The Henri Selmer-Mario Maccaferri guitar was built using the construction techniques of a mandolin with steel strings, with pressure on the top that increases its volume and gave it a trebly tone. The first Selmers, in fact, which were released in England and then in France, were just called a "Modèle Concert" guitar, meaning it was simply a louder guitar. The jazz musicians grabbed onto this instrument because it cut through all the sound and fury of the horns in a jazz band, and Selmer later changed the name to the "Modèle Jazz." So that is how jazz had its influence on the instrument, and in a way you can say Django was part of the reason that change was made, but at the same time, guitars were being created in the United States quite differently.   The Dobro Bell Brass Resonator Guitar for instance designed by Doyeptra is now the preferred acoustic blues instrument..

Reinhardt and other guitarists of the Quintet of the Hot Club of France used  Selmer-Maccaferri acoustic guitars

Selmer produced guitars between 1932 and 1952. Although they produced a wide variety of instruments, they are particularly known for the 'Modèle Jazz' ( changed to 'Modèle Django Reinhardt' later), made famous by Django Reinhardt.
The guitar was initially designed by Mario Maccaferri, with a 12-fret neck and a D-shaped sound hole. When Maccaferri left the company, Selmer made some changes to the model, most notable the introduction of the oval sound hole and the lengthening of the neck to 14 frets. Almost all Selmer guitars were made of laminated Indian rosewood with walnut necks and an ebony fingerboard. The tops are solid French spruce, what defines the sound of the guitar the most (besides the player). Django Reinhardt got an endorsement deal with Selmer, so many Selmer guitars passed his hands (he sold or gave away a lot of them). There are 2 guitars that we are sure of belonged to Django: n°503 and n°704.  N°503 came in Django's possession in 1940 and he played it until his dead in 1952. The guitar was on display in the Musée Instrumental de Paris, Alas now removed - see Ade Holland anecdote. N°704 came into his possession in 1948, just before a tour in Italy. The top was crushed during that tour and replaced by an Italian luthier.

Django Reinhardt used very light silk-and-steel strings ( .010 to .046) on his guitar generally from Argentina.
Django liked to use the thickest guitar picks he could find, most of the time using natural tortoise shell.
Selmer stopped producing guitars in 1952.
Today Selmer guitars are extremely rare and very much sought after. During the entire history of Selmer guitars, less than a thousand guitars were made.
Selmer style guitars are reproduced by luthiers like Michael Dunn and John Kinnard.

Selmer guitars were popularised by the great gypsy jazz guitarist, Django Reinhardt, who began playing them as soon as they appeared on the market and played them throughout his career. Today, they are thoroughly associated with his playing and with gypsy jazz. Few of the Selmer Maccaferri guitars were ever made, thus they are extremely rare and much sought after. Yet because they are so significant to the development of 20th century Lutherie'   they merit appreciation in a work as comprehensive as possible in terms of information and illustration
The luthier François Charle was born in Paris in 1949. He is an authority on Classical, Traditional and Modern French stringed instruments. In 1979 he and his wife Rosyne took over from Daniel and François Sinier de Ridder the instrument shop and workshop in the Galerie Véro-Dodat, an historic arcade in the center of Paris.  His liking for Selmer-Maccaferri guitars took a decisive turn when he had the opportunity to buy the tooling stock of woods and spare parts of the old Selmer workshop. He became fascinated by the somewhat hazy history behind this guitar and the myth that is represented. So he threw himself into a ten year long research project, using archaeological type methods to unearth all the available information on these mythical guitars.   This book is much more than a compilation of the results of this inquiry into "Django Reinhardt's guitar", it is a real plunge into a world whose inhabitants have a passion for instrument making and music.

Henri Selmer and Company - the book - now out of print - outlining the life and times of the illustrious guitarist, luthier, and inventor Mario Maccaferri, without whom there would probably have been no Selmer guitar or story at all.  Key design changes made to the guitar by Selmer craftsmen after Mario Maccaferri left the company in 1933.  Outlines exactly what differentiates a Selmer guitar from a Selmer "Maccaferri" model and helps us understand what has heretofore been an obscure body of esoteric guitar knowledge.

During the 1930's there were many Italian Luthier's settling in France. One who was to become the most enduring was Mario Maccaferri who was born in 1900. An accomplished guitarist himself, he also had an interest in the making of many stringed instruments which he had learned as a young man as an apprentice to the famous Italian luthier Luigi Mozzani which he took up in 1911. During this period he took an interest in playing the classical guitar and at the age of sixteen had gained a high reputation of being a concert guitarist.
Even though he had a career as a guitarist he maintained his interest in the technical side of guitar construction and engineering as a whole as technical advisor to the Mozzani workshops. In 1926 he received the highest possible diploma possible from the Academy of Music in Siena.
In 1923 he left Mozzani and embarked on a European tour. During this period he advertised as the maker of all stringed instruments. In 1926 he settled in London as a teacher and made a comfortable living as such. While here he began to develop the early prototypes of the Maccaferri guitars. He took the first prototypes to Ben and Lew Davis who in turn put him onto Henri Selmer in Paris who was so impressed that he gave him the contract of setting up a factory in Mante le Ville to build what were to become the Maccaferri Guitars by Selmer of Paris.
Within a few years these guitars had become popular with Dance Bands and Jazz Groups across Europe. The most famous of these being Django Reinhardt and The Hot Club de France.
In 1934 Maccaferri left Selmer and this is the period most famous for Selmer as they introduced the Modele Jazz which incorporated the distinctive small oval hole. Which was used by Django, though not exclusively, until his death. His brother Joseph played the earlier D hole, (grand bouche or big mouth), in the Quintet which is still considered today as the rhythm guitar.
Not many originals were made of this style perhaps only 1,000 between 1932 and 1952 and only half being the Modele Jazz. Rare as rocking horse shit as they say. Recently I heard of one bought by a Belgian Gypsy for £4000 it had a neck shaped like a bannana and had to be rebuilt at great expense by Doug Kyle.
The Modele Jazz had a cutaway at the 15th fret incorporated the compensated floating bridge and two glued on moustache bridge extensions made from ebony. A metal tailpiece accommodated either ball or loop end strings, and a radiused ebony fingerboard extending over the soundhole providing a 24th fret under the high E string.
The Oval hole model with the bouche oval or petite rosace only appeared after Maccaferri had left the company in 1934. There were a few odd ball guitars made at this point but settled down eventually to build the Modele Jazz until their closure in 1952.
Model Jazz Guitar Selmer No.85 Pictures and Facts

After a falling out between Mario Maccaferri and the Selmer Company, the petite bouche (or Oval Hole) was developed. These guitars feature a very long scale, 670 mm, and feature a 14th fret neck joint. These were used by Django later on, and are considered by most the "lead guitar" for Gypsy Jazz.

Maccaferri or Selmer

Mario Maccaferri 1900-1993

Internal Resonator The original Maccaferri Grande Bouche models featured a wooden resonator behind the soundhole.

The primary movement of a floating bridge under string tension is vertical, with very little torque or rock, which is why the tone is mid-range dominant. The wide, glued on bridge of a flat-top guitar is driving the soundboard in a more complex way that favours fuller overtone development. The amount of down-pressure on the bridge greatly affects both tone and volume. Greater load favours the fundamental pitch and more volume, while lesser load makes for a richer tone with more harmonic overtones but somewhat less volume. I build my tailpieces with height adjustment screws that allow the player to balance the instruments fundamental/overtone mix by changing the break angle over the bridge. Bridges on these guitars are hollowed out to reduce mass and increase volume. Players today prefer much lower action than in the past, so it is sensible to make the bridge with an in-set saddle for easy adjustment to various string attack.

The dome shape of the top is crucial to the tone and functionality of this kind of instrument. This dome is accomplished in Maccaferri’s design by gluing arched braces to the top that run perpendicular to the grain of the spruce with two short vertical braces under the bridge. This creates a cylindrical section, with the entire arch in one plane. Forcing the top down at the neck and tail blocks attains the dome, which creates a lot of uneven stress on the top. The back is built in a similar way – like most modern flat tops. The tone of these guitars is predictably dry and lacking in overtones. In my experience, ladder bracing favours the fundamental pitch of any note at the sacrifice of the rest of the overtone range. I believe this is because the top is divided by the braces into only a few essentially rectangular vibrating plates. Ladder bracing is used in lute construction, but gluing the braces slightly off parallel ameliorates this problem.

A better solution is to X brace both the top and the back. This creates the compound-complex dome in one setting, with minimal stress on the glue joints of the neck and tail blocks. This allows more of the plate to be free to move as a unit – the trampoline effect. Additionally, breaking the soundboard into more odd sized areas encourages fuller overtone development. It is necessary to support the bridge with additional X bracing under the tails to prevent collapse (discovered the hard way). I like to brace the upper bout solidly to support the fingerboard end for clearer high note playing. It helps to think of the bracing as creating a top with graduated thickness like a violin or arch top guitar.

X bracing the back has the effect of re-enforcing bass response considerably, both in this style guitar and in regular flat tops. When all the tension of the arch is held by the braces, the back is able to pump air more freely and efficiently. Add a cross brace between the X in the lower bout for extra support. The tap tones are very lively with a back braced like this. The backs of Selmer-Maccaferri guitars were laminated, but using solid woods is clearly an improvement.

Use a sanding dish that allows for a 5/16" arch to sand the interlocked XXX top braces as a unit. They can then be easily go-barred to the prepared soundboard in the same dish using paper as a pad. Using more arch risks splintering the plate from too great a stress (the hard way again). The rib assembly can be shaped for a perfect fit in the sanding dish too. Rough plane the sides before the linings are attached using the sanding dish as a pattern. A 4½ degree angle on the blocks is about right to accommodate the dome. Don’t forget to make a side pattern for the next time once you’ve got it right. With the ribs in the mould, rotate on the sandpaper until sanding marks appear on all the linings and end blocks.

The Grande Bouche (Big Mouth) model has much more mid-range tone than a good flat top guitar, but it is considerably more rich than a good arch top guitar. The original had a 12 fret neck, and was preferred for rhythm playing. Most modern makers have given it a 14 fret neck for practical reasons. The "Model Manouche" has a broader tonal spectrum than ladder braced instruments, and is more versatile in its uses. The Petite Bouche (Small Mouth) model has a long 26.25" scale and is preferred for solo playing. The tone is more treble, being closer to an arch top guitar. I have been putting a sound port on the upper bass bout that has opened up the tone of this guitar considerably. Not only can the player hear the instrument better, it has allowed the box to breath, and increased volume and responsiveness. That little hole is cute, but it’s just not big enough to let the sound out. Sound ports are as close as we get in this world to something for nothing! The "Model Eclipse" is very open toned and is capable of a wide variety of tone colours.
Selmer-Maccaferri guitars are unique in the world of guitars and deserve to be toyed with and improved while maintaining the basic character of the instrument. Would Mozart have used a harpsichord today? The demands of the modern player sometimes pull us toward change, but often innovations set a new standard for the musician.