Anechoic chamber

anechoic [ˌænɪˈkəʊɪk] adj.
(Physics / General Physics) having a low degree or absence of reverberation of sound.

In the late forties I found out by experiment (I went into the anechoic chamber at Harvard University) that silence is not acoustic. It is a change of mind, a turning around. I devoted my music to it. My work became an exploration of non-intention. To carry it out faithfully I have developed acomplicated composing means using I Ching chance operations, making my responsibility that of asking questions instead of making choices.

– John Cage, 1990

Here’s another description of Microsoft’s anechoic chamber:

Since I entered the chamber with two other people, the first thing I noticed was how voices changed. They became clipped, truncated, like someone was holding the mute pedal down on a piano. The subtle atmosphere and depth associated with room reverberation that we come to expect when hearing the human voice was totally gone. No echoes, hence the term “anechoic.” My own voice sounded like it was having trouble coming out of my head.

For a moment, I felt genuine disorientation, like the light-headedness you can get with low blood sugar. The guy who showed me the room said that, even though he works in there a lot, he still has moments when he loses his balance, because the ear uses sound reflections—in addition to inner-ear leveling—to position the head and body.

Sometimes we do not realize how much we rely on auditory cues to get a grip on reality.

Relevant.