What does silence sound like?

By Rhys L Griffiths

Simon and Garfunkel famously sang about the sound of silence, but what does silence sound like?

Close your eyes and really listen to the sounds around you.  A lot of the time we can think that we’re sat in silence but if you really listen we can usually hear some sort of sound. For example, if I close my eyes I can hear the faint murmurs of colleagues chatting, the typing of keyboards and an irritating hum from a very chilly air conditioning unit. We are constantly surrounded by sound so how are we to know what real silence sounds like.

An anechoic chamber is a room that absorbs sound whilst also being insulated from exterior noises. The combination of this makes an anechoic chamber a quiet place and I mean a really quiet place. We measure sound in decibels. The more forceful the sound wave, the higher the decibel number and the louder the sound.  The interior of the chamber can typically have noise levels in the 10-20 decibels which is the equivalent to the sound of calm breathing. Rooms such as this can be used to measure noise output of machinery or to test recording equipment quality.

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© Steven Orfield

The image on the left is from the anechoic chamber at Orfield Laboratories in South Minneapolis. It has 3.3-foot-thick fibreglass acoustic wedges, double walls of insulated steel and foot-thick concrete. The room is 99.99% sound absorbent and Steven Orfield, the company’s founder and president, challenges people to see who can stay inside the longest. So far the record is 45 minutes. That may not seem a long time, but sitting in darkness with the absence of sound has the ability to induce hallucinations.  A Study was conducted by Mason and Brady where they placed people in a dark and silent room for 15 minutes to see if they did indeed experience hallucinations.  Some test subjects saw “objects that were not there, five had hallucinations of faces, four reported a heightened sense of smell, and two felt there was an evil presence in the chamber with them.”

This may seem a little extreme but in an environment like this the only thing capable of making any sound is you. You’ll be able to hear your heart beating, your stomach rumbling and even the blood gently pumping through your head.  Usually these sounds are covered by external noises and are inaudible but in the environment it can drive you mad.  in 2004 the Anechoic Test Chamber at Orfield Laboratories won the Guinness World Record for being the quietest place on Earth, giving a background noise reading of -9.4 dB(A) (decibels A-weighted). However that was beaten in 2015 when Microsoft’s anechoic chamber measured an impressive -20.6 dB(A)! Real silence may be impossible to achieve but this is the closest we have gotten so far. To see inside Microsoft’s record holding chamber then watch the video below.

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Posted in Engineering, Technology