Pitch
- For more about the pitch of organ stops, see Organ stop: Pitch and length.
The pitch produced by an organ pipe is determined in two fundamentally different ways. For a reed pipe it is determined mainly by the mechanical properties of the reed and the length of the protruding part. For the flue pipes it is determined by the shape of the air column inside the pipe and whether the column is open at the end. For those pipes the pitch is a function of its length, the wavelength of the sound produced by an open pipe being approximately twice its length. A pipe half the length of another will sound one octave higher. If the longest pipe, C, is 8 feet (2.4 m) in length, the pipe one octave higher will be 4 feet (1.2 m) long, and two octaves above (middle C) will be 2 feet (0.61 m) long. A closed (stopped) pipe produces a sound one octave lower than an open pipe. For example, the lowest Gedackt / closed C pipe (2 octaves below middle C) will be 4 feet (1.2 m) long.
The nomenclature of a rank of open pipes (for example an "8 foot" (8 feet (2.4 m)) Open diapason) refers to the length of the longest pipe in the rank. Thus the longest pipe, (C, two octaves below middle C) is 8 feet (2.4 m) long. An 8 ft (2.4 m) stop sounds at unison pitch, like a piano. In a rank of stopped pipes, the lowest pipe is 4 feet (1.2 m) in length but sounds at unison pitch, so it is known as an 8' stop.
The foot-size for a reed pipe is the same as that of an open pipe with the same pitch. This is unrelated to the actual of the pipe.
Read more about this topic: Organ Pipe
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