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The Fluid Piano

Invented and patented by Geoff Smith, prototype developed and built by Chris Barlow

The Fluid Piano

Fluid Piano Lid open

Geoff Smith approached me a few years ago and asked if I would develop an idea he had patented into a working prototype instrument. He is a composer and performer on the hammered dulcimer with a serious interest in music from beyond Europe. Western classical music uses 12 notes to the octave and the pitch of these notes has been established for many years. Equal temperament (modern pianos and keyboards use this method of tuning) dictates that all semitone steps are the same size. Even in Western music this is wrong in the sense that each note of a piano can never be perfectly in tune with all other notes. Thirds, fours, fifths etc are not ‘perfect’. This phenomenon has been understood from the days of Pythagoras and before (so way before keyboards on pianos appeared) and up to the middle of the nineteenth century western keyboard instruments have been tuned in a variety of ‘temperaments’ other than equal temperament. Most instruments that do not employ a keyboard do not suffer this problem. For instance a violinist can and will make a difference in the pitch of, say, A sharp and B flat completely at will and they can slide the pitch continually from one note to the next. Tuning a keyboard instruments means you have to compromise, even for Western music. Harpsichords and early pianos have appeared throughout history with many more notes to the octave than our present arrangement of twelve. 20- 36 notes examples still exist from several hundred years ago.

A microtonal keyboard on a Viennese fortepiano, dates from around 1795 but similar examples can be found in harpsichords too from the previous two centuries, see below for a fuller list of links and UK patents from the 19th century

microtone piano

The concept of microtonal keyboards dates from the earliest origins of the idea the keyboard itself. When you consider the musical scales that Indian, Iranian, Chinese and other cultures have developed and their more flexible approach to the pitch of any particular note it becomes clear that a modern piano has real difficulty fitting in with such music.

One view, perhaps, is that a western instrument such as a piano has no place within those musical spheres, but development has always led to innovation and innovation has always led to development. Some performers have retuned their pianos to suit but this is still restrictive. Geoff Smith’s idea is to give the performer freedom to adjust the pitch of each note by means of a slider under the strings of each note. Not only can the pitch be easily established before a piece is performed but during it too. It is also possible to bend the pitch as a note sounds. There are examples of instruments with moveable individual bridges to affect pitch and the concept is usually credited to Pythagoras working over two thousand years ago. However moveable bridges may be much older that that and date back to the pyramids. His monochord was at first a scientific device but it developed into a musical instrument too (and not restricted to one string!) My first encounter with a monochord with sliding bridges was doing acoustics for A level physics at shool. Monochords have developed into musical instruments with many more than one string.(see links below) The Koto, Zheng and Gu-Zheng are examples but even viols have moveable frets to adjust the tuning of individual notes.

a Gu-Zheng that I recently made a new set of sliding bridges for.

Zheng Bridges

When Smith approached me with a one note model he asked me to develop this into a working instrument. This would be the first prototype of the ‘Fluid Piano’. The starting point was to adapt the design of a fortepiano, rather than a modern grand, to take the tuning sliders. Cost and technical considerations dictated this.

It was immediately clear to me that the slider design employed in his one note model would not work in any kind of piano. The piano’s hammer blow is upward and the strings must be held with absolute rigidity to withstand this otherwise tone is replaced by extraneous noise of the slider being lifted and snapping down again. This could be shown on his model once the hammer was set up to ‘escape’ at the correct point. The other main problem was that the height of the string was being altered to the point where it would be impossible to regulate an action. Lastly the device took up too much width and it would have stretched the string band by about a factor of two.

Adjusting the sliding bridges in the Fluid Piano.

adjusting sliders

Along with the slider design other problems arose with the action and wrestplank. To accommodate the sliders the plank had to be a least twice the normal width from the player to the far edge. This alters the geometry of the keyboard and action. The plank must also have grooves cut into it which reduce it’s strength considerably so it’s thickness must increased to allow for this. The hammer blow on a fortepiano is around 40mm (about 50mm on a modern grand) and you simply can’t increase this without serious and unacceptable consequences for the player. (Either the key dip must increase or the touch weight will increase). Things seemed to heading for a dead end. I considered that these problems would be less if applied to a harpsichord and then realised that the tangent pianos, popular in Germany and elsewhere around 1800 could work too. The advantages were firstly in the geometry of the wrest plank and action relationship, making use of the resulting very long keylevers and the very light impulse transmitted to the string from the lightweight tangents. I also felt it could lead to an instrument very different to a modern piano but one whose sound and possibilities could give much scope when employed in non western music. Tangent pianos often had bare wooden heads to strike the strings but there were various stops available to modify the tone. One minute it might sound like a harpsichord the next a piano, the next a harp, so, not only Fluid Tuning but Fluid Tone as well. I had also come to the conclusion that to try to add sliders to a conventional piano was only going to result in a poor and compromised instrument. Strike point is crucial throughout the compass but at the treble it affects the duration/decay of the note as well as the tonal characteristics. The starting point of the design of a piano is everything to do with the strings. This is usually called ‘scaling’. Their length, weight and precisely where they are struck are carefully calculated by the designer to achieve the control over inharmonicity. There are undesirable, discordant, partials that he will want to eliminate to achieve a good timbre. Unfortunately adding sliders that change the length of the string and affect the strike position render these fundamental considerations impossible. No consistency is possible when the length of the strings is variable.

I explained my thoughts to Geoff and he agreed that to depart from the fortepiano/piano starting point was a good way forward. He had also specified that the case should be as open as possible. It was another design challenge to compensate for the reduction in strength that eliminating the case sides caused. As a dulcimer player he wanted to be able to access the open strings like a hammered dulcimer. After discussion a section of extra strings was added at a higher level too. These can be struck or plucked like a harp and they have ‘Fluid Tuning too. And so my design and construction work started.

For an early visit from Geoff to my workshop I had prepared three full sized drawings of different possible designs for the general layout of the proposed instrument so that he could choose the one he wanted me to continue to develop. I had also built a model of the tangent action that I had designed so that he could visualize that. I had not finalized the design of the sliders at this point to my or Geoff’s satisfaction but could demonstrate that any lack of rigidity had a severe influence on tone. These, after all, replace the agraffes and pressure bars that are to be found in all modern pianos from the mid nineteenth century onwards.

The frame and wrest plank in place.


The resulting instrument has to be seen as something quite different to a modern piano. Firstly this only ever set out to be a prototype but its tone is quite unique, the action is very responsive but different to the touch, the power is less but it is still dynamically responsive. There is no iron frame to restrict access to the sliders or strings and although it is wooden framed the design of the carcase is more robust than a fortepiano and tuning stability is much better. I designed the frame based on the ‘A’ frame of The Viennese fortepianos but extended it to become a complete ‘A’. This reduces the twisting tendency of early wooden framed pianos and gave me room to develop the design of the additional ‘harp’ set of strings and their sliders. It was a deliberate design consideration to use light bichord stringing (but they are heavier than the old tangentenfluegel of the past). It was anticipated that its power could be boosted electronically if required. The sliders do not eliminate the need for the instrument to be tuned in the normal way and the basic tuning is still A=440 equal temperament when the sliders are in the central position. In fact the sliders inevitably have some adverse effect on tuning stability. I was not able to use the softer iron wire found on early instruments as these broke too quickly with the action of the sliders. Each note can be altered smoothly, plus or minus one semitone. Like some of the Early English pianos the sustain pedal is ‘split’. This allows the treble and bass to be sustained independently or together. As the instrument sounds a little like a cimbalom I felt this arrangement gave extra control and scope. (Historically the instruments that Beethoven and Mendelssohn owned had this facility and have implications for the performance of their music). Another pedal operates what the Viennese makers of the past called a moderator. This moves a thin piece of cloth between the bare tangents and the strings and changes the tone closer to that of a piano. Two more pedals are available to a player standing in the curve of the bentside. The right pedal applies a damper to the extra harp strings (the default position here is undamped but a stop can be operated by the keyboard player to override this if sympathetic vibrations from these strings are undesirable) and the left raises the dampers for the treble main set of strings to allow them to be played. Click to play sample. (the two minute sound clip includes a random selection of sounds to illustrate the potential of the sliders, harp glissandi showing the enharmonic possibilities (C#, D and E#, F. A piece of Scarlatti played on the open sounds of the tangents , and lastly an extract of Haydn played with the moderator on to show the contrasting timbres available )

The history of the piano from Christofori’s first Gravecembalo con piano e forte to the present Concert Grand is strewn with experiments, novelties and patented innovations. It would be incorrect to think that the lineage of the modern piano is just that - linear -a straight line. The Tangentenfluegal and small German Pantalon were a significant branch line. No one is quite sure what Stein’s Saitenharmonika from the 1780’s was. (The surviving instrument was converted back to a ‘standard’ piano years ago). The Viennese ‘Turkish’ Pianos with their bassoon stops, drums and cymbals operated by pedals were highly popular at the start of the nineteenth century. The Euphonicon, the panharmonicon (Beethoven wrote for that one) and the Geigenwerk are sadly unknown today. Perhaps the modern piano is far too standardized and we lack the huge variety from the past.

For a long list of pre 1900 UK patents see Some are quite eccentric but many are to be found in the modern piano. I have noted below a few that relate to the strings and tuning systems of pianos. But here’s a modern experimental piano that’s different: Faziole may claim to make the world’s longest piano at 10ft 1¼inches but have a look at this one at a massive 18ft 9inches

Some UK piano patents from the past.

Jan. 15, 1787 W. THOMPSON. System of tuning by means of a monochord with movable bridges.

Aug. 15, 1788. C CLAGGET. (1) Piano called "Teliochordon". Besides the ordinary ones, two other bridges are placed nearer to the hammers, but in a just, proportion, according to the musical division of the string." Metal bars press down the strings by means of pedals, causing the original bridges to lose their power, thereby producing a more acute sound as the string is shortened by the secondary bridges and metal bars. (2) The keys are covered with glass or enamel, in place of ivory.

Oct, 4, 1859. G. GREINER. (1) Appliance for tuning two strings at the same time. (2) Pedallier with leather covered plectora for pulling the strings.

March 20, 1862. J. G. THOMPSON. Enharmonic scale and shifting keyboard.

Feb. 5, 1863. R. A. BROOMAN (FRAN90IS DE, LSARTE). Method or tuning two strings simultaneously.

Nov 1 1864 W. Moody. New tuning apparatus.

Jan. 17, 1865. K H. LAKIN, Tuning by means of levers on metal plate over wrest plank.

June 30, 1861. R. A, BROOMAN. New tuning apparatus.

Feb. 19, 1875. Z T. BURLING. A system of tuning'

Feb. 17, 1882. EDMUND OUTRMINI. Improvements in the means of stringing, regulating. and controlling the pitch or tone.

Nov. 11, 1885. J. H. SCHUCHT and J. A. SCHONEWALD. Appliance for tuning pianofortes.

Other related links to microtonal keyboards and strange pianos:

Early keyboards: and (microtonal harpsichord of 1555) and for the theory

The Janko keyboard

See and hear the Fluid piano here

Miklós Spányi has specialised in recording CD’s on tangent pianos.

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