However, the working space is much larger than the standing wave tube facility, which is better suited to the laboratory measurement. The random incidences of sound wave are close to the practical conditions and therefore, this method is superior to other methods. The reverberation chamber is applicable to the measurement of the sound absorption coefficient with random incidences. ![]() The unparallel irregular walls are used and the walls are glazed (polished concrete, glazed tiles, painted) to reflect the sound waves as much as possible.Ī diffuse sound field can be formed in the reverberation chamber to provide a random incidence for the sample. The reverberation chamber volume for the measurement of acoustic power from the noise source must be more than 200 times larger than that of the noise source volume. The chamber volume V must be larger than 100 m 3, the maximum line distance must be less than 1.9 V –3, and the measuring low frequency limit is 1,000 V –3. In addition, the reverberation chamber must meet the following requirements : All the side walls of the chamber reflect the sound waves effectively and the sound waves from different directions are nearly the same, to ensure that there is no big sound pressure change in the chamber except for the area close to the sound source. It shall be noted that five measuring positions are selected, and three damping curves with at least a 35-dB straight-line range are needed for each position. The emitting and receiving of sound go through a 1/3 octave filter or an octave filter. ![]() The reverberation time (the time for the sound energy damping of 60 dB) of the empty chamber needs to be measured before measuring the sample, and then the sample is placed in the center of the chamber for the following measurements: The sample has an area of 10–12 m 2, the distance of the sample boundary to the chamber wall is at least 1 m, and the sound source is white noise (i.e., the noise energy is the same in the equal broadband in a wide range of frequencies). Where t x (s) is the time for the energy density of sound by a damping of d (dB).
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