Today, two systems are in use: the German, or Oehler system and the French, the so-called Boehm system, which is widespread in France, Great Britain and the USA.
The term Boehm system is somewhat misleading, since it was not the revolutionary keywork that Boehm invented for the flute that was applied to the clarinet, but merely the ring key principle. It was in fact impossible to use the Boehm mechanism on the clarinet for the simple reason that the clarinet’s fundamental compass was greater than the flute’s: the flute overblows to the octave, the clarinet to a twelfth (octave + a fifth).
A comparison between the German and the French systems
The French model (the standard Boehm model) has seventeen keys (plus seven open tone holes, making twenty-four tone holes all together) and six ring keys; the German version has at least twenty-two keys and five ring keys.
The fingering on the French system is a little easier.
On the underside of the mouthpiece, which tapers to a point, a notch or slot is carved out over which the reed is attached. Together with the rails on either side of the slot this forms the so-called lay, or facing, which allows the reed to vibrate during playing. The form of the lay, especially the angle of the rails to the tip of the mouthpiece, is largely responsible for determining the instrument’s timbre.
bottom view (without reed):
The lay of the German mouthpiece is narrower and slightly concave. The reed is slimmer, longer and heavier, and was traditionally fixed by means of stout twine; nowadays the ligature is used for the fixing. The lay of the French model is broader and flatter, the reed being affixed with the ligature.
The mouthpiece is the part of the clarinet that affords the player the greatest individuality. The differences in material and construction are a result of the various sound ideals favored by the different schools. The question of whether to use a “German” or a “French” mouthpiece is essentially a philosophical one.
German clarinets have a slightly wider bore than French models.
The clarinet’s timbre depends primarily on the player. The German clarinet tends to have a darker timbre.