What is a pipe organ?

While organ tone is simply produced when wind flows through a pipe, there is an array of mechanical equipment necessary to sound the pipe. Typically, a fan blower provides wind to a reservoir, or bellows, which stores and controls air pressure. Next, the air is directed to a wind-chest, beneath the pipes. When the organist plays a note on the console or keyboard, the select value opens, and wind passes through to the pipe.

The system by which the key opens the values is called the organ action. Mechanical or tracker actions have a direct mechanical linkage between the keys and wind-chest valves. When a key is pressed, a series of levers, rods (trackers), and joints which are directly connected to the valve pull that valve open. Electric-mechanical actions employ electromagnets which receive electricity when the key is depressed, and pull the valves open. Electro-pneumatic action uses a leather pneumatic as the valve. An electrical contact, made by depressing a key, activates an electro-magnet. The opening of the electro-magnet deflates the leather pneumatic, allowing wind to enter the pipe.

Pipes vary in size, shape, and materials. Tall or long pipes produce low musical pitches, and shorter pipes produce higher pitches. The relative shape and materials of a pipe influence the tone color. Pipe tone can be divided into three categories: Flutes produce sounds somewhat similar to orchestral flutes. Strings are wind-blown pipes, but produce sounds similar to violins or cells. Reed pipes contain a brass reed tongue, and produce oboe, clarinet, trumpet, and similar tones. Principals produce tones unique to the organ (non-orchestral sounds) which are used primarily to lead hymn singing.