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An anechoic chamber is an experimentation room whose walls absorb sound or electromagnetic waves, reproducing free field conditions and therefore causing no echo that could disturb the measurements. Such chambers are used to measure acoustic or electromagnetic waves under free field conditions, that is to say in the absence of components having undergone a reverberation on the walls. The sound level is 9.4 db, lower than that of a forest (30 db), a whisper (20 db) or the ticking of a watch (10 db). The underwater equivalent exists, with anechoic swimming pools, for example, used by the military to produce complex acoustic coatings.

The room is covered with dihedrals (sometimes polyhedra) generally made of a porous material (polymer foam, glass fibers) absorbing sound waves. The quality of the absorption depends on the size of these dihedrals and the properties of the material used. This type of chamber makes it possible to artificially recreate so-called “free field” conditions (sound propagates without reflection). Such chambers can be used for directivity or sensitivity tests of a microphone as well as for measuring the bandwidth of a loudspeaker or an acoustic enclosure. They are also used to position the most important sources of noise in a machine, or to measure acoustic power while avoiding external noise. Contrary to what would be desirable, anechoic chambers are not so over the entire extent of the sound spectrum: they have a low limit, linked to their dimensions and to the wavelengths in question, below which the field conditions are no longer met and therefore the measurements carried out are invalid.

In an anechoic chamber, our hearing adapts and develops sufficiently to hear the sounds emitted by our body. The absence of external noise disrupts our sense of balance and our brain can no longer locate and orient itself in space and the sounds emitted by our body eventually become unbearable to the point of hallucinations.