在主動式座椅消音器的研究領域中，大部分之研究是使用傳統喇叭來當作二次音源，近年來才開始有少數之研究是使用超聲波換能器當作二次音源於平面波之主動式噪音控制。在漫射音場方面，尚未有使用超聲波換能器來當作主動式噪音控制之二次音源，因此本研究即是使用超聲波換能器來當作主動式座椅消音器之二次音源，並且評估其在單頻漫射音場中之靜音區域大小。初步之結果顯示在單頻漫射音場中使用超聲波換能器當作二次音源所得到之靜音區域比使用傳統喇叭所得到之靜音區域大，這是因為超聲波換能器產生指向性可聽音之音壓不會隨著距離而迅速衰滅，因此可得到較大的靜音區域。又超聲波換能器所產生之指向性可聽音具有方向性，將使得主動式座椅消音器在靜音區域以外的地方音壓放大的幅度不會太高。

Most of researches in an active headrest system used conventional loudspeakers for the secondary sources. Recently ultrasonic transducers have been used for the secondary sources to control the plane wave in active noise control. However there is no research related to active noise control in diffuse fields using ultrasonic transducers. Therefore ultrasonic transducers are used in an active headrest system for the secondary sources to control the diffuse fields in this study. The quiet zone in single tone diffuse fields will be analyzed in this study. The preliminary simulation results showed that quiet zones created using ultrasonic transducers were larger than those created using conventional loudspeakers. This is due to the fact that the audible sound pressure produced by the ultrasonic transducers decays slowly with the distance. Therefore quiet zones created using ultrasonic transducers could be larger than those created using conventional loudspeakers. Also the audible sound produced by the ultrasonic transducers is directional. Therefore, the sound pressure amplification outside the quiet zones in the active headrest system could be lower.