Organs have been made for many centuries. They are usually found in places for Christian worship such as churches and cathedrals, although they may also be found in places like town halls and concert halls or even large private houses. Very small organs can be called “chamber organs”. Organs in large churches, cathedrals or halls are very large instruments indeed, and are built especially for the building they are in. They are called “pipe organs” to distinguish them from modern “electronic organs”.
No two organs are ever quite the same, and they vary greatly from one country to another and one historical period to another. The information here is about organs from Europe, Great Britain and America.
In a pipe organ, the musical notes are made by blowing air through pipes. Every organ must have pipes, something to blow the air and a way of controlling which pipes are played.
The pipes are made of metal or wood. They are lined up in rows in the "organ case" which can be as big as a room. The metal pipes are round tubes. They can be made of different types of metal, but the most common type is an alloy (or mixture of metals) of tin and lead called "spotted metal" because it has round shiny spots on it. This alloy makes pipes sound good as the harder tin provides clarity and definition while the softer lead produces tonal warmth. Very small pipes can sometimes be made of silver, like flutes. Some organs also have some pipes made of brass that sound like trumpets. Most organs have a lot of wooden pipes. The wooden pipes have four flat sides and make a sound different from that of the "spotted metal" pipes. They are not usually seen; they are neatly lined up behind the large metal pipes at the front of the organ which are sometimes painted with colours and patterns. All the pipes have to be made with an end that tapers at the bottom where the air blows in.
Each pipe can play only one note which depends on its size. The small pipes play high notes and the large pipes play low notes. Each pipe has its own special sound which depends on the material it is made from (whether it is wood or brass or spotted metal) and on the shape of the pipe. The pipes are arranged in "ranks" so that all the pipes of the same shape and material can be controlled to play a tune together, without all the others.
To blow air through the organ, there are boxes called "wind chests". When the organist is playing, he/she can see a little gauge that tells whether there is enough air. The wind chests can be kept full in two ways. The old-fashioned way is to have an enormous set of "bellows" which are pumped up and down by a person using a large handle. This sucks in air and fills the wind chest. Pumping the bellows of a large pipe organ is heavy work. For this reason, most organs nowadays have an electric motor and a large fan which fills the wind chest.
The organist uses keyboards like those on a piano to play the organ. A small organ may have just one keyboard, but many organs have two keyboards and a very big one may even have five. Organists do not call them keyboards; they call them "manuals". An organist will talk about "a four-manual organ" (which means it is a large one). The manuals are arranged on the organ "console", and the organist sits on a bench in front of the console to play. Apart from the manuals there are two other important parts of the console. There are a set of long wooden pedals which the organist can play with his/her feet. Each pedal plays a different note.
On either side of the manuals there are rows of "stops" which look like knobs. The stops can be pulled out or pushed in. When a stop is pulled out, it turns on some sets of pipes. The organist can choose whether to play loud pipes or soft pipes, flute-sounding pipes or brassy pipes, sweet pipes or harsh-sounding pipes. As the organist plays, he/she does not just have to think about the right notes. He/she also has to think about the sort of "voice" that the organ should play in. He/she can play different ranks of pipes together by pulling out several stops. Some pipes, usually the biggest decorated pipes at the very front of the organ, are used only for the grandest music. By tradition, these pipes are the symbol of the "Voice of God".
When the organist presses the keys of the organ, the sound comes from the air blowing through the pipes. This is because a valve (an opening with a one-way door) opens up to let the air into the pipe, and closes again when the organist stops pressing that key. This can happen in several ways. Traditional organs have what is called a "tracker action". The trackers are thin wooden rods and wires which move backwards and forwards, opening and shutting all the valves. They are worked by levers under the keyboard. A tracker action organ has to have the console right near the organ, usually under the big front pipes.
A more modern development was to have a "tubular pneumatic" action, in which the console could be away from the organ, but connected to it by tubes through which air could be pushed to open the valves. In the most modern pipe organs, the manual is connected to the organ pipes by electric wires. The power to open and shut the valves is controlled by electro-magnetic switches. The console does not have to be close to the organ. This makes it possible for the organist to sit in a position where he/she has good contact with the people in the church, or with other musicians.
A very small organ may only have one manual (keyboard). Most organs have at least two. In English and American Organs the lower manual is the main one and is called the "Great". The upper manual is called the "Swell" because it operates pipes which are inside a “swell box” which has that can be opened or closed. This makes the music get louder or quieter (crescendo or diminuendo). The organist operates the swell box with a pedal which (rocks to and fro). It is in the centre just above the pedal board. On old English organs the swell box is operated by a lever at the side. This is quite difficult to use. Most of these have now been replaced by central swell boxes.
If there is a third manual, it is called the "Choir" in English-speaking countries. Originally the English called them “chair organs” because they were a separate instrument. The organist had to turn round and face the other way to play it. It is thought that the word "chair" gradually changed to "choir" because it was often used to accompany the choir. In German organs the third manual was called the “Positiv”. The name “Rückpositiv” (“back positive”) was used because the pipes were behind the organist’s back as he/she sat facing the main organ. These started to become popular again with organ builders in the 1950s when it was felt that the Romantic organ was not suitable for old music, and some organ builders started using Baroque principles again so that the music of composers such as Bach could sound like it used to. The Choir manual is nearest to the player, the Great is in the middle and the Swell is farthest away. The Choir or Positiv often contains soft stops which are suitable for accompanying the choir. On French organs from the late 19th century onwards, the three manuals are arranged differently: the Great (“Grande Orgue”) is nearest to the player, the “Positif” is the middle manual and is like a smaller version of the Great, and the Swell (“Recit”) is the top manual. This makes it easy for the organist to build up the music, getting louder gradually, by starting at the top and gradually coming down.
The fourth manual is called the "Solo" because the stops on this manual are used to play out the tune as a solo. This manual is even farther away from the player than the Swell. Large cathedral organs usually have four manuals. The Solo will probably have a very loud stop indeed called the “Tuba” or “Tuba Mirabilis”.