The bandoneon is a subset of a German Harmonica.
Depending on the regionally usage,
these bellow harmonicas are called German Konzertina,
Bandoneon from the Spanish term. Besides these German instruments
there are many other similar, older and newer instruments such as
Aeoline, English Concertina, Accordion
While the first instruments were constructed for single action (worked
mostly only on pressure), later instruments with a valve system allowed
to play on opening (draw) and closing (pressure) the bellow (double action).
and the Apollo-lyra
were able to play in both senses. The early harmonikas were diatonic
instruments for a few tones. In order to have chromatic
instruments with a few buttons, the double action instruments were build
bisonor, that is the note changes with the bellow sense. But with the growth
of the instruments also unisonic versions with equal notes in both
senses became popular.
Although Demian's accordion from 1829 permitted easy accompaniment of
folk music and was highly requested, the fixed chords reduced its musical
possibilities. The tonal distribution of Wheatstone's symphonium (1826),
later known as English Concertina, was thought as a melody instrument
to perform e.g. violin parts in concerts.
Carl Friedrich Uhlig designed a layout with individual notes permitting an
easy play of chords with it dominants in the opposite sense of the bellow.
There are for at least three different of such primitive
nucleus zones named according to their creators:
Uhlig (Chemnitz, 1835) and Band (Krefeld, 1850)
with 56 voices
and Zimmermann (Carlsfeld, 1849) (29 keys) and which were
designed all before 1856. Obviously these
instruments were limited to a few scales and the development went to
increase the number of keys. Heinrich Band achieved this by adding later
buttons around his nucleus zone of the konzertina. This permitted
the konzertina players to change over easily to the new models with
74 to 104 voices. Until 1877 his instruments with 130 voices became common.
Since Band was from Krefeld
(Rhine), his system was also known as Rheinische Lage to distinguish
it from the very many other keyboard designs. Some people began calling
those instruments Bandonium (first in 1854)
because of the marketing system. The
different systems were regionally different and developed independently.
Band's 130 voice keyboard layout
was exported also
to the Rio de la Plata where it was extended to the
142 voice keyboard layout
which is the standard system still today there. The range goes in the bass
from C-2 to a-4 and in the treble from a-3 to a-6. Some missing voices
like C-2 on closing led to build special versions with
with the full chromatic scale on opening and closing.
In Germany a commission proposed in 1924 to unify the different systems,
even konzertina and bandoneon, in order to simplify the edition of sheet
music and teaching and to reduce the number of instrument models.
with 144 voices was
created. This occurred after the time when the bandoneon was already
popular at the Rio de la Plata and where
the Einheitsbandonion was not accepted.
Since it was not possible to join the konzertina and the bandoneon, a new
124 voice Einheitskonzertina
The high popularity of the bandoneon during the 20ies forced the French musette players to learn this instrument too. But because the available bandoneons were too different from the musette acordion, they demanded an instrument much closer to what they were used to but with the characteristic sound of a tango bandoenon. In 1925/6 Charles Peguri replaced the reedboards of a 142 voice rheinische Lage instrument with modified plates, where the reeds for both air flow directions were the same. The unisonoric so-called Peguri Chromatic Bandoneon is based mechanically on the standard 142 voice export models, making it easy to incorporate the modified version into the running production.
The term Chromatic Bandoneon caused confusion among many people because it suggests that the bisonor instrument doesn't permit chromatic scales, and which is not the case. They simply called double action instruments diatonic and single action = chromatic.
Earlier instruments were called Symphonetta (1898) and the swiss Kaspar Wicki based his unisonoric bandoneon keyboard of 1896 on the non-discriminating piano keyboard of Jankó (1882). An other unisonoric bandoneon was designed by in 1927 but with a different mechanical layout.
Which system is the most suitable?
To take a decision you have to know the task
of your work. The demand for unisonoric instruments arose from the need to
change from piano or accordion to bandoneon without having to learn the
complicated keyboard and be able to perform within a moderate time.
There are hundreds of bandoneonists in France with excellent results using Peguri's system. Most of the actual bandoneon production goes into that market.
Why then still a bisonor system?
Both instruments sound different although potentially every instrument sounds different. One reason is, that on acting a voice a brother reed of the same frequency in the same wind channel is “hearing” the sound. This fact couples vibration on its own and which interferes with the driving reed. This additional sound is not strong and only modifies the sound colour.
The most important reason is that a bisonor instrument allows to perform extremely broad chords giving the bandoneon its particular rich sound not possible on other instruments.
For the case you are going to play tango music I would suggest the bisonor system since most compositions take advantage of that particular property. Once you have learned the keyboard you will discover the great advantage of the “chaotic” layout. The original idea of realizing chords easily is still achieved. This is to be considered particularly for modern harmonies.
The choice between Einheitsbandonion and the rheinische Lage depends on your repertory, although less significant.