- Orfield Laboratories
- -24.9 decibel(s) (A-weighted)
- United States (Minneapolis)
The quietest place on Earth is the anechoic test chamber at Orfield Laboratories in Minneapolis, Minnesota, USA. In tests conducted on 19 November 2021, the ambient sound level inside the room was measured at -24.9 decibels.
The anechoic chamber at Orfield Laboratories is designed to enable accurate measurements of the sound levels produced by various test items. It comprises a large masonry and concrete chamber lined with 10.5-cm-thick steel plates, within which there is another, smaller steel chamber supported on vibration absorbing springs. The interior of this space is lined with a layer of heavy insulation covered with glass-fibre wedges that extend 85 cm into the space (including on the floor – users have to stand on a suspended mesh). The actual usable area inside is 3.7 x 3.1 x 3.52 m.
The design of this space means that the ambient sound level is lower than the noise floor (the electrical hiss) of even the most sophisticated scientific instruments. In order to get an accurate measurement, therefore, a pair of Brüel & Kjær type 4145 microphones were used, each with their own preamplifier. Because the electrical noise is random, it was be different between the two channels, while the measurements of the room itself were be the same. The final measurement was obtained by cross-correlating the signals from the two microphones and using the bits of the signal that matched.