Background: Charles Edward "Charlie" Haden (August 6, 1937 - July 11, 2014) was an American jazz double bass player, bandleader, composer and educator known for his deep, warm sound, and whose career spanned more than fifty years. In the late 1950s, Haden was an original member of the ground-breaking Ornette Coleman Quartet. Haden revolutionized the harmonic concept of bass playing in jazz. About him, German musicologist Joachim-Ernst Berendt commented, "His ability to create serendipitous harmonies by improvising melodic responses to Coleman's free-form solos (rather than sticking to predetermined harmonies) was both radical and mesmerizing.
Context: In addition to his lyrical playing, Haden was known for his warm tone and subtle vibrato on the double bass. His approach to the bass stemmed from his belief that the bassist should move from an accompanying role to a more direct role in group improvisation. This is particularly clear in his work with the Ornette Coleman Quartet where he frequently improvised melodic responses to Coleman's free-form solos instead of playing previously written lines. He frequently closed his eyes while performing, and assumed a posture in which he bent himself around the bass until his head was almost at the bottom of the bridge of the bass.  In an interview with Haden, pianist Ethan Iverson noted that Haden's "combination of folk song, avant-garde sensibility, and Bach-like classical harmony is a stream in this music just as distinctive as Thelonious Monk or Elvin Jones."  Haden owned one three-quarter-sized bass, and one seven-eighth-sized bass. The larger bass is one of a small number of basses made by Jean-Baptiste Vuillaume, a French luthier, in the mid-nineteenth century. He greatly valued this bass, playing it only at recording sessions and jobs in close proximity to his home so as not to risk damaging it in transit. He attributed the bass's special and valuable nature to the varnish used by Vuillaume, which is similar to Italian varnish.  Haden suffered from tinnitus, a ringing in both ears that he believed he acquired from constant exposure to playing in proximity to drums, and possibly from an extremely loud concert in which he played during the late 1960s. He also suffered from hyperacousis, or sensitivity to loud noises. As a result, when he played with a drummer, he had to play behind a Plexiglass divider.  "American Quartet" pianist, Keith Jarrett, said of Charlie's way of playing, "He wanted to relate to the material in a very personal style all the time. He wasn't somebody to get into a groove and just enjoy it simply because it was a groove".
Question: Is there anything significant about Haden's musical style?

Answer:
he frequently improvised melodic responses to Coleman's free-form solos instead of playing previously written lines.