Design of a directive source using the radiation mode method and a sound zone algorithm
Résumé
A common mean to achieve narrow directive patterns consists in using loudspeaker arrays. Generally, the
position of the sources in the array is arbitrarily fixed, for instance by using a regular spacing. The filters for each speaker are then calculated to get the desired acoustic field. In some cases, the predefined speaker positions might not be the optimal ones. Moreover, the diffraction on the source body may not be negligible for medium range applications. In this paper, we propose a two-step approach to overcome these problems. First, the radiation modes of the enclosure are computed. They are used in an inverse scheme, to find the most efficient vibration patterns over the enclosure, able to generate a target field at some chosen frequencies. These vibration patterns are then used to define the positions and sizes of actual loudspeakers on the enclosure. In a second step, a sound zone algorithm is used to calculate the signals driving the speakers. This yields a very narrow directivity pattern with reduced side lobe amplitudes. The proposed method is tested both numerically and experimentally and results are reported. A discussion about the pros and cons of the proposed approach is then provided.