A unique feature of vibraphone resonators is a shaft of rotating discs, commonly called fans, across the top. When the fans are open, the resonators have full function. When the fans are closed, the resonators are partially occluded, reducing the resonance of the fundamental pitch. A drive belt connects the shafts to an electric motor beneath the playing surface and rotates the fans. This rotation of the fans creates a vibrato effect along with some volume changes creating a tremolo effect.