trace and the two pressure traces. The graph seems to be telling us that the sound pressure just above a vibrating tongue gets a positive pulse when the tongue just exits the slot, traveling upward. This is counter intuitive, since, for the reed to work with the microphone placed as stated, positive air pressure must be imposed on the same side of the tongue that the microphone is placed. If so, why would the pressure pulse be positive and not negative? I can see that it would be positive, only if the cavity were pressurized, but the reed would then not work. The author doesn’t specifically state that the phase relationships of this graph are correct, as occurring during the experiment. Without such a statement, we really don’t know if the tongue displacement/pressure phase, as displayed, is correct. But that indicates a sloppy presentation, and I’m a bit doubtful that a researcher would do that; especially since modern data acquisition equipment can indeed record correct phases.
I think your interpretation of the wiggles of pressure pulses inside the cavity is reasonable. The phenomenon you describe associated with motorcycle exhaust pipes is the same phenomenon by which most any musical instrument with a resonator works, when operating in sustained mode of vibration. A very close example is the beating reed organ pipe, or say, a clarinet. A positive pressure pulse that moves along the length of the air column is timed to arrive at and strike the reed, opening it at the precise moment energy input, by means of a pulse from the musician’s breath, is required for periodic motion. The original positive pressure pulse is thus intensified as it rebounds and travels back towards the open end, with some of its energy passing into the room, but also much of its energy reflected from the open end as a rarefaction (low pressure) pulse, which in turn travels back along the tube and arrives at the reed when the reed is closed, helping to keep it closed, and rebounding again as a rarefaction, which travels back to the open end and reflects as a positive pulse, completing the cycle. This action is inherent to what we call tuned resonators. The situation inside the free reed cavity is similar in that there are pressure pulses bouncing off walls, but there’s a fundamental difference because the air of the cavity is not tuned, or resonating as a coherent mass in a way (except by happenstance) that is tuned to the motion of the tongue, thus the more complicated shape in the pressure wave form. The effect is more like the sound you hear bouncing off the walls in an empty room.
Best regards,
Tom
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Greetings,
1) The Known Difference
As far as I know, there are two materials most often used in making Western free reed tongues: steel and some Copper alloy, which is most often brass, but perhaps also bronze. It seems to be generally accepted that steel tongues sound different from brass tongues, and most people describe the sound of steel as brighter than that of brass, which is often described as softer, or even less harsh. Steel, however, seems to be the dominant material, and many people prefer it’s brighter sound because it carries further, though others like brass because it provides an instrument that doesn’t unduly dominate when accompanied by the human voice, and that may be primarily because of its lower playing volume. There are of course many nuances on this topic, including the questioned durability of brass, but my main point here is that these different materials produce distinctly different sounds, at least as observed by a great deal of the musical community.
To me, the fact that two different materials sound differently is extremely interesting, and one obvious question raised is, What about other materials? In the 170 odd years of Western free reed manufacture, I’m quite sure many people investigated this question, certainly experimentally, but I’m unaware of any theoretical investigation. Of course, experimentation is the final arbitrator, as long as the experimentation was properly and thoroughly done, with results reproducible by many people. But there are complications. With some technologies, certain practices are established when the results they produce are good enough, and long periods of time pass before a surprising breakthrough appears on the scene. (One interesting example here is the long bow vs. the compound bow.) There are many other issues, some involving the amount of effort it takes to explore different pathways. But suppose there’s an easier way? In this post I’d like to make some suggestions based on three things: 1) the known difference between the sound of steel and brass, 2) a fundamental physical law that describes the vibration of the reed tongue, and 3) an educated guess, based on the previous two.
2) The Fundamental Law
The earliest derived governing partial differential equation for the vibration of a cantilever is associated with the names Euler and Bernoulli. This (E-
formulation neglects both rotational inertia of the cross section and shear force in the plane of the cross section. A more exacting formulation, associated with the names Timoshenko and Rayleigh, came later, and it (T-R) does include these effects. I myself, however, conclude that the difference between the predictions of these two formulations, when applied to Western free reeds in musical instruments, is negligible, and other researchers in universities concur. In fact, I calculate that the difference between these formulations is at least four orders of magnitude less than either prediction. I include the above paragraph because it’s important to note that the E-B equation is so simple, one can make a very general prediction from it, without even solving it. The T-R formulation, however, is too complicated to see such a prediction, and I want to be clear that we can put confidence into the accuracy of the E-B formulation, because that’s the one I base this entire study on.
In the E-B formulation, the only place material properties enter into the dynamical response of the vibrating tongue is through the ratio Y/rho, where Y is Young’s Modulus and rho is density. To me, this is an astonishingly simple result, and it can be used to predict much about the effect of different materials on reed vibration. The result is also quite general. As long as the tongue has the same material throughout, this simple result includes the effect of area change along the tongue, as often happens by means of tapering and profiling.
The above conclusion means that two tongues with the same geometry, each made with a different material, albeit with both materials having the same Y/rho, will vibrate the same, in every way, both in vibrational response and sound. This is perhaps an astonishing statement, but I’ve thought about this for a while, and although I can come to no other conclusion, I’m open to alternative views. I don’t think we understand the details why different materials sound differently as reed tongues, although we continue to talk about it (as in the post, Why does brass sound different than steel?) But for now, I stand by this assertion, and inquire as to its consequences. There are of course many practical issues that will conspire to decide whether any alternative material is suitable as a free reed tongue. Most of such practical issues are beyond the main interest here, although I will address a couple of the most obvious; i.e., that the material be strong enough, and that it allow sufficient playing volume.
In order to get an intuitive feel what this all means, the ratio Y/rho has units of force-distance/mass, or energy per unit mass, and in this case, elastic energy per unit mass. Thinking in these terms, one might conjure some physical intuition why two tongues of the same geometry and elastic energy per unit mass would have the same sound. Such intuition can broaden to include forced vibration as well as free vibration.
3) An Educated Guess
Most all brass and bronze materials have a Y/rho ratio that is about one-half that of most steels, including the spring steels commonly used in making tongues. In fact, it’s remarkable how most all these brasses and steels have very close ratios among themselves. To assist our educated guess, we start with two facts: 1) steel and brass have identifiably different sounds, and 2) the tongue motion/response of different materials can be laid out in a one-dimensional scale, using units of Y/rho. For the purposes of explanation, let’s keep it simple and say that the ratio Y/rho for steel is 1.0 and that for brass is 0.5, which is approximately the case. Thus, all materials having this ratio close to unity will sound like steel and all materials having this ratio close to 0.5 will sound like brass. Thus, why does brass sound different than steel? Because it has a different ratio Y/rho.
What about even different materials? The basic form of the guess here suggests that Y/rho provides a very convenient and simplifying method to guess what all other materials might sound like as reed tongues. For instance, would a tongue material with Y/rho = 0.75 sound somewhat intermediate between the sound of steel and the sound of brass? Would another material with Y/rho = 1.2 sound even more in contrast to brass than steel does? And finally, would a material with Y/rho = 0.3 sound even more softer or mellower than brass?
If such questions spark any kind of intrigue in the reader, the following discussion might prove interesting, and in the remaining discussion, I boldly assume the answer to all these questions is “yes.” Again, the intention here is not to try to sell anyone on an alternate reed tongue material, and if many readers consider all this as simply a whimsical exercise, I would agree, but I myself cannot ignore the fact that nature has seemingly provided us with a relatively simple theoretical assist to a very practical, and difficult problem, so why not see what it might predict?
4) The General Approach
Materials properties for various materials are readily obtainable, and for this study, we need to know at least three things: 1) Y, 2) rho, and for purely practical purposes, 3) a measure of the materials strength. For (3), when it comes to metals, the most useful property in this application is probably the materials fatigue limit over the lifetime of the reed, or what often amounts to the same thing, the material’s endurance limit, Se. A criterion based on Se is generally more conservative than one based on simply the yield strength of the material.
For non-metals, I’m not aware that the concept of fatigue strength is very well understood, or even valid, and so, I present other measures of strength, most commonly, the materials yield strength, or in some instances, it’s flexural strength (also caused modulus of rupture).
For both metals and non-metals, in order to have something to compare strength to, we need a measure of the maximum stress developed while the reed speaks. This can be calculated fairly accurately from the solution to the E-B equation of motion, provided we have an idea how much the tongue bends. In another post (Why do Brass Tongues Break?) I presented similar calculations, from experimental measurements I made on how far the tip of a steel tongue is displaced under maximum playing pressure. Such a parameter cannot be, as yet, calculated from theory. The maximum stress in the tongue occurs at the root of the tongue, and for this calculation, we need the curvature of the bending tongue at that point. The geometric shape of the vibrating tongue is readily obtainable from the E-B equation in the case of free vibration. With forced motion, in principle, the geometry can be different. However, Cottingham at Coe College has indeed measured the shape of the bending tongue, using a technique of laser vibrometry, and he has concluded that the shape in the actual, forced case matches very closely to the theoretical solution for free vibration, at least close enough for the purposes of calculating stress.
With this approach, and assuming that the amplitude of tip vibration scales as the length of the tongue, we can calculate the stress in the tongues and compare it to the strength of the tongues and make some prediction on tongue longevity. If the assumption here about vibration amplitude is in error, this error may not be too serious, simply because such amplitude is a strong function of bellows pressure, and so adjustment of bellows pressure can be part of a process that imposes the same amplitude.
5) The Data/Calculations/Predictions
Table 1 in the Attachment contains a survey for metals, Table 2 a survey for non-metals, and Table 3 presents a comparison between stress and strength for some of the more interesting materials. I don’t mean to imply these surveys are exhaustive, but I did try to focus on the more common and practical materials for which data can be found. I also tried to include enough materials of a given type, in order to get a general feel for what each type offers.
In Tables 1 and 2, the two left columns specify the materials, which are grouped according to major components. At the top are our two reference materials, steel and brass. The right side of the Table gives Young’s Modulus, density, and the ratio Y/rho, normalized with respect to the ratio for our reference steel material, which then becomes unity. For metals, the measure of strength is given by endurance limit, Se, calculated from the materials’ ultimate strength, using common engineering practice. For non-metals, either a yield strength or a flexural strength is given, denoted simply by “Strength.”
The main focus of this (whimsical?) article is contained in the last column of Tables 1 and 2. As proposed, any material with a normalized ratio near unity will sound like the standard steel reed, any material with this value near about one-half will sound like a brass reed, and materials having other values will contain appropriate mixes of tone, as predicted by this one-dimensional scale of “normalized ratio.”
As I explained in a previous post, brass tongues designed to last many vibration cycles should be shorter than corresponding steel tongues that are designed for the same frequency, when the lengths of these tongues are roughly around an inch or more. Smaller tongues should not experience endurance problems, providing that filing and scrapes are not excessive. Such conclusions apply strictly to tongues of constant cross section, though they should carry over to mildly profiled and tapered tongues. Thus, in Table 3, which lists only the more interesting of the materials presented in Tables 1 and 2, the column, “geo fraction,” for Geometric Fraction, shows the fraction of the steel tongue length required for the experienced stresses to be within the capability of the material in question, for the longer tongues. A geo fraction of unity indicates that the material may be as durable as steel. More of this will become clear as individual materials are discussed.
Getting back to the Table 1 and 2, one might not be very interested in materials with values in the rightmost column near unity, because we already have steel tongues that work very well. Likewise, normalized ratios near 0.5 may not spark too much interest, although there are material candidates that are much more fatigue resistant than is brass. Most interestingly, we find materials having a whole range of values, hinting at some very interesting tonal possibilities.
Starting with Table 1, values of Y/rho differ little among all the common steels, and so, I included here only those that show a significant deviation. One example is the invars, with normalized ratios intermediate between spring steel and brass, around 0.7, though Table 3 indicates that it’s length scale should be restricted, for long lifetime. Concerning only tone, here is a material that might satisfy the person who would prefer a concertina sound half way between that of brass and steel, with a corresponding playing volume. Unlike the invars, ductile Iron appears as durable as steel (from Table 3, geometric factor of unity, meaning no required restriction in length, for durability), yet with an intermediate normalized ratio between that of steel and brass (0.84).
Copper and its alloys most all have close normalized ratios around one-half, though there are notable exceptions. Beryllium Copper, Copper Nickel, and Nickel Silver all show a significant departure from brass, towards steel; however, from Table 3, Beryllium Copper is the only one of these without endurance issues for the longer reeds. Beryllium Copper is often used to make springs, because it holds up fairly well at elevated temperatures, and so its cost, availability and formability may not pose serious problems.
The more common Aluminum alloys do not appear useful for reed making, primarily because Aluminum has very poor fatigue strength. This is the reason why airliners must be disassembled and examined after so many hours of operation. For concertina reeds, with cycles going into the tens of millions, my guess is that the Aluminum alloys would not be practical. It is of whimsical interest to note, though, that a tongue made from these materials would probably sound like steel, until it breaks. Similar comments apply also to Magnesium and its alloys.
The Nickel alloys look interesting, providing a range of normalized ratios between that of brass and steel. As can be seen in Table 3, some of these have endurance issues. These materials are generally more expensive and more difficult to machine than spring steels; however, given a particular application, as in the case here, more detailed investigation would be advised before a final decision is made concerning these peripheral issues. The Carpenter alloy is notable because of it’s superior strength, and its normalized ratio suggests a sound perhaps a little brighter than steel. My guess is that this alloy is so strong because of it’s cold work hardening (65%), which is the same reason why brass can be made at least marginally strong enough for reed use. I haven’t investigated the extent to which cold working might possibly induce acceptance of other metals in Table 1 that are otherwise too weak to function as a reed tongue.
Titanium forms one of the most complicated families of alloys, depending not only upon composition, but also upon processing. They are generally difficult to machine and form, but as in the case of the Nickel alloys, detailed investigation would be required in order to draw final conclusions on cost and fashionability. A great deal depends upon the form in which the material can be purchased, and of course, its cost. Most interestingly, however, these alloys possess a wide range of normalized ratios, from 1.1 down to 0.3, with many intermediate values. They are also strong, and as can be seen from Table 3, most of them should hold up well as reed tongues. This family thus presents many candidates for a whole range of different reed sounds.
Moving to Table 2, we come to the thermoplastics, which generally have normalized ratios significantly less than brass, suggesting very mellow tones. If, along with musical tone, the normalized ratio also scales playing volume, such low values may also indicate playing volumes significantly below that of brass. If I might guess, they have a feathery sound. There are many practical issues with plastics, including their general tendency to swell from absorbing water from the air, and also their relatively high coefficient of linear expansion, as compared to metals. When we consider that good reed tongues operate with gaps around their periphery of the order of a mil, these practical issues suggest there may be problems. The temperature issue would be eliminated if the reed plates were made of the same material, and the water absorption issue would have to be investigated further. Another issue is whether a given plastic will hold its tuning, because of such instabilities, as compared to metals.
Apart from these practical issues, it’s interesting that, as shown in Table 3, their stress levels are generally within their strength capabilities, although I must admit to ignorance on their ability to withstand fatigue in this application.
The only thermosets I listed are composites incorporating carbon fiber or glass. Like the thermoplastics, these materials generally have normalized ratios less than brass, suggesting very mellow sounds, and from Table 3, they appear strong enough, although they perhaps offer low playing volume. In the literature, they are often described as “very fatigue resistant,” although any such claim must surely be application dependent, and it remains to be seen how well they would withstand the many cyclic stresses experienced as reed tongues. Incidentally, I think such a determination is quite easily made by a set-up incorporating an electric blower, with results obtainable after a couple weeks or so.
In Table 2, we now come to the woods, which interestingly show a wider range of normalized ratio than do the plastics, some even perhaps sounding more steel-like than does brass, and from Table 3, some look quite strong. With all woods, the direction of the grain is an important consideration. The performance of bamboo appears anomalous. This is perhaps not surprising, since bamboo is sometimes used to make Asian free reed tongues. Its normalized ratio of 7.2 suggests a very bright sound and perhaps a high playing volume, and from Table 3, it’s plenty strong enough to withstand its own generated stresses. Interestingly, its high normalized ratio is obtained not only by its relatively high modulus, but even more by means of it’s very low density. Perhaps it would be interesting to talk about this material with an experienced Asian free reed maker, and maybe this is what you really need to compete with those guitars.
Carbon fiber is interesting in many ways. If one can successfully make a reed tongue out of a bundle of long carbon fibers, with their unmatched strength and modulus, it promises an extremely bright tone, with possibly high playing volume.
6) Summary
In summary, the primary reason for this survey is to suggest to the curious what many hitherto unused materials might sound like, if they were successfully fashioned into free reed tongues. In working through it, we see how unique spring steel is, and perhaps why most other materials have a hard time competing with it for use as tongue material. But then again, there are people who may prefer brass, even accepting its potential drawbacks. Perhaps then the survey has identified an open-ended question with regard to some other possible contenders for tongue material; most notably, Beryllium Copper (1.9%), certain Nickel alloys that have been cold worked, various Titanium alloys, and maybe even a non-metal such as a composite, or even bamboo. These additional materials admit the possibility of a wider spectrum of tone and playing volume, although not completely without some unknown complications.
I’d be very interested in hearing from anyone who has made reed tongues from any of these alternative materials, so that we might compare notes.
Best regards,
Tom
www.bluesbox.biz
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Hi all,
You also my look at this ( http://www.ifm-zwota.de/tonzun09.pdf ) document in German language.
Some interesting graphs are presented, but the main conclusion of this document is also that the Axioms used for modelling limit all predictions.
best regards, Johann
Hi Johann,
Is it too much to ask you to summarize the main purpose, approach, and conclusions of this interesting looking paper? Thanks.
Regards,
Tom
Getting Reeds And Knowing Chamber Sizes
in Instrument Construction & Repair
Posted
Nathaniel, most accordions that I’ve seen make use of an upright reed block design, as opposed to the flat design, which is incorporated in most concertinas. The flat design is used along with the upright design in American made Cajun accordions.
Here’s what I think provides the reasoning behind the tapered upright design, but first of all, let’s consider the dimensions of the reed itself, which is essentially the dimensions of the reed plate (the metal piece on which the reed tongues are riveted). The width of all the reed plates are the same, generally around 0.65 inches, and this is ultimately determined by the required width of the keys, which is as small as possible, but still with the ability to be conveniently manipulated, and that has been largely standardized. The length of the reed plates is influenced largely by the required pitch of the reed, and like the lengths of piano strings, the scaling relationship between pitch and tongue length has been arrived at through much trial and error. Thus, a given tongue length and corresponding plate length will provide a certain range of pitches, and there are a few different length categories that span the pitch range of the instrument.
The length and width of the cavities are directly dependent on the corresponding plate dimensions, with the cavity dimensions slightly smaller, in order to allow the reed to be placed as a cavity cover without leaks.
The depth of the cavity is a little more complicated, but to understand that we first need to understand that the reed is oriented with the free end of the tongue at the top of the upright reed block, away from the air hole. This is to save space. If the larger reeds were mounted with the free end down, their vibrating tips would strike a neighboring reed, unless the spacing between blocks is increased. Thus the taper, giving more room for the tongues to vibrate and thus minimize the distance between reed blocks. The depth of the cavity under the vibrating reed tip is made deep enough so that the vibrating tip does not bottom out. With this dimension fixed for the largest reeds, the overall width of the reed section of the instrument becomes fixed.
The depth of the cavity at the air hole end is determined by the size of the air hole. It’s desirable to make this hole as large as possible, in order to get as much sound out of the instrument as possible. But the air hole dimension in the direction along the length of the keyboard is largely fixed, because, as mentioned, the width of the keys has been fixed. The dimension in the perpendicular direction is also confined in order to keep the size and weight of the entire instrument down, and there are diminishing returns in making this dimension much larger than the first dimension. Apparently, size and weight are of such importance so that the resulting sound volume achieved by dimensioning the air hole according to this requirement has proven adequate. But usually, you see rectangular, nearly square holes, because as Chris points out, they have more area than a round hole with diameter determined by the minimum dimension. With the depth of the cavity now fixed at both ends, the block is simply tapered to fit.
The above gives a general procedure. There can be complications, and most of them arise because of spurious acoustical effects. For instance, I’ve seen some cavities for the smallest reeds stuffed with wood in a curved shape. Since the tongue vibrational amplitude of these reeds is so small, the cavity depth can be made very small at the free tip end, but there needs to be an abrupt increase in order to open the cavity up to the air hole. I’ve also seen some of these higher pitched reeds mounted with the vibrating tip end downward, near the air hole. Their vibrational amplitude is so small, there’s no danger of striking a neighboring reed. I believe these approaches are taken in order to prevent choking of the reed, which can happen when the length of the cavity operates like a quarter wave tube, preventing the reed from speaking. I can only guess, but perhaps also, one can achieve more sound volume by stuffing the cavity for these small reeds.
It’s thus my belief that, apart from exceptional instances, there are no dominating acoustic reasons why the tapered accordion reed block has assumed its present shape. Although I do think it’s possible that tweaking the basic design might affect the sound of the instrument, I’d be pleasantly surprised if anyone can demonstrate a pronounced effect.
Concerning the flat mounted design, there’s no longer a need for a taper in the cavity depth, and this is normally not done. Perhaps there’s an opportunity here for some experimentation. I think it’s generally true that real estate issues require the air hole to be mounted at one end of the cavity, rather than, say, in the middle. Which end can be an issue for the larger reeds, and I think the sound can be possibly be affected. In my experience, I currently find it best to mount the hole at the end away from the vibrating tip, but I sometimes become puzzled by it, and perhaps others can comment on that.
If you’re interested in reading what I’ve written on the acoustic effects of cavity design, you can go here.
Best regards,
Tom
www.bluesbox.biz