Abstract
Obtaining the reverberation time of a multipurpose building is most effective when accurate data is used to simulate the building. Therefore, this study proposes a method of measuring the sound absorption coefficient that is close to the sound absorption performance of the conditions in which building materials are actually used. In addition, a sufficient diffusivity evaluation method for sound absorption coefficient measurement in a reverberation chamber is proposed, to address the sound absorption performance difference caused by internal diffusion of the reverberation chamber. When the sound absorption performance was evaluated after installing the specimen under the condition of minimized edge effect, the result obtained should closely match the sound absorption performance of the specimen surface. The sound absorption performance of the specimen ( α β E ≈ 0 ) with minimized edge effect and the sound absorption performance on the specimen surface ( α ∞ ) were proposed as an evaluation indicator of agreement between the values. Experimental results show that diffusion inside the reverberation chamber is enhanced when α ∞ − α β E ≈ 0 < 0.02, for which sufficient diffusion can be assumed inside the reverberation chamber. In addition, to verify the validity of the proposed evaluation indicator, we investigated the relationship with the objective diffusion evaluation indicator for diffuse field configuration in the reverberation chamber, such as relative standard deviation of decay rate ( S r e l ) and Np values. The results of this study are expected to contribute to a more accurate estimation of the sufficient diffusion condition in the reverberation chamber, in evaluating the sound absorption performance of the material, and that inside the reverberation chamber.
Highlights
The sound absorption characteristics of various finishing materials or vegetation used inside and outside a building are important factors determining the sound environment of the space
If the inside of the reverberation chamber is in the perfect diffusion state and the size of the specimen is infinitely large such that no additional sound absorption occurs due to the edge effect, the sound absorption coefficient value (α∞) of the specimen measured under these conditions will be the sound absorption performance of the specimen surface
Because the edge length is relatively larger than the specimen area, the sound absorption caused by the edge effect is greater than that on the specimen surface
Summary
The sound absorption characteristics of various finishing materials or vegetation used inside and outside a building are important factors determining the sound environment of the space. To evaluate the sound absorption performance of the specimen surface more accurately, it is necessary to investigate a measurement method to quantitatively determine whether sufficient diffusion occurs in the reverberation chamber. In this study, we have investigated a method to quantitatively evaluate the diffusivity necessary for sound absorption coefficient measurement in a reverberation chamber For this purpose, we first define the concept of sufficient diffusion within the reverberation chamber and propose a new evaluation indicator, α∞ − αβE≈0, where α∞ is the sound absorption coefficient of the infinite plate, and αβE≈0 is the sound absorption coefficient of the specimen, which has an almost negligible edge effect. The proposed evaluation indicator was validated by the analysis of correlation between α∞ − αβE≈0, the proposed evaluation indicator, and Srel and Np values, the proposed diffusion evaluation indicators presented in previous studies
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