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Electrostatic organs of Dereux

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The mim possesses three electrostatic organs by the French engineer Jean-Adolphe Dereux (1896-1968). The two largest ones have two keyboards and a pedal (n° 2016.0098.001 and 2018.0079.001), while the smallest instrument (n° 2016.0098.002) has only one keyboard and the musician controls the volume using the pedals (Figures 1a and 1b). The three organs are a gift from Pieter de Jong, who restored them to make them playable.

Dereux considered the electronic organs of his time as not sufficiently capable of imitating the sounds of the pipe organ. He therefore developed a system to visualize the timbres of the organ pipes and to return them electronically in the most authentic way possible. Thus was born in the early 1950s the electrostatic Dereux organ. Sound is created by the current processed by a generator in which a moving disc rotates between two hard disks (Fig. 2a). These hard disks contain information, including sound diagrams.

Using an oscillograph, Dereux made a graph of the vibrations of the organ pipes. These pipes were carefully selected to find the best quality. The engineer's choice were the pipes made by the French organ builder Cavaillé-Coll. Oscillograms allowed photographic recordings of sounds (diagrams). Dereux thus managed to record 24 different organ stops for each of the twelve notes, in seven octaves. He meticulously arranged these diagrams on a disc. As this disc was too large to be incorporated into an instrument, it was reduced photographically to a negative plate, which in turn was reproduced by photo-engraving to a usable size.

This sound information is then applied to one of the two hard disks of the generator, namely the silver side (hard plastic with evaporated silver). The other hard disk, on the copper side, is used to connect to the control box and stops. Between these two discs rotates a movable disc (the scanning disc), composed of a number of silver watermark scanning beams (Figs. 2a and 2b). Each time one of these beams moves along a diagram, a current is generated (electrostatic). This current is sent to the amplifier (and loudspeaker) only when the organist activates one or more stops and presses a key.      

As our musical system consists of twelve tones, each tone of a Dereux organ has its own generator (Fig. 3). All are identical and driven by the same drive belt. The fact that they all operate at different speeds is due to the different thickness of the drive shafts.

Dereux organs do not have an integrated loudspeaker. A loudspeaker (external) is therefore specially designed to mimic the effect of acoustic pipes as much as possible. It is equipped with double-opening column-shaped resonance chambers mounted on the loudspeaker (Fig. 4a and 4b).

It is not surprising that these organs are ideally suited for churches, especially the bigger organs with two manuals and one pedal (Fig. 5). The sales catalogues leave no doubt that clergy and church wardens are appropriate customers. According to the vendors, the instrument had many advantages in comparison with the pipe organ :".... hard-wearing parts... easy to maintain... no risk of damage by heating systems in churches... the wood species[of the case] have undergone special treatment... impossible for the Dereux organ to become unpleasant, its harmonization is absolutely constant.... easy to install in the narrowest rooms[and] of apartments and houses of normal size... the price of an electrostatic organ is about one-fifth of that of a pipe organ..." (around 1960 the price was still 150,000 Belgian francs, a significant amount). 

If these arguments had not yet convinced the potential buyer, the supreme argument remained, the one who calls upon the divine: "Finally, it is a great creation of the human spirit that is placed at the service of God and then of humanity, because it helps humanity to elevate its thoughts towards God and towards the beauties of Art".

Illustrations

1a Electrostatic organ, Jean-Adolphe Dereux, Paris, 1953, inv. 2016.0098.002             

1b The keyboard has 5 octaves but can be extended to 5 ½ octaves if it is tilted from the bottom and a key (a semitone) is shifted. In this way it is possible to transpose

2a Two images from the sales catalogues showing the two hard disks and the rotating scanning disk

2b The scanning disc (top) and a hard disk (bottom) 

3 Tone generators

4 a & b Speaker (bottom)

5 Electrostatic organ, Jean-Adolphe Dereux, Paris, 1973, inv. 2016.0098.001

 

Media
Images: 
1a Electrostatic organ, Jean-Adolphe Dereux, Paris, 1953, inv. 2016.0098.002
1b Electrostatic organ, Jean-Adolphe Dereux, Paris, 1953, inv. 2016.0098.002
2a Two hard disks and the rotating scanning disk
2a Two hard disks and the rotating scanning disk
2b The scanning disc (top) and a hard disk (bottom)
3 Tone generators
4a Speaker
4b Speaker
5 Electrostatic organ, Jean-Adolphe Dereux, Paris, 1973, inv. 2016.0098.001