Influence Of Wall Boundary On Sound Field In Long Space

Acoustic problems are widespread in long space,the traditional theory of room acoustics does not fully applicable in the long space.So the acoustic phenomena and laws in the long space need to conduct a special study.In this paper,take the B-type subway as object,in the frequency range of 50 ~ 1000 Hz,the influence of five boundary conditions on rigid boundary,small damping boundary,unilateral wall sticking sound absorbing material boundary,both ends opening boundary and full absorption boundary at both ends are studied.Known body length 2.6m,width 18 m,height 2.1m,according to the ratio of 1: 5 to simplify the body into a long space model,in the model,the following three aspects are studied:Modal simulation.The modal characteristics of long space under rigid boundary condition are calculated in MATLAB.Then,in the COMSOL Multiphysics,the modal characteristics of long space are simulated respectively under five boundary conditions.Through modal analysis:(1)The modal characteristics of the rigid boundary conditions and the small damping boundary conditions are almost identical,indicating that the small damping has little effect on the modal characteristics in the long space,the first order mode is the rigid body mode.(2)Compared with the rigid boundary condition,the modal order of the long space is increased under the boundary conditions of the sound absorbing material boundary,the end wall full absorption boundary and the end wall opening boundary;The order of the partial moduli changes.(3)The end wall full absorption boundary and the end wall opening boundary have the same modal characteristics,there is no(0,0,0)order mode.Sound field simulation.Firstly,the sound field under rigid boundary and small damping boundary condition is calculated theoretically in MATLAB.Then,the sound field characteristics in long space under five boundary conditions are simulated in COMSOL Multiphysics.Experimental verification.Building experimental model in the semi-anechoic chamber.The steady-state sound pressure distribution of some modes under small damping boundary condition is measured to test the correctness of the experiment.And then measure the frequency distribution in long space under small damping boundary condition,unilateral wall stickers sound absorbing material boundary condition,end wall opening boundary condition,end wall full absorption boundary condition.Through the comparison of experimental and simulation,the following conclusions are drawn: Compared with the rigid boundary,the peak attenuation of the sound pressure level is larger after adding the damping.And the attenuation of the sound pressure level increases with the increase of the frequency.The attenuation effect of damping on sound pressure increases with increasing frequency;The normal frequency is basically the same under the condition of the end wall full absorption and the end wall opening boundary condition.And the sound pressure level is larger and more uniform with the frequency changes under the condition of the end wall opening boundary condition.