Accordions have many configurations and types. What may be technically possible to do with one accordion could be impossible with another:
- Some accordions are bisonoric, producing different pitches depending on the direction of bellows movement
- Others are unisonoric and produce the same pitch in both directions. The pitch also depends on its size.
- Some use a chromatic buttonboard for the right-hand manual
- Others use a diatonic buttonboard for the right-hand manual
- Yet others use a piano-style musical keyboard for the right-hand manual
- Some can play in different registers
- Craftsmen and technicians may tune the same registers differently, "personalizing" the end result, such as an organ technician might voice a particular instrument
The bellows is the most recognizable part of the instrument, and the primary means of articulation. Similar to a violin's bow, the production of sound in an accordion is in direct proportion to the motion of the player. The bellows is located between the right- and left-hand manuals, and is made from pleated layers of cloth and cardboard, with added leather and metal. It is used to create pressure and vacuum, driving air across the internal reeds and producing sound by their vibrations, applied pressure increases the volume.
The keyboard touch is not expressive and does not affect dynamics: all expression is effected through the bellows. Bellows effects include:
- Volume control and fade
- Repeated change of direction ("bellows shake"), which has been popularized by Luiz Gonzaga and is extensively used in Forró and called resfulengo in Brazil
- Constant bellows motion while applying pressure at intervals
- Constant bellows motion to produce clear tones with no resonance
- Using the bellows with the silent air button gives the sound of air moving, which is sometimes used in contemporary compositions particularly for this instrument
The accordion's body consists of two wooden boxes joined together by the bellows. These boxes house reed chambers for the right- and left-hand manuals. Each side has grilles in order to facilitate the transmission of air in and out of the instrument, and to allow the sound to project better. The grille for the right-hand manual is usually larger and is often shaped for decorative purposes. The right-hand manual is normally used for playing the melody and the left-hand manual for playing the accompaniment; however, skilled players can reverse these roles.[notes 2]
The size and weight of an accordion varies depending on its type, layout and playing range, which can be as small as to have only one or two rows of basses and a single octave on the right-hand manual, to the standard 120-bass accordion and through to large and heavy 160-bass free-bass converter models.
The accordion is an aerophone. The manual mechanism of the instrument either enables the air flow, or disables it:[notes 3]
A side view of the pallet mechanism in a piano accordion. As the key is pressed down the pallet is lifted, allowing for air to enter the tone chamber in either direction and excite the reeds; air flow direction depends on the direction of bellows movement. A similar mechanical pallet movement is used in button accordions, as well as for bass mechanisms such as the Stradella bass machine
that translates a single button press into multiple pallet openings for the notes of a chord.
The term accordion covers a wide range of instruments, with varying components. All instruments have reed ranks of some format. Not all have switches. The most typical accordion is the piano accordion, which is used for many musical genres. Another type of accordion is the button accordion, which is used in several musical traditions, including Cajun, Conjunto and Tejano music, Swiss and Austro-German Alpine music, and Argentinian tango music.
Right-hand manual systems
Different systems exist for the right-hand manual of an accordion, which is normally used for playing the melody. Some use a button layout arranged in one way or another, while others use a piano-style keyboard. Each system has different claimed benefits by those who prefer it. They are also used to define one accordion or another as a different "type":
- Chromatic button accordions and the bayan, a Russian variant, use a buttonboard where notes are arranged chromatically. Two major systems exist, referred to as the B-system and the C-system (there are also regional variants).
- Diatonic button accordions use a buttonboard designed around the notes of diatonic scales in a small number of keys. The keys are often arranged in one row for each key available. Chromatic scales may be available by combining notes from different rows. The adjective "diatonic" is also commonly used to describe bisonic or bisonoric accordions—that is, instruments whose right-hand-manual (and in some instances even bass) keys each sound two different notes depending on the direction of the bellows (for instance, producing major triad sequences while closing the bellows and dominant seventh or 7-9 while opening). Such is the case, for instance, with the Argentinian bandoneon, the Austro-German steirische Harmonika, the Italian organetto, the Swiss Schwyzerörgeli and the Anglo concertina.
- Piano accordions use a musical keyboard similar to a piano, at right angles to the cabinet, the tops of the keys inward toward the bellows
6-plus-6 accordions use a buttonboard with three rows of buttons in a "uniform" or "whole-tone" arrangement. The chromatic scale consists of two rows. The third row is a repetition of the first row, so there is the same fingering in all twelve scales. These accordions are produced only in special editions e.g. the logicordion produced by Harmona.
Left-hand manual systems
Typical 120-button Stradella bass system. This is the left-hand manual system found on most unisonoric accordions today.
Different systems are also in use for the left-hand manual, which is normally used for playing the accompaniment. These almost always use distinct bass buttons and often have buttons with concavities or studs to help the player navigate the layout despite not being able to see the buttons while playing. There are three general categories:
- The Stradella bass system, also called standard bass, is arranged in a circle of fifths and uses single buttons for chords.
Belgian bass system is a variation used in Belgian chromatic accordions. It is also arranged in a circle of fifths but in reverse order. This system has three rows of basses, three rows of chord buttons allowing easier fingering for playing melodies, combined chords, better use of fingers one and five, and more space between the buttons. This system was poorly traded outside of its native Belgium.
- Various free-bass systems for greater access to playing melodies on the left-hand manual and to forming one's own chords. These are often chosen for playing jazz and classical music. Some models can convert between free-bass and Stradella bass; this is called converter bass. The free-bass left hand notes are arranged chromatically in three rows with one additional duplicate row of buttons.
Reed ranks and switches
Inside the accordion are the reeds that generate the instrument tones. These are organized in different sounding banks, which can be further combined into registers producing differing timbres. All but the smaller accordions are equipped with switches that control which combination of reed banks operate, organized from high to low registers. Each register stop produces a separate sound timbre. See the accordion reed ranks and switches article for further explanation and audio samples.
All but the smallest accordions usually have treble switches. The larger and more expensive accordions often also have bass switches.
Classification of chromatic and piano type accordions
In describing or pricing an accordion, the first factor is size, expressed in number of keys on either side. For a piano type, this could for one example be 37/96, meaning 37 keys (three octaves plus one note) on the treble side and 96 bass keys. After size, the price and weight of an accordion is largely dependent on the number of reed ranks on either side, either on a cassotto or not, and to a lesser degree on the number of combinations available through register switches. Typically, these could be announced as Reeds: 5 + 3, meaning five reeds on the treble side and three on the bass, and Registers: 13 + M, 7, meaning 13 register buttons on the treble side plus a special "master" that activates all ranks, like the "tutti" on an organ, and seven register switches on the bass side.
Accordion player in a street in the historic centre of Quito
The larger piano and chromatic button accordions are usually heavier than other smaller squeezeboxes, and are equipped with two shoulder straps to make it easier to balance the weight and increase bellows control while sitting, and avoid dropping the instrument while standing.
Other accordions, such as the diatonic button accordion, have only a single shoulder strap and a right hand thumb strap. All accordions have a (mostly adjustable) leather strap on the left-hand manual to keep the player's hand in position while drawing the bellows. There are also straps above and below the bellows to keep it securely closed when the instrument is not playing.
Various hybrid accordions have been created between instruments of different buttonboards and actions. Many remain curiosities — only a few have remained in use:
- The Schrammel accordion, used in Viennese chamber music and klezmer, which has the treble buttonboard of a chromatic button accordion and a bisonoric bass buttonboard, similar to an expanded diatonic button accordion
- The Steirische Harmonika, a type of bisonoric diatonic button accordion particular to the Alpine folk music of Austria, the Czech Republic, Slovenia, the German state of Bavaria, and the Italian South Tyrol
- The schwyzerörgeli or Swiss organ, which usually has a three-row diatonic treble and 18 unisonoric bass buttons in a bass/chord arrangement — a subset of the Stradella system in reverse order like the Belgian bass – that travel parallel to the bellows motion
- The trikitixa of the Basque people, which has a two-row diatonic, bisonoric treble and a 12-button diatonic unisonoric bass
British chromatic accordion, the favoured diatonic accordion in Scotland. While the right hand is bisonoric, the left hand follows the Stradella system. The elite form of this instrument is generally considered the German manufactured Shand Morino, produced by Hohner with the input of Sir Jimmy Shand
Pedal harmonypump organ-like bellows attached, a type of accordion used sometimes in Polish folk music, which has a pair of