Design of distributed mode loudspeaker through evolutionary structural optimization

Abstract

The distributed mode loudspeaker (DML) is a flat panel loudspeaker that consists of a thin plate as a diaphragm and several driving exciters. In designing the DML, a number of flexural resonance modes are encouraged to be excited. Thereby, complex vibration is produced in the diaphragm, and the sound field around the DML is diffuse at high frequencies. In the DML design procedures, choosing proper aspect ratio of the diaphragm, driving points, and suspension points are important to deliver flexural resonance modes as many as possible. In this research, the authors focus on the shape of diaphragm. The authors try to optimize the diaphragm shape that delivers more equalized interval between the natural frequencies of the diaphragm so that it does not have many degenerated modes. To achieve this, Evolutionary Structural Optimization (ESO) method, which is one of structural topology optimization methods, is adopted. The scheme is based on the idea that, by gradually removing inefficient materials, the structure shape evolves toward optimum one. This method enables us to select the best shape of the diaphragm from shapes given in the process. Trial designs demonstrate that the ESO method is effective in designing the diaphragm of the DML.