The typical pipe organ is actually made up of several sub-sections or mini organs, and also several major subsystems. With regard to subsystems, the typical electric or electropneumatic pipe organ comprises the following:
The winding system.
The electrical system
The operator interface (console)
The sound producing system (Organ Pipes and possibly some other instrumentation).
The winding system is responsible for producing and supplying air at a carefully regulated pressure to the various pipes of the instrument, and if an electropneumatic instrument, it also supplies the necessary air to power all of the pneumatic elements or devices that comprise the action of the instrument.
The electrical system provides the necessary direct current or DC to power all of the electrical elements in the instrument and transmits signals from the console to the rest of the organ. In many instruments the electrical system may also include a complex array of various relays and multi-contact remotely controlled switches, known collectively as an organ relay, and in most modern work, electro-mechanical relays will be replaced by transistors, diodes and possibly a computerized controlling system which determines exactly which pipes sound at any moment depending on what stops the musician has selected and what keys and pedals he may be playing.
The operator interface or console is where the musician who plays the instrument does so by means of standard musical instrument keyboards, a pedal keyboard of two and a half octaves at floor level, suitable stop controls for controlling which ranks of pipes and other effects may be in use at any particular moment, and a means also for controlling the volume of at least some of the sections or divisions of the instrument.
The sound production system of course represents all of the various tuned pipes which produce the musical tones of the instrument, and in the case of concert and theater organs, it frequently also includes various tuned steel, brass or wooden bars and tubes to produce the sounds of, for example, a marimba, a harp, a glockenspiel, a celesta, chimes and may also include various real drums and cymbals as well as sound effects devices such as wood blocks, sirens, bird whistles, castanets, a tambourine and a triangle as well as imitation thunder, surf and rain. On such an instrument the creation of almost any conceivable mood is possible, all of this necessary for proper accompaniment of silent movies.
The various subsections or divisions of the instrument often have the following names. Great; Swell; Choir; Pedal; Solo; Orchestral; Echo; among others. So what exactly does all this stuff really mean? Well, let's take a look.
As you may infer from the preceding, the pipe organ, particularly when a larger instrument, may indeed become an extremely complicated machine comprising sometimes miles and miles of wire, thousands of individual switch contacts, and sometimes well over a million individual parts.
Unlike pianos, which, whether a studio upright, a spinet, a baby grand or a huge concert grand all have essentially the same number of keys and strings, pipe organs can vary considerably in their available tonal resources, and number of keyboards. Most modern pipe organs are standardized however with respect to the number of keys on each keyboard, the number of the pedals on the pedal keyboard, and certain critical console dimensions, so that a musician does not need to make any really major adjustments as far as general playing is concerned when playing different instruments. That is, the relationship of the keyboards to the pedals, the height of the great manual above the middle E pedal, and the spacing between individual keys and also individual pedals are standardized to a large degree between instruments of different makers. However, the number of available tonal resources may vary considerably. Likewise, the entire tonal scheme of one pipe organ may be completely different from that of another instrument. The pressure of the air that sounds the pipes may be very different also, and in many instruments, there may be several different pressures. Likewise, the placement of different sections or divisions in a large instrument in a big building may vary to the point that each pipe organ becomes in a sense a unique instrument unlike any other. Power to supply the compressed air to an instrument might be a fraction of a horsepower in a small instrument of modest tonal resources in a small room to hundreds of horsepower for a very large instrument using high wind pressures in a big building.
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