A string orchestra is an orchestra that consists solely of instruments in the violin family. Such orchestras are often comparable in size to the strings section of major orchestras and are likewise divided into five sections: first and second violin (each usually playing different parts), viola, cello, and, usually, double bass. However, they can also be smaller, down to chamber orchestra size, with as few as a dozen musicians and sometimes performing without a conductor. Compositions for the string orchestra have been written by many well-known composers including Mozart, Haydn, Mendelssohn, Tchaikovsky and Barber.