Sound absorption and reflection with coupled tubes

This paper describes a special sound absorbing technique with an accompanying efficient numerical design tool. As a basis pressure waves in a single narrow tube or pore are considered. In such a tube the viscosity and the thermal conductivity of the air, or any other fluid, can have a significant effect on the wave propagation. An important aspect is that due to the viscothermal wave propagation sound energy is being dissipated. This has been applied to configurations consisting of a manifold of tubes, the so-called coupled tubes. A design strategy was developed to create broadband sound absorption for a wall with configurations of coupled tubes. The viscothermal wave propagation in tubes is accounted for in B2000 via one-dimensional T2.VISC and T3.VISC elements. Also further applications of coupled tubes are described: a network of small coupled tubes is used as a numerical representation of conventional sound absorbing material and increased damping of flexible plates connected to a small air layer is created with tubes coupled to this air layer.