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 Figure 2. The parts of a reed (lingual; a) and a flue (labial; b) organ pipe. As shown in b, the cut-up is the distance between the lower and upper lip.
The ranks can be activated by a drawstop. The so-called slid- er (Figure 3) is a wooden plate that has a number of holes in it, corresponding to the position of the pipes standing in a row. By activating a stop by one of the drawstops, the holes of the slider plate let the air flow from the tone chan- nel into the pipes having the same timbre. All organ pipes produce sound by means of air flowing into the pipe so that each sounding pipe “consumes” a certain amount of air. A tracker action is both the connection between the keys of the keyboard and the tone valves in the windchest (sound tract) and is also the system for switching the stops (registers; reg- ister tract). When a key is pressed, the corresponding valve in the pallet box opens and air
The required pressure of the wind in the pipe organ is set by the organ builder by placing weights on the top of the bellows. (4) Finally, the wind duct connects the wind system with the pallet box (lower part of the windchest), thereby providing the air supply for the pipes. In large pipe organs, multiple wind systems can be present and operate at the same time, but each provides air to a different set of ranks.
As mentioned above, there are two kinds of pipes that are similar in function to other wind instruments: flue (labial) pipes (like a recorder or a transverse flute) and reed (lingual) pipes (like a clarinet or a saxophone). The sound of a reed pipe is produced by a vibrating brass strip known as a reed (tongue). Air under pressure (wind) is directed toward the reed that vibrates at a specific pitch. This is in contrast to flue pipes, which contain no moving parts and produce sound solely through the vibration of air (see Figure 2). In a typical pipe organ, there are considerably more flue pipes than reed pipes. The main parts of a reed and a flue pipe are shown in Figure 2.
In the next sections, the physics of flue pipes is discussed. The discussion is based on an earlier publication (Miklós and Angster, 2000) complemented by certain results of European research projects carried out in cooperation with several or- gan builder enterprises. In this paper, the reed pipes won’t be examined (but see Fletcher and Rossing, 1991; Miklós et al., 2003, 2006).
  flows into the tone channel and the pipes selected by the draw- stops. When the key is released, a spring closes the valve, block- ing the airflow.
The pressurized air is provided by the wind system that consists of four essential parts. (1) The blower (electrical fan) is the air supply of the instrument. The blower pumps air into the wind system according to the “wind consumption” of the instru- ment. (2) The roller valve regu- lates the airflow from the blower into the bellows. (3) The bellows ensure that the pressure in the windchest remains constant.
Figure 3. A sketch of a pipe organ and its most important parts.
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