Rheology? Don't know much about rheology...

[sunburst]

...explain rheology...as it relates to the mandolin?

To expound on my earlier post, elsewhere in Understanding Wood we can learn about the structure of wood. We basically have a bunch of tubes (cells, fibers, vessels), think of straws, held together by a matrix of "goo". The goo is lignin, hemicellulose and such, and it has some amount of viscosity. Under constant strain, the tubes can slowly slide past one another and the wood can deform or bend.
It is important to know that heat can greatly speed up that process by lowering the viscosity of the goo so that the tubes can slide past one another faster and easier. That's what happens when we bend sides. That is also what happens when we leave a mandolin in the car on a hot summer day, and besides the longevity of our glue joints, it is a good reason to avoid overheating our instruments.

Anther way it relates to the mandolin is the effect of time on strained wood. We often hear that the luthier must strike a balance between structure and function. The lighter and more delicate the instrument, the greater the response to the string energy that makes it all work, yet it has to be heavy and strong enough to withstand the strain placed upon the structure by string tension. When we understand that wood creeps, or deforms from strain over time, we realize that we must overbuild somewhat in order for our instruments to remain structurally sound over time. If we make a mandolin with minimal strength and it becomes overheated the structure can deform or fail. If we make a mandolin with minimal strength, it may not withstand the effects of time and string tension.

Actually, none of that has a lot to do with rheology, but the viscosity, or the flow, if you will, of the "goo" that binds wood fibers together, would come under the general heading of rheology. The thing is, I can understand enough about wood movement to be informed in my mandolin building decisions without knowing anything about rheology, and without even knowing the word, which frankly, I didn't know until this thread!

[sblock]

(geologist and engineer speaking),

I've never associated thixotrophy with rheology. I associate the former as a material property where the elastic properties are contingent on dynamic state (i.e., micaceous sandstone, ketchup) but I assocate the latter as using a fluid example as a surrogate for the behavoir of a solid. So, if you want to explain how a saturated soil will compress under a newly-placed load, you need to understand how the water has to get out of the way first. You really want to know how the solid will behave, but you have no choice but to acknowledge there's a fluid-flow component.

Then again, I could be wrong. . .

f-d

Gee, I don't mean to tell you that you're wrong (sounds too harsh!), but your familiarity with the term 'rheology' is perhaps just a bit too limited. Yes, both thixotropy (shear-thinning, like ketchup) and rheopecty (shear-thickening, like cornstarch in water) are considered to be rheological properties, that is, behaviors relating to material flows. These properties are often exhibited by so-called "non-Newtonian fluids," that is, fluids without simple viscous behavior, and also by certain fluid-solid mixtures (e.g., slurries; you brought up the example of fluidized beds from your engineering background), and by fluids mixed with either long or branched polymers. And under SOME (not all conditions), it might even be appropriate to model wood as a viscoelastic plastic (which means a deformable semi-solid!) that exhibits hysteresis -- as, for example, when it's being SLOWLY bent and set into a shape by heat. But this same physical model is NOT at all appropriate when considering how wood acts as a vibrating medium during sound production, so one has to be careful about picking the right model! The importance differences involved here have to do with (1) very different time scales, (2) different temperatures, and (3) different stresses.

That said, one can certainly talk about wood from a rheological perspective some of the time. I am not sure, though, that simply using science-jargon terms like this leads to greater insights. The devil is always in the details, and the agreement of any possible rheological models with actual experiment. But science is great when it's applied appropriately -- which is when it works! And engineering is the 'art' of reducing science to practice, you could argue.

[Eric Oliver]

I was of course looking for clues as to the mandolin and the new word that is found in a book about wood. After searching that word on the web I was trying to apply "everything flows" to wood. It seemed to me that it must be related to breaking in of the mando's wood, but which also must include the finish as well as glue.
I think Randy Wood was quoted saying, I paraphrase, you need to get the top or back replaced within a couple of days or the body will move too much if not in a mold.
This suggests that the wood would/could continue to flow after many years as a whole mando. Or more likely, rebound some from the released forces...to a new stasis.
Another scotch?

[sunburst]

...you need to get the top or back replaced within a couple of days or the body will move too much if not in a mold.
This suggests that the wood would/could continue to flow after many years as a whole mando. Or more likely, rebound some from the released forces...to a new stasis.
Another scotch?

If you take an instrument apart is moves. If the back is removed from a mandolin it will not fit back on like it came off even within a few minutes let alone a couple of days. We always have to force the rim and plate into alignment to re-glue a removed top or back plate. Whether it is rebounding or responding to stresses from string tension, humidity changes or perhaps many other influences, I don't know. It could be one or another, a combination, but whatever, wood is a dynamic material. It is constantly in motion unless it is well seasoned and in a condition of absolutely stable temperature and humidity and under no strain whatsoever. Those conditions don't apply to instruments, or wood in general unless perhaps on the space station in a climate cell in zero gravity. Many of the classic joints used in wood, many of the historical techniques used in woodworking, the reason "quartered" wood is considered best for many situations, all came about because of wood movement. The joints and techniques that worked became the standards.

[CedarSlayer]

Gee, I don't mean to tell you that you're wrong (sounds too harsh!), but your familiarity with the term 'rheology' is perhaps just a bit too limited. Yes, both thixotropy (shear-thinning, like ketchup) and rheopecty (shear-thickening, like cornstarch in water) are considered to be rheological properties, that is, behaviors relating to material flows. These properties are often exhibited by so-called "non-Newtonian fluids," that is, fluids without simple viscous behavior, and also by certain fluid-solid mixtures (e.g., slurries; you brought up the example of fluidized beds from your engineering background), and by fluids mixed with either long or branched polymers. And under SOME (not all conditions), it might even be appropriate to model wood as a viscoelastic plastic (which means a deformable semi-solid!) that exhibits hysteresis -- as, for example, when it's being SLOWLY bent and set into a shape by heat. But this same physical model is NOT at all appropriate when considering how wood acts as a vibrating medium during sound production, so one has to be careful about picking the right model! The importance differences involved here have to do with (1) very different time scales, (2) different temperatures, and (3) different stresses.

That said, one can certainly talk about wood from a rheological perspective some of the time. I am not sure, though, that simply using science-jargon terms like this leads to greater insights. The devil is always in the details, and the agreement of any possible rheological models with actual experiment. But science is great when it's applied appropriately -- which is when it works! And engineering the the 'art' of reducing science to practice, you could argue.

Having spent most of my life making things work despite the engineers crazy ideas, I would agree that engineering is an art.

I would tend to agree about the application of rheology here. I don't see the strong cross tween rheology and acoustics myself, but then I have never had any luck proving a negative. Someone may find a visualization that helps them master an odd quality so the cross over may be worth it.

When Pasteur managed to combine a few schools of thought and advanced his crazy theories the established practitioners were quite correct in considering him dangerous. Cross over between disciplines can result in some crazy jargon and expensive boondoggles. For every great discovery there are a lot of really nifty things that almost worked. When someone manages to nail down a new method it is a wonderful thing, well worth the multitudes of crazy failures.

Independent luthiers, by my observation, are usually a breed of precise craftsmen who also practice alchemy. If one of them can take the study of nifty fluids that can flow faster or siphon without a vacuum and turn it into nifty instruments, then I applaud them.

Personally I will stick to the tried and true method of talking to the wood and asking what it thinks I should do next.

Bob

[belbein]

Fluid dynamics was at the heart of my diploma thesis (confined vortices, or canned tornadoes if you will), but this term is new to me, too. Don't tell me it's about Navier-Stokes solutions inside the scroll...

You'll appreciate this, Bertram. I had with a friend who was aerodynamics faculty at Georgia Tech. I took him sailing with me one day. It was a glorious day: cloudless, about 70 degrees, probably a 10 mph wind, nobody else out there. It was the kind of day where sailing is like meditation, and you just want to hold your breath and take it all in because you know it won't last. I finally realized that my friend was staring up at the mains'l, not saying anything. I asked him what was wrong. He said, "I was just looking at the disruption of laminar flow..." and then he was off into turbulence and vortices and God knows what.

[Dave Hanson]

It sounds like technical gobbledegook for the sake of sounding technical to me, I never heard of Lloyd Loar mentioning rheology.

Dave H

[Bertram Henze]

He said, "I was just looking at the disruption of laminar flow..." and then he was off into turbulence and vortices and God knows what.

You're right, that's me
You can see the turbulence yourself: when the trailing edges of your sails vibrate, it's all turbulence, because in laminar flow they should be still as a rock. When you hear the wind blow, it's all turbulence, because laminar flow is silent.

Talking about hearing (and flowing solids to be back on topic), it is interesting that sand makes sound. Viewed like this, the desert is just a terribly dehumidified big mandolin

With compliments from the sandman-dolin

[Petrus]

I wonder if someone could explain rheology, a new word I learned in Mr. Hoadley's book that Sunburst often mentions, as it relates to the mandolin?

The technicalities of it escape me (humanities major, sorry), but I guess it would become a matter of interest if someone was playing the mandolin underwater, for one thing. Or in different types of atmosphere, where the effects of the environment would have an influence on the sound of your instrument -- say, on Mars or Titan, which are very different from one another. Not to mention Venus, where the atmospheric pressure (90x that of earth, or about equal to being a mile underwater) would require additional bracing to avoid the top caving in.

[Ivan Kelsall]

Praise the good Lord that Lloyd Loar didn't know about Rheology or Thixotrophy,he & his gang just built mandolins. IMHO,there comes a time when too much 'knowlege' gets in the way of practicality. That isn't to say that the 'knowlege' per se isn't important in the right application,but i don't think that mandolin building is one of them. I believe that far more important than any 'ologies',is the impirical knowlege gained by observation & experience when building musical instruments. It's exactly that sort of knowlege that created some of the greatest Orchestral stringed instruments which are still being played & sounding totally wonderful today,
Ivan

[fscotte]

I'm not sure what Loar knew, he was a very interesting gent to say the least. Considering the work he had done and experiments, I'm fairly certain he may have understood that wood will sag under pressure if given enough time.

[sblock]

Praise the good Lord that Lloyd Loar didn't know about Rheology or Thixotrophy,he & his gang just built mandolins. IMHO,there comes a time when too much 'knowlege' gets in the way of practicality. That isn't to say that the 'knowlege' per se isn't important in the right application,but i don't think that mandolin building is one of them. I believe that far more important than any 'ologies',is the impirical knowlege gained by observation & experience when building musical instruments. It's exactly that sort of knowlege that created some of the greatest Orchestral stringed instruments which are still being played & sounding totally wonderful today,
Ivan

Actually, in addition to being a fine performing musician, Lloyd Allayre Loar was an acoustical engineer -- NOT a luthier! He may have worked for a short stint at Gibson, for about 5 years, and where he helped to design and perfect the F5 model we all know and love, but that was only a tiny part of what he did over his long career. He was deeply interested in the science of acoustics, and he served on the faculty and taught classes in acoustics for a number of years at Northwestern University in Evanston, IL. He was one of the pioneers in the development of electrified string instruments, and he held several patents, in addition to founding the Vivi-Tone company to distribute these.

So actually, Lloyd Loar knew a whole lot about the physics of sound (acoustics) and he also studied the physics of sound production by stringed instruments. He studied both physics and engineering, and he wrote (and taught) about these topics. In fact, you could even argue that he was more "scientist/engineer" than he was "luthier/artist," although he was obviously a bit of both.

So Ivan, I would have been absolutely astounded if Loar didn't know quite a bit about rheology! He studied that stuff (physics of fluids and gases). "He and his gang" did NOT "just build mandolins," as you wrote! In fact, what he accomplished at Gibson was very heavily influenced by his scientific/engineering ideas of how to improve sound production and sound projection.

Roger Siminoff has written quite a bit about Lloyd Loar, so please check out the biograophical information at his website, at:

http://siminoff.net/loar-background/

Based on what we know about him, I very much doubt that Lloyd Loar would ever agree with the statement that "too much knowledge gets in the way of practicality." He was coming from the very opposite perspective, namely, that instrument design can, and should, be guided by the best science. How can you have "too much knowledge" he might have asked?!

[Petrus]

Never mind Loar, what about all those early masters who built great instruments (maybe not what we would recognize as the modern mandolin) for centuries without benefit of our modern discoveries in "natural philosophy" (their term)? Trial and error and the natural evolution impelled by immediate necessity (i.e., loudness in an orchestra without benefit of artificial amplification) are great motivators.

[sblock]

Never mind Loar, what about all those early masters who built great instruments (maybe not what we would recognize as the modern mandolin) for centuries without benefit of our modern discoveries in "natural philosophy" (their term)? Trial and error and the natural evolution impelled by immediate necessity (i.e., loudness in an orchestra without benefit of artificial amplification) are great motivators.

Yes, the trial-and-error process of engineering is time-tested and can be extremely effective. There can be no doubt about that. But it cannot compete, especially in the longer run, for developing a deeper knowledge based on understanding. The Egyptians built the pyramids largely by trial and error, in fact. And the first several pyramids either collapsed or had to be revised, once they surpassed a certain size, like the famous "Bent Pyramid," before the largest ones (at Giza) were produced. But when the Romans invented concrete, centuries later, and folks began to understand the mechanical properties of the ARCH and VAULT, things really began to pick up. From then on, architecture also involved mechanical engineering, in addition to style and art. Today, no one in his right mind would design a skyscraper these days without recourse to the very best of science and engineering to guide the mechanical design.

Acoustical musical instruments are built from materials, after all: some natural/organic (like wood) and some man-made (like metal). Usually BOTH. No doubt about it, it pays to understand these material properties if you're going to harness them to produce beautiful music. A "seat-of-the-pants" understanding can only take you so far. A scientific understanding has the potential -- at least in principle -- to take you a bit farther. It shouldn't be discounted! That said, natural materials like wood are EXTREMELY complex and it is pretty hard, in practice, to model these accurately with our current understanding. So there's plenty of room for improvement. But science has some genuine value in luthierie, and one should not be too quick to say "we don't need it" because folks like Antonio Stradivari had no access to it. But I bet if he HAD, he would have used it! We're all in pursuit of the same goals: beautiful music from beautiful instruments. And there are many ways to skin a cat.

[sunburst]

With a little understanding of materials science, engineering, and acoustics, instead of hundreds of years for the violin to develop, it might have taken tens of years or less. With the understanding we have (or at least is available to us now), we can conceivable advance the mandolin faster than it would advance by pure trial and error... that is if we can admit that factory mandolins produced nearly 100 years ago are not necessarily the pinnacle of the mandolin's development.
No such thing as too much knowledge. It informs us in our decisions, and more often than not, it informs us what not to try so we can more likely stay on the track to improvement.

[Larry Simonson]

I have been following this thread since it started and the question that comes to my mind is: What has science accomplished in guiding the luthier to building better mandolins? I would be a bit skeptical of any such claims until science has produced objective measures of excellence in this instrument. This is not the fault of science, a mandolin is just a very tough puzzle. Once these measures are accepted (don't hold your breath) then scientists will have no trouble devising good experiments to demonstrate that progress is made. Experiments that show how a mandolin works are interesting and may be very useful in the quest toward the goal but when it comes to a scientist defining perfection to an artist, there will likely be some disagreement.

[sunburst]

...when it comes to a scientist defining perfection to an artist, there will likely be some disagreement.

There won't be any disagreement because no scientist would try to define perfection to anyone when it comes to mandolins.
What has science accomplished in guiding the luthier to build better mandolins? Well, for this particular luthier, it has taught me what claims to ignore, or at least view with suspicion, and by not wasting time following unreasonable ideas down blind alleys, to stay on task trying to improve mandolins by sticking to what might actually work.

[Bertram Henze]

What has science accomplished in guiding the luthier to building better mandolins? I would be a bit skeptical of any such claims until science has produced objective measures of excellence in this instrument.

It takes two for this: the luthier must tell the scientist what the goals are and how he can tell if they have been reached; the scientist then can tell the luthier what might work (and how it works) to reach the goals.

[Pete Jenner]

After recent dust ups it's probably best I go with the flow on this thread.

[Bernie Daniel]

It takes two for this: the luthier must tell the scientist what the goals are and how he can tell if they have been reached; the scientist then can tell the luthier what might work (and how it works) to reach the goals.

Luthiery is an art but a luthier can be "scientific" in his approach and application of his art?

[Bertram Henze]

Luthiery is an art but a luthier can be "scientific" in his approach and application of his art?

One person can wear more than one hat. A luthier has to have a closet full of them, I guess.

[CedarSlayer]

Yes, the trial-and-error process of engineering is time-tested and can be extremely effective. There can be no doubt about that. But it cannot compete, especially in the longer run, for developing a deeper knowledge based on understanding. The Egyptians built the pyramids largely by trial and error, in fact. And the first several pyramids either collapsed or had to be revised, once they surpassed a certain size, like the famous "Bent Pyramid," before the largest ones (at Giza) were produced. But when the Romans invented concrete, centuries later, and folks began to understand the mechanical properties of the ARCH and VAULT, things really began to pick up. From then on, architecture also involved mechanical engineering, in addition to style and art. Today, no one in his right mind would design a skyscraper these days without recourse to the very best of science and engineering to guide the mechanical design.

Acoustical musical instruments are built from materials, after all: some natural/organic (like wood) and some man-made (like metal). Usually BOTH. No doubt about it, it pays to understand these material properties if you're going to harness them to produce beautiful music. A "seat-of-the-pants" understanding can only take you so far. A scientific understanding has the potential -- at least in principle -- to take you a bit farther. It shouldn't be discounted! That said, natural materials like wood are EXTREMELY complex and it is pretty hard, in practice, to model these accurately with our current understanding. So there's plenty of room for improvement. But science has some genuine value in luthierie, and one should not be too quick to say "we don't need it" because folks like Antonio Stradivari had no access to it. But I bet if he HAD, he would have used it! We're all in pursuit of the same goals: beautiful music from beautiful instruments. And there are many ways to skin a cat.

I like what you said here, but Antonio was probably not as primitive as everyone seems to think. Antonio Stradivari did indeed have access to acoustical science and the level of science he had was pretty darn good. Before Stradivari was born, Marin Mersenne had measured the speed of sound, written Mersenne's Laws describing the frequency of oscillation of a stretched string, defined semitones mathematically and produced most of the formulas that we use today. We have good evidence that Antonio was an amazing craftsman that tinkered with quite a few things. It seems quite unlikely that he and a lot of other contemporary luthiers would not have heard of, obtained and studied Mersenne's work. He did not have Chladni, but what he had was not that far from what we have today. It is quite certain that the acoustical math and physics of the day was well advanced over what quite a few superb living luthiers are using.

Bob