Percussion instruments produce sound when struck, scraped, or shaken. They include drums, cymbals, triangles, and many others. The drum set became popular in the late 1800s after the invention of the bass drum pedal, allowing one person to play multiple drums. Other important percussion instruments include timpani, which are kettle-shaped drums that can be tuned, and melodic instruments like the xylophone and harp. String instruments produce sound through plucking, bowing, or striking their strings and include instruments in the guitar, violin, and harp families.