Active sound scatterers based on the JMC method

The principle of formulating the JMC method to produce secondary sources that function as active scatterers on a hypothetical scattering surface is established, to be applied, e.g., in concert halls. The examination is based on the modified JMC method, to ensure that the logic does not lead to the need of changing the primary sources. The actively reflecting plane serves as an example of the JMC formulation for the active scatterer. The solution is extended to a general planar JMC element with well-defined reflection and transmission properties. The solution works on the local control principle: each reflecting subarea needs information of the primary field only at that subarea. The solution can also apply approximately to piecemeal planar surfaces and to smooth convex surfaces. Further, general active boundary condition elements are defined. Based on the element definitions, simple reflecting source, the pressure- and velocity-reflecting boundaries, and the impedance boundary are introduced. Boundary condition elements do not work on the local control principle: in a general case secondary sources on each subarea need information of the primary field at each subarea. True boundary condition elements are also defined based on their net sound power radiation.