The Black Bar is called the "Mandolin Rail". It is controlled by the Roll. It has cloth tabs with metal clips on the lower part of the Tab. When it comes down it puts the tabs between the Hammers and the Strings. When a Hammer goes forward to hit a string, it first hits the Tab and the metal tip hits the string, producing a metallic sound from the string - instead of a pure tone. The process is called (1) A mandolin effect, (2) a "rinky-tink" sound, (3) or a Honky-tonk sounding, piano. Most Player Pianos also have a button you can push to over-ride the Roll-Control and lower the bar anytime you wish. It was a well-advertised feature of most Player Pianos. - Max