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Update, January 2024: I've converted the 17-string Hybrid Extended Classical guitar into an 18-string Contraguitar.  In the process, I've renamed it as C4.  You can read about the conversion process in this blog post and this blog post.

or many years, I have imagined a classical guitar with both steel and nylon double courses. 

Origin
Though it has never existed, I could hear this hybrid steel and nylon voice in my mind.  This was different in two ways: classical guitars have only single-string courses, and to my knowledge, there has never been a double-course instrument of any kind that utilized a hybrid nylon/steel course schema. In the early-to-mid 2000s, I spoke with two luthiers with whom I've worked in the past about such an instrument.  They both told me what I already suspected: that such an instrument was impossible.  As I knew all too well, steel-string guitars and nylon-string classical guitars require entirely different, and in my ways opposite, construction methods.  The construction, bracing, and voicing are entirely different with nothing in common between the two.  To build a classical guitar that could withstand the extreme physical stress of double-courses and the added tension of steel strings would result in an overbuilit, lifeless, unresponsive instrument. It just couldn't work.  However, the thoughts of it, and hearing it in my head, never went away. For many years, I had resigned myself to the fact that this instrument was physically impossible and could never exist.

Until the arrival of the KK-15.

The incredible voice of the KK-15 had me once again dreaming of a hybrid classical guitar.  And because it was a double-course classical guitar, I knew that the strength and resonance of carbon fiber would be ideal.  A double-course classical guitar had never existed prior to the KK-15; not only was it a new voice in the guitar world because it was a double-course instrument, it also hinted at the possibility of the elusive hybrid double-course classical guitar.

Design and Build
In early 2016, I spoke with Alistair Hay at Emerald Guitars in Ireland about the concept of a hybrid double-course classical guitar.  Alistair said exactly what I had suspected: that with carbon fiber, this instrument could work.  I set to work immediately on the design specification, and determined the number of courses.  The success of the Emerald Kevin Kastning Series KK-15 Extended Classical guitar proved that a double-course classical guitar was not only possible, but resulted in a beautiful new voice.  An instrument voice that I used far more than I had originally imagined when we designed the KK-15.   I knew the problems of a hybrid classical instrument could be solved as we delved further into the design.

After using the KK-15 for almost three years, I knew that I wanted to expand the single-course low E and B strings into double courses, but keep the low F# as a single course  That made for a total of 17 strings: one single-course, and eight double-courses.

Throughout 2016 and early 2017, Alistair and I exchanged many emails about this project, and discussed specs, design, and some unforeseen challenges during late-night Skype sessions.  I finalized a spec, and the building process began in early 2017.

Evolution
Fan-fret (multiscale) -- Visually, the most striking feature is the fan-fret, or multiscale design.  The scale length is based on a 650mm scale, with the fan spreading between 27^1/4 inches on the bass side, and 24^1/2 inches on the treble side.  This provides a different scale length for each string.  After playing the KK-15 for close to three years, I knew this system truly allows the wide range of string pitches to sound better, be more in balance both in voice and tension, and avoid string breakage to due to overly-high tension in the trebles.  Multiscale seems like a modern concept, but was actually developed for the Orpharion, a lute-family instrument, in 1581.  The multiscale proved to be perfect for this instrument; the string tensions are even, and the tonal response is very balanced across all registers.  The playability of the multiscale feels very natural, even in the cello position.

Alistair Hay
"When Kevin says the words “I have an idea,” I make sure I'm sitting down before he proceeds, but then again after the previous series of instruments that we have collaborated on nothing surprises me any more. I was intrigued by the idea of combining nylon and steel strings together and had some concerns that the steel strings might overpower the nylon. I knew getting tonal balance would be key. The great thing about working with carbon is the incredible strength yet light weight that can be achieved. This allows us to get the right balance between structural integrity to resist the 17 strings, and responsiveness to make the nylon strings sufficiently loud. While much of the build was similar to the KK-15, this one had some added headaches when it came to setting up the action and getting the right intonation points. I don't mind saying that if I had hair I would have been pulling it out during a few late night sessions, but I have been doing this long enough to know that the best takes time and in the end when you get to hear it properly tuned up for the first time it's all worth it. I really love the contrast of the nylon and steel strings. The steel gives powerful punchy notes while the nylon rounds it all off with a darker, more complex tone. Together they harmonize perfectly. It sings like a harpsichord. I hadn't expected to like It so much, but now I cant wait to try this combo on one of our regular 12-string guitars."

The Way Forward
The KK-17 arrived in January 2018.  Alistair created an instrument of stunning aural beauty and depth.  My suspicions about carbon fiber being the ideal platform for a hybrid classical instrument proved to be correct.  The voicing, the responsiveness, the balance, the playability, and the flawless action are wonderful.  The intonation is very accurate; no mean feat on a multiscale instrument with 17 strings.  I feel as if the KK-17 establishes an entirely new voice in the guitar world.  It will be on many album recording projects in 2018 and beyond.  Here is a short piece wherein you can hear this new guitar voice.

To Alistair and everyone at Emerald Guitars in Ireland, my sincere gratitude.

– Kevin Kastning
   Massachusetts, US
   3 January 2018

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Photos

The KK-17: During the setup process at Emerald Guitars in Ireland.

The KK-17: During the setup process at Emerald Guitars in Ireland.

The KK-17 bridge.  Here you can see the blend of both nylon and steel strings.

Strings and Tunings

F# Bb Ee Aa Dd Gg BB EE AA

For actual string gauges and string types, refer to the Strings and Tunings page.

Specifications

17-string Hybrid Extended classical
Body: X20
Bridge: Half classical tie-on type; half ball-end steel
Neck: Fan-fret, based on 650mm scale
Multiscale dimensions: 27.25 inches bass side to 24.5 inches treble side
Nut width: 4.00 inches / 102mm
24 frets
Saddle: Graphtech custom
Fingerboard radius: flat
Double truss rods
Cello end pin
K&K stereo system (bass side = stereo L / treble side = stereo R)
Tuners: Gotoh 510 series, 18:1 metro black
Color: Transparent black

Other instruments in the Emerald Kevin Kastning Signature series:

    The Emerald Kevin Kastning Signature model 30-string Contra-Alto guitar

    The Emerald Kevin Kastning Signature model 36-string Double Contraguitar

    The Emerald Kevin Kastning Signature model 15-string Extended Classical guitar

    The Kevin Kastning Signature model 15-string Extended Classical guitar at Emerald Guitars

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