A Short Discourse Upon the Innermost Secret Workings of the Portative Organ

by David Swan

The Portative organ is a small pipe organ that sits on the player's lap while being pumped with one hand and played by the other. It was one of the more common musical instruments of later the middle ages but is practically unknown in modern times. It has survived only in contemporary iconography and in writing, usually as an item in an inventory. To my knowledge, no working portative organ nor any substantial portion thereof has survived. The only text that I could find that described its construction pertained to a style that was clearly (by a survey of iconography) uncommon in the extreme.

My interest in the workings of this unique instrument stems from my desire to obtain one. When I found out that they were not to be had for less than thousands of dollars, and even then in a non-period style, I set out to build one. It was then that my research foundered, and I have been forced to infer much from the available iconography of portative organs and from texts describing the much larger instruments of the day.

It took no real effort to collect two dozen examples of portatives represented in paintings or carvings, but before trusting a painter's viewpoint, I first had to study how the medieval artist viewed things and how reliable his powers of observation and how accurate the resulting pictures were. Fortunately, this is a topic upon which a wealth of opinion has been written, and most of it agrees that while the settings may be fanciful (fourteenth century clothing worn by figures from biblical times, etc.) and therefore suspect, the actual hardware (buildings, instruments, etc.) was usually rendered very reliably, given the limitations of the artist's perception.

The study of the larger pipe organs was similarly eased by the wealth of reliable material available. To further expand my understanding of what I was trying to study, I fabricated several prototypes to prove or disprove various interpretations that the data have lent themselves to.

As a result of my efforts, I find myself in a position of disagreement with several authorities concerning the actual inner construction of the instrument. These authorities postulate a design far more complex than it needs to be and predicated upon an accuracy in joinery that is difficult to achieve even with today's modern tools. Here, I shall present unto you, my dear reader, a brief synopsis of my findings, opinions and conclusions.

The pipe organ is unusual in that it did not derive from a previous instrument but was developed, from scratch, by the efforts of a single engineer who lived in Greece during the Hellenistic Period. After the fall of Rome, the knowledge and engineering skills needed to produce a pipe organ were lost to Europe until their re-introduction in the eighth and ninth centuries.

When Theophilus wrote On Divers Arts in 1122 c.e., the state of the art for building pipe organs in Europe was still very primitive. The organ he describes spanned but one diatonic octave of eight notes with three pipes for each note.

By the fourteenth century, the technology had burgeoned. Large organs were restricted mainly to churches, since other instruments had been "profaned" by secular use, and could take up to 75 people working huge bellows to provide sufficient wind to operate a single instrument.

It was during this period that the smaller organs flourished. Among them were the positive (a table-top organ with several octaves and two bellows) and the portative. The portative could be carried about and even played while walking, leading to extensive use in both religious and secular venues and pictures show it being played by Angels, Kings, Goddesses, entertainers, gentle ladies and beggars.

The inner workings of an organ, known as the action, is what allows the moving of keys to control the flow of air into the pipes. The organ builders of the fourteenth century had three basic actions to choose from: the slider action, the pin action and the tracker action.

The first organs in ancient Greece used the slider action (see figure 1) as did the organ of Theophilus. It was still in use by the end of the middle ages, but was too inefficient and difficult to play and was dying out even as early as the thirteenth century. The only remnant of the slider action that remains even to this day is used not to control the flow of air to the pipes of one note (a key), but to control the flow of air to a rank of pipes at once (a stop).

Fig 1.

Fig 1: Slider action closed (left) and open (right)

Fig 2.

Fig 2:  the pallets in the wind chest from above (top)
        and from the side (in cutaway, bottom)

Fig 3.

Fig 3:  Pin action

Fig 4.

Fig 4: Tracker action

To know the action, however, is not enough. There is another engineering problem involved. The frequency of the pipe is dependent upon its length. The longer the pipe, the lower the note. To get the same force and quality of tone from pipes of different lengths, they also need to be of different diameters; the longer pipes needing to be larger around than the shorter ones. For instruments spanning but a single octave, this is not a big problem, but many icons clearly show pipes of varying diameters in portative organs. The keys, however, are all of equal size and have equal spacing. The arrangement shown in figure 5, which is unacceptable, is what would result if this problem were not solved.

Fig 5.

Fig 5:  An unacceptable situation

Fig 6.

Fig 6:  A popular, but implausable, solution to the problem
        shown in figure 5 as seen from below (top) and in
        cutaway from the side (bottom)

What they do show is keys or buttons immediately in front of the pipes, but the deck steps up 2 inches or more thus elevating the feet of the pipes several inches above the keys. Since there is no room for channels in the horizontal axis, they must be in this space!

I have proven to my own satisfaction that this engineering problem could be solved as shown in figure 7 using simple tools and easily acquired skill. The channels to guide the wind from the groove to the pipe are easily made using a simple drill! Furthermore, this solution dictates a form that agrees with the iconography and allows for larger grooves which, in turn, allow the air pressure to help create and maintain the seal and thereby reduce the required strength of the pallet spring.

Fig 7.

Fig 7:  My preferred solution, seen from the front
        in cutaway.  For a side fiew, see figure 3.

A pipe is very sensitive to anything that could perturb this flow. Any object placed in close proximity to the pipemouth will affect the sound; it usually silences the pipe.

Therefore, a second rank of pipes, touching the first but facing the back of the organ, would work just fine and there are examples within the existing iconography that show the back of a portative and clearly show the mouths of the back rank facing backwards.

However, there would be no way to install a third or any other subsequent rank, in close contact with the other ranks (as is shown in the iconography), and still have the instrument able to speak from all of its pipes. It is likely that the artists have neglected to detail the spacing needed in such an arrangement.

Of final consideration, the bellows that are shown are almost without exception of the rounded variety (see illustration at the beginning of this article). It took very little in the way of experimentation to discover why: a square bellows needs a pleated leather, which requires stiffeners and is definitely non-trivial to make; a rounded bellows just needs to be fitted out with soft leather and it works just fine.

It is my hope that this instrument will someday be once again popular and to that end I welcome any correspondence upon this topic. Write to me at:

           David Swan
           Box 322
           Greenwood, N.S.,
           CANADA
                  B0P 1N0