An anechoic chamber is a room with walls that absorb sound and vibrations, often used for testing microphones and instruments. The first wedge-shaped anechoic chamber was built in 1940, and special chambers are also built for testing electromagnetic devices. Research in anechoic chambers has led to the development of loudspeakers that project virtual sound around the listener.
An anechoic chamber is a room with special walls that absorb as much sound as possible. Anechoic means “without echoes”. Sometimes the entire room even rests on shock absorbers, canceling out any vibrations from the rest of the building or from outside.
The material lining the walls of an anechoic chamber uses wedge-shaped panels to dissipate as much audio energy as possible before reflecting it away. Their special shape reflects the energy at the tip of the wedge, dissipating it as vibrations in the material rather than in the air. Anechoic chambers are often used to test microphones, measure the precise acoustic properties of various instruments, determine exactly how much energy is transferred in electroacoustic devices, and perform delicate psychoacoustic experiments.
The world’s first wedge-shaped anechoic chamber was built in 1940 in Murray Hill, at Bell Labs in New Jersey. It is enclosed in more than a meter of concrete to protect it from outside noise. Its creators boasted that the chamber absorbs over 99.995% of incident acoustic energy above 200Hz. The wedge-shaped panels are incapable of absorbing lower frequencies, but these frequencies carry little energy and are inaudible for the human ear. At one point, the Murray Hill room received a Guinness Book of World Record award for being the quietest room in the world.
John Cage, a famous experimental composer, was inspired when he entered Harvard’s anechoic chamber in the 1940s and heard the sound of his own blood circulating. He ended up composing a three-minute piece that consisted of nothing but silence, to allow the audience to reflect on the reality that no person has yet been able to escape noise entirely, except presumably the deaf.
Special anechoic chambers are also built for testing a variety of electromagnetic devices. Differently shaped wedges allow for the reflection of different frequencies, such as radio.
Research in anechoic chambers into the specific ways in which the human head reflects sound energy has led to the development of loudspeakers that project virtual sound around the listener. These speakers exploit the way we hear sound to make us think it’s coming from one direction when it’s actually coming from another. One day it may be possible to simulate entire orchestras with just a couple of speakers.
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