| As an acoustic baffle set on the noise transmission path,the sound barrier has obvious noise control effect.The existing traditional sound barrier is based on porous sound absorption or material sound insulation,which has limitations in low-frequency noise reduction,but there are a lot of low-frequency noise in urban traffic environment.The periodic structure has the characteristic of band gap,and the wave propagation in the frequency range of the forbidden band is suppressed.The application of periodic structure to noise barrier engineering is of great significance to solve the problem of low frequency noise in traffic environment.In this paper,aiming at the urban traffic environment noise,the field measurement is carried out in Beijing.Three kinds of urban road traffic noise conditions and six kinds of urban rail transit noise conditions are selected for a total of nine different traffic environment noise conditions.The time history analysis and spectrum analysis of the test results are carried out,to obtain the spectrum distribution and the main frequency range of traffic environment noise.Aiming at the measured main frequency range,according to the periodic structure theory and acoustic Helmholtz resonator principle,a new type of "rotary" periodic sound barrier is proposed.The insertion loss curves of the two types of barriers,the upright type and the fully enclosed type,verify the noise reduction performance of the new periodic sound barrier.At the same time,the influence of geometric parameters is discussed,and on this basis,a recommended configuration is given,whose bandgap range can cover the main frequency range of traffic noise under all nine operating conditions measured.Through the above work,the conclusions are as follows:(1)The measured urban traffic noise is mainly low-frequency noise,and its main frequency ranges from 28.6Hz to 72.5Hz.(2)The peak of the frequency spectrum of urban traffic noise is obvious,and the sound energy is concentrated near the peak frequency.Urban traffic noise can be controlled by aiming at the dominant frequency.The installation of traditional sound barriers on rail transit lines will disperse the originally concentrated sound energy.(3)The new "rotary" periodic sound barrier has sound band gap,which has a good noise reduction effect on sound waves in the range of band gap.(4)The band gap range can be adjusted by changing the geometric parameters of the "rotary" periodic sound barrier.Increasing the number of circles,reducing the barrier spacing and the thickness of the barrier structure can make the band gap move to the low frequency,so as to realize the effective control of the low frequency noise.(5)The band gap range of the new "rotary" periodic sound barrier with the recommended configuration can cover the measured 28.6Hz～72.5Hz of the main frequency range of traffic noise under all nine working conditions. |
