An anechoic room is a special acoustic laboratory room whose boundary surfaces are designed in such a way that almost no sound is reflected.
The minimisation of sound reflection from the walls and ceiling is achieved by covering the room with absorption material, usually glass or mineral wool. In these materials the energy of the incident sound is converted into thermal energy. The energy can only be extracted by friction of the moving air. This means that the sound velocity must be greater than zero. Depending on the frequency, this is maximum at a certain distance from the concrete wall of the room. Porous material must then be present at this point to optimally dampen the corresponding frequency. In order to achieve the most complete sound absorption possible, the sound impedance must correspond to that of the air in the widest possible frequency range. This is achieved by constructing the lining from individual wedges of absorption material.
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