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Parameter Overload

(Caution: this turned into a long-winded think-out-loud essay on the finer points of guitar design. TLDR: Experts disagree on some key geometries; rather than blindly pick an expert to model, I need to bring my own – albeit amateur – woodworking experience to bear in the decision.)

I’ve been making myself slightly crazy by diving into texts and plans written by a variety of classical guitar builders. While the general parameters of a classical guitar are fairly settled (scale length, length and width of body), there are lots and lots of details with the potential to significantly affect the quality of the sound and playability. 

I’m a science guy, and I like mathematical models. It turns out that a few hard core acoustic scientists have tried to model the parameters that affect the quality of a guitar’s sound, but most professional builders have concluded that their information does not provide great guidance. In order to assess the effect of, say, the bracing pattern under the top, all other parameters (shape, thickness, overall manifold topology) have to be held constant. But if you go and then alter one of those other crucial parameters, the information gleaned about bracing patterns goes out the window. There are too many parameters to model.

When I have a statistical model with lots of parameters, I use computer algorithms to “hill climb” to an optimal solution for my problem. There might be hundreds of parameters to tweak – all the computer needs to know is that tweaking one parameter in a particular direction results in a better or worse fit to my desired outcome. The computer algorithm tries to efficiently simultaneously adjust everything at once in order to arrive at an optimal solution.

There are at least two reasons that approach won’t work for a builder. First, the sense of an “optimal” sound and playability is not static; every player wants something a little different in terms of sound color and string action. Some professionals have a quiver of instruments, each selected for playing a particular genre of music. So optimizing design parameters is not a one-off challenge; one has to understand how all of those might change depending on how one wants to color the sound. And the “color” of sound is itself a complicated quality to describe – another multi-parameter space. 

The second problem is that incremental iterations toward an ideal sound happen one instrument build at a time. Even professionals working full time can at best turn out one instrument a week, and that’s with many of the processes automated. It takes years of iteration to gain an intuition of how altering a particular parameter set influences the final product. 

Of course, I want to hit as close to a target of “good sound” as I can for guitar #002. One approach is to stand on the shoulders of giants – to pick a set of plans that have been evolved by an expert builder over decades, and use that as a model. After all, the expert has already gone through dozens if not hundreds of tweaks to his/her design in order to arrive at a good baseline. This is what I set out to do, basing my guitar on a design by J. S. Bogdanovich and published in his classical guitar making book. To triangulate against his designs, I’ve also been scrutinizing the text by Cumpiano and Natelson, as well as revisiting the guide I used for guitar #001, the classic text by Irving Sloane.

I’ve got an overall outline and bracing pattern (straight out of Bogdanovich), and many of the other parameters (top thickness, etc) are given in his book and are in accordance with other sources. There is just one place where all three texts disagree – somewhat radically – and it has major implications for the build. This is the geometry (or is it topology?) of the top and its relation to the neck angle.

The simplest approach is that of Sloane – the top face of the neck (before the fingerboard is glued on) should be completely coplanar with the entire top, which itself is a simple plane. Now, it’s known that once the guitar is finished and the strings are tuned up, the tension on the top face (transmitted through the bridge) can tend to distort the top over time, pulling it up (bulging) behind the bridge and depressing it slightly in front (under the strings). If this distortion is severe it can affect the playability of the instrument, and then some replaceable pieces (namely, the nut and saddle) may have to be re-shaped.

There is one camp of builders that pre-stress the top by pressing it into a gentle curve and holding that shape with curved internal braces. Both Bogdanovich  and Cumpiano & Natelson use curved tops. But now that I thought I had my parameter explosion under control, again I see subtle distinctions.  Bogdanovich both curves the top and tilts the lower bout (the fat part of the body) back at an angle; essentially this compensates for the increased height of the bridge produced by the curve. Push the top out, tip it back, and in theory the bridge ends up in the same spot it would have been in an unstring, planar guitar. Cumpiano & Natelson curve the top but don’t perform any sort of tilting compensation. Then, just to make it really interesting, I’ve come across builders who curve the top but tilt the upper (smaller) bout of the guitar back, to change the overall angle at which the string intersects the top. This is the so-called elevated fingerboard design (this page by Howard Klepper describes his particular approach).

Here’s the last issue – some of these top geometries are much hard to execute than others for an amateur builder. Obviously, the flat plane is easiest. Next easiest would be the overall dome of Cumpiano & Natelson – the standard solution is to create a dished out work board that the top is pressed into when braces are glued on the underside. I’ve already taken the plunge and ordered two pre-made work boards with different degrees of curvature. My big problem is Bogdanovich’s approach – the combination of a curve and a tilt means that one has to (pretty laboriously) hand-shape some of the work board, and there’s an aspect of his neck angle that still doesn’t make 100% sense to me.

And that’s the final rub, my lightbulb moment – whatever I choose for a plan going forward, it has to make sense to me as a builder. I clearly don’t have all the answers, but I’m not a completely blank slate, either. To my eye, there are just too many tweaks that Bogdanovich has to make to his components (shaving a bit under the fingerboard, etc.). So I’m inclined to either go with the general curve of Cumpiano & Natelson (not compounded with a tilt), or punt entirely and use a purely planar design. Maybe someday I’ll come to understand the advantages of Bogdanovich’s lower bout tilt (which is exactly the opposite of the elevated fingerboard approach used by Klepper and others).

At this point I’ve reduced my parameter space to a single binary choice – planar or generally curved. I think I can live with that and move forward, holding the other parameters constant.

Committed to #002

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I built my first (and only) classical guitar during my senior year in college. I’ve been feeling the itch to tackle a major project lately, and playing some high end guitars at local shops inspired me to take a second crack at it (having presumably learned something since my last attempt).

Since my last build, the Internet happened. Now I have access to several luthier forums where amateur builders can trade tips and tricks. Several amateurs have started their own web sites where they meticulously document their project (I don’t plan on being one of them, though – the market is saturated with those photo essays, and I’m more interested in documenting the inner journey). One professional luthier – J. S. Bogdanovich – has published a book, DVD series, and most importantly, full size blueprints of his design (my annotation of his top appears above).

So I’ve pushed the button – my wood is acclimating to the local climate, and I’ve purchased some of the specialized tools needed (e.g.,  an electric bending iron). Most of the work will take place at The Sawdust Shop, although some of the detailed hand work could just as easily be done on my dining table.

I’m hopeful that this will also kick start another round of blogging. A recent Facebook post by an old college friend mentioned a mid-life career crisis, and I was shocked at how many of our mutual friends chimed in “me too.” There is something about approaching 50 that makes one (or at least, me) take stock of what I want the next few decades to look like. Working with my hands brings me to a state of flow that I find hard to achieve otherwise; we’ll see whether any useful insights come from this next project.

 

 

Baby steps… again

I came home tonight in a bit of a funk.  The rain was dripping from the spruce branches, and it was already dark outside. The music to Barrios’s La Catedral sat on my stand, neglected for months. But that first movement, played slowly, reminds me of the soundtrack one might hear in a movie, as the camera focuses on rain droplets trickling down a window pane. I pick up my guitar, fingers cramping into the upper frets for the first few bars. The high string cries in soprano, while thumb and finger pluck the harmonies. After 10 minutes my hands are spent after too many weeks of not playing, but it’s a start.

Use it or lose it – one of those universal lessons. It’s so easy to stop practicing something when other live events intrude – playing music, jumping a mountain bike. And the body, eager to conserve resources, begins to atrophy the neural-muscular network that enables these activities. One saving grace is that we never have to completely start over; the body retains echoes of memory, the fingers find their places without conscious thought. Yet, it’s frustrating to expect the experience to “flow,” and to have to stumble like a toddler learning to walk, brow furrowed in concentration as I remember how one foot goes in front of the other.

Blogging is another skill that atrophies with neglect; let’s see if I bring this back as a regular practice.

I’m a data scientist!

At a recent Cyberlearning Research Summit organized by some colleagues, Bill Finzer proposed that we think about the Data Sciences as a distinct educational goal. Briefly, the data sciences exist at the intersection of three domains: math & statistics, a substantive area of knowledge (economics, psychology, education, etc.), and “hacking” or the ability to construct algorithmic solutions to problems.

What Bill described was essentially my current professional life. It usually takes me a couple of minutes to describe what I do when I meet someone at a party (I don’t have a simple job descriptor like “tax lawyer”).  Now I can tell people “I’m a data scientist!” (Of course, they won’t know what that means, and it’ll take me two minutes to explain that, anyway).

Still, I’ve felt like I’ve assembled an odd hybrid of skills and interests in my professional life, and I’m not eager to part with any of them.  I’ll take the bit of external validation I got from watching this video.  :-)

I haven’t been blogging much over the past months, but I have a collection of ideas starting to backlog and will be writing more frequently in the near future.  Stay tuned.

Chasing the unknown

I had a small epiphany last weekend, and it shouldn’t have come as a surprise:  I really enjoy tackling problems that nobody has ever solved before.  That’s what led me into a career in research, and that excitement (and the mirror attribute of high uncertainty tolerance) was captured in this recent essay The Importance of Stupidity in Scientific Research.

The epiphany wasn’t so much remembering what gets me excited – it was how other challenges feel by comparison.  Lately I’ve been considering building another classical guitar project in the wood shop.  I built my last (and first) guitar while still in college 25 years ago.  Guitar building requires extraordinary patience and a high degree of exactitude in certain operations (namely the cutting of frets and placement of the bridge & saddle).  But the rewards are great – the home builder can take the time to fine-tune the sound board and use high quality woods that would normally be found in guitars retailing for several thousands of dollars.  The more I contemplate setting up my shop for instrument building, the more excited I get.

So here’s the epiphany – while there is a personal challenge in rising to the technical proficiency needed to execute another guitar, that problem has largely been “solved.”  Sure, the challenge is new to me, but there are plenty of people out there who know how to build a decent guitar. What I’d really like to do is branch out and explore alternatives to the standard design. Recently some luthiers have tinkered with using space-age composite materials in the sound board, and several now include sound ports on the side of the guitar near the neck, both as “monitors” for the player as well as to enhance the overall tonal palette.  Oh, and let’s not forget “fan fretted” guitars – these instruments look like they were built while the maker was staring into a fun-house mirror. All of these are innovations that solve particular problems of playability.

But… as anyone who has invested years in research will tell you, it takes a long time to become acquainted with a domain and develop that instinct of where the interesting problems (and solutions) lie. As the article cited above points out, most of the time you fail, but you get a little more insight into how to ask the question better, and which avenues might be more promising next time. And researchers benefit enormously from reading about the trials of their peers (I’d argue that we don’t publish enough about our failures – the community benefits from hearing those stories, too).

Will I ever know enough about instrument building to branch out into a promising innovation? It’s a daunting prospect, but then again, what else do I have but time? Bob Taylor in his book Guitar Lessons points out the virtues of getting an early start.  He regretted not planting a particular tree back when we wasn’t sure whether he’d be keeping his current house – had he planted the tree, it would have matured by now and he could be enjoying (literally) the fruits of his labor. Sometimes innovations are begun on a hunch and take 10 years to reach fruition. But if I don’t begin, I’ll never know.

Stay tuned for a progress update as the days grow shorter and I start spending more evening time at the work bench.

Main power restored

That line – “main power restored” – always seemed to mark the turning point of a Star Trek episode. Scotty or Giordi or Chief O’Brien would work their magic, the captain would receive word in the nick of time, and the crew would begin to claw its way out of whatever trouble they were in.  The situation would flip from dire hopelessness to a promising light at the end of the tunnel.

That is what recovering from obstructive sleep apnea (OSA) feels like.

After a brief false start, I’ve now been on CPAP therapy for about a week.  It truly feels like a second chance at life. I was lapsing into depression, had stopped even trying to exercise after work, could barely drag myself out of bed in the morning… basically, life was a drag. After a week my body is starting to feel like its old self (I put in a couple of intense biking days last weekend), and the rest of my mind/spirit is sorting itself out.  I’m not sure how long full healing will take, but I’m feeling very patient now that treatment is at hand.

People ask how long I’ve been suffering the effects of OSA, and it’s difficult to pinpoint. My best guess is that it started setting over the winter, but the effects can be gradual and cumulative, so it might have been even earlier.  You’d have to ask the people around me – when did I start acting like the walking dead?  ;-)

My enthusiasm for work (both small-w work and the Work of Life) is returning, but I’m still feeling a bit out of sorts. I hope to return to updating this blog on a more regular basis soon, but again, am remaining patient.

It feels good to be back among the living!

Chronic sleep deprivation. Fuzzy-headedness.  Not being able to recall names or facts or those words on the tip of the tongue.  Craving a nap at all hours of the day, coming home after work and feeling like I’ve already been up past midnight. I’ve given up on evening bike rides or practicing music or anything else that requires concentration. One silver lining is that I’m catching up on reading (which I usually don’t do much of when the sun is still shining outside).

I took the home sleep test last week (wired up to a few sensors that all fed into a wrist-watch data recorder), but will probably have to wait another week for results, and then more time to see a doc and get the next steps of treatment rolling.  For sanity’s sake I’ve set July 1 as the day when I’ll be getting a proper night’s sleep again.  I can suck anything up for another month.

I miss writing, and playing music, and having that inner spark that smiles at life. Right now I feel like I’m just existing.  Have to remember that this too shall pass…

Till next time!

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