Accordions from A to Z (Part 1, A to C)

By David Tong

Learning to play the accordion is quite a challenge, but it helps if you know how it works and what’s inside it. This multi-part series presents information on a whole series of interesting topics taken alphabetically. 


According to the Concise Oxford Dictionary an accordion is ‘a portable musical instrument with reeds blown by bellows and played by means of keys and buttons’.

The parts of an accordion

The parts of an accordion

The picture shows an example of a full-sized 120-bass piano accordion, with the various parts labelled.  The actual model is a top of the range professional instrument with five bass voices and five treble voices, two of them in cassotto.

American Tuning

Musette or Tremolo Tuning with detuning by about 5 cents is often known as American tuning.   Effectively this is equivalent to no detuning at all (‘straight tuning’) because tuning cannot be absolutely precise, and all reeds drift to a slight extent over a period of time.  American tuning is ideal for classical music, but may not satisfy those who associate the accordion with French and other folk music.

Bass Coupler Labels

Bass couplers are not always labelled and when they are, the symbols used are not as standardised as are the treble symbols. However the symbols below are in common use.  They are shown as they would be seen (with difficulty) by the person wearing the accordion.  Only the largest accordions have five bass voices. Most only have four, and some only three.

Bass coupler symbols

Bass coupler symbols

From left to right the five individual dots indicate the individual bass voices, beginning with the deepest, as follows: bassi, terzetto, naturale profunda, naturale, and naturale acuta or ottavina.  Of course the dots usually appear in combination rather than singly.  The right-hand symbol indicates that all five bass reeds are selected.

These symbols indicate the voices that are used when you press a bass or a counterbass button.  The voices used when you press a chord button are different and do not include the deepest voice or voices.  This gives you the option to force whichever chord inversion you wish to have by combining the chord button with an appropriate bass or counterbass button.

Bass Mechanism

Bass pallets before bass mechanism is fitted

Bass pallets before bass mechanism is fitted

A typical accordion has two rows of twelve pallets in the bass section.  Pallets in the back row (furthest from the buttons) activate the lowest two voices, and those in the front row activate the highest two or three voices.  Pallets in the same position along each row produce the same note in the chromatic scale (but in different octaves).

Same bass section after completion

Same bass section after completion

Pressing each chord button activates the correct pre-programmed combination of between three and four pallets from the front row only (i.e., the higher pitched voices) to produce the desired chord.

Pressing a bass or counterbass button activates the pallet for the desired note in both rows at the same time.  Thus a bass note is always deeper in pitch than a chord and this is what gives the characteristic ‘oom pah pah’ type of bass accompaniment.

Hohner's modular bass section

Hohner's modular bass section

The two photographs above show the traditional Italian style of bass mechanism before and after the button mechanism has been assembled.

The third photo shows the bass mechanism used by Hohner in their Amica range of instruments which are assembled in China. This is built as a subassembly and tends to be more shock-resistant than the traditional style of construction.

Bass Voices

In accordions with four bass voices the highest pitched voice (called naturale) is equivalent to the octave that includes middle C from the mid-range treble reeds (clarinet).  The other voices extend lower an octave at a time and are called naturale profunda, terzetto, and bassi.

The four reed sets in an accordion with four bass voices.

The four reed sets in an accordion with four bass voices.

In this photograph, each reed block carries two of the four bass voices.  The extra voice in accordions with five bass voices is one octave higher than naturale and is called naturale acuta or ottavina.

The lowest bass note is seldom quoted in manufacturers’ literature, but E to C are all found depending on the maker and the model.  Lower reeds generally use more air than higher ones, so larger accordions tend to extend deeper into the bass.


Mechanically and musically the bellows do for the accordion what the lungs do for the singing voice.  As well as providing a flow of air past the reeds to produce the sound, they are also the main way of adding expression to the music.

‘Bellows control’ is the most crucial and difficult aspect of playing the accordion.  The aim is to avoid bellows changes in the middle of musical phrases and to use the pressure to control the dynamics in a musically sensitive way.  It takes a lot of practice before this becomes intuitive.

The bellows are made from a special cardboard reinforced with cloth and cunningly folded.  Typically soft leather is used for the corner pleats as these are subject to the most bending.  The long edges are reinforced with special decorative tape and the corner edges with curved metal pieces that are pressed into place.

The bellows need to be airtight and also very flexible so as not to waste energy.  The number of sections varies from model to model.

Bellows Straps

Accordions are seldom completely airtight, especially older ones, and if the accordion is not standing upright on its four feet the bellows will slowly fall open.  To avoid this a leather strap with a press-stud is usually fitted to each end of the instrument to clamp the bellows shut.

Bellows straps tend to spoil the clean lines of the instrument and many French accordions dispense with a clamp altogether.  In some Hohner accordions an internal latch is fitted for the purpose.

Button Accordion

Button Accordion

Button Accordion

This could refer to a diatonic instrument like a melodeon, but in accordion circles it means ‘chromatic button accordion’.  These are very similar to piano accordions except that the treble keyboard uses buttons instead of piano keys.

Several ‘systems’ for mapping the notes to the buttons exist.  These tend to be associated with specific countries or regions.  The so-called B and C-systems are both offered by most manufacturers.  The C-system is the standard in France.

Cassotto (Tone chamber)

Pressing a treble key opens the air valve (or ‘pallet’) that normally closes off the air supplies to the reeds concerned.   It uncovers a hole through which the air passes and through which the sound emerges. In a non-cassotto accordion, these holes are arrayed on a flat aluminium plate beneath the decorative grille, and the sound comes straight out, as it were, fresh from the reed.

Showing the mouth of a cassotto chamber

Showing the mouth of a cassotto chamber

In contrast the holes associated with voices that are ‘in cassotto’ are arrayed on the side wall of a rectangular box maybe 12cms deep and 3cms wide which runs the full length of the keyboard.  The photograph shows the mouth of the tone chamber in a four-voice Beltuna Prestige model.

Just as talking into cupped hands alters the timbre of the voice (try it!), the effect is to alter the timbre of the sound.  It takes the edge off the ‘reediness’ and makes the sound more mellow.

Celluloid Finish

Traditionally, accordions have been finished with a thin decorative layer of celluloid that is applied as a kind of shrink-wrapping.  It comes in many colours and designs, including a very characteristic pearloid effect.  As well as providing a very durable surface it also adds strength to the overall structure.


A cent is a pitch difference of one hundredth of a semitone.  Differences of less than about 5 cents are inaudible to most people if they hear the two notes separately.  However if you hear two notes simultaneously you can detect very small pitch differences.  The two waves go into and out of step and ‘beat’ together giving a tremolo effect.  If the two notes have frequencies 2Hz apart, for example, they beat together twice per second.

Since there are 12 semitones in an octave, and 100 cents in a semitone, the frequency ratio between two notes one cent apart is the 1200th root of 2, or 1.0005778.  Knowing this, and the fact that A above middle C has a frequency of 440Hz, you can calculate the audible beat to be expected for, say, a given degree of tremolo tuning or French musette tuning.

For example, sharpening middle A by 20 cents as in French Musette shifts the note from 440Hz to 440 x (1.0005778)20 or 445.1Hz.  This is 5Hz higher than the unshifted note, so the two played together produce 5 beats per second.

Chest Mat

A chest mat is a durable protective flap made of padded nylon material fastened to the back of an accordion with press-studs.  It protects the bellows from damage from items of clothing, and vice versa.

Not all instruments come with them fitted but they are easy enough to fit provided you are brave enough to apply woodscrews to your shiny new accordion.


Chest mat

Chest mat

Although a chord button produces the chosen chord when pressed, it may be in root position, first inversion, or second inversion.  The actual inversion will depend on the chosen button and on which note the manufacturer selected to be the lowest in each of the bass voices.

It is the lowest note in a chord that defines the inversion and the reeds controlled by the bass buttons are always at least an octave below those controlled by the chord buttons.  So by playing a bass button and a chord button together you can make the inversion the one you want.

For example the C-major chord button plays C, E, and G, but the actual inversion depends on the way the bass voices are allocated within the instrument. Playing the C bass as well forces the overall chord to be in root position.  Similarly E counterbass forces the first inversion, and G bass forces the second inversion.

Chromatic Accordion

A fully chromatic accordion can play all the semitones in an octave and can therefore play in any key.  The term ‘accordion’ used alone usually implies ‘chromatic accordion’.  It also implies an instrument that plays the same note for each bellows direction. The keyboard may have piano keys or buttons.


A set of couplers, or ‘switches’, is used to select a particular group of voices out of the ones available.  Then when a key is pressed all the selected voices play at the same time.  All except very small accordions have couplers on both the treble and bass sections. They are usually engraved to show which voices will sound when each one is activated.

An accordion described as having ‘11 + 7’ couplers or switches has eleven treble couplers and seven bass couplers, whereas ‘11 + 7 + M’ means that there is also a bar fitted to the edge of the keyboard.  When pressed with the palm this immediately cancels the existing selection and selects the master coupler.

Some accordions have chin-couplers so they can be operated without taking the hands from the keys.  On French button accordions, the treble couplers are usually operated by sliders mounted just behind the edge of the keyboard and conveniently placed for the right thumb.