Posted on May 5, 2021May 22, 2025 by Dale Phillips Rule of 18 vs Rule of 17.817 Rule of 18 vs Rule of 17.817 by James Buckland Published online by Guild of American Luthiers, May 2021 At the 2014 GAL Convention, I conducted a lecture/presentation entitled “Mythbusting the Rule of 18”. The intent was to explore, and possibly refute, some of the misconceptions concerning the Rule of 18. As conventional wisdom goes, the old rule of 18 was, at best, an approximation on how to calculate fret positions. In truth, it is a better formula than it’s generally given credit. Unlike many historical predecessors, such as Juan Bermudo’s approaches using Pythagorean ratios, the Rule of 18 is based on the concept of equal temperament, probably before the term existed in the vernacular. But, most importantly, Rule of 18 includes its own compensation factor in regard to the position of the bridge. Most commonly used today, is the square root of two, or 17.817, as the factor with which to divide string length. The result is believed by many to be more accurate based on the fact that it places the 12th fret at the exact midpoint of the vibrating string length. Since we all know that the 12th fret is the octave above the open string, it makes common sense that it should be in the exact middle of the vibrating string length. However, it is also well known that a guitar built this way will play out of tune, with intonation problems increasing the further one plays up the neck. The solution is to compensate by increasing the string length slightly, generally by moving the bridge position. But, by how much? Examine enough classical guitars fretted with a “650MM scale”, and you’ll find the actual vibrating string length is generally longer, by 2 to 4MM. There doesn’t seem to be much more than vague empirical evidence in just how much to use. In other words, a little bit of “Kentucky Windage” is considered good enough. (For you non-shooters, Kentucky Windage is the practice of adjusting your aim to compensate for wind, without the use of any mechanical features on the weapon.) To me, this is a seemingly strange attitude considering the derision generally cast upon the good old Rule of 18. Maybe “17.817” just sounds more precise than saying “18”? So, here’s a practical example of the similarity between the two approaches when bridge compensation is taken into account. I began by calculating a fret scale for a 565MM string length (as might be used for the terz guitar in GAL Instrument Plan 80) using the “Rule of 18”. The results are shown in Table 1. Then, I took the resulting value for the distance between the nut and 12th fret (280.446MM) and multiplied it by two. Next, the resulting value (560.892MM) was used to calculate a fret scale using the contemporary 17.817 factor. The calculations are shown in Table 2. Table 1 Table 2 Notice the outcome! Although the vibrating string lengths are different (560.892MM vs 565MM) the results for the fret placements are generally from about a tenth of a millimeter at the first fret, approaching one millimeter towards the higher frets. To put that into context, consider real world variabilities typically introduced during fretboard fabrication, from layout, to slot cutting, to fret dressing and crowning. Or, compare this to the guesstimate made by many luthiers when choosing bridge placement compensation. But, what about the issue of the difference in string lengths? Well, as stated above, most luthiers know that to satisfactorily use the 17.817 approach, one must add their own bridge compensation (hence the “Kentucky Windage” analogy). So, if you add 2-4MM bridge compensation to the 560.892MM string length, you can see that resulting vibrating string length gets pretty close to 565MM! But, there is another way of looking at the data that shows even more surprising results. The tables of values reflect the string length from the nut to the respective fret(s). What about the other length of the string, the vibrating string length from the fret to the bridge, the part of the string we actually hear? The greatest discrepancy between the two tables is found with the 24th fret. In the case of the Rule of 18, the distance from the 24th fret to the bridge is 143.312MM. In the case of the 17.817 factor, the distance is 140.221MM. Add 2MM compensation, and the value increases to 142.221MM. Add 3MM compensation, and the value increases to 143.221MM. Add 4MM compensation, and the value increases to 144.221MM. In other words, the discrepancy between fret placement values calculated with either the Rule of 18 or the Rule of 17.817 is less than the variables introduced through the subjective choice of bridge compensation which must be made when using the latter rule. When comparing the other fret values, the difference between the two table of calculations is even less. Does the use of the Rule of 18 vs 17.817 result in a significantly discernible difference, given other contributing factors? Maybe the old guys knew more than they’ve been given credit? ◆ Thanks to Nitin Arora for writing the fret calculating program “Eighteen Rules” found on his website. At the 2014 GAL Convention, author James Buckland also demonstrated the use of proportional dividers for marking fret positions. Set the big end of the dividers to the scale length. The little end now shows you the distance from the nut to the first fret. Re-set the long end to the distance form the first fret to the bridge. You are off and running. Ron Fernandez tries it. All photos by Tom Harper.
Posted on April 7, 2021May 16, 2025 by Dale Phillips In Search of the Perfect Cone In Search of the Perfect Cone by Tim Earls Originally published in American Lutherie #30, 1991 and Big Red Book of American Lutherie Volume Three, 2004 I think I've got it. I have here an untested method of finding the exact, correct multiple radius for any given fingerboard using simple barnyard geometry and no computer. Danny Rauen and Tim Olsen wrote interesting articles on multiradiused, or conical, fretboards in American Lutherie #8. (See Big Red Book of American Lutherie Volume One, p. 298.) Great stuff! Let’s talk about cones for a moment. A cone is a tapered cylinder extended up to a point. Or a tapered cylinder is a cone with its point lopped off, take your pick. You knew that. Bear with me. In a two-dimensional view, this looks like Fig. 1. The circular base of the cone is seen as a horizontal line, since you’re looking at its edge. The height of the cone, what I call “true length” is measured on the centerline from base to point. The side line of the cone I call “true distance.” The radius at any spot on this cone can be found by drawing a horizontal line from the centerline to the true distance line and measuring it. You probably knew that too. Become A Member to Continue Reading This Article This article is part of our premium web content offered to Guild members. To view this and other web articles, join the Guild of American Luthiers. Members also receive 4 annual issues of American Lutherie and get discounts on products. For details, visit the membership page. If you are already a member, login for access or contact us to setup your account.
Posted on June 22, 2020May 22, 2025 by Dale Phillips Brazilian Guitar Makers Brazilian Guitarmakers by Roberto Gomes Originally published in American Lutherie #33, 1993 and Big Red Book of American Lutherie Volume Three, 2004 The guitar has been the main musical instrument in Brazil since it was brought by the Portuguese colonizers centuries ago. In those times, Baroque guitars were the most common string instruments. They had five courses of gut or wire strings. Since then it hasn’t changed much, as we can see in the “Brazilian viola” which is used for a kind of Brazilian country music called musica sertaneja (countryside music). The shape of the soundbox of this viola today resembles more a small classic guitar. Unfortunately there are very few records of those times, making it difficult to make a better study of those guitars and their makers. It’s known that most of the instruments were made in Portugal, Italy, and France. The first decade of this century brought three immigrant families from Italy: the Gianninis, the DiGiorgios, and the DelVecchios. These families were luthiers in their country of origin and later they founded the main Brazilian guitar factories which became the backbone of Brazilian-made guitars for nearly eighty years. They made mostly classic guitars and some violins, along with Brazilian violas. They also made mandolins, first with vaulted backs like lutes and later with flat backs, which are used to play choro music. Become A Member to Continue Reading This Article This article is part of our premium web content offered to Guild members. To view this and other web articles, join the Guild of American Luthiers. Members also receive 4 annual issues of American Lutherie and get discounts on products. For details, visit the membership page. If you are already a member, login for access or contact us to setup your account.
Posted on March 12, 2020May 23, 2025 by Dale Phillips It’s a Kabosy It’s a Kabosy by Paul Hostetter Originally published in American Lutherie #35, 1993 and Big Red Book of American Lutherie Volume Three, 2004 Madagascar is a huge island about the size of Washington, Oregon, and California combined. Situated 180° around the earth in any direction from these three states, this single-language country lies in the Indian Ocean off the east coast of Africa. I shall probably recount more about music from Madagascar than about construction details of this delightful little instrument for this simple reason: the kabosy’s musical raison d’être exceeds in interest the technical complexity of the instrument itself. Nonetheless, it’s worth a long look because, like most things Malagasy, there’s nothing quite like it anywhere else. Despite obvious superficial appearances, Malagasy culture is not particularly African at all, but is an extraordinary mélange of Polynesian, Southeast Asian, Arabic, African, and, more recently, European influences. (Madagascar was a French colony until 1972.) Like the legendary flora and fauna of that far-away island, Malagasy culture and music bear but a passing resemblance to culture elsewhere on the planet. Fortunately there are numerous recordings now available of just about every stripe of this remarkable musical culture. A discography follows. Become A Member to Continue Reading This Article This article is part of our premium web content offered to Guild members. To view this and other web articles, join the Guild of American Luthiers. Members also receive 4 annual issues of American Lutherie and get discounts on products. For details, visit the membership page. If you are already a member, login for access or contact us to setup your account.
Posted on August 23, 2019May 23, 2025 by Dale Phillips Intonation in the Real World Intonation in the Real World by Mike Doolin from his 2006 GAL Convention lecture previously published in American Lutherie #92, 2007 Getting guitars to play in tune has been a major topic of interest for many years, both for guitar players and guitar makers, and it has been a major source of frustration as well. During our current “Golden Age of Lutherie” the bar has been raised for standards of craft, playability, and tonal quality, as players have become more sophisticated in their expectations and builders have become better educated and more demanding of their own work. Expectations for accurate intonation have come along with all that: it’s no longer acceptable for a guitar to only play in tune for the first five frets, or in a few keys. Modern players are using the whole neck, exploring extended harmonies, and playing in ensembles with other instruments. They are looking for instruments that play in tune with themselves and with the rest of the musical world. It turns out that guitar intonation is a huge can of worms, because it is really two topics: ▶ What does it mean to be “in tune?” ▶ How do I make a guitar do that? Become A Member to Continue Reading This Article This article is part of our premium web content offered to Guild members. To view this and other web articles, join the Guild of American Luthiers. Members also receive 4 annual issues of American Lutherie and get discounts on products. For details, visit the membership page. If you are already a member, login for access or contact us to setup your account.
