The transept organ of Cologne Cathedral was built after the Second World War by the Johannes Klais company from Bonn (Opus 1000), in the northeastern corner of the crossing.
It was set up when the cathedral had not yet been rebuilt, but the nave was still separated from the transept by a shield wall. The transept organ with 68 stops (and two transmissions) on three manuals and pedal was built in 1948 and inaugurated on the occasion of the 700th anniversary of the cathedral.
The transept organ is located on a concrete platform at a relatively low height in the eastern side aisle of the north transept. This location is unusual for Gothic cathedrals, but can be explained on the one hand by the fact that the Cathedral's nave was closed until 1956 for reconstruction work, and on the other hand by the fact that before the Second Vatican Council the liturgy was more strongly oriented towards the choir and the high altar than it is today.
The transept organ is spacious and freely placed on the gallery. Some of its divisions are arranged on two levels. It is enclosed as far as visible by speaking pipework, which forms an open facade. It is disposed in a classical manner, with features of the neo-baroque oriented organ style.
After completion of the nave and removal of the separating wall, the transept organ was too small for the cathedral's acoustic requirements. Therefore, in 1956 it was extended by a fourth manual and its stoplist was partially changed and expanded to 86 stops. In 2002 the instrument was equipped with a high-pressure solo section with two foundation stops and three tuba stops. In 2011 a (free reed) clarinet was added; the wind pressure of these stops is 270 mm WS. In the solo work (4th manual) we find the old mixtures of the organ from 1948, as well as an old quintadena, which was supposed to be omitted when the instrument was reorganized.
Today the Querhaus organ has 89 stops (plus ten transmissions) and two effect stops on four manuals and pedal. The action is electropneumatic.
The nave organ was consecrated in 1998 as second main organ. It remedied the unsatisfactory sound situation of the post-war period, especially with regard to liturgical organ playing.
The nave organ is acoustically well positioned in the Gothic church interior. The organ is constructed as a swallow's nest organ and weighs about 30 tons. It is about 20 m high and hangs about 20 m above the floor on four 35 mm thick steel rods anchored in the roof structure. It hangs directly in front of the northern nave wall without touching the wall.
The nave organ comprises a total of 53 stops (3,963 pipes), distributed over a pedal and the three manual divisions: Rückpositiv, Great and Swell. The organ is located in a framework stabilized by the rear wall of the organ case and a case band about 71 cm wide. The case band is clamped to the nave pillars. The organ framework consists of a steel skeleton with four iron grids, which constitute four functional levels. Optically, the top level makes up about half of the nave organ. In the middle and at the top there are the bellows and the pipes of the Great, Swell and Pedal sections. Some pedal pipes are in the front (Violon 32'). The highest level ends at the bottom with the case band. Underneath, the casing gets narrower. The second level is in front of the triforium passage. On the third level below is the Rückpositiv.
The nave organ has its own console but can also be played from the console of the transept organ.
In 2006 the organ ensemble in the cathedral was extended by a high-pressure division with two high- pressure stops: a Tuba episcopalis 8' and a Tuba capitularis 8'. This bombarde division is located in the western gallery of the Cathedral, laterally in front of the large western window between the towers, on the triforium benches at a height of about 20 m. The stops are divided into C and C sharp sides and are arranged on both sides of the central arch. The 122 pipes of the two reeds project horizontally into the nave and are arranged vertically one above the other.
The fanfares are intended to provide a impressive sound even when the church is fully occupied and are only played during festive services on high feast days and on special occasions. These stops are also played from the central console of the transept organ; they can be coupled to any manual and to the pedal. In addition, the tonal volume can be expanded by sub-octave and super-octave couplers.