Free Reed Instruments

Corona II Classic Accordion
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There are two categories of instruments that employ a reed—fixed reed instruments (think the saxophone and oboe), and free-reed instruments, such as the accordion or melodeon.

Here's the difference:

Fixed reed instruments are generally mouth-blown, and the vibrating reed is used to vibrate a column of air, making the sound. The dimensions of the column of air determine the pitch or frequency of the musical note produced. Air can only be blown or moved in one direction.
Free-reed instruments are generally bellows-driven, in which moving air vibrates a reed in a chamber to produce the sound. In free reeds, the pitch is determined by the reed's length, thickness and stiffness. In some free-reed models, compressing or expanding the bellows moves the air in different directions across the reed, producing distinct sounds.

Now that free-reed instruments have been defined, read on for descriptions of the primary free-reed instruments used in Celtic music and some of the chief differences between them. Since all three are closely related, the distinctions are on the subtle side.

Accordion (or Accordeon)

It is helpful to lead off with a description of the accordion, not because its use is so dominant in Celtic music (it’s not), but because many free-reed instruments are considered to be part of the accordion family. Accordions have a bellows with many folds; another consistent feature is a keyboard with from five to 50 keys. Accordions are unique because they may have a keyboard similar to that of a piano—with the familiar white and black keys—or they may have several rows of round button keys, as do the other instruments in the accordion family. To provide instant clues as to which type of keys are used, some people prefer a variant spelling for button key instruments (accordeons with an “e”) instead of accordions (with an “i”), the spelling always used when referring to accordions that have piano keys.

Depending on the model, the accordion can be described as single-action (diatonic type) or double-action (chromatic type). Double-action (unisonoric) accordions produce the same notes when the bellows are expanding as when they are contracting, while single-action (or bisonoric) accordions give different notes when the player expands and contracts the bellows. For reasons that are obvious if you’ve ever seen one in action, single-action models are sometimes called “push-pull” accordions.

Melodeon

So what makes a melodeon a melodeon? A melodeon is most definitely a type of accordion, but with a few restrictions. First, a melodeon always has button keys (two or three rows of them), never a piano-style keyboard. In addition, a melodeon is always single-action (see above); pulling the bellows out generates a different note than pushing the bellows in. For all practical purposes, two players—one talking about his melodeon, and the other about his two-or three-row diatonic button-key accordion—will be talking about the very same thing.

Concertina

Two characteristics that distinguish the concertina are its size (smaller than other free reeds) and its shape (hexagonal). Rows of buttons are at each end, and the different types vary only in the layout of the keys. Another key difference between concertinas and accordions is that a concertina’s buttons are laid out in the same direction as the bellows, while accordion buttons are set perpendicular to the direction that the bellows move. The three main types of concertina are described below.

Anglo—An Anglo concertina is single-action, so compressing and expanding the bellows produces different notes. Buttons for the high notes are located on the right-hand end of the instrument, low-note buttons on the left.
English—English concertinas play the same note whether you are pushing or pulling, and are fully chromatic.
Duet—Duet concertinas offer what some would call the best of both worlds, while being the trickiest to master. Like the English, the same note plays whether squeezing or extending the bellows, but like the Anglo, the treble notes are on the right hand end, and the bass notes on the left.