Definition and background:
Aerophone (Air- vibrated metal reed without resonator), Free aerophone, Wind InstrumentThe bandoneon was developed by Heinrich Band in the 1840's. Although invented in Germany, it quickly made its way to Argentina and became synonymous with the Argentine tango. The first instruments were constantly being changed and most of the early versions of the instrument have different number of buttons in different positions on the face plates. In 1924, the number and positions of the buttons were standardized to include 72 buttons that cover a five octave range. Both the accordion and concertina were being developed around the same time as the bandoneon.With the appearance of a square accordion, the bandoneon is actually closer to the concertina (using all buttons rather than a traditional piano keyboard as the mechanism to sound the notes). Each end of the bandoneon is a square wooden box containing a small reed organ operated by several rows of buttons. These boxes are connected by a folding bellows. Expanding and contracting the bellows provides air to the reed organs producing the sounds, and depressing the buttons directs air to the appropriate reed. The right side is a descant reed organ with 37 buttons for playing the melody notes. The left side is a bass reed organ with 35 buttons for playing bass notes. Unlike the accordion, the bandoneon buttons are not arranged like a normal keyboard and the bass buttons do not sound full chords. Each button can sound up to two notes, one note with the air flowing out (blowing as the bellows are compressed) and a second note with the air flowing in (sucking as the bellows are expanded). This means with 72 buttons there are 144 possible notes. This is arranged with 37 buttons (74 possible notes) on the descant side for the right hand and 35 buttons (70 possible notes) on the bass side for the left hand. The descant side also has a thumb lever that disengages the reed organ, so the bellows can expand or contract without sounding any notes.Sound is produced by the vibration of the metal reeds (often called tongues) of the reed organ when the air flows across them.Since some of the descant and bass notes overlap, and some buttons sound the same pitch regardless of the direction of air flow, the actual chromatic range is five octaves or 56 notes. The bass side starts with the C below the bass clef staff and goes almost three octaves to the A-sharp above the bass clef staff. The descant side goes slightly over three octaves, from the G below the treble clef staff to fifth- space A above the treble clef staff.See also Accordion, Concertina.
For more information on the music term "Bandoneon" check out these other resources:
Wikipedia - Glossary of Musical Terminology
Virginia Tech Multimedia Music Dictionary
ORB -- Medieval Music Glossary