Fokker organ

A unique 31-tone organ

The Fokker organ is a unique 31-tone organ that was built in 1950 by organ builder B. (Bernard) Pels & Zoon in the Teylers Museum in Haarlem, on the initiative of and according to the design by the Dutch physicist Professor Adriaan Daniël Fokker. It is the showpiece of the Huygens-Fokker Foundation, which manages the instrument and organises its performances.
The instrument is based on the 31-tone system, that is, 31-tone equal temperament, which corresponds to meantone temperament but with 19 additional tones. The instrument therefore contains 31 (fifth) tones in the octave, instead of the usual 12. The great advantage of this system is that modulation to all keys becomes possible, something that was previously only partially feasible within meantone temperament, which has purer thirds than the common 12-tone equal temperament.
The organ was restored in 2009 by Pels & Van Leeuwen and rebuilt in the Muziekgebouw aan ’t IJ in Amsterdam. Despite its seemingly large number of pipes, the 31-tone organ is a relatively modest instrument in terms of size, with no more than six stops, but it produces a full sound powerful enough for the Small Hall. In total, the instrument contains 648 organ pipes, divided over six stops.
The Fokker organ has a console with two 31-tone manuals and a pedal (main keyboard). The console is movable and can be placed anywhere in the hall, though it usually stands in the centre beneath the organ pipes, with the 31-tone manuals facing the audience. Originally, the organ also had a console with 12-tone manuals and a pedal (auxiliary keyboard) on which part of the 31-tone scale could be played. However, since there was not enough space in the Small Hall for two large consoles, this auxiliary console was not restored in 2009 and was replaced by two master keyboards by the brand Fatar.
This was possible because during the renovation the instrument was fitted with MIDI technology (in & out), which means that today it can be fully computer-controlled. The Fokker organ can now record live music in MIDI, play and perform MIDI files, programme any mode or selection of the 31 tones onto the 12-tone keys, trigger digital stops in addition to its acoustic registers (played through four identical speakers inside the organ), perform all Euler-Fokker genera (more than ever before) via a laptop, and even be played remotely by sending MIDI signals over the internet.
With MIDI programming, it is also possible to use additional (artificial) couplers, providing greater flexibility in registration than in the original specification of the Fokker organ. For example, octave couplers can increase the maximum volume beyond six simultaneously sounding stops, which can be useful in certain passages. Furthermore, there is no loss of time when changing registrations, as all changes can be fully automated via computer using special software.

The tuning of the 31-tone organ is a’ = 443 Hz (in the Muziekgebouw, originally a’ = 440 Hz in the Teylers Museum). During the renovation it was decided not to retune the instrument lower, once it became clear that the Fokker organ sounded higher due to the warmer climate of the Small Hall in the Muziekgebouw compared with the cooler central hall above the entrance of the Teylers Museum. Whereas in this hall all the organ pipes stood on the floor in a cabinet space with large double doors, the pipes are now located above the glass wall of the Small Hall in the Muziekgebouw, where one can take in both the Fokker organ and the skyline of Amsterdam in a single view.

The specification of the 31-tone organ is as follows:
Manual I: Quintadena 8′ and Prestant 4′ on the lower manual with a range of C–g′′′ (4½ octaves), with 143 pitches/pipes and 319 keys
Manual II: Salicional 8′ and Rohrflute 4′ on the upper manual with a range of C–g′′′ (4½ octaves), with 143 pitches/pipes and 319 keys
Pedal: Subbass 16′ and Gedackt 8′ (transm.) with a range of C–f (1½ octaves), with 45 pitches/pipes (Gedackt 8′ has 31 of its own pipes) and 45 pedals
Couplers: P + I and P + II, belonging to the pedal, and I + II, belonging to manual I (Note: Gedackt 8′ uses the 14 lowest pipes of the Subbass.)

The Quintadena on manual I and the Rohrflute 4′ on manual II are flute-like stops, of which the Quintadena is the softest stop of the organ. Originally the Quintadena had a different sound, traditionally with more fifth in it. However, it soon became apparent in the Teylers Museum that this fifth interfered with the more tempered fifth of the 31-tone system and with meantone temperament in general. To solve this problem the organ builder removed the fifth as much as possible from the Quintadena, resulting in a sound close to that of the Rohrflute, but an octave lower. The Rohrflute is somewhat louder than the Quintadena, even when the latter is played an octave lower.
The Salicional on manual II is a string-like stop with a singing tone. This stop is louder than the Quintadena of manual I. The Prestant on manual I is a principal stop and the loudest single stop of the Fokker organ. Adding the Prestant to other stops adds brightness and creates the effect of a large organ. Manual I can be coupled to manual II (i.e. when playing manual I, the activated stops of manual II will also sound). The pedal can be coupled to manual I and/or manual II. The two pedal stops have a similar sound: flute-like and fairly soft, especially in the 16-foot range. However, the Subbass provides the necessary depth, even when the full organ is used.

The disposition on the old auxiliary console with two standard 12-tone manuals is, incidentally, the same as that of the main console, except for the pedal. Since it encompassed one octave more, the Gedackt 8′ was omitted. The 12-tone manuals of this original console are connected to the rest of the organ in a special way. By means of nine push buttons, one of nine pre-selections of 12 notes from the 31 notes per octave could be linked to the keyboard. Eight of these were fixed pre-selections, while for the ninth, pitches could be freely chosen using switches. The fixed selections were the Euler–Fokker genera with fifths, major thirds and harmonic sevenths, forming scales of 12 notes per octave: [3³.5²], [3².5³], [5³.7²], [3³.7²], [5².7³], [3².5.7], [3.5².7], [3.5.7²].
In the programmable selection, meantone temperament with E♭ and G♯ could be chosen. This provided the pitches used by 17th- and 18th-century composers, thus reviving the old beauty of their compositions. As Adriaan Fokker said of this: “This is the keyboard that looks back to the classical past. The other keyboard with the 31-tone manuals is the keyboard that looks towards the future.” This second console is still kept at the organ builder’s workshop.

Both 31-tone keyboards have an identical layout and consist of white, black and blue keys. The seven white keys per octave correspond to those of the piano. The same applies to the black keys, except that two black keys are placed one above the other, which brings the total to ten keys per octave. In meantone temperament, and therefore also in the 31-tone temperament, there is a difference between, for example, B♭ and A♯, with the B♭ sounding one fifth-tone higher than the A♯. The upper black keys are therefore connected to the flats, and the lower ones to the sharps.

The seven white keys and the ten black keys together make 17 keys. The remaining 14 of the 31 Fokker organ keys are therefore blue and operate all the intervening fifth-tones of the 31-tone system. The dimensions of the keys, including the space between them, are 12 x 40 millimetres. The keys are arranged in such a way that the span of an octave on the 31-tone organ is in fact the same as on a piano, but with 31 keys within the same space. For this reason, among others, the keys are considerably smaller and are placed one above the other. In addition, the keys rise diagonally upwards from left to right, and there are duplications of keys on the keyboard, which makes it possible to play complex chords in different ways. This ingenious keyboard by Adriaan Fokker is also designed in such a way that an ultra-chromatic scale of fifth-tones emerges when the keys that stand directly above one another are played vertically upwards or downwards.

The Fokker organ is the only fully acoustic 31-tone organ in the world and has great musicological value. Because of the unequal semitones of the equal-tempered 31-tone system, the sound experience of each piece of music on this extraordinary instrument is a unique event in itself. The organ can hardly render compositions in any way other than differently and in its own right. This means that the performance of each work provides, in many cases, a better alternative to the conventional equal-tempered 12-tone system — precisely as Christiaan Huygens and Adriaan Fokker once envisioned their music of the future.

History of the Fokker organ

In 1950 the unique Fokker organ was built by the Dutch organ builder Pels. But the history of this 31-tone organ already goes back to the previous decade. The renowned physicist Professor Adriaan Fokker, professor in Delft and Leiden and nephew of the famous aircraft manufacturer Anthony, had, as curator of the Physics Cabinet at the Teylers Museum in Haarlem, been committed since the early 1940s to having microtonal instruments built and played in order to demonstrate purer intervals.
His source of inspiration was Christiaan Huygens, who had already described the 31-tone system in his 1691 article Lettre touchant le cycle harmonique, which Fokker studied during these years. This resulted around 1940 in the construction of a 31-tone guitar and, in 1943, in the construction of the Euler organ, on which Euler–Fokker genera of the third degree could be played. This small organ is still on display in the Teylers Museum.
In 1945, after the end of the Second World War, Professor Adriaan Fokker resumed composing and other musical activities. He focused more and more on the theory of temperaments, particularly in relation to just intonation and the 31-tone temperament. He also began work on a larger project in the field of instrument building, namely an organ with the full range of 31 notes per octave. Fokker subsequently secured sufficient financial support to begin construction. The organ, built to his own design, was built and installed in 1950 in the central hall of the Teylers Museum in Haarlem by the organ builder B. Pels & Zoon. It should not go unmentioned that the laboratory assistant of Teylers, Mr J. M. Verbeek, was closely involved in the project. By his own account, most of his work in the 1940s was connected with the construction of the organ. Correspondence with the Amsterdam city council shows that it was Fokker’s intention to find a prominent place for his organ in the capital. However, this did not succeed and the museum then became the location. The two manuals were placed on the floor level of the rotunda at the height of the balcony, while the organ pipes, wiring and other components “disappeared” into a large cabinet space, the doors of which were opened as widely as possible during concerts. During the monthly performances the audience was spread over the rotunda and the small antechamber of the auditorium.
Fokker became a fervent advocate of the 31-tone system. For him, it was a system that contained unprecedented new musical possibilities. He saw the organ as an instrument that opened doors to the music of the future, free from the limitations of the twelve-tone system. Fokker gave lectures all over the world and succeeded in winning over various singers, musicians and composers. As a result, a true 31-tone movement emerged. Dutch composers such as Peter Schat, Henk Badings, Hans Kox and Jan van Dijk, and abroad among others Alois Hába, Ivan Wyschnegradsky and Alan Ridout, made important contributions to the 31-tone literature and the repertoire of the 31-tone organ in particular.
Under the pseudonym Arie de Klein, Fokker himself also wrote a number of short compositions for “his” organ. It was only many years later that this remarkable instrument came to be called the “Fokker organ”. The first organist was Paul Christiaan van Westering. The first concert on the new 31-tone organ was given on 10 September 1951, with compositions by Jan Pieterszoon Sweelinck, Paul Christiaan van Westering and Jan van Dijk. From 1952 Anton de Beer was also involved as the regular organist of the 31-tone organ. Concerts on the organ took place regularly during the period 1951–1955, with performances of newly written 31-tone music on the main console and early music in meantone temperament on the auxiliary console with 12 keys per octave.
In the years thereafter, concerts were held on the first Sunday of every month, with the exception of January. From the 1990s onwards, Joop van Goozen succeeded Anton de Beer as the regular organist of the Fokker organ in the Teylers Museum. 

Since 1960, the Huygens-Fokker Foundation has managed the 31-tone organ, which from 1950 stood in the hall of the museum on the Spaarne in Haarlem for almost fifty years, during which various microtonal concerts were organised. In 1999, it became clear that the instrument had to make way for a disabled lift in the museum, after which it was removed by the original organ builder three months before the year 2000 and stored in ’s-Hertogenbosch until 2008.
At the end of 2006, the search for a new suitable location for the instrument began, which was eventually found in the then-new Muziekgebouw aan ’t IJ in Amsterdam. Thanks to the impartial efforts of M3H Architects, structural calculations, realistic drawings and simulations of the organ in the Small Hall were made before the actual renovation of the Fokker organ began, showing how this extensive 31-tone instrument would be installed.
After an intensive search for additional funding, the Fokker organ was completely renovated and modernised in 2008 and 2009 by Pels & Van Leeuwen Organ Builders, under the commission of artistic director Sander Germanus of the Huygens-Fokker Foundation, and converted into a hypermodern organ. This extraordinary 31-tone organ was then permanently installed above the glass wall of the Small Hall in the Muziekgebouw aan ’t IJ (read more about the extensive renovation in the online archive).
New was that from that moment the instrument could also be operated by laptops, as it was fitted with MIDI technology. As a result, since 2009 the Fokker organ has been not only the only 31-tone organ in the world but also one of the first “hyperorgans,” according to a PhD study at Harvard University. The celebratory inauguration concert of the Fokker organ took place on Sunday, 17 May 2009, organised and presented by Sander Germanus and attended by many guests, including Aad Fokker, the son of Adriaan Fokker, and a large part of the rest of the Fokker family.
The 31-tone organ was played by former Fokker organist Joop van Goozen, with the assistance of his regular musical guest of the 1990s, Jos Zwaanenburg (flute & live electronics), and other musical guests, namely Guus Janssen (Fokker organ), Raymond Honing (traverso), Cees van der Poel (Fokker organ) and Elske Tinbergen (baroque cello). Since September 2009, Ere Lievonen has been the regular organist of the Fokker organ.
From that moment, the first season of the Fokker organ concert series also began, which continues to be organised successfully to this day. In 2009, the “silent” keyboard, a portable 31-tone keyboard from 1964 for practice, was also equipped with MIDI technology. This made it possible to play digital 31-tone organ sounds via a laptop on this previously soundless keyboard, which was also useful for giving concerts outside the Small Hall of the Muziekgebouw aan ’t IJ. 

Since the resurrection of the Fokker organ in 2009, the microtonal instrument has occupied a central position in both the Dutch and international music world, in the fields of contemporary as well as early music. During the first fifteen years following its renovation, a wide range of new compositions and musical styles have been presented. In addition to early music and contemporary (microtonal) music, non-Western music has also been performed regularly, including music from China, Indonesia, India and Turkey.
A recent development, enabled by the installation of four large identical speakers in the organ in 2018 and the addition of digital 31-tone organ stops via a laptop, is the performance of Romantic organ music in meantone temperament, when a concert programme calls for it. Previously, this was impossible without software for quick and easy modulation and without the many additional organ stops required for Romantic music.
The new MIDI technology has also led to various remarkable experiments, including performances of the Fokker organ by a performer in Australia, with live video and an audience in the Small Hall. These possibilities subsequently enabled a joint concert with the Orgelpark in Amsterdam.
In addition, the Fokker organ has frequently been used in concerts and festivals organised by the Muziekgebouw itself, such as the World Minimal Music Festival, the Andriessen Festival, the Pärt Festival, the Ongehoord Bruckner Festival, the Ligeti Festival, the Kurtág Festival, An Evening Today, and The Rest is Noise. It has also been featured in independent concerts and festivals, such as Lost & Found, the Gaudeamus Festival, the Sweelinck Festival, and Sonic Acts. This is alongside a highly varied own series of six concerts with the Fokker organ, in which many guest musicians have participated.
With the founding of the in-house ensembles Ensemble SCALA (2010) and Vokalprojekt 31 (2015), the Fokker organ has secured a permanent place in two ensembles for microtonal music, allowing the instrument to be heard as part of a larger instrumentation. Over these very active years, the renovated 31-tone organ has attracted more attention than ever before, partly due to the growing interest of composers and audiences in this unique instrument and the underlying microtonal system. Audiences from all continents now travel specifically to the Muziekgebouw in Amsterdam to admire the extraordinary keyboard and hear the world-famous Fokker organ in performance.

Mens en Melodie (1948): Organ in the temperament of Huygens

The organ builders B. Pels & Son in Alkmaar received a commission from Prof. Dr A. D. Fokker to construct an organ in the temperament of Christiaan Huygens, which would be installed and playable in the Teylers Museum in Haarlem on 1 March 1950. This Huygens temperament is a meantone temperament, which has been made cyclic through refinement, an equal temperament with 31 fifth-tones per octave. On this organ in Huygens temperament, it would initially be possible to hear seventeenth-century early music in its own sound, and additionally future music featuring harmonic sevenths.
Manual I is equipped with an 8-foot Bourdon and a 4-foot Principal. Manual II has an 8-foot Salicional and a 4-foot Flute. The range of both manuals is C to g”’. The pedal receives a 16-foot Subbass, ranging from C to f.
The manuals must accommodate all 31 keys of the octave within hand span. This is achieved by arranging eleven rows of keys in a staggered “roof-tile” pattern, without overlapping. The seconds are found in straight rows from left to right, e.g. c-d-e-f♯-g♯-a♯-b♯-c♯♯-d♯♯, etc. Halfway between e and f♯, 0.5 cm higher and slightly further from the player, comes the key for f. From there, the seconds extend to the left as E♭-D♭-C♭-B♭-A♭, etc., and to the right as g-a-b-c♯, etc. Between c and d, the D♭ is positioned slightly higher and further from the player, so that c : D♭, a minor second, lies in the same relative position as e : f. Between c and d, but slightly lower and closer to the player, lies C♯, so that the minor second C♯ : d again lies in the same relative position as e : f. 
In the illustration, 24 of the 31 keys are shown. The natural notes are white. The sharps and flats are black. The double sharps, such as F♯♯, and the double flats, such as E♭♭, are blue, as are B♯, C♭, E♯, and F♭. Each key occupies a space of 12 x 38 mm. To allow easy use of the thumb and little finger (also with underlay!), there are two keys for each note, one for the long fingers and one for use with the thumb and little finger—hence the eleven rows of keys.
For the pedal, the arrangement of the keys is the same, although doubling the number of keys is not required. The action is electric-pneumatic.

A. D. Fokker: On the construction of the 31-tone organ

First of all, entirely new keyboards had to be designed. On these, all the pitch distances can be found aligned straight from left to right, the large semitones arranged diagonally upwards to the right, and the small semitones diagonally downwards to the right. The white piano keys are also white here. For each black piano key, there are two black keys, and the remaining keys, between white and black, are blue. Above and below each white key is a blue key (see Fig. 1).
Two features facilitate playing: finger technique in one key does not need to be replaced by a different technique in another key (as on a normal keyboard), and for each note there are two keys available, in some cases even three. The keys (319 on each keyboard) do not pivot on a pin in the centre or at the end. They are made of resin blocks measuring 11 × 38 × 15 mm, which are pressed vertically downwards. At the bottom of the key lever, which provides guidance, there is a contact (see Fig. 2).
For good playability, it was necessary that the keys have a depth of only 5 mm; otherwise, the difference with the keys behind, which are always 6 mm higher, would be too great. This shallow depth and the correspondingly very short so-called “dead travel” of the keys required extremely precise work. The use of very high-quality, non-shrinking materials made this possible.
The upper manual connects directly to the lower one and is also set at an incline. The distance to the back row of keys on the upper manual is therefore kept as small as possible with the 22 rows of keys that together form the two keyboards. The pedalboard has 45 keys (almost 1½ octaves). These keys are made of three types of wood, which give the three colours of the keys. The height of the keys is chosen so that, as a whole, the pedalboard forms a cylindrical shape. Because a large part of the keys is always played from the back, they pivot at the front, unlike a conventional design.
The windchests are of the cone chest system and are split into three sections. This was necessary because, due to the large number of pipes, the length of the windchests had to be abnormally long. The total number of pipes is 648. In a conventional organ with the same stops, there would have been 266.
Calculating the dimensions of the pipes was naturally a time-consuming task, as an entirely new size division had to be created.

Because tuning according to a circle of fifths now requires 31 steps instead of 12, the likelihood of errors is much greater. In a trial tuning, it became apparent that the pipes influenced each other too strongly to allow accurate tuning by ear. The pipes are now tuned using a tone generator and a cathode-ray oscillograph. In this procedure, only one pipe sounds at a time, eliminating mutual influence. The correct pitch is then determined “by eye” on the screen of the oscillograph.
When working according to this method, tuning is done according to a circle of thirds rather than a circle of fifths, because the beats of the thirds are much slower. This allows for much more precise work.
To enable organists who are not familiar with the large console to play the organ, a second console with standard keyboards was constructed. This console is specially connected to the organ. Using nine push-buttons, nine types of stops or tone families, each containing 12 of the 31 notes per octave, can be connected to the auxiliary console. Eight of these families are fixed, and the ninth can be selected at will using switches. The cabinet housing this electrical system is located in the organ chamber (see Fig. 4).
Both consoles are situated in the upper portico of the museum. They are connected to the organ and the switch cabinet by cables, comprising a total of 533 wires.

Disposition of the organ:

• Manual I C–g”’ (143 notes): Quintadena 8′, Prestant 4′

• Manual II C–g”’ (143 notes): Salicional 8′, Flute 4′

• Pedal C–f (45 notes): Subbass 16′, Gedekt 8′ (transmission)

• Couplers: (P + I); (P + II); (I + II)

• Pitch: a’ = 440 Hz

The disposition on the auxiliary console is the same, except in the pedal. Here, the Gedekt 8′ has been omitted because this console extends one octave further in the pedal, namely C–f. As the stability of the tuning was the most important factor, no 2-foot stop is included in the organ.