Vibration localization prediction and optimal exciter placement for improving the sound field optimization performance of multi-channel distributed mode loudspeakers

Abstract

This paper describes a method for improving the sound field control performance of multi-channel distributed mode loudspeakers. Recently, studies for sound field control have been conducted using distributed mode loudspeakers rather than conventional cone-type loudspeakers because distributed mode loudspeakers can use the structure itself as a diaphragm. However, when a distributed mode loudspeaker with multi-channel signal processing is used for sound field control, the sound field control performance deteriorates owing to the resonance modes of the panel. In this regard, we improved the sound field control performance of multi-channel distributed mode loudspeakers by increasing vibration localization near the excitation points. To achieve this, we proposed a new formula for predicting the vibration localization near the excitation points in relation to the resonance mode of the panel. Unlike the localization factors currently in use, this formula is designed to predict the vibration localization near the excitation points regardless of the material properties, size, and measurement region of the panel. Thus, this formula can effectively predict the vibration localization in cases where it is difficult to measure the entire region of the structure or in different types of structures. Through this prediction formula, optimal exciter placement is achieved, which maximizes vibration localization near the excitation points. The directivity, radiation efficiency, and reproduction error of sound field optimization are used as measures of sound field control performance. The simulation and experimental results indicate that the rapid increase in reproduction error and the rapid change in sound pressure are suppressed at the natural frequencies of the panel because of the optimal exciter placement.