sounding-board
n
(a) board or canopy placed over a platform, stage, etc to direct the speaker´s voice towards the audience, so enabling him to be heard more clearly 增音板(装在讲台、 舞台等上方增加音响洪亮度的板或顶篷).
(b) means of causing an opinion, a plan, etc to be widely heard 宣扬意见、 计画等的手段
The magazine became a sounding-board for its editor´s political beliefs. 那杂志成了编辑宣扬其政治主张的传声筒.