But they paid extra attention to any minor feature that might bring unwanted sounds into the room. “The chamber itself is one that is commercially available so anyone can buy it,” says Gopal. Gopal and his team even suspended a specially designed air conditioning system and sprinkler system in the 4ft (1.2m) gap between the chamber and the concrete wall of the room it sits within. Seals around the doors of the chamber and the rooms surrounding it also help to keep noise from leaking in. A floor made from steel cables – the same kind used to stop fighter jets as they land on aircraft carriers – are knitted together like a trampoline net above the foam wedges on the bottom of the chamber. Each of its six surfaces is lined with clusters of 4ft-long (1.2m) wedges of sound absorbing foam, helping to prevent any echoes bouncing off the walls from any sound produced inside. The anechoic chamber is a cube measuring 21ft (6.36m) in each direction. I often joke that I aged six years in that time.” “It is why it took us more than a year and a half to build this thing. “This means the chamber doesn’t make direct contact with the building around it at any point,” says Gopal. The chamber itself floats on top of 68 vibration damping springs mounted on its own separate foundation slab. “This insulation makes a huge difference,” explains Hundraj Gopal, principal human factors engineer at Microsoft who led the team that built the anechoic chamber. If a jet was taking off just outside the building, you would hear little more than a whisper inside the final concrete bunker where the chamber is. This nest of rooms within rooms – each with walls up to 12 inches thick – helps to cut the noise reaching the chamber by around 110 decibels. The chamber sits at the heart of six concrete onion layers that help to block out sounds from the outside world. I don’t stay inside with the door closed very often.” “When you stop breathing, you can hear your heart beating and the blood flowing in your veins. “It is a very unique experience inside with the door closed,” says Munroe. The limit of human hearing is thought to be around 0 decibels, although just because our ears cannot pick it up, it does not mean no sound present, hence it is possible to get a negative value. It gets close to the limit of what should be possible to achieve without creating a vacuum – the noise produced by air molecules colliding with each other at room temperature is estimated to be about -24 decibels. To put that in context, a human whisper is about 30 decibels while the sound of someone breathing normally comes in at just 10 decibels. Microsoft’s engineers built the room – known as an anechoic chamber – to help them test new equipment they were developing and in 2015 it set the official world record for silence when the background noise level inside was measured at an ear-straining -20.6 decibels. Products like the Surface computers, Xbox and Hololens have all been developed here. The specially constructed chamber is hidden in the depths of Building 87 at Microsoft’s headquarters in Redmond, Washington, where the firm’s hardware laboratories are based. His office is the quietest place on the planet. While many people work in places filled with the tip-tap of keyboards, the hubbub of chatter from colleagues and a constant hum of computers, Munroe is surrounded by almost total silence. If LeSalle Munroe stands still for a few moments in his “office”, something unsettling can happen – he can hear the blood rushing around his body and his eyes squelch as they move in his skull.
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