great posts here!
i´ve not read it completly, but i´d like to share a little experience related to this thread.
while reading an interview from a well-known improv artist i know many years ago, he was asked about the meaning of “improvised music”. he answered improvised music doesn´t exist truly, because we´ve been previously experiencing that instrument (practice), or we´ve been taught on how to play it (theory).
i assume he was talking in a figuratively way…or maybe joking, because he´s a formed musicican/player. but taking his words on a daily basis, we´re improvisers since we wake up every morning 
i remember having lots of fun in a improvisation workshop from his partner in sound. we were just a few people using found materials, very simple things made from polyurethane foam, rubber, etc…almost everythin was recycled from rubbish. the place had amazing acoustics, so it helped to amplify the experience. honestly, it was one of the best sound-experiences i´ve dealed with. of course, we had no previous experiences using these materials as “instruments”…i don´t know if there was improvised sound-music-whatever, but it was funny and refreshing to me.
