High-end professional accordions often feature a "converter" switch that toggles the left-hand buttons between Stradella (chords) and Free Bass (melodies) modes. 2. Specialized "Bass Accordions"
Accordions are categorized by the number of bass buttons they possess, which determines their musical range and weight. Bass Accordions
Because they require large reeds and bellows to produce low frequencies, they can be quite heavy and air-hungry. 3. Comparison of Bass Button Sizes Bass Accordions
The most common system. Buttons are arranged in rows and columns based on the Circle of Fifths . Bass Accordions