Pipe organ: design, history, and musical role

Organs of various types and sizes are usually found in churches, but also in concert halls, conservatories (practice organs), schools (school organs) and even private homes (house organs). A small, single-manual organ without pedal is called a positive or, if it is compact enough, a chest organ. Small portable organs are called portatives. A special form of this is the Regal, which has only reed pipes.

Larger organs usually have many stops; large organs are those with about a hundred stops or more. The organ in the Atlantic City Convention Hall with 314 stops and 33,114 pipes is currently considered the largest organ in the world, but it has since had to cede its rank as the loudest organ in the world to the Vox Maris in Yeosu (South Korea), an open-air organ with only one stop.

Installation and acoustics

The organ builder has the complex task of setting up the instrument as acoustically, visually and functionally as optimally as possible, but this is often only possible to a limited extent due to structural conditions. Ideally, the organ sound should be balanced and transparent in every point of the room. The reverberation should not obscure the sound image too much.

In churches, the placement of an organ often reveals much about its liturgical purpose and possible uses. While the oldest instruments often appear near the choir or as swallow's nest organs, from the 17th century onwards the organ on the west wall becomes common. Traditionally, the choir organ (or in Italy/Spain, the Gospel/Epistle organ pair) was intended for a Catholic liturgy that took place largely in the chancel of the church. When congregational singing became more important after the Reformation, the organ moved to the west wall in the organ loft (more rarely behind or above the altar as an altar organ) and also tended to become larger and louder, because now it had to be able to lead a congregation singing in a packed church. Depending on their location, organs are also called nave organs or transept organs. In small church halls or those with special architectural features, the organ often has to be set up to suit the architecture, irrespective of its liturgical significance.

The size of the organ loft says much about the organ's purpose. For example, in the large churches of central Germany in the 18th century it was often customary to place choir and instrumental ensemble in the organ gallery, which meant that the main organ also came into its own as an accompanying instrument.

In concert halls the organ is usually mounted on the wall above the orchestra podium.

Furthermore, at the beginning of the 20th century, so-called attic organs were installed above the nave in organ chambers specially built for this purpose.

Appearance

Large organs determine the effect of the room in which they are placed with the design of their case and the front (organ prospect). In the Renaissance, and even more so in the Baroque period, the importance attached to the visual aspect was demonstrated by the fact that it was not uncommon for the cost of the organ case (with sculptural decoration, ornamental carving, paintings and gilding) to exceed that of the organ itself. The organ case, together with the other sculptural and pictorial decoration and decoration of the church, often served an overall architectural concept.

Materials

The traditional material mainly used for the construction of an organ is wood. The case, the windchests, the keys and some of the pipes are made of wood. On instruments with a mechanical action, wood is often also used for the mechanical parts. The metal pipes are usually made of tin-lead alloys (so-called organ metal), since the 19th century also of zinc and in the 20th century of copper (occasionally also of porcelain, Plexiglas and other plastics). Bovine bone (rarely ivory) and various woods (ebony, blackened pearwood, grenadilla) are used for the facings of the keyboard.

The pipework of the organ consists of several rows of pipes, each containing organ pipes of the same type and timbre. A row of pipes (sometimes several) is combined to form a stop which can be switched on and off from the console. In mechanical action the stops are operated by means of stop pulls or knobs called manubrien, which have to be pulled out to switch on and pushed back in again to switch off; this is where the old terms "pulling" and "pushing off" for switching stops on and off come from. In electric and pneumatic action, the stops are switched on and off by means of pushbuttons or switches.

The composition of the stops of an organ including the playing aids (couplers etc.) is called the disposition of an organ. It is agreed between the organ builder and the client when the instrument is built and determines the possible uses of the organ.

Registration

By combining different stops in a planned way, the so-called registration, different timbres and volumes can be adjusted. The art of the organist is to find a registration from the existing sound stock that best suits the music to be played. Each epoch preferred its own special sound, which the well-trained organist knows. It is therefore not possible to play every piece on every instrument in a way that is true to the historical style. Despite the possibility of a certain "typification", there are seldom two organs that are identical, since each instrument is adapted in size and design to its installation space or depends on the taste of the time of its creation.

differentiation by pitch

The stops can have different pitches, the pitch being indicated by what is known as the footnote number. Thus a stop in the normal position (i.e., the key c1 makes the note c1 sound) is called an 8′-(eight-foot) stop, since the length of the lowest pipe, capital C, of an open labial stop is about 8 feet (1 foot = about 30 cm). A stop one octave lower is a 16′ stop with pipes often twice as long; 4′ refers to a stop one octave higher and usually has pipes half as long as an 8′ stop. Fifths always have footnote numbers with thirds fractions (e.g. 2 ^2⁄3′ or 1 ^1⁄3′ - this is the 3rd partial of the natural overtone scale), thirds with fifths fractions (e.g. 1 ^3⁄5′ - 5th partial). In addition, there are sevenths (e.g. 1 ^1⁄7′) with the 7th partial, ninths (e.g. ^8⁄9′) with the 9th partial, and other higher partial stops.

The different pitches represent the overtone series. By combining a basic register (usually 8′-pitch) with one or more overtone registers (such as 2 ^2⁄3′ or 1 ^3⁄5′), also called aliquots, existing overtones are amplified (or missing overtones are added), changing the timbre.

Differentiation according to design

The stops differ not only in pitch (foot position) but also in their construction, and thus in their pitch, overtone content (timbre) and volume.

A distinction is made between lip pipes or labials (producing sound like a recorder) and reed pipes or linguals (producing sound like a clarinet). Labial pipes can be open or crooked; the crooked pipes sound an octave lower for the same length. There are further differences in materials, pipe shape and bore (the proportions of the various pipe dimensions). There are also the mixed voices. These are stops in which several pipes sound for each key. These include the sounding crowns (or mixtures) and colour stops such as the sesquialtera and the cornet.

The physical explanations of the influence of the design of the pipes on the timbre are explained in more detail in the article Organ Pipe.

Subsidiary register

The tremulant is classified as a stop. It periodically changes the wind pressure and thus causes the tone to vibrate, usually as a combined tremolo and vibrato. In more recent organs the speed of the oscillation can sometimes be adjusted. The tremulant affects all the stops of the organ in which it is installed. On old organs there is sometimes a tremulant for the whole organ, and on some organs one that acts only on a particular stop (such as the Schwebeflöte, Vox humana).

Special effect stops, such as chimes, cuckoo, birdsong, thunder or timpani, supplement the disposition of some organs.