Research on "Invisible Noise Barrier"

点击翻译按钮获取中文摘要

The basic idea to control the traffic noise by this active noise control method is to use a network of microphones and secondary sources. This network of the secondary sources is just the "Invisible Noise Barrier". In our case, the primary source corresponds to the individual vehicle or a small portion of traffic flow and the network of the secondary sources is rather transparent state than the usual noise barrier.(1)The theory to treat the complex three-dimensional sound field is needed.(2)ln order to follow up the changes of the condition of propagation path of sound, the adaptability must be included in the filter system. It is shown by the JMC theory that a source-free volume can be shielded against noise from outside by cancellation sources along its surface. In order to demonstrate the "Invisible Noise Barrier" system in our laboratory, an experimental setup was constructed as the simplified model of the barrier- system. The main control filter is constructed by a DSP(digital sig … More nal processor)system(Lorry Plus ; by Mtt Co.)of which purchase was supported by a Grant-in-Aid for Scientific Research from the Ministry of Education, Science and Culture.Simulated results agree with the measured results in a broad sence. The level of sound pressure field behind the tripole sound sources were reduced around the error microphone. The size of the reduced area increases as the distance between each tripole increases. However, when the distance is 0.6 lambda, some high pressure region penetrates the reduced pressure area. This means that there exists the best condition about the distance between each tripole. In this experiment, the maximum number of tripole sound source was three. As the numerical simulation, we can carry out some calculations. In the case of 17 tripoles and the distance between each tripole, 0.2 lambda, the size of reduced area becomes half-horizontal plane. This shows the meaning which Jessel have already spoken out. We can, however, only discrete secondary sound sources as the tripole, there remains problem how to distribute such discrete tripoles in order to cancel the distributed noise field as the best condition. Less