The main differences between the acorden and the bandonen lie in their size, sound, and playing technique. The acorden is larger and produces a brighter, more versatile sound, making it suitable for a wide range of musical styles. In contrast, the bandonen is smaller and has a more melancholic, expressive sound, often associated with tango music. These differences impact their roles in traditional music by influencing the types of melodies and emotions they can convey, with the acorden being more versatile and the bandonen being more specialized for specific genres like tango.