The two-part harmony the Chapin Sisters have mastered didn’t come automatically. The duo, made up of Abigail and Lily Chapin, was once a trio. Fellow founding member Jessica Craven departed in early 2010 after having a baby, but that didn’t stop Abigail and Lily. The pair forged on, adjusting to life with only two voices. They released the group’s second album “Two” in the United States back in September, and have been playing shows off and on for the last 14 months. The Chapin Sisters perform at Jammin’ Java on Monday.

“The dynamic is very different in every way,” said Abigail during a recent phone interview. “It took us a while to realize how it was different and even musically how it was different, how to approach songs differently and how to arrange them. We had to really sort of learn how to tailor things differently.”