“Mozart wrote so beautifully for strings plus, probably better than anyone,” Bill says at the beginning of this week. Our listening starts with Mozart’s quartets for strings plus oboe and flute, then his quintet for strings plus clarinet. In Tuesday’s hour, we will listen to Samuel Barber’s Dover Beach, written for a string quartet and baritone. Barber sang the baritone part at its premiere in Philadelphia. Bill then adds to our playlist Hindemith, Mahler, and Bartók. Strings Plus is a colorful listening experience that ends with the chamber music of Johannes Brahms, and Joan Tower’s Petroushskates played by the eighth blackbird ensemble.