IV.

Controls

When a key is depressed, small valves open to allow air from the wind chest to enter the pipes and cause them to sound. A “stop” mechanism allows any rank of pipes to be prevented from sounding. The ranks are controlled by knobs or switches (called stops) set near the keyboard. By extension, the ranks of pipes they control are sometimes called stops.

Until the 19th century the connections linking the keys and pipe valves—including mechanisms to couple keyboards so that ranks of pipes may be multiply controlled—were achieved mechanically by a system of levers and cranks connected by strips of wood called trackers and stickers. Builders in the 19th century began to devise electrical and pneumatic actions to make the key-to-valve and stop connections. Because many organists believe these actions to be less responsive and sensitive than direct mechanical linkages, in the 20th century organs were again being built with the traditional tracker action.

The keyboards, wind chest, and pipes of small organs are contained in one unit. In large organs the keyboards and other controls are built in a separate unit called the console. Many organ consoles have a number of controls, called pistons, which allow the organist to bring into play at one stroke a combination of several ranks or stops.

Each organ is unique in that it must suit the acoustics and architecture of the room that houses it. The room itself has an intimate acoustic relation to the organ, profoundly influencing the sound of the organ by the amount of reverberation it allows.