Physically these are mostly identical to the two row diatonic but instead of being “fourth apart” . the two rows are just one semitone apart, i.e instead of being 4 whole notes apart, they are 1/2 a note apart (not strictly true but it makes explaining it simpler). If Celtic traditional music is your thing then this is definitely the starter box for you.
Common keys for these are
- B C . Originally Used for Scottish music and more recently Irish traditional music
- C C# . I have never quite worked out what these are for but back in the old days these used to be all you could get! a lot of older two row CBAs are in this key and these were used in English and Irish music until they diverged
- C# D . More modern and becoming popular these are commonly used for Irish and Scottish traditional music
- BCC# Actually a three row these are a Scottish beastie and may have unisonoric stradella bass end . i.e the same note plays push or pull
Whilst there seems to be a bit of a Celtic bent here anything can be played on these and a good way to think of them is as a one row with a full hand of accidentals on the second row. Theoretically this makes them chromatic. This is a brilliant system to learn but it will confuse the hell out of you if you ever pick up a fourth apart box and vice versa
- One row diatonic button Accordion or Melodeon (e.g Hohner HA114 . including cajun quebecois etc)
- Two row Diatonic Button Accordion or Melodeon (e.g Hohner Pokerwork including 2 1/2 row)
- Club Accordion (eg Hohner Cub IIB)
- Three row Diatonic Button Accordion (e.g Hohner Corona)
- Two row Chromatic Button Accordion (e.g Hohner Double Ray small)
- Chromatic Button Accordion (full size)