The combination of a string quartet is 2 violins, 1 viola and 1 cello. A string quartet is a musical ensemble consisting of four string players who play instruments that are typically bowed or plucked, such as violins, viola, and cello. The most common and traditional combination of a string quartet is two violins, one viola, and one cello. This combination of instruments provides a wide range of sound and tone, and allows for complex and intricate harmonies to be created. While there are other combinations of string instruments that can create beautiful music, the combination of two violins, one viola, and one cello is considered the classic and most recognized form of a string quartet.