Poême électronique
A synesthetic arousal of images in motion, sounds and lights. I can only imagine how impressive Poême électronique was when presented live in the form of performance at the 1958 Brussels Worlds Fair. 425 speakers were placed all throughout the space created by LeCorbusier and Iannis Xenaki, with the purpose of having Edgard Varêse's sound appear to move in space, all around the audience. A sort of precursor of surround sound.
In LeCorbusier's own words: "I will not make a pavilion for you but an Electronic Poem and a vessel containing the poem; light, color image, rhythm and sound joined together in an organic synthesis". Documentation and images here.
Audio Arts archive
Audio Arts was an audio cassette magazine set up in 1973 by Bill Furlong as an advanced and experimental project. Its archive comprises artists' interviews, voices and sound art and it is now exhibited at the Tate Britain until the 27th August, where 4 hours of recordings can be accessed for free and listened by using headphones. The same material can be accessed and explored online here.
Silence
You probably already know about the experience of John Cage in the anechoic chamber at Harvard University, a room especially designed to completely absorb every single sound. In that occasion, Cage entered the room persuaded to be able to hear silence, but he discovered the impossibility of it instead. In fact, even in that extreme condition, two sounds were present: the low frequency sound of the blood in circulation and the high frequency sound of the nervous system. That experience led to the composition of 4'33''.
It is fascinating to think of our body as the primordial, true instrument.