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accordion, free-reed musical instrtme t, patented in 1829 under the name accordion by Cyril Demian in Vienna and under another name in 1822 by Friedrich Buschmann in Berlin.
The free reed of an accordion is a metal tongue fastened over a slot accurately cut in a metal frame. The reed is sprung up above its frame and vibrates when air flows around it from this upper side; air flow in the opposite direction does not cause vibration. The reed sounds a definite pitch and can be tuned by filing near the free end to raise the pitch and near the fixed end to lower it. In an accordion, a bellows is fastened between two oblong wooden structures that carry the reeds. Wind is admitted to the reeds selectively through pallet valves controlled by a keyboard or set of finger buttons. Each key or button admits wind to a pair of reeds, one of which is mounted to sound on the press of the bellows, the other, on the draw.
In some accordions, including the early designs, the paired reeds sound adjacent notes of the scale, so that a button will give, for instance, G on the press and A on the draw (“single action”). With a single action, ten buttons suffice for a diatonic (seven-note scale) compass of over two octaves, with each note available with a bellows movement in one direction only. For the left hand there are typically two keys, or basses, one providing a bass note, the other a major chord. These sound the tonic (keynote and chord) on the press and the dominant (fifth note and chord) on the draw in the tonality (key) of the melody reeds.
This single action has been developed, chiefly in Austria and Switzerland, by adding a second row of buttons giving the F scale (the first-row scale being C), so arranged that almost every note of the diatonic series is available both with a C-row button on the press and an F-row button on the draw, or vice versa.
Semitones are provided by additional rows, and the number of basses is increased. The piano accordion, with piano-style keyboard for the right hand, was introduced in the 1850s and later perfected in Italy by Mariano Dallap?. In its “double action,” the two reeds of each pair are tuned to the same note, thus making every note and bass available from the same key with both directions of bellows movement. Steel reeds, instead of brass, give a steadier pitch. Couplers or “registers,” developed in the 1930s, bring into action extra sets of reeds, one pitched an octave below the main set and another off-tuned from the main set to give a tremulant through “beating” (sound-wave interference). Other registers may include a high-octave set and a second tremulant. Each set may be used alone or with others.
The left-hand provision is also extended, with up to 120 basses actuated by six rows of buttons. Two rows give bass notes arranged in cyclic order of tonalities (D, G, C, F, etc.), one row being offset against the other at the interval of a major third for convenience in fingering melodic passages in the bass. The other rows give three-note chords, respectively, major and minor triads and dominant and diminished sevenths. There are up to five registers for the basses, causing each bass note to sound over as many as five octaves if desired and each chord to sound in three.
A variant of the accordion is the Bandoneon, a double-action instrument with square shape and finger buttons, invented by Heinrich Band of Krefeld, Ger., and the leading solo instrument in modern Argentine tango orchestras.
