Trevor Cox of BBC Science Focus, talks about creating absolute silence. October 2020.
To get rid of all external sound, you might travel to a remote barren desert on a windless day or head to an acoustic laboratory with an anechoic chamber. But even then, you might be surprised to find a lack of absolute silence because your body makes sound.
You might hear a faint thud from the blood pumping close to your ears or a quiet hiss caused by auditory neurons spontaneously firing in the brain. Normally these are hidden by external sounds entering the ears, but in an anechoic chamber or silent desert they can become just audible.
Avant-garde composer John Cage wrote about hearing these when he visited the anechoic chamber at Harvard University, and this inspired his famous silent work4’33”.https://tpc.googlesyndication.com/safeframe/1-0-37/html/container.html
Because of the different setting, silence in a desert feels very different from what you experience in the laboratory. The silence in the anechoic chamber feels oppressive. This happens because anechoic chambers are covered in large foam wedges that muffle all the reflections from the floor, walls or ceiling. You can see walls, but you can’t hear them. When you talk in the chamber, your voice sounds oddly muffled, and listeners feel like their ears are partly blocked.
Microsoft’s anechoic chamber in Redmond, WA, USA holds the World record for the quietest place at -20.6 decibels, but actually many anechoic chambers are silent enough to experience no external sounds.
To achieve such low noise levels, chambers are built from heavy concrete and brick, separated from the fabric of the surrounding building by being mounted on springs to stop vibrations getting in through the floor. The same technique is how classical music concert halls and music studios are made quieter, though none of these achieve the silence of an anechoic chamber.
Read more about the science of sound:
- What’s a bitrate, and what has it got to do with music quality?
- How do amplifiers work?
- Bluetooth, AirPlay, Chromecast… Does it matter how I connect to my wireless speakers?
- Why does light travel faster than sound?