A summing-up by the Original Poster.
As I have accomplished what I set out to do when I started these two threads (one on the Delcamp English forum, and one in the ERG forum at sevenstring.org), and as I feel that it is very unlikely that I will go any farther with any radical guitar design process myself, I feel that it is time to sum up the results of my researches and to thank everyone who has helped me in the process. It has been interesting to observe that the Delcamp forum has generally been quite conservative, as reflecting its classical orientation, and the sevenstring.org forum has been generally encouraging of more radical ideas, reflecting its orientation toward electric instruments and eclectic modern musical styles.
The final result of this three year process is a 9-string fanned fret classical guitar tuned
F#1 - B1 - E2 - A2 - D3 - G3 - B3 - E4 - A4.
This is, of course, the standard tuning of the six string guitar with one additional treble string and two additional bass strings.
The longest string (F#1) measures 72 centimeters.
The shortest string (A4) measures 60 centimeters.
The "right-angle" fret is the third. (On my 9-string prototype of 2013, the right-angle fret was #5, and this resulted in difficulty with first-position work. The third-fret right-angle is far better. The increase in the angle of the upper frets is not significant.)
The string spacing is 9mm at the nut (left-hand) end, and 11mm at the bridge (right-hand) end.
It has four 20mm piezo discs wired together into a single jack and glued to the underside of the top. This pickup combination was made for me by JJB electronics. It is slightly bass-heavy, easily corrected with EQ.
Tuners: Schertler. These are the only classical guitar tuners I have found that are not 3-on-a-plate and come individually. I had to buy two complete sets anyway. They have an 18:1 ratio and are very sweet tuners.
I have abandoned fluorocarbon strings and am using rectified nylon. The high A4 is now a D'Addario .021". The low F@1 is a wound .075" - Savarez or La Bella, I don't remember. The La Bella lute strings, sold by Strings by Mail as single strings, are a blessing, because a normal guitar D string is not long enough to reach the end of the peg head.
With these specifications my design can be reproduced. The details of the specific build, realized in February and March 2016 by Paracho luthier Salvador Castillo, will be discussed below. I am very happy with the design and am playing the new guitar exclusively, not without some physical problems as mentioned below.
In 2012 I had Castillo build me a straight fret seven-string guitar with string length 65 centimeters, tuned as a standard six-string plus a low B1. Although this was a beautiful instrument and I played it for several years, two further considerations arose. (1) It appeared to me that the low B string was not long enough at 65 centimeters. (2) I began to desire an additional treble string, an A4, but for this purpose, 65 c. was clearly too long: all available strings break at that length and pitch.
Researching the question, I looked at the "Brahms Guitar" design played by Paul Galbraith. I could not find at that time any specific information on the critical dimensions: length of longest and shortest strings, number of the "right-angle" fret, and fingerboard width (which is to say, string spacing). By the time I had found this information, the more radical designs of the fanned-fret electric guitars being shared on the sevenstring.org forum - which have up to eleven strings - had led me to consider a 9-string design instead.
For the reader who is looking for specs on the "Brahms Guitar", these seem to be the usual norm (if there is one) based on Galbraith's design:
Longest String (B1) 65 centimeters.
Shortest String (A4) 61.5 centimeters.
Right-angle Fret: Number 7 or 8.
String Spacing: I assume 9 mm at the nut. (This could well be a personal choice, as many players prefer narrower spacings; some classical guitars have 8 mm or 8.5 mm spacing at the nut. However, some players, myself included, have made the mistake of choosing an impractically narrow spacing, as I did on the 2013 9-string prototype (7.5mm at nut.) Electric guitars are often very much narrower than classical guitars.)
These specs of Galbraith's show a concern with minimizing the width of the fan, at the expense of the tone quality of the "added" strings B1 and A4. My own recommendation for a fanned fret 8-string, based on my own experiences now with a number of ERGs (3 7-strings and 2 9-strings), would be to make the A4 at 60 centimeters and the B1 at 68 centimeters. This will much improve the quality of those added strings at the expense of making the fan more than twice as wide (but only 2/3 as wide as my new 9-string). The appropriate location of the "right-angle" fret should then be determined empirically through making multiple drawings, cutting them out and putting them on cardboard mockups. Probably the fifth fret would be fine.
The advantages of my nine-string design are:
(1) The upper six string are tuned as a Renaissance lute in A. This gives me direct access to the entire lute literature of the sixteenth century on my regular instrument. The range, although not the tuning, of these upper six strings is also the same as the Mexican Requinto, allowing me to closely imitate that instrument also, although with slightly different chord forms under the fingers.
(2) The standard six-string tuning is preserved intact, so that all legacy repertory is portable without modifications, except for some occasional intonation issues which mandate moving some very high passages to the upper (lute) string set, requiring re-fingering.
(3) With the addition of a low B1 as on the Brahms guitar or on my 2012 7-string, a guitar has a nominal range from B1 to C6 (with 20 frets) which is the same as the 4-octave keyboard which accomodates most of the keyboard music of J. S. Bach. However, on 7- or 8-string instruments, the low register is not accessible at the same time as the high register. On the contrary, with the 9-string, the desirable low bass notes around C2 are moved up to the middle of the fingerboard, and the desirable high register in the 5th octave is moved down five frets, requiring less crawling around above the 12th fret. The cutaway, however, makes the uppermost register very accessible also. The extreme angles of the upper frets are not a disadvantage and in fact are better ergonomically (whereas an extreme angle at the other end near the nut is a decided disadvantage, based on my experience with the 2013 9-string prototype).
(4) The addition of two extra bass strings gives me a full bass register. The four strings F#1 B1 E2 A2 essentially are, together, a four-string bass tuned one whole step higher than normal. This allows me to use my regular instrument to play bass when I want to. The low F#1 played open remains a little bit unfocused in sound. I conclude that to make that low a pitch resonate is just below the capacity of a normal-sized classical guitar body. However, the note G1 is better, and the note A1 is the equal of all of the higher notes. Playing the F#1 string higher on the neck, it is perfectly and beautifully functional, and has none of the unpleasant clickiness that the F#1 on the 2013 prototype exhibited at 68 centimeters length. It does not appear to me to be worth it to build another guitar with the F#1 at 75 c., although I have thought about it, because of the following issue:
Apologies for whining, but for the sake of sharing the complete info, here it is. On receiving the instrument around the first of April 2016, I began to practice long hours. Within two months I had abused my left wrist thoroughly by attempting many full barres and stretched-out positions (particularly in my study of the Bach two-part Inventions), which translated then into a chronic sore elbow which has persisted. In June I was forced to reduce my practice schedule to only a very few hours a week in order to be able to maintain my 10-hour-a-week performance schedule, due to pain in my left elbow and wrist. I have been too stubborn to go back to a smaller instrument, as I really like playing this one. I am 60 years old, and a younger player might be able to adapt more easily. Naturally I don't admit defeat and have high hopes that I will overcome this obstacle in time, with care and patience. I have had many episodes of tendonitis, but mostly with the right hand in the past, seldom with the left.
This difficulty met another: the new guitar was developing a dip-and-bulge around the bridge. I had ordered a variety of strings (three different thicknesses for each of the nine) based around a nominal tension of 7 kilograms per string. Castillo, in my necessary absence, chose from the strings I had sent him, and chose those that made the guitar sound like one of the flamenco guitars which are his regular stock in trade, and in fact complained that a couple of the strings could be higher tension yet. Yes, it sounded great, and when I first picked it up, it seemed quite easy to play - until I had been at it a couple of months. In the interest of sparing both myself and the guitar, I have recently replaced the strings with thinner ones at 6 kilos of tension. (I have ordered more thinner strings and intend to try 5 kilos next, depending on how things go.) The bulge-and-dip flattened out considerably when I put the thinner strings on, to my relief, and I find it easier to play. This move to thinner strings requires that I be content with less projection - in theory, but the fact is I haven't really noticed much difference except the greater ease of playing. Amplified, this is not a problem anyway. Also, ornaments are easier.
When I had Castillo build the 9-string prototype in 2013, we were both aware that there are many 10-strings around (of the Yepes pattern - it's a popular design with the university students here) which have developed structural problems due to the extra string tension.The 2013 prototype was perhaps overbuilt, and it never quite sparkled. With the new 2016 build, it appears that it may be underbuilt. Viewed through the soundport, the spruce top is quite translucent and looks scarily thin. The lattice bracing is gossamer, and does not extend all the way to the sides, so the entire top seems to float. However, it sounded fabulous from the first time I picked it up, and continues to sound better. I would not trade this beautiful sound for mere sturdiness, even if it is necessary to reduce the string tension more. The original strings at 7 kilos tension made a total of 63 kilos (that's like 140 pounds) of tension, as opposed to about 42k for a six string. At 6 kilos the total is reduced to 54. At five kilos tension it would be down to 45k total, not much more than a six string. For many years while I played six string, I went for that bright, digital, naily, high tension sound that had become the norm for the 20th century classical guitar, and I was able to do that with the seven string, too, but with nine, something has to give, chiefly my hand muscles, and so the situation requires reevaluation. in order to accomplish the musical results.
The Cocobolo back has a big X-brace on it. You will appreciate that the line between overbuilding and underbuilding is a complete crapshoot with such an experimental design. In this case, the displaced soundhole (placed away in the bass side of the upper bout in order to free up some room for the top to vibrate around the A4 end of the bridge) also made an unpredictable design variable. At any rate, I am very happy with the sound, and as it was impossible for me to physically continue playing it with heavy gauge strings, it appears that going with lighter gauge strings is a happy compromise for both me and the guitar.
So once again, I want to thank all of the interested people who have helped me with advice, encouragement, and even cash, during the three-year-plus process of designing this guitar and having it built. It has been quite an experience and worth it all the way. It feels like a summing up of my lifetime as a musician. Hope I get another couple of decades to play it! I also hope that some young players will pick up the design and run with it.
The promised CD is on ice for a few months at least.
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Last edited by jack_cat on Fri Aug 26, 2016 2:10 pm, edited 2 times in total.