NOISE BARRIERS WITH REACTIVE SURFACES

The boundary element numerical modelling method is used to study the i nsertion loss of rectangular, T-shaped and cylindrical edged noise bar riers with rigid, absorbing and soft surfaces. The most efficient desi gn is a T-shape with a soft upper surface, it is found that a uniform series of wells in the upper surface of a T-shaped barrier produce ins ertion loss values equal to those of a soft surface over a significant range of frequencies. At low frequencies the insertion loss is less t han that expected for a rigid upper surface. The use of wells tuned to two different frequencies widens the spectral range of the soft surfa ce effect. It is found that the performance of the wells can be descri bed accurately in the numerical model by a simple analytical expressio n for the specific impedance of a plane surface. Experimental measurem ents on scale models are compared with the results of numerical modell ing. (C) 1997 Elsevier Science Ltd.