When looking at the different types of accordion, something you will often hear is the phrase double or single Cassotto or even tone chamber. The word Cassotto is an Italian word meaning ‘Box’ and when we use the word in the context of the accordion, we are referring to a special sound box or chamber that the sound travels through before it reaches the listeners ear and this gives the accordion a more mellow tone that is often associated with instruments used for – although not confined to – Jazz music.
Although the purist musette player will not allow his accordion to have any reeds in a cassotto chamber, I personally feel it adds to the flexibility of the instrument giving an extra depth and quality to the sound. It is usual that only the better quality instruments and usually instruments with handmade reeds that will employ the cassotto chamber but there are always exceptions.
The term single or double cassotto refers purely the number of reed sets that are playing through the chamber. If you look at fig.1 on the illustration , you will see the standard accordion reed layout. In fig. 2 however, you can see the more common layout of a double cassotto instrument. Cassotto adds both weight and due to it’s more complicated construction, a higher cost price to the accordion. But in my opinion, its an acceptable trade for the far superior tone that can be achieved.