Soundproof doors are always equipped with a door frame to be fixed to the wall and can be hinged or sliding. In the case of large dimensions, the opening and closing operations are electrically or pneumatically servo-controlled. Solutions are available with a pedestrian door inserted into a large door, or high insulations up to 60 dB(A) achievable with two doors in series that can be opened simultaneously, both sliding and hinged. They are used for cogeneration plants, compressor rooms, engine testing rooms, television studios, etc.