近年來車廠除了不斷提高駕駛的安全性以外，在乘坐的舒適性上也是相當受到重視。乘客在同樣的車室中如果都能聽到自己想要聽的音樂或是資訊，而不會互相干擾，對於舒適性駕駛會是很大的進步。因此，本研究將利用振幅調變技術結合一列8 個超聲波換能器來產生一個可聽音的指向性音束，使得車室內不同之乘員可聽到不同之音樂並探討音束之音場分布特性，且藉由改變每個換能器的權重值來探討其影響。本研究採用H2 控制法則找出每個換能器最佳之權重值，使音束的寬度能夠接近理想的寬度進而呈現出良好的指向性。研究中所選用的主頻為40kHz，採用單邊載波。結果顯示本研究所使用之H2 控制方法能有效的控制音束之寬度並且產生良好指向性之音束。

Vehicle safety has been improved by the manufacture in recent years. Comfortable riding has also been considered as an important factor. Passengers in vehicle cabin can listen to their favorite music or information without disturbance each other, then the comfortable driving will be improved significantly. This study used amplitude-modulating for an array of 8 ultrasonic transducers to produce directional audible sound beam. Therefore different passengers in vehicle cabin can listen to different music. In this study sound field distribution for the sound beam has been investigated. The effect of different weightings for the transducers on the directivity of the sound beam has also been evaluated. H2 control was used to calculate the optimal weightings of the transducers for better directivity of the sound beam. Carrier frequency of 40kHz has been chosen for single side-band modulating. The results showed that the beam width can be controlled and good directivity of the sound beam can be produced by using H2 control.