The career path of a professional musician is not standard, by any means. The steps are only loosely prescribed, and the journey is wildly varied. Those who make it create their own opportunities, especially a young string quartet striving to carve out a place in a field with no job description. Meet the Hausmann String Quartet — first violinist Isaac Allen, second violinist Bram Goldstein, violist Angela Choong, and cellist Yuan Zhang — a dynamic young quartet that’s on the way up, pursuing a lifetime of chamber music one day at a time.