How is a string quartet similar to a soprano, alto, tenor, and bass vocal ensemble?

A string quartet and a vocal ensemble consisting of soprano, alto, tenor, and bass (SATB) voices are similar in that both are defined as a quartet—a musical composition or group of four performers.1

The fundamental similarity lies in their structure as four-part ensembles. Just as a vocal quartet utilizes four distinct voice ranges to create a balanced harmonic texture, a standard string quartet—comprising two violins, a viola, and a cello—uses these four instruments to achieve a similar four-part musical arrangement. In mature Classical compositions, such as those by Joseph Haydn, the string quartet is characterized by the equal participation of all four instruments, mirroring the way an SATB ensemble balances the four distinct vocal parts to form a cohesive whole.21