The anechoic chamber refers to a room with a free sound field, that is, there is only direct sound without reflection sound. In practice, it can only be said that the reflected sound in the anechoic chamber is as small as possible. In order to obtain the effect of the free sound field, it is required that the six faces in the room have a high sound absorption coefficient, and the sound absorption coefficient should be greater than 0.99 in the frequency range of use. Acoustic cusps are usually laid on six sides, and the wire ropes are installed on the ground.
The other structure is a semi-anechoic chamber, the difference is that the ground is not treated with sound absorption, but the floor is tiled with a tile or terrazzo to form a mirror surface. This muffling structure is equivalent to half the height of the anechoic chamber, so we call it a semi-anechoic chamber.
The anechoic chamber is designed to free the sound field, and the indoor anechoic cusp structure is required to achieve sufficient noise reduction. It is also necessary to isolate the outdoor air sound and structural sound transmission. Therefore, the anechoic chamber needs to adopt strict vibration isolation and sound insulation measures in the overall structure to obtain a lower noise floor.
Usually, the anechoic chamber adopts a double-wall structure with completely separated foundations, and correspondingly, the door of the anechoic interior and exterior wall also adopts a soundproof door or a double door. In order to isolate the transmission of solid sound, the anechoic chamber is usually placed on the vibration isolator, and the natural frequency of the isolator system is designed to be around 5 Hz.
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