FREE REED PHYSICS - 3

[ttonon]

Greetings.  In my first post in this series, I forgot to mention the fact that in the comparison plots between brass and steel, the tongue lengths are adjusted so that the brass and steel vibration has the same frequency.  In my second post comparing carbon and steel, the two tongues have equal length, and in this post, I give results for carbon and steel tongue lengths having the same frequency.  

The amazing thing in this comparison is that the carbon normalized harmonics are enormously larger than those for steel.  I honestly didn’t expect such dramatic results.  And they show large difference even for the smallest bellows pressure.  For me, this increases my curiosity over what a carbon fiber reed tongue would sound like.   Notice also the dominance of the 5th harmonic over the 4th, for all but the lowest bellows pressures.  I've noticed before the contentious battle between these two harmonics, and here it's well displayed.  

 

The docx file for this case is the same:  https://app.box.com/folder/79305691686

 

Best regards,

Tom

[Johann]

36 minutes ago, ttonon said:

Greetings.  In my first post in this series, I forgot to mention the fact that in the comparison plots between brass and steel, the tongue lengths are adjusted so that the brass and steel vibration has the same frequency.  In my second post comparing carbon and steel, the two tongues have equal length, and in this post, I give results for carbon and steel tongue lengths having the same frequency.  

The amazing thing in this comparison is that the carbon normalized harmonics are enormously larger than those for steel.  I honestly didn’t expect such dramatic results.  And they show large difference even for the smallest bellows pressure.  For me, this increases my curiosity over what a carbon fiber reed tongue would sound like.   Notice also the dominance of the 5th harmonic over the 4th, for all but the lowest bellows pressures.  I've noticed before the contentious battle between these two harmonics, and here it's well displayed.  

 

The docx file for this case is the same:  https://app.box.com/folder/79305691686

 

Best regards,

Tom

Tom this is a bit to less info how you set up the test condition.  

[ttonon]

12 minutes ago, Johann said:

Tom this is a bit to less info how you set up the test condition.

Hi Johann, what's the confusion?  What would you like to know?

Tom

Edited June 15, 2019 by ttonon

[Johann]

I personal think it is a waste of time to to make reeds with Carbon (CFK) it is impossible to bend a carbon reed to set it correctly. This is important it is not enough to be able to sand the reed. And i personally would not like to do the job with this carbon dust. I did use carbon sheet material for some time not for rees but oherer parts. 

[Johann]

10 minutes ago, ttonon said:

Hi Johann, what's the confusion?  What would you like to know?

Tom

Hi Tom, the complete test condition described. How did yo make the reed? Dimensions off the reeds. that were compared.  Johann

[Jake Middleton-Metcalfe]

I think Dana Johnson mentioned making an experimental carbon fiber reed once, maybe he will chime in with what he found out by doing it. I have used carbon fiber to make other things in the past but never reeds. 

[ttonon]

10 hours ago, Johann said:

Hi Tom, the complete test condition described. How did yo make the reed? Dimensions off the reeds. that were compared.  Johann

Hi Johann, I believe you're under the mistaken impression that I experimentally measured different reeds that I made.  This is not the case.  I'm presenting theoretical results from a physical model and mathematical solution.  The plots I present are the results of calculations from this analysis.  

 

If it helps, I present the geometric parameters I used in these calculations, below'

Width of tongue = 3/16 inch

Thickness of tongue = 0.010 inch

Thickness of plate (shoe) = 0.125 inches

Length of steel tongue = 1.4 inches

Length of brass tongue (same pitch as steel) = 1.19 inches

Length of titanium tongue (same pitch as steel) = 2.77 inches

Length of carbon tongue (same pitch as steel) = 2.75 inches

 

Best regards,

Tom

 

[Johann]

1 hour ago, ttonon said:

Hi Johann, I believe you're under the mistaken impression that I experimentally measured different reeds that I made.  This is not the case.  I'm presenting theoretical results from a physical model and mathematical solution.  The plots I present are the results of calculations from this analysis.  

 

If it helps, I present the geometric parameters I used in these calculations, below'

Width of tongue = 3/16 inch

Thickness of tongue = 0.010 inch

Thickness of plate (shoe) = 0.125 inches

Length of steel tongue = 1.4 inches

Length of brass tongue (same pitch as steel) = 1.19 inches

Length of titanium tongue (same pitch as steel) = 2.77 inches

Length of carbon tongue (same pitch as steel) = 2.75 inches

 

Best regards,

Tom

 

Hi Tom, yes you are correct i did mistake the info in this respect! Ok this explains all. For me it is obvious that changing only the length be keeping all other dimensions the same for the same pitch must result in timbre change. So are my practical experiences.  Johann

[ttonon]

3 hours ago, Johann said:

Hi Tom, yes you are correct i did mistake the info in this respect! Ok this explains all. For me it is obvious that changing only the length be keeping all other dimensions the same for the same pitch must result in timbre change. So are my practical experiences.  Johann

Hi Johann, I'm glad to hear that you have the impression that these results are realistic.  If you have recordings that can give us Fourier spectrum we can make some quantitative comparisons.  One quirk that's interesting is the competition between the 4th and 5th harmonics, something that occurs throughout these calculations, and therefore must have something to do with how the different aspects of dissipation interact with each other and the intermittent pressure forces from the bellows.

Best regards,

Tom

[Johann]

On 6/16/2019 at 12:26 PM, ttonon said:

 

Hi Tom my survey is surely not representative further observations would be need. Also be aware that the two sound files are with some background nice from the wind machine.  Recordings war made with constant air pressure of 500 PaN/m2 Dimensions of bothe reeds are absolutely the same only the filing profile is a little be different to tune to the same pitch. Best regards Johann

 

Quote

 

 

 

Edited June 17, 2019 by Johann

[Dana Johnson]

Hi Guys,  re Jake’s comment, I don’t remember making a carbon fiber reed, though I may we’ll have opined on the subject at one point.  I am still reluctant to consider them on a practical level.  It was enough of a chore ( months of work ) to adjust my steel reed profiles to provide a smooth grading of stiffness from the lowest reeds to the highest to get a homogeneous sounding and playing instrument.  I wouldn’t know where to begin with carbon fiber.  ( not to mention the self destructive aspect mentioned in 1 or 2 of this series.  I do remember an incident where the carbon fiber tail of an airliner self destructed when subject to the turbulence of the wing vortices left in the air from a 747 that had gone before it.)

   I think Tom’s exploration is at least academically interesting if it can shed some light on how different properties affect reed vibration, especially from a point of efficiency.  Since this all seems to be a result of calculation rather than physical trial, i’m Not sure it is fair to blame the raw materials for the tonal differences people ascribe to brass or steel.  Listening to Johan’s sound files of a steel reed vs a titanium one, I really couldn’t tell the difference.  The chart does show the different strengths of the harmonics,  but our ears probably aren’t designed to distinguish between sounds that are proportionally so similar, especially since both seem to have strong odd harmonics as the defining feature of the tone.

  I am not sure how you can control for variations in stiffness in these models so all reeds are equally stiff at the designated pitch.  Since the point of physical profiling is to take a reed of practical length and tinker with its mass distribution and overall stiffness to reach the desired pitch with the desired response to bellows pressure,  I don’t know how you can create mathematical reeds of these materials that differ so much in density and modulus of elasticity so that at a set pitch, stiffness and swing amplitude you can make a comparison of harmonic amplitude.

   I still have no idea how the musical harmonic series is created (which it certainly is ) when the reed’s natural cantilever bar mode harmonics are decidedly non linear.  Tom doesn’t’ agree with Benade’s explanation and convinced me it may not be correct, but that is as far as I got.

have fun guys,

my brain is tired

Dana

[Johann]

" Listening to Johan’s sound files of a steel reed vs a titanium one, I really couldn’t tell the difference.  The chart does show the different strengths of the harmonics,  but our ears probably aren’t designed to distinguish between sounds that are proportionally so similar, especially since both seem to have strong odd harmonics as the defining feature of the tone. [...]

 Tom doesn’t’ agree with Benade’s explanation and convinced me it may not be correct, but that is as far as I got.

Dana"

 

 

Hi Dena use headphones and you should hear the difference. Is not as much as one would expect and under real conditions it may be even less. Still i expect a more mellow sound as brass. This are all hypothesis that need to be proven in real Instruments. Also it is not so important for people who build instruments to understand way the different sound are produced. Important is that we know we can influence the sound by changing Profile and reed length.  We just have to accept that reed produce beside the "normal" harmonics, that are more or less  in a known relationship to each other, also harmonic frequencies that are in amplitude much less but don't fit into this scale. Changing profile will result in varying this frequencies and amplitudes of this so called inharmonic frequencies (additional mode frequencies). Relay on your ear by making reeds there is no real practical mathematical background that would really help in making reeds sounding more pleasant to our ears.    Please point me to the differences of Bernard's explanation.  Best regards Johann

[Wolf Molkentin]

1 minute ago, Johann said:

Still i expect a more mellow sound as brass.

 

From my limited experience (George Case + Wheatstone brass reeded treble English concertinas) I would hesitate to describe the "brass" sound as "more mellow" - I find it rather bell-like, especially in the higher range, i.e. it has an improved clarity or transparency to it which is not to be found with steel reeds.

 

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?

 

Best wishes - ?

[Johann]

I may be well wong on how the final instrument with titanium alloy reeds sound, i only know small accordions with brass or bronze reeds. All would need intense verifying and making complete sets with titanium alloys. Also keep in mind we only talk about reed sets my experience is that the instrument itself has also influence on the resulting sound and with "typical formant range" in the spectrum. We have et list some different filtering depending on the instrument. Comparing ist therefore alway not so easy.  Best regards Johann

Edited June 18, 2019 by Johann

[ttonon]

I should clarify.  When I hypothesized that higher harmonics in the first mode vibration of the tongue might translate to musical tone, I didn't mean to imply that the musical tone would be the result of only those harmonics.  Harmonics associated with sudden changes in pressures and velocities of air motion due to the vibration are indeed a major cause for what we hear, as acoustic models and experiments verify.  My hypothesis is based on the fact that different materials seem to sound differently to many listeners, and if that's the case, how else can they be heard?  In more detail, it's possible tongue motion harmonics do not directly contribute, but only indirectly, as for instance if the minute motion of the harmonics superimposed on the main sinusoidal motion first affect the chopping of air flow through the slot.  So rather than sound emanating directly from the quivering surface of the tongue (which is my hypothesis), that quivering mostly affects the time dependence of the chopping phenomenon, which is really what we do hear.  However, whether indirect or direct, these higher harmonics need only make a contribution to the sound, enough so that we can discern it in the musical timbre.  For anyone who claims that these tongue harmonics do not affect the musical tone, I ask by what mechanism can different materials affect the sound?  I mean between two metals that can be fashioned into geometries having equal levels of preciseness.  

 

So Dana, I never disagreed with Benade's explanation, and I'm assuming here his explanation has to do with the mainstream idea that pressure wave harmonics are associated with chopping airflow.  My hypothesis simply adds to it, in the growing comprehension of how complicated Nature really is.  As an aside, I'm curious whether Benade attempted any explanation for how different materials can be distinguished.  

 

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.

 

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.  

 

11 hours ago, Dana Johnson said:

I am not sure how you can control for variations in stiffness in these models so all reeds are equally stiff at the designated pitch.  

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?

11 hours ago, Dana Johnson said:

I don’t know how you can create mathematical reeds of these materials that differ so much in density and modulus of elasticity so that at a set pitch, stiffness and swing amplitude you can make a comparison of harmonic amplitude.

Again, can you please elaborate?

 

I do hear a difference between Johann's steel and titanium tongues, and to me surprisingly the titanium sounds brighter.  This is emphasized while wearing headphones, as Johann suggests.  There is a definite preponderance of the higher frequencies from titanium, and I notice that the steel first sounds much more "mellow," until about 2.5 seconds (where you can actually see a slight increase of amplitude on the graphics) higher frequencies ensue, but don't seem to dominate as much as with titanium.  I agree that my perception seems to contradict what the frequency spectrum suggests.  

 

As interesting as Johann's data is, it cannot be decisive.  Important information is left out.  Most importantly, what kind of a microphone was used, where was it placed in relation to the reeds, is that relationship the same for both, was the same microphone used for both, what is the pressure level, what are the thicknesses and lengths of the tongues, what is the width and is it constant with tongue length, is there any profiling, etc.  All these can have important influences.  I'm struck by the very large 5th harmonic.  In my experience, it seems exceptional.  I notice that around the 6th harmonic, there's a blip that might suggest a slight contribution from the second bending mode of the beam.  There's also a blip around the 16th and 17th harmonic, suggesting a third bending mode, however, we can't say for sure because we don't know if the geometry conforms to that of a simple constant area cantilever, for which such conclusions can be made.  Additional blips might be contributions to torsional modes, though that's not too likely, but if pressures are high enough, maybe so.  Then we have to wonder about the quality of the recording equipment and the software used to calculate the Fourier coefficients.

 

It's clear that theoretically, experimentally, and practically, a full understanding of tongue material would require considerable effort. 

 

Best regards,

Tom

 

 

 

 

 

[Johann]

45 minutes ago, ttonon said:

As interesting as Johann's data is, it cannot be decisive.  Important information is left out.  Most importantly, what kind of a microphone was used, where was it placed in relation to the reeds, is that relationship the same for both, was the same microphone used for both, what is the pressure level, what are the thicknesses and lengths of the tongues, what is the width and is it constant with tongue length, is there any profiling, etc.  All these can have important influences.  I'm struck by the very large 5th harmonic.  In my experience, it seems exceptional.  I notice that around the 6th harmonic, there's a blip that might suggest a slight contribution from the second bending mode of the beam.  There's also a blip around the 16th and 17th harmonic, suggesting a third bending mode, however, we can't say for sure because we don't know if the geometry conforms to that of a simple constant area cantilever, for which such conclusions can be made.  Additional blips might be contributions to torsional modes, though that's not too likely, but if pressures are high enough, maybe so.  Then we have to wonder about the quality of the recording equipment and the software used to calculate the Fourier coefficients.

 

It's clear that theoretically, experimentally, and practically, a full understanding of tongue material would require considerable effort. 

Please look at the attached pictures i also mentioned that test condition is totally equal and air pressure was 500 PaN/m2. Reeds were mounted equally on the same tunningtabel on exactly the same place. Nothing special about the microphone is an electrede micro. I don't say this are ideal test condition but enough to see differences in the chart. It my be you war mistaken steel has much more higher harmonics look at the chart and listen again. Don't take the blips to seriesly the my be caused by the wind machine i would need to repeat the test again with different pressures so i could tell for sure if the are from the windsource or not. The test condition should be carried out in a  special noce damped room as well, i could do this in the sound laboratory at my former workplace. But this test was made on may workplace. All together would be a fillings subject for a dissertation. For now i don't have more. Best regards Johann   

Edited June 18, 2019 by Johann

[ttonon]

Hi Johann, you're right that the picture shows a tapered tongue, and 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. 

 

The biggest question I have about the spectral data is the prominence of the 5th harmonic.  Since there's no red color on the bump - or at the base of the bump - I assume that particular harmonic shape is duplicated by steel and titanium, since all other harmonics show a dark color whenever the values for steel and titanium overlap.  I think you'd agree that this puts into question the accuracy of that harmonic measurement, because it's unlikely that both steel and titanium would have an identical 5th harmonic response.  It's probably caused by an artifact somewhere in the recording.  Perhaps a resonance in the microphone?  Do you have a copy of the frequency response for your microphone?  Maybe it's in the electronic circuit or some feedback to the microphone common to both metals.  But it's very curious that it occurs precisely at the 5th harmonic.  If we truly hear that harmonic, for any reason, and it's not something hidden in the electronics, you'd agree that such a large harmonic could dominate the sound of both reeds.  If that's the case, a hearing test would be invalid.  The art of experimentation is an art;  it's usual very difficult to obtain good data, and as you know, bad data is worse than no data.  

 

In my previous post, I forgot to point out that the first harmonic in my plots dominate the others by only a couple/three orders of magnitude - for the higher pressures, only one.  Johann's data, and with other measurements I've seen, it dominates by about four - excluding the spurious 5th harmonic.  This is a huge difference in relative amplitude, and perhaps lends more credence to my hypothesis, that higher harmonics from the reed displacement can perhaps contribute to the overall sound.   

 

Best regards,

Tom

 

[Johann]

10 minutes ago, ttonon said:

Since there's no red color on the bump - or at the base of the bump - I assume that particular harmonic shape is duplicated by steel and titanium, since all other harmonics show a dark color whenever the values for steel and titanium overlap.  I think you'd agree that this puts into question the accuracy of that harmonic measurement, because it's unlikely that both steel and titanium would have an identical 5th harmonic response. 

Hi tom, the are not equal. I have attached the same chart but this time with blue line on top.