In dance organs, a stopped flute pipe or chimney flute with a special tremulant, consisting of a pallet covering the outside opening of a small hole drilled in the back of the pipe, opposite the mouth. When a jazz tremolo (or vibrato) effect is desired, the pallet opens and closes rapidly while the pipe is being sounded in the normal manner. The opening and closing of the hole causes a pronounced and rapid vibrato. See vibratone (a related pipe).
MBSI
Musical Box Society International