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.

Carrillo piano

A remarkable 96-tone piano

The Carrillo piano, also referred to as the 96-tone piano (or officially the 1/16-tone piano), is an exceptional musical instrument offering extensive microtonal possibilities. Developed in the 1950s by the Mexican composer Julián Carrillo (1875–1965) in collaboration with the German piano builder Carl Sauter, this piano has inspired countless composers and musicians to explore new musical avenues. Today, this rare instrument is held by institutions such as the Conservatoire National Supérieur de Musique et de Danse in Paris and the Huygens-Fokker Foundation at the Muziekgebouw aan ‘t IJ in Amsterdam.

The Sauter Carrillo piano is tuned in 96-tone equal temperament, which divides the octave into 96 equal steps. This means the interval between two adjacent keys is a 1/16-tone, or just 12.5 cents. Sixteen keys are required to span a whole tone (for example, from C’ to D’), and eight keys for a semitone (such as G’ to G♯’). The keyboard contains 97 keys and 291 steel strings. The Carrillo piano stands 116 centimetres tall and visually resembles a standard upright piano but covers only one octave in pitch range, from C1 (middle C) to C2. Its visual octave span, however, extends over eight octaves, which may be potentially confusing for performers.
The Carrillo piano is a vertical instrument with a mechanism similar to that of a traditional piano. It is fully triple-strung and has two pedals: a sustain pedal and a soft pedal. Unlike a traditional piano, the soft pedal does not alter the tone colour but merely shortens the distance between the hammers and the strings (see brochure). In contrast to some other Carrillo pianos, the instrument at the Huygens-Fokker Foundation lacks a third (moderator) pedal but has a manual moderator, allowing a layer of felt to be placed between the hammers and strings to produce a muted, mysterious sound.

Within the 96-tone system of the Carrillo piano, which enables 16th-tone playing, various other tuning systems are also embedded, including the conventional 12-tone system, the 24-tone system (quarter tones), and the 48-tone system (eighth tones). It can also be played according to just intonation. Despite the 96-tone Carrillo piano and the 31-tone Fokker organ being based on two different (almost incompatible) systems, the instruments can sound remarkably in tune together, as the tones deviate by no more than 6.25 cents in the worst case. Due to their very different timbres, this slight difference is virtually imperceptible. Most notes on the Fokker organ thus have an almost perfectly corresponding note on the Carrillo piano.
Only when constructing consonant chords must occasional compromises be made, causing a particular note to deviate slightly more than 6.25 cents from the 31-tone organ. However, in most compositions for the 96-tone piano, only consonant intervals (two notes simultaneously) are played, since the large distances on the keyboard require four hands for full harmonic chords. A single performer can therefore play only intervals or micro-clusters on the Carrillo piano. (Check here for a chart showing the corresponding pitches between the Carrillo piano and the Fokker organ.)

To notate music for, among others, the 96-tone piano, Carrillo developed, in addition to a system of small marks placed before the notes, a numerical notation by simply assigning every pitch within the octave a number from 1 to 96. However, this proved difficult for performers to read. Today, scores are generally written in standard piano notation (usually over two staves), as if the pitch range extends from CCC to c5. Although the notation contains extreme leaps (all intervals on the keyboard are eight times larger than normal), in principle, any pianist specialised in contemporary music can read the score directly without learning a complex new system. The same applies to the piano keyboard itself, which is identical to a traditional piano but has 97 keys instead of 88. Carrillo anticipated the advantages of a conventional keyboard from the outset, as creating a specially designed keyboard for 96-tone music would have been impossible. In this way, the remarkable Carrillo piano ultimately became a practical instrument with readable sheet music.

The Carrillo piano distinguishes itself from traditional pianos by its unique character. Firstly, it produces a highly recognisable percussive sound, almost like a prepared piano, due to the absence of low notes, which prevents certain overtones from sounding. Whereas standard pianos use semitones as the smallest interval, this piano explores the subtle nuances between these notes. Carrillo’s refined 96-tone system can, in fact, approximate any interval or chord with remarkable accuracy. On the Carrillo piano, spectral chords can be performed to produce a wide variety of overtone sounds almost perfectly.
Furthermore, due to the small distances between keys, the instrument can be combined effectively with instruments tuned in other systems for polymicrotonal music (‘multiple division music’). Its derivation from the 12-tone system also allows it to be easily tuned and played together with conventional pianos, enhancing performance possibilities. Additionally, the extremely small pitch increments enable nearly any tuning of non-Western instruments to be reproduced on this extraordinary piano, which, unlike many other microtonal instruments, can be played by any pianist. This presents new challenges for both composers and performers and opens avenues for experimental music. With its innovative design and fascinating sounds, the 96-tone Carrillo piano has played a significant role in the history of microtonal music.

History of the Carrillo piano

The Carrillo piano, an instrument that pushes the boundaries of traditional music, is closely associated with the Mexican composer and music theorist Julián Carrillo (1875–1965). Carrillo, a pioneer of microtonal music, developed a revolutionary theory called Sonido 13, in which he proposed that music could evolve further through the use of intervals smaller than a semitone. His work inspired the creation of new instruments, including the famous 96-tone piano (or 1/16-tone piano), which represents a significant milestone in the history of microtonal music and a revolutionary step in the understanding and performance of pitches beyond the traditional Western scale.

Julián Carrillo was born in Ahualulco, Mexico. He began his musical education in a church choir and later studied violin, composition, and music theory at the Conservatory of Mexico City. During his studies, he became fascinated by the physics of music. In 1895, through experiments with a violin string, he discovered that he could divide a whole tone into sixteen equal parts. This formed the basis of his microtonal theory. In 1925, he devised his own notation for these ideas. After further studies in Europe, including at the Conservatory of Leipzig and the Royal Conservatory of Ghent, where he excelled as a violinist and composer and laid the foundation for his later innovations, Carrillo returned to Mexico. He became an influential figure in Mexican musical life, working as a conductor and teacher, and introduced a new musical direction with his Sonido 13 theory (“The Thirteenth Tone,” which essentially represented the first tone beyond the conventional twelve), through which he introduced microtonal intervals smaller than a semitone. He created new compositions, founded ensembles, and designed innovative instruments to make microtonal music possible. In 1950, Julián Carrillo was nominated for the Nobel Prize in Physics, though he did not win.
However, his work often clashed with traditional musical conventions, encountering resistance both in Mexico and internationally. Despite Carrillo’s artistic genius and support from prominent figures such as Leopold Stokowski, with whom he founded an ‘Orquesta Sonido 13’ and toured during the 1930s, his work was regularly criticised and marginalised. Nevertheless, Carrillo continued to experiment tirelessly with microtonal systems and collaborated with instrument makers to realise his revolutionary ideas, including the 96-tone piano, as well as customised harps and string instruments. Throughout, he remained true to his own vision, resulting in a body of work that is both experimental and deeply rooted in traditional structures.

In the 1940s, Carrillo designed and patented fifteen so-called metamorphoser pianos, each tuned to a specific microtonal system, ranging from whole tones, quarter tones, to 1/16-tone intervals, and all divisions in between. The 96-tone piano is among the most remarkable of these instruments. With ninety-six keys per octave and intervals of only 12.5 cents between adjacent keys, the instrument opens an entirely new and highly detailed sonic universe. The pianos, built by the Carl Sauter factory in Spaichingen, were first presented at the Brussels World’s Fair in 1958, where they were awarded a médaille d’or (gold medal). Three of these instruments are now held at the Conservatoire de Paris (two in sixteenth-tone and one in third-tone), while others are located in conservatories in Nice, Mexico City, Freiburg, and Vancouver. Later models of the 96-tone piano can be found in cities such as Buenos Aires, Montréal, Lisbon, and at the Hochschule der Künste in Bern.
Carrillo’s microtonal instruments, including the 96-tone piano, have influenced many composers worldwide, including György Ligeti and Giacinto Scelsi, who built on Carrillo’s ideas, though often from different aesthetic perspectives. His work also resonated with other microtonal pioneers such as Ivan Wyschnegradsky and Alois Hába, who likewise developed new systems and instruments for quarter tones and sixth tones, respectively. Furthermore, his work inspired composers and researchers to continue experimenting with microtonal music. The 96-tone piano, a symbol of Carrillo’s vision and perseverance, continues to present new musical challenges for both performers and composers. Although Carrillo received both praise and criticism during his lifetime, his contributions have proven invaluable. His work challenges conventional musical boundaries and emphasises the potential of microtonality to explore new musical worlds. (Read more about Julián Carrillo in the online archive of the Huygens-Fokker Foundation)

Between 1997 and 2000, the original German piano maker Sauter produced a new series of ten Mikroton 1/16 pianos, which have been referred to as Carrillo pianos by the Huygens-Fokker Foundation since 2010. One of these rare, difficult-to-sell, and particularly expensive instruments reached the early 21st century, through the good contacts of Robbert Westera with Sauter, at the piano dealership Westera in Winterswijk. From this location, work began on the possible performance of the instrument in the Netherlands, which among other things resulted in an initial collaboration with the Huygens-Fokker Foundation.

On 5, 6, and 7 August 2005, as part of the Hortus Festival organised by saxophonist and festival director William Raaijman (and with financial support from the foundation), a series of concerts took place in Utrecht, Leiden, and Amsterdam, featuring among other instruments the Carrillo piano, played by pianist Maarten van Veen, who had encountered the instrument in Winterswijk in 2004.
In 2008, the Huygens-Fokker Foundation, now under the leadership of artistic director Sander Germanus, contacted the firm Westera in a first attempt to acquire this remarkable 96-tone piano. However, it was not until early 2011 that the instrument—approved by Sauter, with additional sponsorship from the importer, a substantial donation from the Netherlands Acoustical Society (originally co-founded by Professor Adriaan Fokker), and support from six well-known consulting engineering firms—was definitively acquired by the Huygens-Fokker Foundation.
The first concert with the Carrillo piano, entitled Carrillo vs Fokker, took place later that same year, on 16 October 2011, in the Kleine Zaal of the Muziekgebouw aan ‘t IJ, performed by organist Ere Lievonen on the Fokker organ and again by Maarten van Veen on the Carrillo piano. Following this successful performance, multiple Fokker organ concerts have been organised annually, in which the 96-tone piano played a musical role, and a repertoire has emerged for both the 96-tone piano solo and in combination with the 31-tone organ. In 2013, the Carrillo piano also became part of Ensemble SCALA, the microtonal house ensemble of the Huygens-Fokker Foundation. In this context, the instrument is played by pianist Anne Veinberg, who has since specialised in the instrument. In 2021, a long-cherished wish was realised when the Carrillo piano was equipped with a manual moderator by Sauter, allowing the sound to be made significantly softer. With all these capabilities, the 96-tone piano has proven to be a sublime addition and will remain of great musical value to the Huygens-Fokker Foundation for the Fokker organ concert series and beyond.

31-tone guitar

The 31-tone guitars around the Fokker organ

The 31-tone guitar is one of the other microtonal instruments owned by The Huygens-Fokker Foundation. Or rather, 31-tone guitars, since there are multiple instruments, both acoustic and electric. Instead of the usual twelve-tone system per octave, as found on standard guitars, the 31-tone guitar is based on a tuning with 31 tones per octave. This system, known as the 31-tone system, offers a rich palette of sounds and harmonies that would not be possible on a 12-tone guitar.
The origin of the 31-tone system dates back to the 16th and 17th centuries, when the Italian composer Nicola Vicentino and the Dutch scientist Christiaan Huygens proposed dividing the octave into 31 tones in order to preserve the pure thirds of meantone temperament while still being able to modulate to all keys. This idea was later further developed by the physicist Adriaan Fokker, who in the 20th century advocated for the construction of instruments capable of realising this tuning. A well-known example of this is the 31-tone organ, built in 1950 by organ builder Bernard Pels on commission from Fokker and installed in the Teylers Museum in Haarlem.

Even before that time, Adriaan Fokker had a 31-tone guitar built to support his lectures with musical examples. It was probably in 1941 (or no earlier than 1939) that Fokker acquired a jazz guitar from the Dutch firm Amka, whose brand name consisted of the first letters of the forenames of the Veneman family. The company had moved from Haarlem and Amsterdam to The Hague to produce violins and, slightly later (1938), guitars. It is unclear, however, whether Fokker commissioned Amka to build a guitar with 31 frets per octave, or if the addition of the many frets was subcontracted to another instrument maker. What is known is that by 1941, Adriaan Fokker already owned this 31-tone guitar, as evidenced by a lecture he gave that year in which the instrument was discussed.
Below is a quotation from the texts (page 481) of the lectures that Adriaan Fokker (1887–1972) and his colleague Balthasar van der Pol (1889–1959) gave at the Teylers Museum in Haarlem on 20 and 27 December 1941:
“It is crucial to become truly acquainted with the tones. To this end, I had a guitar made with thirty-one frets per octave, at the distances calculated according to HUYGENS. It is not easy to play, because one must place the fingers much more precisely than on a regular guitar, but one can still play many chords. Thus, I can let you hear a chord of E major third, e-gis’-b’-e”. If I play as’-b’- e”, you will hear that it is out of tune. That difference I cannot demonstrate on the piano. Once again, I play a minor third chord g-b-e. If you play b and e each a semitone higher, ces and fes, it is again out of tune. Now a chord with the harmonic seventh. I hope that when I play g’-b’-eis”, you will find it satisfactory, and that you agree it transitions nicely into g’- c”- e”. But now I play g’-b’-f”. Compare that with g’-b’-eis”, and it is clear which chord is better: the latter. If I play b’-f” and add as’, so as’-b’-f”, the chord is again correct. We can hear how the interval b’-f” resolves into bes-ges”. That is correct. Here we find what HUYGENS noted confirmed: the tritone b’- eis” (5:7) resolves into the third c”-e”, its complement, the diminished fifth, b’- f” (7:10) resolves into the sixth bes’-ges”.”
The lecture, centuries after Vicentino’s 31-tone music, possibly presented the very first acoustic demonstrations of the 31-tone system in the Netherlands and beyond, nearly a decade before the construction of the 31-tone organ (Fokker organ). This makes the Amka 31-tone guitar a historic instrument, even though the frets have partially pressed into the wood over the years and the instrument is no longer professionally playable.

The Huygens-Fokker Foundation also owns 31-tone guitars that are used in the concert series centred around the 31-tone organ. These are played by the resident 31-tone guitarist, Stefan Gerritsen. In 2010, the foundation acquired a fine, conventional acoustic Spanish guitar (model 3A) from the Amsterdam guitar maker Otto Vowinkel, which was later refretted from 12 frets per octave to 31 frets per octave by Sebastian Nuñez, an Argentinian maker of early string instruments now living in Utrecht. The guitar features a spruce top, a wood renowned for its exceptional resonance qualities. The back and sides are made of light and durable Indian rosewood, which also has excellent tonal properties. The fingerboard of this guitar was designed by the prominent microtonal thinker Siemen Terpstra (born 1948), a Dutch Canadian residing in Amsterdam, who has himself built numerous microtonal guitars and designed microtonal fingerboards. The spacing of the individual frets was calculated with precision by Terpstra. All the guitar’s fret spaces are painted in different colours (colour-coded) by Siemen Terpstra to help maintain orientation. Because the frets are much closer together than on a conventional 12-tone guitar, the 31-tone guitar is significantly more challenging to play. Guitarist Stefan Gerritsen is a specialist in playing this unique (left-handed) 31-tone guitar. He was also the one who, in 2018, acquired a (likewise left-handed) electric guitar from the Fender brand (Stratocaster series), with the aim of using it for the microtonal ensemble Ensemble SCALA. To achieve this, it had to be possible to detach the neck from the body. In 2019, for this purpose, the Huygens-Fokker Foundation commissioned instrument maker Sjaak Pronk from Broek op Langedijk to create a 31-tone guitar neck, suitable for both left- and right-handed players, thus enabling the construction of an electric 31-tone guitar. The fret positions were again calculated by Siemen Terpstra.

Regarding his Integrated Color-Code for Microtonal Guitar Fretboards (in the spaces between the frets on the fingerboard), Siemen Terpstra once wrote in an article: “The first time that I visited Ivor Darreg (in 1981) he was living in Glendale, California. I was impressed by his amazing array of experimental instruments, but what grabbed me most was his re-fretted guitars. He had a large collection of them, guitars that he had carefully altered over the years. There were so many that it was a veritable feast to me! I had never played re-fretted guitars before, and it was almost overwhelming. Many of his guitars were pretty trashy – Ivor was not a wealthy man, but his dedication to the exploration of alternative tunings was quite impressive. A handful of them were pretty good – I think that I played all of them for a few minutes that unforgettable day. He had guitars in 19-ET, 22-ET, quarter-tone, 17-ET, and other odd divisions, but the sweetness of the 31-ET guitar impressed me most. It was also right at the `edge’ of the possible, or so it seemed to me. There were so many frets, so close together, how could you possibly put more frets on a guitar? Some years later I played a 34-ET guitar, and it largely confirmed the sentiment. From that day forward, I had an interest in 31-ET guitars.
Although I could `noodle’ my way around the fretboard, I soon found that it was almost impossible to play because I would invariably get lost. What fret am I on, and what chord is this? I then realized that the problem could be solved if some colour-cocle would be painted onto the neck for visual guidance. Ivor had a colour-code (rather complex) for his megalyra steel-guitar, but his `normal’ guitars were generally unmarked. On standard guitars, we generally use an inlay dot at the 5th, 7th, and 12th frets as the `colour-code’, and arguably this is adequate for 12-ET, but 31-ET is so complex (rich) that this traditional system no longer proves adequate. I began several years of experiment with alternative colour-codes trying to come up with an optimal design.
In fact, I caught the `guitar-altering bug’ from Ivor, and when I was back in Canada I acquired a semi-trashy electric guitar which seemed perfect for `experimentation’. (What is there to lose?) I had never done a guitar fret job before, so I assumed that the results would be pretty bad. To my surprise, the scale turned out to be pretty close to accurate, there was only a minimum of `buzzes’, and I now had my own 31-ET guitar! At this point, my irnerest in colour-codes intensified. By 1984, I had several designs which arguably have some consistent logic underlying them. The purpose of this little article is to lay out the reasons for my chosen design. Here is why I ended up with this particular pattern.” The electric 31-tone guitar with colour coding by Siemen Terpstra was acquired by the Huygens-Fokker Foundation in 2013 and was used in concerts until 2018.

A microtonal guitar frequently used in the concert series of the Huygens-Fokker Foundation is the beautifully sounding 31-tone guitar designed by Bert Terpstra (not related to Siemen Terpstra) and built by Dirk Janssen. On this instrument, however, only a subset of 17 of the 31 tones can be played. Compared to the piano keyboard, this corresponds to the seven white keys and twice the five black keys (for both five sharps and five flats). This makes the instrument easier to play than a full 31-tone guitar and produces a more pleasing sound, as there are fewer frets on the fingerboard that might alter the tone. Furthermore, by modulating from the key of C, almost all classical keys can be reached. For much early music in meantone temperament and even many pieces in the 12-tone equal temperament, this subset of the 31-tone system is sufficient, while still allowing enjoyment of the pure thirds the system offers. Bert Terpstra has written about his guitar: “My guitar is a good classical acoustic guitar. I did not choose the 31-tone system to play microtonal music, but precisely to play 16th-century Renaissance music (Dowland) and 17th-century Baroque music (Bach). The 31-tone system was already devised in the 16th century. For that kind of music, you do not need all 31 tones. That is why I left out all the tones on my guitar that are unnecessary for this music. Hence, you can see that my guitar has an incomplete set of frets. This makes it relatively easier to play. And yet it is still quite challenging to play Bach on this guitar.” This (left-handed) guitar is also played by the regular 31-tone guitarist Stefan Gerritsen.

Building a 31-tone guitar requires a thorough redesign of the traditional instrument. The fret layout on the neck must be adjusted so that 31 equal intervals fit within an octave. This means the distances between frets are significantly smaller than on a standard guitar, requiring greater precision in string adjustment and intonation to produce the correct microtonal steps. The playability of a 31-tone guitar differs substantially from that of a conventional guitar. The closely spaced frets demand a new technique for playing chords and melodies, as traditional fingerings are not directly applicable. Additionally, due to the many frets on a 31-tone guitar, there can be a slight loss of tonal quality. One of the main advantages of a guitar based on the 31-tone system, however, is the ability to play purer intervals. Moreover, the system provides access to intervals such as the harmonic seventh, which are absent in standard equal temperament. The 31-tone guitar has now attracted the interest of musicians and composers seeking new sound possibilities and wishing to acquire a relatively affordable 31-tone instrument. Since 2011, the Huygens-Fokker Foundation has had the expertise of guitarist Melle Weijters, a skilled performer in the field of microtonal guitars, who has become a regular participant in Fokker organ concerts and other musical activities.

Archiphone

The archiphone by Neonvox

The archiphone is a historic analog electronic instrument from 1970. Since that year, four archiphones were built by Herman van der Horst of the firm Neonvox in Wilp, Gelderland, commissioned by Anton de Beer. Two of these archiphones are in the possession of the Huygens-Fokker Foundation.

The layout of the keyboard is essentially the same as that of the Fokker organ. The keys are closer together, allowing for faster playing. Transistor oscillators form the sound source and are mounted on removable circuit boards. There are approximately 40 different timbres, evenly distributed over the 8- and 4-foot “registers.” The unique aspect of the archiphone is its microtonal keyboard design. The instrument is played on an unusual five-octave keyboard (from c – c) with 333 keys (white like piano keys, black for sharps, blue for half-sharps, dark gray for flats, and gray for half-flats), based on Huygens’ microtonal 5th-tone scale (Christiaan Huygens, who in 1691 rejected well-tempered tuning and argued for the 31-tone system). The sound is generated using the organ-register method: combinable pipe organ, piano, woodwinds, flute, trumpet, strings, and a series of mixable filters, vibrato, and bass/treble settings, all controllable with manual sliders. The archiphone is housed in a lacquered wooden case that, together with a 50-watt amplifier and speaker boxes, makes it relatively easy to transport.

The instrument was inaugurated on November 1, 1970, at the Teylers Museum. Anton de Beer quickly wrote a demonstration piece with various “tricks” using higher harmonics and pure thirds and sevenths. A scene from Joel Mandelbaum’s opera The Dybbuk was also performed with the archiphone, accompanied by a vocal quartet and a violin duo.
Several compositions have been written for the archiphone since 1970, including works by Adriaan Fokker, Henk Badings, Anton de Beer, Joel Mandelbaum, and Bill Coates. An instructional method was produced by Anton de Beer: Guide for the use of the archiphone (1976).

The four archiphones are now located at:
1–2. Huygens-Fokker Foundation (Muziekgebouw aan ‘t IJ, Piet Heinkade 5, Amsterdam)
3. William Bromhead Coates (140 Station Street, Blackheath, New South Wales, Australia)
4. Webster College (St. Louis, Missouri, USA)

Description of the manufacturer
The archiphone has a keyboard range of five octaves (from c – c) and can be divided into two octaves for the bass and three for the treble. Both bass and treble have ten registers. For the bass side, it is numbered A; for the treble, B. The registers include the following voices:

Tone controls may be used separately or in combination with each other. Each of the two channels is fed into a separate amplifier and corresponding speaker. Panel C compises six controls:

Panel D.

The archiphone has two pedals. The left-hand pedal controls speaker volume. The right-hand panel is used whenever a sustain effect is to be achieved. Its function is comparable to the loud pedal on the piano. The keyboard is made up of 333 keys; key switches are of the reed contact type, which is basically a tiny switch inside a glass tube; the switch is activated by a ring magnet. The keys are made out of hard plactic material in five colours:

Plug-in printed circuit boards are used throughout. The unit is portable. Two 50-Watt amplifiers, frequency range 20 – 80,000 Hz. Two speaker boxes, each equipped with one Lowther speaker with a range of 25 – 22,000 Hz. Approximate overall measurements 116 × 40 × 15 cm. The instrument is housed in a cabinet which can be supplied in different kinds of wood finished with high-grade lacquers.

     
  The concert archiphone of the Huygens-Fokker Foundation at the Conservatorium van Amsterdam (2017)