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FREE REED PHYSICS - 3


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2 minutes ago, Johann said:

I have attached the same chart but this time with blue line on top. 

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

 

Best regards,

Tom

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18 minutes ago, ttonon said:

I don't see much filing, so I'd guess that the tongue thickness is constant (no profiling) and that guesses about modal frequencies are probably reasonable.  I apologize for not looking at that picture more closely. 

Tom the tongue thickness is not constant it has the usual profile and the tongue bends in a smooth curve similar to the steel profile. But the titanium alloy reed is approximately 1/3  less stiff to get to the same pitch. So your theoretical model uses different parameter, with the same stiffness but different length. To get to the same pitch with nearly equal reed dimensions stiffness mast the different what results in less strong higher harmonics.  That is for me a known circonstance if i make reedsets with different stiffness. Johann

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3 minutes ago, ttonon said:

I can see that you simply reversed the colors for steel and titanium, and now, titanium is red. 

No Tom see the index on the right. I did not change anything just the lins are now drown ble on top of orange.

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14 minutes ago, Johann said:

No Tom see the index on the right. I did not change anything just the lins are now drown ble on top of orange.

Okay, I misunderstood what you mean by "on top."  I thought you meant "above."

 

But the important thing is what I described, the titanium dominance of the 5th harmonic can very easily make the titanium sound brighter than steel.  Do you agree?

Best regards,

Tom

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15 hours ago, ttonon said:

But I think this indeed explains why titanium to me sounds brighter than steel.  It's that fifth harmonic, which dominates all except the first, by at least a factor of 50 in amplitude.  It's often very difficult to make guesses about how different spectrums will sound unless there's clear dominance among enough harmonic amplitudes, but in this case, and you may not agree, if I saw that spectrum, I'd be confident to guess that titanium would sound brighter.  

Tom i have the real sound not only the recording, and i think it depends strongly on the individium how we charge the sound. I had my hearing cuve checked some Years ago and then the test showed that i don't have any dropouts and i here quote high tone very well. Other my manly hear the lower components of the sound.  So it may be well so that for you the titanium sounds brighter and for me it is the steel. Quite explanable with this 5th harmonic. 5th harmonic is 5:4 major 3rd (c to e1). If the 5th gets dominant it is more like a 3rd mayor is present. You may experiment with the sound by using equalizers try to inforce just the 5th or on the other hand enforce a wider range on the high end.   I is common practice to brighten a sound by enforcing  Frequencies above 1 khz. 

 

Best regards, Johann

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

Tom

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Hi tom, we keep on thinking and doing our best, but in the end we never know how others hear the same sound. For me spectrum carts are not as informative as the actual sound i hear. I wish we would have better tools to visualise sound and timbre.  But in the end well trained ear is more precise. That's what i realised.

 

I also would like to to some dow back on my opinion about additional mode frequencies, and how much the cont in the resulting sound. I still think such frequencies are more or less present especially under transient conditions, but when a reed is sounded constantly i can't say that i hear or cn measure this additional mode frequencies. Don't trust this single test that all would need much more intense investigation. Especially on very low pitched reeds i have the impression the are noticeable but i don't have a practical way to influence the sound by profiling the reed. My be i am completely wrong with my hypotheses in this respect. As with all as time goes by the opinion on subjects may change especially if no one could come up with a prove. Still i hope younger people will put time in this subject. Unfortunately it is not of major interest to scientists. Still it is good to talk about it so it may be some one will get on it as well.

 

Best regards, Johann   

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23 hours ago, Wolf Molkentin said:

Possibly a feature of real good brass reeds (not entirely sure about the George Case in this respect, but the reeds of my Wheatstone model 6 are fantastic, definitely TOTL (and quite loud as well; only the model 24 is positively exceeding the volume) - however it might be in accordance to @ttonon's findings (that the significant difference was in the higher, but not the very high harmonics), might it not?

High Wolf, it is really difficult how we charge sound and timbre. The main key is for me the human vocal tract how we form speech.  The frequencies that count to distinguish vocals. So the answer for me, as with most things is somewhere in the middle. Read about https://en.wikipedia.org/wiki/Speech_recognition. This is a part from the german wiki can't find the same in the engisch: "Auf akustischer Ebene spielt insbesondere die Lage der Formanten eine Rolle: Die Frequenzanteile gesprochener Vokale konzentrieren sich typischerweise auf bestimmte unterschiedliche Frequenzen, die Formanten genannt werden. Für die Unterscheidung der Vokale sind insbesondere die zwei tiefsten Formanten von Bedeutung: Die tiefere Frequenz liegt im Bereich von 200 bis 800 Hertz, die höhere im Bereich von 800 bis 2400 Hertz. Über die Lage dieser Frequenzen lassen sich die einzelnen Vokale unterscheiden." Here is the link to the topic in englisch: https://en.wikipedia.org/wiki/Formant To get on we would should think about this.

 

Best regards Johann

 

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18 hours ago, ttonon said:

When I chastised Johann for spreading false concepts, I didn't mention that higher harmonics of the acoustic reed sound can be coupled to the air in the cavity, affecting the harmonics, and thinking back on it, that may be all he was referring to.  But this is a very weak form of coupling, and it's far different from the "acoustic coupling to an air column" usually referred to with such terminology.

Hi Tom, yes Tom exactly, still if we look deeper into the subject it may be important to remember that the western reed still  behaves comparable, even we can get away with a much simplified model. Sure there are differences in the reed and in the cavity and where the reed is mounted. The circumstances remain the same, we still have a cavity and a reed and a mounting point of the reed all differs dramatically but the reed needs the air to sound. With the western reed, the reed is the dominant part and the cavity, it is nearly neglectable. I also like to point out again on very low reeds it is even more important how this cavity is formed and how big the cavity is. On the very high pitched reeds we all know that we have to take measures to improve the speaking of the reed. All my thinking is influenced by building helicon boxes now for about 20 Years and optimising the sound.  My theoretical influence is strongly influenced from may former profession working and teaching in the field telecommunication. I never would say i can't be wrong if someone comes up with other explanations that fit better. The usual models and explanations are for me always a bit to much simplified.

 

Best regards Johann

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6 hours ago, Johann said:

 My theoretical influence is strongly influenced from may former profession working and teaching in the field telecommunication. I never would say i can't be wrong if someone comes up with other explanations that fit better. The usual models and explanations are for me always a bit to much simplified.

Johann, I've mentioned it several times in this forum that James Cottingham has done extensive experimental investigation of free reeds.  You can see a list of his publications at: https://www.researchgate.net/scientific-contributions/58932239_James_P_Cottingham

 

Jim is joined by many others on these investigations, both theoretical and experimental, and I think you would be interested in the many details and the precision with which this research is done, using the scientific method, and proceeding far beyond anything we have discussed here.  We often lead ourselves in circles, and unfortunately don't include the deep insights uncovered in the literature.  This forum interests me mainly because of the interesting information provided by makers and doers and the resulting personal contacts.  It still can't come close to an adequate stage to present all the knowledge about free reeds currently available.

 

Best regards,

Tom

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Hi Tom, i have red some of P. Cottigham's publications now. especially "Analysis of free reed attack transients " Since it is quite a long time as i was talking about additional modes in reed motions in some forums. I am surprised that this letter now more or less confirms my hypotheses i made years ago. Then i was criticized about my theses. Over time i even was not sure anymore, since i could not find a real prove expect that i could hear some of this mode related pitches.  I have found some way to control low reeds, without special tool only by hearing and changing the profile, but not as good as i would like to be in control off this. I will read more of P. Cottigham's Publications. Takes time. I am quite happy that there is some research done on the subject. As far as i can see his research are made under comparable conditions as mine. He also uses Matlab and similar equipment. I did not have high speed camera i used strobe light and sycron photography about 20 Years ago. As i told you i am now more in the practical phase of work. 

 

Best regards Johann

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  • 1 month later...
On 6/18/2019 at 9:47 AM, ttonon said:

 

 

Dana, I appreciate your explanation of the practical issues involved with different tongue materials and find it fascinating.  The scope of any theoretical contribution I can make to the issue is very small, and it's the maker who carries the real burden.  In fact, I wouldn't object to anyone describing my suggestion as a flippant remark from a theoretician.  

 

Can you please explain further what you mean by "equally stiff at the designated pitch."  I recall you explaining that you used a scale to measure spring force of tongues.  Do you use that in this process?

Again, can you please elaborate?

 

Tom

 

 

 

 

 

Hi Tom, I haven’t been following this that closely and missed the request for clarification.

When I make a set of reeds, there are a number of things that are important to me as a maker.  First, the reeds all need to respond at the same starting air pressure,.  Second, they need to do this at as close to the same spot in their pressure-volume curve so the reeds individual dynamic ranges are in sync with each other.   Given the extreme difference in reed length and area,  perceived volume  of the individual reeds need to be as close as practical to each other so that larger reeds don’t overwhelm smaller ones.  

   While a reed of a given pitch can be made within a wide range of length/width aspect ratios and with a wide range of lengths, even without varying the material, by adjusting the overall flexibility of the reed tongue and how the moving mass is distributed along its length,  (reed profile ) the playing requirements listed above severely limit what is actually practical.  When I talk about reed stiffness, I am referring to the amount of force required to deflect it by a certain defined amount.  Another term for this is spring coefficient.  Since I don’t think this number is linear for flat springs like reeds, I measure it for 2 degrees of deflection on the bold assumption that such a small deflection will be in a more linear part of the curve.  I have found that a stiffness curve for MY reeds that starts at about 14 gm / 2 degrees deflection for c below middle c and reaches a high of around 20 gm/2 degrees for mid range reeds  about e above middle c to d an octave above that then dropping to about 8 gm/2 degrees or less at g6 on a c/g Anglo.  It looks like a shallow bell curve, with each reed being close to the ones on either side.  This distribution makes for reeds that all sound like one family, whose harmonic content changes similarly as playing volume increases.  Other ranges are perfectly possible depending on what the maker is after.  Accordion reed are matched with each other to make lighter or heavier sets for similar reasons.

   In making a reed, I start with a blank of a given width and length that fits the concertina, has been proven to produce the right volume for balance, and then adjust the thickness profile so that it has a finished pitch, a smooth bend, and an overall stiffness that allows it to respond properly with the rest of the reeds.  No reed profile ( of mine anyway) is straight.   Low reeds are thick at the tip, thinner in the middle and going back to thicker at the root.  Middle reeds have a little thinning in the center  and high reeds are very thin at the tip an thicker at the root, but not in a straight slope.  There is a neutral place in a reed where varying the thickness balance the pitch lowering of reduced stiffness and the pitch raising of reducing the moving mass.  I use this area to adjust the stiffness of the reed to fit on my curve.

   I am sure that a set of formulas could be created to describe the profile curve, taking into account the mod of elasticity of the material, it’s density, along with some way of scaling for volume at a given pressure, aspect ratio etc., but there is a range of possible solutions that work.  When trying to make a mathematical model, choosing the simplest reed possible in order to see how the materials compare, having two reeds that have things like length width and deflection and pitch at a given pressure in common sounds like a good challenge, certainly beyond me.  I know that side clearance has a strong effect on tone, but I don’t know how the traverse time of things like the reed tip effects tone if it is thicker or thinner.  What I can’t figure out and hopefully you can is whether the differences in stiffness and density of the different reed materials  varies how they vibrate, or simply force a different geometry in the reed that changes how it traverses the window.  

Best wishes,

Dana

 

   

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