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New research: Power efficiency in the violin


jdevries
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Summary: Power efficiency in the violin

 

Full article: The evolution of air resonance power efficiency in the violin and its ancestors

 

The abstract from the article:

 

The fact that acoustic radiation from a violin at air-cavity resonance is monopolar and can be determined by pure volume change is used to help explain related aspects of violin design evolution. By determining the acoustic conductance of arbitrarily shaped sound holes, it is found that air flow at the perimeter rather than the broader sound-hole area dominates acoustic conductance, and coupling between compressible air within the violin and its elastic structure lowers the Helmholtz resonance frequency from that found for a corresponding rigid instrument by roughly a semitone. As a result of the former, it is found that as sound-hole geometry of the violin's ancestors slowly evolved over centuries from simple circles to complex f-holes, the ratio of inefficient, acoustically inactive to total sound-hole area was decimated, roughly doubling air-resonance power efficiency. F-hole length then slowly increased by roughly 30% across two centuries in the renowned workshops of Amati, Stradivari and Guarneri, favouring instruments with higher air-resonance power, through a corresponding power increase of roughly 60%. By evolution-rate analysis, these changes are found to be consistent with mutations arising within the range of accidental replication fluctuations from craftsmanship limitations with subsequent selection favouring instruments with higher air-resonance power.

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Thank you immensely for posting this  :) .

 

From the MIT news article:

 

"But were the design changes intentional? To answer this question, the researchers worked the measurements from hundreds of Cremonese-era violins into an evolutionary model, and found that any change in design could reasonably be explained by natural mutation — or, in this case, craftsmanship error.

In other words, makers may have crafted violins with longer sound holes and thicker back plates not by design, but by accident."
 
;)  :lol:
 
Now I know why the Markie with the overextended F-holes I sold early last year played so well and got snapped up so fast.
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WOW. 

 

Well, lets look on the bright side. The Office of Naval Research funded this clown to write this paper. If they funded him to produce military research to this quality then a lot of innocent people would have died.

 

I really don't know where to begin when it comes to shooting down this particular dodo. It is so astonishingly unremittingly wrong on so many levels. 

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Roman Barnas is one of the authors.

 

I wouldn't presume he has anything to do with the mad ideas in it. North Bennet Street School would have been delighted to "collaborate" in an MIT project, and that's probably just about the size of what got his name stuck to it. The "ethics" of joint authorship in scientific works can end up with a rather broad cast of characters. 

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Many thanks for posting this, jdevries.  Try as I did, I couldn't bring this up on the Royal Society website last night.  

 

As for the quality of the science, I certainly will take note of shortcomings that are obvious to the social scientist in me (method is not necessarily method everywhere we go; but some knowledge of the construction of valid methodologies at least prepares the schnozzola for sniffing out errors in research design).  Of greater interest to me are the dimensions they studied in reaching their conclusions.  We know that Strad and others were seemingly tireless experimenters.  While studying dimensions of many instruments representing different makers over time may not offer conclusive proof,  it at least can offer suggestions as to what was going on.  And those suggestions are good enough for me to help expand my thinking about my own experimentation down the road.

 

As for Roman's involvement, I would not expect him to have contributed much if anything to the scientific method behind the study -- though I don't know him that well and he may well have scientific bona fides of which I am unaware.  I expect he provided the violin-making and historical expertise and perhaps his knowledge of the documentation that is out there.  It may be damning with faint praise, but at least they involved someone who knows about the trade!

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I have my doubts about this reseach, which stem from one key point -

Within a specific maker's life any changes would have been deliberate.  The f-holes, just like the rest of the instrument, were constructed using geometrical rules, not tracings.

 

Right. I have a very hard time believing that the ff holes are somehow (in any way) random.  I too wonder what the hell Zyggy is doing in the acknowledgements.  But I will love to read the article. 

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I would love to see the data set that they used. Actually I wouldn't - just being sarcastic. 

 

There is an awful lot of waffle about what it is, but if they had properly, accurately and scientifically analysed instruments we should expect to see data sheets for each on at the very least... wouldn't we????

 

It seems like there is one hell of a lot of looking at paintings and extrapolating fantasy ideas of medieval instruments, which can have absolutely no validity for a scientific paper of this sort - Helmholtz resonance is a factor of the volume, not the area of the sound hole, so not knowing the thickness of the soundboard of a rebec in a painting (or if the holes are undercut) invalidates it. As for the 470 Cremonese instruments, I'm guessing these have all been extrapolated from secondary sources - photos etc, and there again haven't really been examined properly and even the methodology reveals that this clown thought that he could justify pretty crude quality of data. Words like "estimated" and "average" don't really have much of a place in the precise claims this joker is trying to present.  

 

So, they made it up as they went along... you can read their own words, but if you don't have time (or the will to live after the first sentence) "we bullshitted" will do. 

 

 

Sound hole shapes of the violin and its prominent European ancestors were obtained from contemporary iconography or extant instruments showing: (a) circular sound holes for the 10th Century Medieval fithele [15, 16]; ( B) semi-circular sound holes for 12th-13th century lyras [16- 18]; © c-holes for 13th-16th century Medieval and Renaissance rebecs [15, 18]; (d) the addition of taper, circular end nobs and central cusps to c-holes in vihuela de arco's and viols of the 15th- 17th centuries [15, 16, 19]; (e) classical Cremonese f-holes of the 16th-18th centuries [15-17, 20, 21]; and (f) decorative rosettes in the lute [22-24] and the harpsichord [25]. Time series of design parameters in Figs 4c and 5, that have an at least or nearly first order effect on temporal changes in radiated acoustic power at air resonance, are based on measurements of 470 classical Cremonese violins. To construct these time series we made measurements of f-hole lengths of 338 violins from images in Ref. [26]. Measurements of f-hole lengths and characteristic lengths for air-cavity volume estimation of 110 violins (see SI Section 8) were taken from existing measurements in technical drawings and images in Refs. [27-34]. Mean air cavity heights were determined from characteristic length measurements for air-cavity volume estimation of 110 violins (SI Section 8). We reduced average plate thickness data of 22 violins from existing thickness maps in Refs. [29, 35]. Eleven of the 470 classical Cremonese violins used to generate Figs 4c and 5 coincide with the 26 classical Cremonese violins (2 Nicolo Amati, 17 Antonio Stradivari, 7 Guarneri del Gesu) for which acoustic air resonance frequencies have been reported [1-3] and shown in Figs 4b and S1. Of these measurements, the mean air-resonance frequency of the Guarneri data is greater by roughly 2/3rd of a semitone from that of the Stradivari and Amati data, which is consistent with the elastic analysis of Section 9. For Stradivari violins ‘Betts’ 1704, ‘Titian’ 1715 and ‘Wilmotte’ 1734, all six design parameters and air resonance frequency measurements [1-3] are available. Air resonance frequency estimates from elastic analysis match well, to within a fifth of a semitone and 1.4% RMS error, with measurements for these three instruments.

During the Cremonese period, each master maker produced roughly 10 violins per year on average [26], indicating a generational-period of roughly 0.1 year. The sound hole perimeter lengths of violins made by Savart and Chanot are determined from available technical drawings and images in references [36-38]. 

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Did anyone else notice that Sam Zygmuntowicz is credited in the Acknowledgements?  One wonders what for?

 

His name comes under the contributions for "interesting and motivating discussions."  That means that they talked to him, I guess.

 

I generally skim over papers like this to see if there's anything that might be interesting or useful, and then spend more time if it looks promising.  On the plus side, I won't be losing any shop time reading this thing carefully.  Even if all the conclusions are right (and I have my doubts), I still don't see anything that would help make a better violin. 

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Just "thumbed" through it.  Seems like really studying it would be akin to panning for gold today the old-fashioned way in someone's played-out stake from the Gold Rush era.  Skeptical of the return on investment.  Still will give it a more thorough look, though, believing as I do in diversity in bedtime reading.  Just finished the rollicking ride of Abbey's Monkey Wrench Gang so this piece may restore balance to my little corner of the cosmos.

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His name comes under the contributions for "interesting and motivating discussions."  That means that they talked to him, I guess.

 

 

Not that I'm suggesting that he did, of course, but that could mean that someone used interesting language and motivated one to leave.  It sounds like something some diplomat would put in a press release.  I'll have to remember that turn of phrase.  :lol:

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Rarely is anything all good, or all bad.  But somehow we humans find comfort in painting things all one way or the other.

 

Thanks for posting an interesting article.

 

 

Is it by chance or by genius if:

 

A maker is considering three slight variations.  He builds two examples of each. Complete success! Of course, he sees that all six instruments are actually different.  He's sharp enough to see which things worked and which didn't.  One of the things he likes wasn't 100% planned.

 

All this experience influences his choices in the next round of building.

 

I believe this is more or less what they are describing as 'chance' and 'evolution'.  

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“People had to be listening, and had to be picking things that were more efficient, and were making good selection of what instrument to replicate,” Makris says. “Whether they understood, ‘Oh, we need to make [the sound hole] more slender,’ we can’t say. But they definitely knew what was a better instrument to replicate.”

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I have my doubts about this reseach, which stem from one key point -

Within a specific maker's life any changes would have been deliberate.  The f-holes, just like the rest of the instrument, were constructed using geometrical rules, not tracings.

Was Strad an artist (doing free hand drawing) or a draftsman (using compasses and straight edges)?  How would you know?

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...Helmholtz resonance is a factor of the volume, not the area of the sound hole...

 

 

Not true.  Actually, the frequency is determined by the aperture, the volume, and other factors such as the stiffness of the cavity.  The authors apparently have considerable expertise in fluid dynamics, and it looks to me like they're onto something.

 

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The initial reactions people are having to the publication of this research are largely defensive and skeptical. It's not suprising with inflammatory headlines such as these:

 

"Accidental Genius: Why a Stradivarius Sounds So Good" -Times

 

"Study finds the accidental genius of Stradivarius violins" -Telegraph

 

If I were to read these headlines at a glance, It seems to make one of the most celebrated luthier's out to be less than "genius". "Accidental" is not the word I would have chosen (I'm also not in the media business). The lay person might assume this study was more in a continued onslaught of findings to disparage the romanticised reputations of the Cremonese masters. Science once again raining on everyone's parade.

 

      There was a similar reaction seen in response to Joseph Curtin's comparitive study of the old and new.  It is not suprising to see the media emphasize what will most likely controversial.

 

Relax everyone, the study doesn't subtract from the Cremonese maker's competence, it verifies it. It may heighten your respect for the master's ability to distinguish subtle change over time and adapt. It seems to be a beautiful example of artificial selection. "craftsmaship error" is hardly the most interesting part of the article. I encourage people to reserve their judgement until after they understand the research.

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The issue of "are the changes intentional" is a question of more complexity then may be first apparent.  It assumes pure randomness or mistake.  As if "the knife just got away from me somehow".   There was an article that was written by Joe Curtin that stuck with me.  He talked about when we try to copy something we often exaggerate the parts that we like and tend to ignore parts we don't like or don't understand.  He was talking about antiquing I think, but it seems that this applies to making as well.  So another way to interpret this idea of "non-intentional" changes over 800 years, is that at least part of those changes had to do with unstated / unknown (unconscious) preferences of the person making the "mistake".  

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Was Strad an artist (doing free hand drawing) or a draftsman (using compasses and straight edges)?  How would you know?

The compass point marks left on the inside of the belly of the Muir Mackenzie are a good indicator that they're constructed (drafting), not based off a template (free hand).  (ref. Roger Hargrave's Strad poster)

 

Add to that Sacconi's book on Stradivari's methods which describes his construction methods.

 

and some research, as done by some well learned people.

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Not true.  Actually, the frequency is determined by the aperture, the volume, and other factors such as the stiffness of the cavity.  The authors apparently have considerable expertise in fluid dynamics, and it looks to me like they're onto something.

 

 

I think we might be talking at ever so slightly cross purposes, don't worry :)

 

The point that's worth sustaining is that the height of the "neck" of the helmholtz resonator (i.e. the thickness of the plate) is as important as the overall area. Moreover there are always significant variations in thickness of a soundhole wall, these thicknesses cannot be normalised across a violin or across a body of a single maker's work, and moreover there are complex changes that take place depending on if the soundholes are (a) undercut ( B) perpendicular to the violin, or perpendicular to the top © with softened, rounded edges. Although the author goes into some crackpot ideology about 2% variables in recutting the same soundhole (with implications of some cooked up Darwinian ideal), he completely ignores that by "estimating" an "average" he may be miscalculating the volume of air in the neck of the helmholtz resonator by as much as 60%.

 

The man has three choices.

 

1 - He can't ignore "neck height" and volume (i.e. the thickness and shape of soundhole walls), and find himself required to do some very complex proceedures for data capture on physical objects that would be incredibly time consuming and costly

 

 

2 - He can work on an exclusively 2-dimension laboratory experiment (cutting soundholes out of a piece of perspex of known and consistent thickness) and admit the limitations of a 2-dimensional explanation of a 3-dimensional object.

 

3 - falsify your data, write this paper, put out the press release claiming to know more about Strad than any dumb-arse violinmaker and pat himself on the back for putting them in their place.

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