Sound Gate: The gate used in an optical sound head, instead of a sound drum, to keep the film sound track precisely aligned on the scanning beam slit during sound reproduction.

• 声门：光学声音头上用的片门，代替声鼓，使得胶片的声轨在声音重现过程中正好和扫描狭缝光束精确地排列成一直线。