The “indispensable” Emerson String Quartet (Newsday) embarks on an intrepid three-concert series pairing Beethoven’s “Razumovsky” Quartets with the complete Bartók cycle. For this second pairing, the illustrious ensemble delves into the folk influences of these inventive European masters. The exotic Russian folk elements in Beethoven’s “Razumovsky” Quartet in E minor, named for the Russian ambassador in Vienna, mirrors the vibrant folk echoes in Bartók’s Second and Fifth Quartets, alive with the dancing spirits of traditional Hungarian, Romanian, and Slovak songs.