Principle

A reed is a lamella made of reed, metal or plastic polymer, which vibrates when submitted to human or mechanical breath, producing then an audible sound.
A free reed is fixed at one end and vibrate through a window having a size slightly larger than the reed itself. The reed start vibrating when the air stream hits its external side.
In free reed instruments, these ones are placed on both sides of a base in such a way that a sound is produced whatever the flow direction. In order to avoid the parasite sounds from the non-vibrating reeds, a leather or plastic valve is fixed on the opposite side.

Reed tuning is obtained by scratching some material at the base (fixed) to lower the tone, or at the free end yo raise it.

Harmonica

Diatonic harmonica

The diatonic harmonica has only a diatonic scale (no accident), and is mainly used for traditional music.
Main models have 10 holes, and they are found in different scales.

Chromatic harmonica

The chromatic harmonica was invented by Hohner around the end of the XIXth century, to extend its capabilities to all music styles and scales. It is composed of two diatonic scales with half a tone shift, which can be openned with a sliding register.
The most common models have from 12 to 16 double holes.

Tremolo harmonica

The tremolo harmonica is a diatonic one, where the notes are duplicated both vertically and horizontally.
The reeds are tuned with a small difference, which produces the tremolo effect. These harmonicas have generaly 40 holes and some have holes on both sides.

Accordion

It was invented by the Austrian Cyril Damian in 1829, but some authors claim that the inventor is the German Friedisch Bushmann at about the same period.
It is a free instruments, the air flow being produced by means of a bellows which connects two sound boxes held by the musician in each hand.
The right hand box contains the free reeds to produce the melody, as the left hand one conatains the accompaniment with chords and bass notes.
At he beginning, the accordion is based on a diatonic scale with a 3 octave range. It is a bi-sonorous instrument as it produces two different sounds depending on the bellow direction.
It exists several sorts of diatonic accordions, with one, two or three button rows for the melody, a variable number of voices, chords and bass notes.
The chromatic accordion is issued from the improvements done on the diatonic one at the beginning of the XXth century, in order to expand itds capability.
First of all it is a uni-sonorous instrument, as the same button produces the same note whatever is the bellows direction. As a consequence, the notes on the keyboard are better organised, but its size increases accordingly to the number of buttons (one per note).
The left hand keyboard is also more complex and has chords in all tones.
There are several sort of chromatic accordions: the chromatic button accordion, the chromatic piano keyboard, and the concert chromatic accordion or harmoneon.

Melodeon

It is a diatonic accordion with only one row of buttons for the melody; it has generaly four voices (two medium, one bass and one trebble) which are actuated by meqns of push-pull registers. At left hand there are only two buttons with bass note and chord but with three voices.
The melodeons are often based on a C major scale, but there are some built in D major.

Two-row diatonic accordion

These diatonic accordions have two rows of buttons, each one based on a diatonic scale spaced with a fourth. In France or in America, the scales are mostly G (outer row) and C (inner row), but other tones exist such as D/A (France), C/F (Germany), D/G (U.K.), etc...
In Ireland the two scales are spaced by half a tone, which allows playing a chromatic scale. The most common types are B/C and C/C#, but other types exist such as C#/D and D/D#. This type of setup allows playing whithout too many changes in bellow direction, as the bow on a violin strings, which is often playing with.
The melody keyboard has generaly two voices, but sometimes a third one can be added using a register.
On trouve souvent des altérations placées sur les deux boutons supérieurs du clavier mélodique, ce qui rend leur usage quelque peu acrobatique car ils sont assez éloigné des notes naturelles auxquelles ils correspondent.
The two-row diatonic have from 8 to 12 buttons at the left hand, which are groupped by pair (bass notes and chord), and fitted to the melody scale tone.
Some models have a register to close the third in the chords in order to be able to play major or minor modes.

Three-row diatonic acordion

There are two main types of three-row diatonic accordions: three diatonic scales separated by a fourth, and two diatonic scales with a third (inner) row for the accidentals and some inverted notes (pushed when the same not is pulled on the wo other rows).
The first type results in two accordions in a single instrument, with a few additional possibilities due to the accidentals. An example of this type of accordion is the A/D/G one which can be found in France.
The second type is built in order to have the accidentals in the vicinity of the natural notes on the other rows. The simple systems have two buttons on the third row, which are often a duplicate of the two upper buttons on the diatonic rows. The complete systems include a full row that includes all accidentals for the full range, as well as some duplicate notes in the reverse direction (i.e. pulled G and pushed A).
At the left hand keyboard, the number of buttons varies from eight to twelve or sometimes eighteen.

Chromatic button accordion

This is the most common accordion that everyone konows from trafitional music to musette and jazz or classical.
The right hand keyboerd (melody) includes three to four rows of buttons (44 to 72). The talbature varies according to three systems: French, Italian, Belgian.
The left hand keyboard (accompaniment) includes from 60 to 120 buttons, splitted between bass notes and chords (major, minor, fifth, etc...).

Piano keyboard chromatic accordion

This accordion type appeared around 1850, and is still used mainly in North America and Eastern Europe.
The right hand keyboard is similar to a piano one and have from 37 to 41 keys. The left hand keyboard is identical to the button chromatic accordion one.

Harmoneon

Also named concert accordion, it was invented by the French Pierre Monichon around 1948 to make the instrument a classical one. It is made of two identical melodic keyboards, which allows any note combination.

Concertinas

It was invented by the English Charles Wheatstone more or less at the same time than the accordion by Damian.
It is a small hexagone shaped instrument similar to the accordion with two melodic keyboards.
There are several types of concertinas: English, Anglo and Duet

English

The english type is unisonorous and the chromatic scale jump alternately from right to left hand. The 48 buttons are placed on four rows, of which the two central ones are the diatonic scale.

Anglo

The anglo (anglo-german) tyype is a diatonic and bi-sonorous instrument, the scale of which starts at the left hand to continue on the right one.The 20 to 30 buttons are placed on two rows for two diatonic scales. The most common tone are C/G and G/D

Duet

The duet type is uni-sonorous and chromatic. The notes are placed on each keyboard in order to have the bass notes at the left hand and the trebble ones at the right hand. The 46 buttons are placed on four to five rows allowing a duplicate range close to an octave on both keyboards.

Bandoneon

It was invented by Heinrich Band around 1840 from the Wheatstone concertina. Its specific sound comes from the shape of its reeds, which vibrate by pairs spaced with one octave.
It exists two types of bandoneon: diatonic bi-sonorous, and chromatic uni-sonorous.
In fact the modern Argentinian instruments are bi-sonorous and include all accidentals. The keyboard tablature varies according to the country and manufacturer.

Melodica

It is a free reed instrument that combines human breathe and a piano type keyboard. The blow is applied by means of a mouthpiece (only positive blow), and the reeds are uncovered by the keys. It was invented by Hohner around 1959, and is generaly made of plastic except the reeds, which are made of metal.

Accordina

It was invented around 1938 by the French André Borel who was a chromatic accordionist. It is a mouth instrument with a chromatic button accordion keyboard. It has 44 buttons on three rows, whch makes a 3.5 octave range.

Harmonium

It was invented by the French François Debain around 1842 for replacing the pipe organ in private houses. It is a piano type keyboard instrument, but the sound is produced by free reeds, and the wind is produced by bellows actuated by the musician's feet. Each key can access a large number of reeds that can be openned or closed by registers, which gives the instrument a lot of capabilities.