Optimization Design Of Sound Absorbing Materials Used For Noise Reduction Of Ehv And UHV Substation

According to the characteristics of low frequency noise as primary in substation and the current situation of poor low frequency sound absorption performance of the existing sound absorption material, aluminum fiberboard, polyester fiber, ceramic fiber and Helmholtz resonator were chosen to systematically study the influence of the parameter of thickness, density and cavity on the low frequency sound absorption performance with impedance tube. On this basis, different sound absorption materials and structures were combined into composite sound absorption structure in order to obtain good low frequency sound absorption performance by optimizing the structure parameters. From these composite structures, several kinds of structures with best low frequency sound absorption performance were chosen to be made into reverberation chamber samples and measured for the sound absorption coefficient in reverberation room in Building Environmental Testing Center of Tsinghua University. Through the above research, the following conclusions were drawn.(1) The effects of surface density, thickness, cavity and aluminum foil on the low frequency sound absorption properties of aluminum fiberboard were studied systematically. The maximum sound absorption coefficient of aluminum fiberboard at 100 Hz was 0.715 while the maximum average sound absorption coefficient over 100~500Hz was 0.856. But the two maximum values couldn't be reached at the same time.(2) The effects of thickness, bulk density and cavity on the low frequency sound absorption properties of polyester fiber were studied systematically. Polyester fiber was easy to achieve a sound absorption coefficient of more than 0.9 at the middle and high frequency though its low frequency sound absorption coefficient was low. By increasing the thickness, the maximum sound absorption coefficient of polyester fiber at 100 Hz was 0.697 while the maximum average sound absorption coefficient over 100~500Hz was 0.870. The same sound absorption effect could be achieved by adding a cavity to the back of the polyester fiber.(3) The effects of thickness and bulk density on the low frequency sound absorption properties of ceramic fiber were studied. The maximum sound absorption coefficient of ceramic fiber at 100 Hz was 0.527 while the maximum average sound absorption coefficient over 100~500Hz was 0.733. The low frequency sound absorption performance of ceramic fiber was very poor and was excluded in the follow-up test.(4) Helmholtz resonator had high sound absorption coefficient at the resonance frequency of 100 Hz which reached 0.946. But the frequency range of sound absorption of Helmholtz resonator was very narrow that it was not widely used on its own.(5) Among the composite sound absorption structures, the aluminum fiberboardHelmholtz resonator composite structure had good sound absorption coefficient of 0.985 at 100 Hz and had poor sound absorption coefficient of 0.754 over 100~500Hz. The sound absorption coefficient of the polyester fiber-Helmholtz resonator composite structure increased with the increase of the thickness of the polyester. The maximum sound absorption coefficient of polyester fiber/Helmholtz resonator composite structure at 100 Hz was 0.939 while the maximum average sound absorption coefficient over 100~500Hz was 0.821, which showed good low frequency sound absorption performance. When aluminum fiberboardpolyester fiber composite structure had double cavity structure and appropriate size of the front and rear cavity, its maximum sound absorption coefficient at 100 Hz was still a little small, which was 0.609. But its maximum average sound absorption coefficient over 100~500Hz was very good, which was 0.923.(6) polyester fiber-Helmholtz resonator composite structure and aluminum fiberboardpolyester fiber composite structure were chosen to be made into a series of reverberation chamber samples and measured for the sound absorption coefficient in reverberation room. The sound absorption coefficients of the polyester fiber-Helmholtz resonator composite structure in the reverberation chamber over 100~5000Hz were more than 0.9 except for that it was 0.85 at 125 Hz. The sound absorption coefficients of the aluminum fiberboardpolyester fiber composite structure in the reverberation chamber over 100~5000Hz were more than 0.9. It was indicated that the two kinds of composite sound absorption structures not only had excellent low frequency sound absorption performance, but also had good high frequency sound absorption performance, which could provide some reference value for substation noise reduction.