Among all the classical music mediums, the string quartet possesses a singular combination of intimacy and immediacy that's rare in other forms. As part of the Eastman-Ranlet Series, the storied Takács Quartet takes to the stage Sunday at Kilbourn Hall to perform string quartets by two of the greatest melodists in compositional history: Mozart, with his String Quartet No. 21, and Mendelssohn, with String Quartet No. 6. But perhaps most compelling here is Bartók's darkly beautiful and enigmatic String Quartet No. 1. As a whole, the program is an excellent blend of sonic comfort and dramatic tension.