Prepared piano in the context of "Prepared guitar"

Henry Dixon Cowell (/ˈkaʊəl/; March 11, 1897 – December 10, 1965) was an American composer, writer, pianist, publisher, teacher and the husband of Sidney Robertson Cowell. Earning a reputation as an extremely controversial performer and eccentric composer, Cowell became a leading figure of American avant-garde music for the first half of the 20th century — his writings and music serving as a great influence to similar artists at the time, including Lou Harrison, George Antheil, and John Cage, among others. He is considered one of America's most important and influential composers.

Cowell was mostly self-taught and developed a unique musical language, often blending folk melodies, dissonant counterpoint, unconventional orchestration, and themes of Irish paganism. He was an early proponent and innovator of many modernist compositional techniques and sensibilities, many for the piano, including the string piano, prepared piano, tone clusters, and graphic notation. The Tides of Manaunaun, originally a theatrical prelude, is the best-known and most widely-performed of Cowell's tone cluster pieces for piano.

An experimental musical instrument (or custom-made instrument) is a musical instrument that modifies or extends an existing instrument or class of instruments, or defines or creates a new class of instrument. Some are created through simple modifications, such as cracked cymbals or metal objects inserted between piano strings in a prepared piano. Some experimental instruments are created from household items like a homemade mute for brass instruments such as bathtub plugs. Other experimental instruments are created from electronic spare parts, or by mixing acoustic instruments with electric components.

The instruments created by the earliest 20th-century builders of experimental musical instruments, such as Luigi Russolo (1885–1947),Harry Partch (1901–1974), and John Cage (1912–1992), were not well received by the public at the time of their invention. Even mid-20th century builders such as Ivor Darreg, Pierre Schaeffer and Pierre Henry did not gain a great deal of popularity. However, by the 1980s and 1990s, experimental musical instruments gained a wider audience when they were used by bands such as Einstürzende Neubauten and Neptune.