Numerical study on performance of noise barriers with opened tubes at the edge

Efficiency of an array of opened acoustic tubes installed at the edge of a noise barrier is numerically investigated using two-dimensional boundary element method. For a basic test, sound pressure distribution around an opened tube in a free field is calculated. Results show that sound pressure is significantly small at the open ends of the tube and behind it when the tube length equals a half of the wave length or an integer times of it as a result of tube resonance. Next, performance of the noise barrier with an array of opened tubes is calculated. It is found that the opened tube array is effective when it is installed at the receiver side of the barrier edge and that installed at the source side does not work well. To avoid frequency dependency of the efficiency of the tube array, barriers with two arrays of different types of tubes are also tested. In terms of practical use, the opened tube array has two advantages over a closed tube array. The one is easiness of production by absence of a closed end. The other is that we are required no measures to prevent water and dust accumulating in the tubes.