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Functioning and build-up of the organ
The technical and artistic works in organ building are interesting and diversified. The organist sits at the console and plays with his hands and feet on the various banks of keys, named claviature.
With his hands he plays on the keys of the manuals, of which an organ can have multiple stacked one on the other. A manual resembles a piano claviature, but has a smaller key extent.
The pedal piano is for playing with the legs.Besides the claviatures are the organ stops. With these the organist can activate or deactivate different pipe rows, named organ stops.
The wind chest
The heart of an organ is the wind chest. Each keyboard has one or more wind chests. An organ with 3 manuals and 1 pedal normally possesses at least more than 4 wind chests.
Each wind chest has a wind box, which is fitted with play valves. Is a key pressed, then the wind flows trough a small canal under the pipes. The different pipe rows sit on the upper part of a wind chest. Only when an organ stop is activated can the wind flow through the pipe and create a sound. In front of each pipe there is a double wind sealing.
Each pipe row (organ stop) has a special timbre and comprises large deep vocal and small high vocal pipes. Based upon the material of the pipes we can distinguish between wood and metal pipes. Based upon the type of the physical creation of the tone there are flue pipes and reed pipes(labial and lingual pipes).
Dimensions of an organ
A small organ has 10 to 15, a medium organ 15 to 40 and a big organ 40 to more than 100 organ stops and many hundred to many thousand pipes accordingly.
The mass of the pipes (mensures) is from 5mm to more than 10m and 3mm to 60cm diameter.
The mechanical part of an organ
The connection between the keys of the manuals and pedals and the tone valves in front of the pipes are called traction mecanique in French and Spieltraktur in German or tone control. The connection between the organ stops on the console to the organ stop valve is called organ stop mechanic.
The transmission of the movements was carried out earlier in a mechanical way with leverages, billows, etc.
Around 1900 this transmission was performed through pneumatics and during the 20th century it was replaced by electrical connections.
Today the tone control is guided mainly by the mechanical principle, because of the fact that this system is the most sensible and most direct for the player.
The organ builder must know all of these systems in order to maintain and restore older instruments.
The wind system and the wind supply
The wind reserve is created by special bellows, who serve as wind storerooms. Today the bellows are inflated with the help of an electric ventilator. It creates a uniform air flow, which flows trough the wind chest in the pipes and produces tones.
In restorations it is usually tried to also maintain the manual mode. The stepping on the bellows was earlier carried out by a person, a blower. An organist was able to rehearse only if a person pumped the air for him.
The housing
The wooden housing is a framework for the organ parts and acts as a coat and resonance box in the same time. The housings were less or more artistic decorated, depending on the era they were built. A heyday for organ building was the baroque era.
As prospect of the organ, as face, the front visible side is designated. The prospect presents itself most of the time as marvellous, festive and is dominated by the sumptuous principal pipes. On older organs it is mostly rich decorated and painted.
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