Experimented with new techniques for playing the piano, including strumming the strings and playing complete tone clusters. gershwin babbitt cowell ives

Cowell

Explanation:

The first one who experimented with piano strings and clusters is Henry Cowell.  

He was the first one who asked the pianist to manipulate string and then when he discovered the sound.

Before that new sound, he discovered also tone clusters. Tone clusters were achieved by hitting the piano keys with elbows or fists.