The sound level of an average anechoic chamber is only around 30 decibels, but this Guinnes World Record quietest room in Orfield Labs, Minneapolis is having -9 decibels of sound level in the room, according to MPR News. Threshold of human hearing starts from 0 decibel and imagine you are trapped in a room with -9 decibels sound level? Definitely will go crazy after sometime. According to the experiment, the longest a person has ever spent alone in the chamber is 45 minutes as human start to hallucinate as the surrounding is too quiet.
Any way, just for your information, the world quietest room is built not for entertainment or just to break record. Orfield Labs built and uses this anechoic chamber to test the noise levels of various products such as LED lights, medical equipment and so on. "But watch out: it could easily become a place to drive people mad." - News Discovery
*Attention!* Check this link which is about Charlie who produce the podcast Composer Quest (not the point though). But this guy has a great blog sharing his experiences and knowledge about music composition, production, sound and psychology that might makes you 'Wow' about facts that you might not know earlier. And pss.. he had already visited the quietest chamber!
Note: Anechoic chamber (an-echoic meaning non-echoing/echo-free) is a room designed to completely absorb reflections of either sound or electromagnetic waves. They are also insulated from exterior sources of noise. The combination of both aspects means they simulate a quiet open-space of infinite dimension, which is useful when exterior influences would otherwise give false results. Source by wikipedia