Simulationsumgebung für einen Lautsprecher in einem beliebigen Gehäuse

A simulation tool is to be developed pointing out the influence of the enclosure on the radiation characteristic of a loudspeaker box. The radiation of a piston diaphragm in an infinite baffle can be seen as frequency-independent on the loudspeaker axis at a certain distance. The installation into an enclosure changes the frequency response due to edge diffraction. The wave propagating towards the edge “recognizes” an increasing surface (double the size “as expected”).

The Effect of diffraction can roughly be described as follows: The wave propagation behind the edge has half of the sound pressure amplitude in phase with the piston. The propagation of the reflected waves towards the front also has half of the sound pressure amplitude but with inverted phase. Hence a destructive interference of –6dB appears at low frequencies on the loudspeaker axis at a distance of for example 1m. At higher frequencies interferences change between destructive and constructive ones (+/-6dB) dependent on the dimensions of the edges, the piston diaphragm und the point of view. The Simulation is made with Matlab. The loudspeaker diaphragm is modelled using one primary source or a distribution of sources and the diffraction effects at the edge of the enclosure represent the secondary sources. The point of view may vary in horizontal and vertical direction, so that every angle towards the loudspeaker axis can be regarded. The implementation is made in a modular way, which allows to choose different source forms to control and analyse computation time and accuracy. Finally real measurements on enclosures are made to proof the correctness of the simulation results.