I recently came across this cool piece from Minnesota Public Radio about the Guinness World Record holder for World's Quietest Room. It's an anechoic chamber at Orfield Labs in Minneapolis, MN. A typical quiet room measures about 30 decibels. A normal conversation is about 60 decibels. This room has been measured at -9 decibels.An anechoic chamber is a room in which sound is absorbed, rather than reflected. In this room, the walls, floor and ceiling all absorb sound instead of letting sound bounce off them, as most surfaces do. Orfield Labs' anechoic chamber is 99.99% sound absorbent. This is accomplished with thick double-insulated walls made of steel and concrete, lined on the inside with 3.3-foot thick fiberglass acoustic foam wedges.It's so quiet, you can actually hear your own internal organs at work: your beating heart, your gurgling stomach, even the tiny noises produced by your ears. People have reported hallucinations after spending 30 minutes in the room. It's a completely disorienting experience. It's so unpleasant that the longest anyone has ever spent alone in the chamber is 45 minutes.Listen to the interview at MPR here