Scientist at Orfield Laboratories in South Minneapolis have created an anechoic chamber that is 99.99% sound-absorbent.

Usually, a quiet room has a sound level of about 30 decibels, the anechoic chamber has a sound level of -9 decibels.
Obviously, the peculiar looking ceiling, floor and walls absorb sound rather than reflecting sound waves like normal objects do.

The've tested the room on a number of people. Apparently, after 30 minutes goes by, people in the chamber tend to begin hallucinating.
Nobody has been able to sit in the room alone longer than 45 minutes.

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