Here’s a valuable resource on the string quartet and its history.
Coursera offers an on-demand free course called The World of the String Quartet. It was developed by the Curtis Institute of Music. It is taught by Arnold Steinhardt, first violin of the Guarneri String Quartet, and Mia Chung, an interpretive analysis instructor at Curtis.
The seven-week course (this is a suggested timeframe, it is go at your own pace) covers the following topics:
Week 1: An Overview
Week 2: Haydn, Mozart, and Beethoven
Week 3: Schubert, Mendelssohn, Schumann, and Brahms
Week 4: Smetana, Dvorak, Tchaikovsky, Borodin, and Bartok
Week 5: Debussy Ravel, Barber, Shostakovich, and Britten
Week 6: Schönberg, Webern, Berg, Ives, Cage, and Reich
Week 7: The Next Frontier
In addition, the course has its own webpage that includes links to performances and other online music resources. There are discussion forums so you can connect with others taking the course, and quizzes to check if you’re on the right track.
Individual videos are fairly short, typically under ten minutes, which makes it easy to watch one when you have a little spare time. So pour yourself a cup of coffee and get to know the string quartet!
Image attribution: Free clipart made available by clipartsheep.com.