Design process - Combining stability, dynamics and ergonomics

Design overview of the making of the first Multi in 2014 :

-The goal for it is to include 12 long sympathetic string as part of an arched-top harp-guitar type instrument, that is comfortable to hold and play.

Oftentimes, the harp-guitar can feel bulky, and more like a standard guitar to which an -offset to the left- body part is added to cover for the extra-strings factor.

Multi manages to be sleek looking while serving its acoustic and ergonomic functions.

From the build-picture below, you can see how its original sketch is translated into an instrument that is thinner-bodied in the ribcage area of player. Its carving is worked into an organic feeling soundbox. 
Mult-harp-guitar-Thierry Andre Instruments
Mult-harp-guitar-Thierry Andre Instruments
Mult-harp-guitar-Thierry Andre Instruments
Thinner bass-side-of soundbox view- for Mult-harp-guitar-Thierry Andre Instruments
Mult-harp-guitar-Thierry Andre Instruments
Mult-harp-guitar-Thierry Andre Instruments
Mult-harp-guitar-Thierry Andre Instruments
Inner-soundboard for 12 sympathetic strings to Mult-harp-guitar-Thierry Andre Instruments
Materials for Multi are mainly local woods: Its soundboard (below) is carved from beautiful Alaska yellow cedar, whith American Poplar for its soundbox. Both materials are 50+ years old and have straight and quartered fibre orientation. 
Fingerboard is Macassar ebony, used along aluminium inlays. Aluminium dust is added to its thin, two coats nitrocellulose laquer top finish. Its back features an thin and responsive epoxy and oil varnish. 
atelier-multi-carve - hr.jpg
Multi's soundboard bindings are worked as a first step in its process. The top is also carved without the cutaway/soundhole part : This part is carved separately, set on the body at an angle to permit upper frets access, and is rounded into a horn-like shape.
First exhibited at the Woodstock invitational luthier showcase 2015. Multi received great comments from players, which helped shape later Multi 2 (2016), and the upcoming Multi 3 for 2022.

Below is a
demo of Multi, played by Jean-Marc Hébert, and a picture from meeting the one and only David Torn. 
One amazing guitarist (and human being) in which I find inspiration ; One of the nicest meeting you can ask for at a guitar show...David Torn, giving Multi a spin, at the Woodstock Invitational Luthier Showcase 2015.
Jean-Marc Hébert playing Multi in a demo recording.
He is a composer. Trained as a classical guitarist, he turned to electric guitar while he always kept with a finger style approach that is gentle yet expressive.

Acoustic ? Electric ? Tell us more ..

The guitar is the main focus, in all its forms... Steel strings, nylons, Arched tops & electrics are worked, while keeping open to merging characteristics of each when appropriate. 

Electric guitars are often designed with acoustic attributes in mind, while the acoustic guitars can display sonic and playability aspects of the electrics. By experience, It is beneficial and creative not to sub-categorize a guitar while its being created (or ordered), and let its combined attributes ultimately define it.
JM7-7string-nylon-Thierry Andre Instruments
JM7 is a thin, electric guitar-like nylon string guitar, designed to be played on stage. It gives deep tone while avoiding feedback issues.
Electrics :
Kouai (below) has the mass and sustain of a solid-body electric, while offering some -airy- qualities heard on more flexible hollow-body guitars. Its top wood is indian rosewood, and is coupled with Honduras mahogany. Its upper bout -ports- (initiated with Zyra) give a chanting aspect to its unplugged acoustic sound. 
Kouai hollow-body guitar 2014 Thierry Andre Instruments
Although a guitar such as Kouai inherently falls short of being a semi-acoustic, it has great unplugged qualities that one can hear from it when amplified and well recorded (Hear -Élégie-, a 2:00 solo guitar piece by Jean-Marc Hebert).
A larger and thicker version of it (more archtop-like) is yet to be exploited.
Kouai played solo by Jean-Marc Hébert
Kouai-hollow body electric guitar build- by Thierry andre Instruments
Electrics have a strong physical link between neck and bridge.

Too often, the neck pickup cavity represents a detrimental -void- in the system : 
-See how Kouai, from its rosewood top-plate apparently -aesthetic- design, has pillar-like elements surrounding its neck pocket. First meeting with neck, then circling around the neck pickup cavity, theses -pillars- go straight to bridge. This helps overall structure and the transfer of energy along the strings axis.
Acoustics :
Soundbox details
The MAYA is the largest guitar in the lineup.

From this picture one can see the buttressing
neck wings that tie its sides to its neck block.
This feature isn't new in history, yet it is mandatory for having responsive acoustics & logical mechanical engineering:

-Even with laminated sides, one can see that the soundboard still has to give a lots of its strength in the upper bout, just to -resist- the forces inherent to string pull. etc.

neck wings are thus used on all acoustic instruments, even on the Muti-type or Sun-Moon type carved-shell bodies. They do add long-term stability to the guitar.
Inside the box to the Maya Bass 2015: -Typical laminated -neck wings- support attached to neck block.
Also visible are: Beveled hardwood tail block, glued-in side brackets, tubing for pickup lead wire going to tail, faceted spruce cutaway in place on soundboard, and resulting cut on treble-side of body.
Lattice-type bracing is used on top plate, with long / radial type bracing pattern on back plate.
Neck mortise is to be cut once box is closed. 
Hear a short -workbench- demo of the Maya model  :
Neck wing supports as adapted to each soundbox :
Multi-Harp guitar by Thierry Andre Instruments
Multi-Harp guitar by Thierry Andre Instruments
Neck wings being fitted (above) for Multi's neck pocket (picture on the right) : Its neck will be glued directly on top of these supports, to couple with the soundbox in a 3-point triangular fashion.
atelier-oudtar-bowl-done-Thierry Andre Instruments.jpg
atelier-oudtar-bowl-done-Thierry Andre Instruments.jpg
Inside and outside the soundbox to Oudtar, 2013: -Typical laminated -neck wings- support attached to neck block, Kasagami Japanese paper reinforces every seam of the 22 - rib structure. 
Below pictures are the Greyhound mandoline's bowl-back completed, and the Old-school archtop rim assembly, both having soundbox -neck wings- glued in position. 
Geyhound Mandoline by Thierry Andre Instruments
These extra steps in the fabrication process are a way to give long-term stability to these instruments, for string action and soundbox integrity.

The neck to body connection are as efficient as possible, while keeping the instrument traditional.
Clara-archtop-Thierry Andre Instruments
Inside the box to the Clara archtop, 2020: -Typical -neck wings- support attached to neck block. 
Also visible are beveled tail block, glued-in side brackets for pickup lead wire going to tail, laminated rosewood
internal pickup support that holds the pickup suspended and clear of the top (see Clara's page), long -x- brace on Ziricote back, coupled with cross/ladder braces reinforced with rosewood top element.
The neck mortise is to be cut once box is closed. 
Soundboard details
Different bracing patterns have been studied and worked over the years. The -ladder-bracing- is certainly a worth to mention influence.
Originally found on the
Oud, Lutemandoline, etc. And many, many other instruments : - It eventually found its way on guitars, and one can safely say that it is, the early guitars bracing pattern.
_DSC9857 - Table.jpg
Guitare-fruit Wurcer (2018) features an intermixed fan (parallel bars) and ladder bracing for its soundboard. Its alternative ivory rosette is reinforced from the back by a cross-grain rosewood ring, while other materials are Red spruce over a Western red-Cedar soundboard,
Ongoing interest about the early type of ladder-bracing relates to a true understanding of how rich and complexe the guitar can sound today. 

The Lute and the Oud remain historic references and benchmarks today, because of their genuine sound qualities : There is certainly a tone that is ingrained and deeply-rooted that can be heard from the sound of both these two that is worth keeping in mind. Different bracing patterns (shown below) are designed to merge these historic qualities with the acoustic power of the modern steel-string guitar.
Oud-masmoudi - Thierry Andre Instruments
Oud Masmoudi, (2013) .
Different bracing combinations :
Old-school-archtop by Thierry Andre Instruments
Old-school archtop (2017): -Intermixed fan (parallel bars) and ladder bracing.
Materials are Red spruce over a Douglas Fir soundboard,
Oudtar by Thierry Andre Instruments
Oudtar-bracing-Thierry Andre Instruments
Oudtar : soundboard prior to its voicing stage (2013): -Intermixed x-brace  and a sequential ladder bracing inspired by thee Oud.
-Oudtar-, literally Oud and Tar) is worked as a crossbreed between Oud and Guitar.

Materials are Red spruce over a Red spruce soundboard, with a cross-grain Padauk bridge plate,
Raga guitar by Thierry Andre Instruments
Raga Guitar (2017): -Traditional x-brace with fan-type lower bout segment.  Materials are Red spruce over a Carpathian spruce top, with Rosewood angled-grain bridge plate.
Clara archtop by Thierry Andre Instruments
Clara archtop by Thierry Andre Instruments
Clara archtop  (2020): -Intermixed x-brace and ladder bracing.
Materials are Red spruce over a Western red Sinker cedar top, with Rosewood cross-grain reinforcements below F-holes.
Clara archtop by Thierry Andre Instruments
Clara archtop by Thierry Andre Instruments
sun-moon-and-vibrations by Thierry Andre Instruments
sun-moon-and-vibrations by Thierry Andre Instruments
Sun, Moon, and Vibrations  (2019): -Bracing in the works and angled cutaway in place.
Traditional x-brace with fan-type lower bout segment..
Materials are Red spruce over 45 year old Western red cedar, with Padauk cross-grain bridge plate, with ebony insert to receive string ball ends.

You can hear this unique guitar below. 

Demo 1 lets the guitar ring. Second demo is mainly tapping harmonics around the 12th fret . Demo 3 uses palm muting & folk strumming.
sun-moon-and-vibrations by Thierry Andre Instruments
Elongated-body acoustic guitar - Sun, Moon, and Vibrations - completed, December 2018.
Cutaway options:
Since 2011 a slanted cutaway is worked in different variations.
It is made more acoustic by using the same material as the soundboard itself, to execute it.

Taking the Raga-guitar (pictured) as an example ;

A cut-off from its Carpathian spruce soundboard material is first saved, then bent to shape and joined at an angle with the main soundboard.

Using soundboard material for making this functional part is all about continuity of form and sound.

It also effectively keeps intact the strong arched-structure of the traditional guitar's upper-bout.

Alternatively to this type of cutaway, the standard cutaway,  is also offered. 

Below is the JM7 as an example:
Raga guitar-cutaway view- Thierry Andre Instruments
JM7-nylon 7 string guitar by Thierry Andre Instruments
JM7 nylon 7 string guitar by Thierry Andre Instruments
Visual examples of different techniques used to make the cutaway part of the guitar:
Oudtar-by-Thierry Andre Instruments-workshop view of cutaway work (2011)
Oudtar by Thierry Andre Instruments
Maya 2 acoustic bass by Thierry Andre Instruments-photo Carolyn Amanda Photography
Sun, Moon, and Vibrations by Thierry Andre Instruments
Sun, Moon, and Vibrations - Workshop view and cutaway binding work- Thierry Andre Instruments
Maya bass- acoustic bass by Thierry andre Instruments
maya-workbench-cutaway-work-Thierry Andre Instruments