James Andreassi’s long locks swing forward, his expression hardens, and his gestures become more dramatic: The actor is slipping into his part seemingly without realizing it. In a dressing room at Lyric Stage Company, he’s talking about his role as Ludwig van Beethoven and about the composer’s “Diabelli Variations.”

“The great biographical research to be done is to listen to the music. I just get lost in it,” he says. “So much of the work was produced when he was deaf, and that frustration, that anger, is apparent.”