Inside Microsoft’s headquarters in Redmond, Washington, there is a room where sound behaves in an unfamiliar way. Noise from outside does not penetrate, and any sound made within its walls fades out almost instantly. The space is known as an anechoic chamber, designed to completely absorb echoes rather than reflect them. A simple clap of hands disappears within a few seconds, leaving behind a stillness that may seem unnatural. During ultra-sensitive testing, the average background noise level was measured at minus 20.35 decibels. According to the World Records Academy, that reading set the record for the quietest room in the world. This figure sits below the limit of human hearing, making the chamber one of the quietest controlled environments ever created for scientific and acoustic testing purposes.
Microsoft’s anechoic chamber holds the record for the world’s quietest room
The room is designed as a room within a room. The room consists of a large masonry and concrete shell that is lined with thick steel plates. Inside it is a small steel chamber supported on vibration-absorbing springs. The goal is isolation from both airborne sound and structural vibration. The interior is covered with heavy insulation and glass fibre wedges that extend approximately 85 centimetres into space. These wedges line the walls, ceiling, and floor. Visitors stand on a suspended lattice floor that is positioned above additional wedges located below. The background noise inside the chamber is so low that it approaches what mathematicians describe as the theoretical limit of silence. It is close to the absolute zero of sound, a point beyond which there is almost nothing left to measure. A vacuum is the only quiet place, as sound can’t travel without air. In practice, the room represents the lowest level of sound ever recorded in a controlled setting. On that scale, it is the quietest place in the world.
measuring sound below the noise floor
Since the room is quieter than the electrical hiss of most instruments, standard measurement tools are not sufficient. The engineers used two Brüel & Kjaer type 4145 microphones, each with its preamplifier. Electrical noise varies randomly between channels, while the actual room signal remains consistent. By correlating both recordings and separating matching elements, technicians obtained the final reading. This is a technical process, but it is necessary when the signal itself is almost indistinguishable from silence.
How Do Companies Use Anechoic Chambers?
Anechoic chambers are used to test sound from high-precision products. Microsoft, among others, relies on such features to check microphones, headphones, and speakers. The chambers also help analyse subtle noises from keyboards, cooling fans and display components. Devices like Surface tablets, Xbox consoles, and HoloLens headsets have been acoustically tested in similar environments. Software products with strong audio elements, including Skype and the Cortana assistant, also benefited. In such places, even small hums become visible.
