Study On Influence Of Edge Effect On Measuring Absorption Coefficient In Reverberation Room

As China has gradually stepped into a well-off society, people have more and more requirements on the spiritual level. Architectural acoustics is gotten more attention in our life. It goes without saying that sound absorbing material is very important in reducing noise and improving sound environment, while the sound absorption coefficient is the key to evaluate the performance of the sound absorption material. There are many ways to measure the sound absorption coefficient, in which reverberation chamber method can reflect the actual engineering requirement. However, there are some problems in the sound absorption coefficient of acoustic materials testing in a reverberation room, due to the non-ideal factors of its experimental facilities and experimental conditions. One of the problems is that the measurement of sound absorption coefficient of the same material in different reverberation chamber can sometimes be very large deviation, so that the measurement results do not have lateral contrast; Two of the problems is that the size of sound absorption coefficient varies with the change of the material area and the location and arrangement of the material in the room; Three of the problems is that in some strong sound absorption material test, the sound absorption coefficient of the high frequency band is likely to be more than 1. The main work of this paper is focus on sound absorption mechanism of acoustic material and its selection, reverberation time distribution of the empty reverberation room, and the influence of edge effect on measurement of sound absorption coefficient in reverberation chamber. First of all, sound absorption mechanism of acoustic material and its selection. This paper introduces basic knowledge about acoustics, explaining the sound absorption mechanism of some sound absorption materials, analyzing several test methods of sound absorption coefficient, and, at last, illuminating the reason why to choose the glass wool as the testing material of this study. Secondly, reverberation time distribution of the reverberation room without specimen. On the beginning this paper introduces trait characteristic in reverberation room sound field. Then, it clarifies the reasons for the space error of measurement of reverberation time in reverberation room. By means of measurement of reverberation time at different frequency under the condition of the empty reverberation chamber, comprehensive comparative analysis is done to illustrate the influence of space error on measuring sound absorption coefficient in the reverberation chamber.Thirdly, the influence of edge effect on measurement of sound absorption coefficient in reverberation room. By using a lifter in a standard reverberation room, the test sample can be moved up or down to make its top surface to be above or flush with the ground in order to achieve the effect that the edge effect exists or is eliminated, and then the corresponding reverberation time in different conditions is tested, and the absorption coefficients under different circumstances are subsequently calculated. By means of comparative research and related acoustic theory, the research results show that the sound absorption coefficient of glasswool was increased by edge scattering on high-frequency bands, but it was not the only factor making the absorption coefficient greater than 1. However, as a whole, edge scattering is limited on the sound absorption coefficient. The acoustic impedance may be the main reason cause the absorption coefficient greater than 1 on the medium frequency.