Many piano accordions and chromatic button accordions have switches between the right hand keyboard and the right hand body of the accordion. They are often called couplers, switches or acordion registers.
These register switches select various combinations of voices changing the sound of each note.
As an example, a two voice accordion can have up to three registers (one for each seperate voice and another for both voices playing at the same time).
A three voice accordion can have up to seven different registers and a four voice accordion can have up to fifteen.
Sometimes the number of switches can be different from the number of registers.
On a two voice accordion, for example, it is common to have only one register (both voices sounding together) with no switches to change between different combinations.
It is also common that a two voice accordion might have three switches with one of the switches selecting both voices together and the other two switches both selecting the same reed which means it has three switches but only two registers.
For all our accordions, we specify the number of available “registers” separately to the number of “switches” on the accordion.