12-String Classical

Table of Contents

Introduction
The Concept
The Sound
The Music
Roots
Construction: String Tension and Guitar Structure
Construction: String Separation and Neck Width
Construction: The Head and the Tuners
Playing Considerations
Some Parting Thoughts

For a printable version of this document (16 pages in PDF format), please email me.

Introduction

We often hear about classical guitars with 7, 8, 9, 10, 11, or more single strings - but not with double courses.  Some years ago, I wondered what it would be like to play and hear a 6-course, 12-string classical guitar.  In my mind, I could imagine a rich, mellow sound quality.  When I eventually built one, the guitar exceeded my expectations.  Here I'll share with you some words on the concept and sound, some thoughts on related history, the key construction details including measurements, and some playing considerations. 

One of the key features of this guitar (as I built it, but only an alternative) is a new design for mounting the tuning machines - a head / subhead arrangement - see the construction section for details.

 
The 12-string classical is accessible to the player because it looks and feels much like a 6-string guitar and is tuned the same.  It's accessible to any luthier because building it is just a few variations away from building any classical guitar.  If you're a guitar player and you want to play one, you can ask any luthier to build you one.

The Concept

My concept in building this instrument was to create one in the Torres style that looked like, felt like, played like, and sounded like a classical guitar, but with the added sound texture provided by a second set of strings tuned in unison.  It was not intended to be a conventional 12-string guitar adapted for nylon strings; nor was it intended to be a period instrument or to be played like one.  To share some of the sound qualities of such instruments, though - a definitely yes.

I've been asked why I use unison tuning, and not octave tuning for the lower two courses.  The answer is that octave tuning, as it existed on baroque and post-baroque guitars (referred to as bourdons), and as it exists on 12-string guitars and some other double-and triple-coursed instruments today, is primarily of advantage for strummed music.  The classical style of playing uses relatively little strumming.  I want the intended note to sound, not the same note an octave away.

In the same vein, why does the top course (the chanterelle) have two strings, not just one as with baroque guitars?   Our forefathers faced an intonation problem because a doubled top course, i.e. the course most important to the melody, did not work too well with gut strings.  Due to their unequal dimensions and unequal stretching, a pair of gut strings rarely played in tune with each other all the way up the fingerboard.  Therefore single-string chanterelles were preferable.  In the nylon world, the problem is virtually eliminated.  On my instrument, the doubled chanterelle actually provides a key element of the sound quality, and I can't imagine going without it.
 
The Sound

The 12-string classical guitar provides a sound texture which goes beyond that of the 6-string guitar.  There is a richness to it which is suggestive of a harpsichord, of historical double-coursed instruments, and of modern-day folk instruments.   If you can imagine the warmth of nylon combined with the shimmering sound of a 12-string, but without the sustain of steel, you've now got the sound in your mind. 

There are three things that are happening in the production of the textured sound:
  • First, the finger or thumb will often strike two strings instead of one, transferring up to twice as much energy through the saddle and bridge to the soundboard, but with a very slight time delay between the attack on the first string and that on the second. 
  • Secondly, because the two strings in each pair will be ever so slightly out of tune with each other, there is a dissonance (a shimmering or beating effect) produced, not only at the fundamental, but also at any audible harmonic overtones. 
  • Thirdly, any strings not played or muted become sympathetic strings, and through the energy of the bridge and saddle are activated to vibrate at their fundamental notes and at their harmonic overtones, and again this vibration is transferred to the soundboard in dissonance.   
I use the word "dissonance" in this narrative in a different context from its normal musical definition.  The term "inharmonicity" is perhaps better, although it too has a more specific meaning in relation to string vibration.

Usually, very small differences in the tuning and intonation of the string pairs will produce the desired effect.  I like to deliberately adjust the tuning of six of the strings by one or two beats (cycles) per second to accentuate the dissonance, instead of leaving it to chance and error.  (Interestingly, tremolo harmonicas are constructed with two sets of reeds, slightly out of tune with each other, to produce this kind of rich sound).  Since the fingers, when they strike one string only, are most likely to strike the first string in the pair, and the thumb, which is coming from the opposite direction, is most likely to strike the second, what seems to work is to lower the second E', B, and G string and the first D, A, and E string.  That way the six strings most likely to be plucked remain in tune with each other at A=440, and the other six strings although slightly sharp (or flat) are themselves also in tune with each other, but a beat or two lower.

The rich texture doesn't come free; the guitarist needs to use appropriate playing technique to bring it out (see the section below on Playing Considerations).  That said, be aware that because technique is more difficult, the instrument is likely to play somewhat noisily, as did guitars in the baroque era.

The irony is that we have been conditioned for the past two centuries of classical guitar to revere consistently clear articulation.  This frame of mind goes back at least as far as Aguado, who in his 1843 guitar method focused on "producing full, rounded, pure, and agreeable sounds".  Concert and recording artists over the last century have of course continued this focus.  An exception is with flamenco, in which harsh sounds are recognized to add to the excitement of the performance.  And the occasional noise seems to add to the character of the 12-string classical - simply put, it makes it more gutsy.

There are some music samples in the following section, but to start with the basics, here is a C-scale on the 12-String (played with the rest stroke):
Audio Sample 1

For comparison, here is the same thing played on the 6-String (#002 Cataluña), a cedar-topped guitar which you can see on the Instruments page:
Audio Sample 2

Finally, here are some chromatic runs on the 12-string, played on the top four strings (with the rest stroke):
Audio Sample 3

The Music

There's no reason why the instrument can't be played with any type of music.  At the 2011 G.A.L. convention, I heard a lot of different styles of music played on it, including some classical, flamenco, Mexican, folk, country, and jazz.
 
My style of playing is classical guitar, and I find baroque and renaissance music to be most suited.  This might have something to do with the chordal structure in such music, or it might stem from association with the sound of the harpsichord or of other double-coursed string instruments of the periods.
 
You can play anything on the 12-string classical, with no change to your left- or right-hand fingering, but some pieces simply won't sound as good as on a 6-string.  For example, Lagrima might be just passable, but Adelita is a definite no-no.  Rapid pieces might not work too well because there might not be enough time for the textured notes to ring before their time is up.

On the other hand, for pieces that do work well on the instrument, there is the potential of getting a sound that will make a 6-string pale in comparison.

Here are some audio samples to help you appreciate the sound of the instrument.  I offer them with the disclaimer that I'm not a very good player.  Also, I've been very much out of practice over the past few months, and I don't feel I used enough of the "appropriate playing technique" referred to in the above paragraph during the recordings.  Still, you will hear much of the sound quality.

Here first, is Robert de Visée's Prélude & Allemande from the Suite in D minor, first played on the 12-String (with fade), and then for comparison on the 6-String:

Here is an arrangement of Handel's Harmonious Blacksmith, first played on the 12-String, and then for comparison on the 6-String.  When I play this, the textural difference sounds even more pronounced than when I hear the recording:
Audio Sample 6
Audio Sample 7

Finally, here's another piece I have fun with on the 12-String - an Irish Jig, accompanied by my wife Shirley on Ukulele.  I find that the 12-String gives this piece some texture, perhaps suggestive of an accordion or harmonica or fiddle - a quality that is lacking when I use a 6-String:

Other pieces that I've found work very well include the Bourrée from Bach's first lute suite, Greensleeves, and some (but not all) Sor pieces.

Roots

The 12-string classical has varied roots.  My own inspiration was the merging of the sound qualities of the 6-string classical guitar with those of the steel-stringed 12-string.  But the 12-string classical is very similar, if not identical to the Guitarra Doble, an obscure Mexican instrument, and can claim some ancestry from the Vihuela de Mano of the Renaissance, and the 6-Course "Transitional" Guitar of the Post-Baroque period.

The Steel-Stringed 12-String Guitar

This instrument, familiar to all of us in blues, folk, and rock music, was itself derived from earlier double-coursed guitars either of European origin or of Mexican origin.  It was the 12-string of Maine folk singer Gordon Bok in particular that inspired me.  His 12-string, co-developed by Sam Tibbets, Bok himself, and luthier Nick Apollonio using heavy gauges and a thin structure, was intended to reproduce the sound of Bok's mother's nylon-string guitar.
  

The Guitarra Doble

When I exhibited my instrument at the 2011 G.A.L. convention, I was informed by luthiers Richard Bruné and Elias Perez that a similar instrument exists in Mexico, and Elias was able to pinpoint it to the Veracruz area.  That instrument is the Guitarra Doble, described by the Atlas of Plucked Instruments thus: "the Mexican 12-string guitar, with all strings double - and in unison (so not like our 12-string guitar, with strings in octaves).  It seems not much in use anymore."
 

The Vihuela de Mano

The Vihuela de Mano was a guitar-like instrument popular in Iberia during the Renaissance with six courses each with a pair of gut strings, was tuned much like a modern guitar, but with the third string tuned a semitone lower.
 
The vihuela de mano had lost its popularity by the end of the 16th Century, and therefore historically there is a quantum leap through time to get from that instrument to the one I built.  The vihuela was succeeded by the 5-course guitar, which later evolved into the 6-course "transitional" guitar, which in turn shortly afterwards begat our familiar 6-string.

The Post-Baroque 6-Course Transitional Guitar

Using modern-day guitar tuning, the 6-course "transitional" guitar was quite popular in the post-Baroque period particularly in Spain, but it fell out of favour in the late 1700's to early 1800's as players' preferences shifted to the 6-string guitar.  The 6-course guitars generally used octave tuning for the lower courses, although one source indicates that they were tuned in unison (I suspect it was really up to the owner / player).  The chanterelle or upper course was sometimes a single-string.  So some were 12-string, and some were 11-string.

There is some interesting history, beyond the scope of this document, as to why the 6-course guitar evolved out of the guitars of the Baroque period, why it fell out of favour in the late 1700's and early 1800's, and why it did not survive as an alternative type of guitar in the world of what we today call "classical" guitar.  But what is relevant is that there was still some 6-course guitarmaking going on in Spain as late as the 1840's, and many of these instruments survived as playable instruments into and beyond the Torres era.

What if a player or aficionado had commissioned Antonio de Torres to build a 6-course guitar?  No doubt he would have introduced the larger soundbox, as he did with the 6-string, to do justice to the 6th course.  And no doubt he would have applied the saddled tie-block bridge.  Surviving instruments of this type would eventually have become sought after.  José Romanillos would have catalogued and described them in his book on Torres and his instruments.  They would have been copied in detail by builders of authentic period reproductions.  Luthiers to this day might occasionally still be making 6-course guitars for the classical guitar market.

Two other developments since Torres' day would probably make the 6-course guitar a more viable instrument today than it was in its era.  The first is the abundant transcription of baroque music for guitar which took place in the 20th century, as baroque music was rediscovered and once more became popular.  The second was the advent of nylon strings, solving the intonation problem which existed with pairs of gut strings.


More Recently

Whatever its similarities to other ancient or newer double-coursed instruments, I'm not the first to make a nylon 12-string in the modern era, as I found out.  Luthiers Jeffrey Elliott and Cyndy Burton made a nylon 12-string for Leo Kottke in the late 1970's, and Cyndy Burton made another for Ralph Towner (as a practice instrument) a few years later.  David Freeman of Timeless Instruments tells me that a student of his also made one.  I've also heard that in the opening track of Jimi Hendrix's album "Blues", Hendrix is playing a 12-string nylon guitar.  And I expect that there have been a number of other one-off instruments of this type made by other guitarmakers over the years. 

My slant on it appears to be different in the sense that my underlying motive is the playing of guitar music using classical technique (be it Bach, Beatles arrangements, or something else - whatever works).  And if you like, the head design is unique (see below).

Construction: String Tension and Guitar Structure

The 12-string classical (as I made it) involves only a few minor deviations from the measurements and processes used to produce any Spanish guitar. Any soundbox outline and depth, bracing pattern, neck dimensions, and head design can be used.

The first consideration is the internal structure.  If we double the string tension by adding the second set of strings, what do we have to do to the structure of the instrument to support that? 

First, the soundboard structure has to be stiffened accordingly.  For my instrument, I applied the Cube Rule, a structural engineering principle which states that the strength of a beam is proportional to the cube of its thickness.  So to double the stiffness, we need to make the soundboard and bracing thicker by a factor which, when we cube it, will roughly equal a factor of 2. In my instrument, the soundboard is 25% thicker than I would otherwise have made it, and the fan bracing is 25% taller.  (1.25 * 1.25 * 1.25 = 1.95 which is approximately a factor of 2).  The soundboard in is 2.5mm. (0.10") thick on average.

Secondly, I used a bridge with a larger dimension front-to-back, 35mm, as compared to other guitars which are often around 20 - 25mm.  This allowed a larger gluing surface.  For added security, I inserted three short dowels in the saddle slot down through the soundboard and into the bridgeplate.  The 35mm dimension also allowed a significantly larger tie block, and combined with the string holes in the tie block being bored in two tiers, this reduced the likelihood of the tie block fracturing due to string tension.

I used the conventional Spanish slotted neck joint and scarfed head joint, confident that there was adequate strength in these to handle the additional string tension.  But I did do a few other things to be safe: a carbon fibre bar in the neck, a backplate on the head, a relatively hefty bridgeplate, and a fourth back bar.  And perhaps it helps that the African Satinwood I used is dense and stiff.

In reality, the string tension in my instrument is not double that of a typical 6-string classical, but less for two reasons.  First, I use normal tension strings, in order to reduce the pull on the bridge and in order to increase playability.  Secondly, those strings are D'Addario Pro Arté Normal Tension EJ45's, which I understand have about 10% less tension than other normal tension strings. 

Combined with the fact that most good guitars are already overbuilt, my plan for the next 12-string classical is to shoot for a tension factor of somewhere between 1.5 and 1.6, rather than 2.0.  Applying the cube rule, that will mean that the soundboard thickness and brace heights will have to be about 1.15 times what I might otherwise have made them.  What I may actually do however, is to rely more on the increased height of the bracing, and less on the thickness of the soundboard, in order to come up with a lighter, more responsive soundboard structure.

Construction: String Separation and Neck Width

This area is one of trade-offs.  If we provide a lot of space between the two strings in a pair, we reduce the chance of string collisions.  If we provide a lot of space between string pairs, we reduce the chance of the player's fouling the strings (accidentally sounding or muting a string in an adjacent course).  If we do either one of these, it affects the other, or otherwise it affects the neck width.  If we make the neck wider, we alleviate these problems, but we also make playing more difficult (particularly barrés).

I first approached this question by blowing up a picture of a baroque guitar in American Lutherie #19 (the "Marie Antoinette" guitar) to full scale and measuring the string separation.  Not quite satisfied, I built the prototype 12-string with a significantly wider neck, more space between strings in a course, and more space between courses.  It was quite playable, albeit with a tinny sound quality, but I came around to thinking that considering my design goal, the primary consideration was really to have a neck width with a familiar shape and feel.   Going this way would result in string spacing something like that of Baroque guitars.  If Marie could handle it, so could I.

Above: a little diversion.  This is the sad-looking prototype, after the bridge exploded due to the increased string tension and a check in the walnut used to make the bridge.  (This resulted in my redesigning the bridge).  You may be able to notice the increased neck width.  Other features: plywood body with screw-on plywood soundboard, hand-drawn rosette, subhead, bolt-on neck, screw-on bridge, and popsicle stick saddle. 

And so in my instrument, the neck width is 51.5mm at the nut, 62.0mm at the 12th fret.  At the nut, the separation within a string pair is 2.3mm for the high e-course, and working down for the other five courses, 2.5, 2.7, 3.2, 3.2, and 3.2mm.  The space between courses, starting between the e-course to b-course is 4.7 mm, and working down from there, 4.9, 5.0, 5.1, and 5.2mm.  There is about 4.5mm between the sides of the neck and the closest strings, at the nut end.  (These numbers add up to 51.0 due to rounding errors).

This arrangement is perhaps the optimum, but I've been considering increasing the neck width for the next 12-string classical by a small degree - definitely not more than 5mm.

Construction: The Head and the Tuners

There are a few options for accommodating 12 classical tuners on a classical guitar head.  One is to use friction pegs, as in many traditional-looking flamenco guitars.  Another is to use twelve individual tuners, or to use custom-made tuners, 6 to as side.  Some builders of additional-string guitars saw the ends off tuning machine plates, and then mount them on the side of the head in such a way that the edges of the adjacent plates are invisible, or nearly so.  I chose a different way, which I offer here in case anyone wishes to use it or to adapt it.

My method, which as far as I have been able to ascertain is original, uses 1/4" brass rods in the head over which the second set of strings are pivoted, dropping directly down to a second set of tuner barrels on a removable subhead which is held in place by a combination of rare-earth magnets and string tension. 
I have not checked patents on this, but nobody who has seen the guitar has suggested to me that anything like it has been used before.  

I used this technique in part because it is an inexpensive solution (two sets of off-the-shelf tuning machines), in part because it is easy to tune (compared to friction pegs), and in part because it allows the guitar to fit in a standard guitar case (the head being only 1/2" longer than with a 6-string classical).  Two heads are better than one, you might say.  But perhaps an overriding reason was that having proved the idea on the prototype, I wanted to bring it to fruition with the real instrument.  The solution works well.

Theoretically, a removable head also facilitates playing the guitar in 6-string mode, and although I don't do that with this instrument, one of the design goals for the next 12-string classical is for that guitar to be a convertible 6 / 12-String.

The guitar as I built it appears to be head-heavy, and that is indeed somewhat the case, although it should be remembered that the body structure is also heavier, and the neck and head are made of Spanish Cedar to lessen the weight at that end (as compared to Honduras Mahogany).  In the classical playing position, one never or rarely seems to notice any imbalance.

The tuners on the subhead point downwards, and the tuners on the main head point upwards.  The two tuners for a given course are aligned one above the other, and turn in the same direction to tighten a string.  The appearance may be a little surprising at first, and it's something of an eye-catcher.  On first sight, people are usually most curious about this feature, although in my opinion it's the least significant thing about the 12-string classical.   

(My original thought had been to have both sets of tuners pointing downwards.  But this technique would have required a spacing block at least 1" thick positioned between the two heads in order to provide any finger room at all for rotating the upper tuning knobs.  The spacing block could be full-width and contoured at the top, but it would have to be narrow the rest of the way down.  The subhead would need a headplate and probably a backplate in order to stay in one piece because of the upward pull of the strings. You can probably understand now why I chose instead to have the upper tuners pointing to the sky.)

On my instrument, the subhead is shaped much like the head so that the outline and the slots will line up.  The holes for the pivot rods in my 12-string were bored before the sides of the head were tapered, going almost right across the head and allowing three through-rods to be used.  Measurement for this is method a little tricky, because barrel holes are bored after tapering.  Another way to do it would be to bore the holes for both the barrels and the pivot rods after tapering, in which case six shorter rods would be needed. 

The pivot rod holes are positioned half an inter-barrel distance beyond each barrel (17.5mm).  The barrel holes in the subhead must be positioned such that the string drops directly vertically down from the outside of the pivot rod to the outside of the barrel on the subhead.

The holes for the pivot rods are bored slightly above the level of the barrels, to provide clearance for strings crossing over barrels to reach pivot rods.  The ends of the rods are ideally concealed by the tuning machine plates, which also allows the rods to be removed for polishing; alternatively, 1/4" wooden plugs made of neck/head material can be inserted at the ends to conceal them, in which case the pivot rods will not be removable.

Unlike the main head which has a headplate and a backplate, the subhead has no need to be reinforced with a stiff plate - it butts firmly against the main head.  Where the head blends into the neck, the subhead has also to taper off, hopefully in a somewhat elegant way.  There's an opportunity for some artistry here.  In my instrument the subhead is perhaps less than ideal in its elegance, and so my next effort may attempt to blend it in with the main head a little more smoothly.

The subhead is removable primarily to allow the first set of strings to be installed or removed with less obstruction in the slot area. The first set of strings takes a little longer than with a 6-string because the pivot rods present a minor obstacle.  The second set of strings takes longer still - about 45 minutes in my experience - because the two heads are attached at this point and there is not much room to work.  A pair of miniature pliers and a small screwdriver are useful for moving the string end around as the string is wound.  A minor delay and well worth it.

The rare-earth magnets I used are from Lee Valley, a 3/4" one in the upper area of the head, and a 3/8" one between the slots in the lower area.  The magnet with its backing disc goes in the subhead, and the attraction disc goes in the main head.  It's very important to do it this way, because once the magnets are in place in their slots, you can't get them out without using a much larger magnet (contact your local auto-wrecking yard) or without destroying the surrounding wood.  If anything, you want to destroy the subhead and not the neck / head assembly. 

There is no reason to install the magnets until immediately before setup, i.e. after the finish has been applied to the instrument.  The magnets lock the subhead roughly in place against the back of the head, but when the second set of strings have been brought up to tension, the subhead is very firmly in place.

Playing Considerations

The 12-string classical is very accessible to the player.  Anyone can pick it up and play a piece from memory or from sheet music, having to adapt a little only because of the left-hand insecurity first encountered when feeling pairs of strings rather than single strings under the fingertips, and to a lesser extent because of the more closely-spaced strings and the extra finger pressure required.

But the instrument is difficult to play well when using classical guitar technique, and challenging to master.  To some, that might be discouraging, but others might see opportunity and fun in the challenge.  I get a lot of satisfaction from playing a phrase or a piece in a manner in which I feel that I've brought out the essential character of the instrument.

In short, the secret of playing this instrument is to use generally-familiar classical guitar technique to try to bring out the textured sound quality wherever possible, or at least where the listener will most notice it.  Those techniques include use of the rest stroke (apuyando), a downwards rather than upwards motion of the fingers and thumb, angle of attack, hand position relative to the soundhole, vertical left hand fingering, depression of strings for their full intended duration, and playing at an appropriate tempo. 

The 12-string classical has its nuances, and so some of the techniques are harder to execute, but when appropriate to the music, it's worth the effort and it provides a challenge which makes guitar playing even more fun.

If you would like a more detailed explanation of playing considerations for the left hand, right hand, etc. (3 pages, PDF), please request one by email.

Some Parting Thoughts

You may be wondering if an existing classical guitar can be converted to a 12-string in this way.  I would have to say that that is unexplored territory - my short answer would be no - but if you succeed, please share your experience.  I made the observation earlier that most good guitars are overbuilt, but I've also heard that many inexpensive factory guitars (i.e. the kind of guitar you might want to try this on) are underbuilt.  At a minimum, I would recommend using normal-tension strings, particularly if you don't enhance the structure in any way.  I would also suggest replacing the bridge with one that would provide a much wider gluing surface and tie block, and two-tiered string holes.  The head slots would need to be extended by about a half inch if you wanted to use the subhead method; otherwise complete head replacement would be required.  You might also have to deal with the neck bending under the increased stress, affecting your action and possibly intonation, eventual collapse of the soundboard, and perhaps head joint failure. 

I hope this narrative was useful to you.  My reason for creating this document has been to promote an instrument that I firmly believe in.  For me, it's been a fun project to build, and as a player, I play the 12-string classical as much as I do the 6-string, choosing which music sounds best on each.  If you as a player or builder would like any more information on the subject, please email me and I'll try to help.

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