Apart from a relatively few orchestral organs built on classical lines in the first quarter of the 20th century, virtually all theatre organs are built on the extension principle and described as ‘unit’ organs. Indeed, the original Hope-Jones Wurlitzer instruments were marketed as “Unit Orchestras”.
What does the word ‘unit’ mean in this context? It takes in a wide range of concepts and the description is unavoidably involved. One of the best is an article by Frank Hare which appeared in the sadly now-defunct Theatre Organ Review, volume 22 numbers 85/86, which is reproduced below, with kind permission from Frank.
This article is an excellent primer for those who enjoy listening to music but, perhaps, have no musical training or previous experience of organs. It also explains the origin of stop pitch nomenclature and how this relates in orthodox (“straight”) and theatre organs.
Among our readers there are many who possess some degree of theatre organ technology, but the postbag after each issue of the Review shows that there are many more who do not, for we must remember that there was a time when not one of us knew anything about the mysteries of the instrument. “What are units?” and “What is unification?” are two of the most regular questions, and whilst some people realise that units are sets of pipes they ask how, say, eight sets of pipes can form a complete organ and give steady evolution of traditions. So much tonal variety. How? Through the magic of unification, which simple statement brings us back to where we started! The theatre organ is a complex machine and it is not easy to explain all its workings in print, particularly bearing in mind that although all readers enjoy hearing theatre organ music, some may have no knowledge of music itself.
Let us start, therefore, by explaining that the range of all standard keyboard instruments is measured in octaves, an octave being the distance between one note and a note of the same sound higher or lower in the scale – or, for those who remember the tonic sol-fa, the distance between one Do and the next Do higher or lower. If one strikes a white key of a piano and, counting that as number one, then (ignoring the black keys) strikes key number eight, the same sound will be heard an octave apart. There are seven white keys in the octave and five black keys between them, making a total of twelve keys. A piano keyboard usually provides just over seven octaves, with a total of eighty-eight keys, whereas an organ keyboard (called a manual usually has five octaves plus top C, totalling sixty-one keys. The organ pedalboard usually has thirty-two notes, providing just over two and a half octaves, these merely being enlarged versions of the manual keys.
Thus it will be seen that, compared to a piano, an organ roughly lacks an octave at the bottom (bass) end and an octave and the top (treble) end and, in theory, should be short of extreme bass and extreme treble. But, unlike the piano, the organ keyboard is not confined to playing in one pitch, as the stops enable it to be connected to sets of pipes ranging from the extremes of bass and treble. Until stops are brought into use an organ keyboard is as dumb as it is when the blower is turned off, but if any stop marked ‘8’ is drawn (or perhaps, as we are dealing with theatre organs, we should say pressed down) any key will sound the same note as the equivalent one of the piano, provided in each case one is sitting opposite the middle of the keyboard.
The figure on an organ stop denotes the pitch, the “8” originating from the fact that an open flue pipe sounded by the bottom note of the keyboard (bottom C) is approximately 8 feet in length. Flue pipes include diapasons, strings and open flutes, but although other types of pipes may be much shorter they do, of course, retain the same pitch denomination. The pipes decrease in length with each rising note until, when the first octave is reached, the pipe is half the length of the lowest one, i.e. four feet in length. At the second octave, the length would be two feet, and so on.
Now, if the bottom octave of pipes is removed, and all the remaining pipes are moved down the windchest it will be realised that the bottom key will sound a pipe four feet in length and an octave higher than the pipe originally there. When sets of pipes are installed in this manner, the stops are marked “4”, while others are placed so that the bottom note sounds a pipe only two feet in length, the stops then being marked “2”. In the reverse direction, if the original set of pipes marked “8” is moved an octave upwards on the windchest, a new octave of greater length would have to be installed to give deeper notes, and now the bottom note would be twice the length of the original pipe, i.e. sixteen feet in length, the stop being marked “16”. If four sets of pipes covering the above examples are placed in individual windchests, we shall have one set starting with a pipe sixteen feet in length, another with a pipe eight feet in length, another with a pipe four feet in length, and yet another with a pipe two feet in length. Thus, by playing any note on the keyboard, four pipes will sound and each will be an octave apart, the sounds actually covering four octaves. Any sets of pipes may be selected by means of the stops, and it will now be realised that in an organ containing many sets at varied pitches, numerous permutations are possible.
Additional to the basic 16, 8, 4 and 2ft. pitches, organs include what are termed “mutations”, these being sets of pipes designed to enhance the basic sound with harmonics, and in the church, to provide additional clarity. A stop marked “2 2/3” is called a Twelfth, because its bottom note sounds twelve white notes above that sounded by an 8ft stop. Bottom C of the keyboard would sound a pipe giving G in the next octave above. A stop marked 1 3/5 is called a Tierce, its bottom note being seventeen white notes above that sounded by an 8ft stop: in this case,. bottom C would sound a pipe giving E in yet another octave above. These are only two examples of mutations, an enlargement of this idea being found in the ‘mixtures’ of the orthodox organ. Here sets of pipes in several pitches sound together but further complication is likely to be caused by going more deeply into the matter!
In the orthodox organ, every speaking stop controls an individual set of pipes, each set being called a rank, therefore an organ with four stops on the Pedal, six on the Choir [bottom manual – Ed], ten on the Great and seven on the Swell [top manual – Ed] would contain twenty-seven ranks of pipes. This type of instrument is commonly called a “straight” organ and examples were installed in cinemas until the mid-twenties [nineteen-twenties – Ed].
Many years ago it was realised that much pipework was wasted in the Pedal department, where not more than two keys are pressed at anyone time. For instance, there might be three ranks of flutes, at 16, 8 and 4ft. pitches, involving a total of ninety-six pipes, of which not more than six could be sounded together, With an overall range of only about four and a half octaves, it was seen that one set of fifty-six pipes would suffice if an action was made whereby the lowest thirty-two pipes would be connected when the 16ft. stop was drawn, the thirty-two pipes commencing at the first octave when the 8ft. stop was drawn, and the top 32 pipes connected when the 4ft. stop was drawn. Termed “extension”, this method was carried out with selected pedal ranks, and the practice is still used in many otherwise “straight” organs.
Further thought showed that an expensive 16ft. reed rank need not be duplicated on the manuals and pedals if some action could connect its lowest thirty-two pipes to the pedals when the appropriate stop was drawn, and, again. this method is frequently used still. When a rank in a “straight” organ is made available in a department other than its own, it is said to be “borrowed”, although “duplexed” is a more correct description for a rank which is made freely available on the various manuals and the pedal section. There have been examples of organs built completely on the duplexed system, these having a number of “straight” stops with the same stops appearing in each department, so that they may be drawn as desired.
Although the “extension” and “duplex” system are independent, certain people, particularly the famous Robert Hope-Jones, appreciated the feasibility of linking the two, enabling extended ranks of pipes to played at any desired pitch throughout the organ instead of merely in one tonal department. Where, for example, a “straight” organ might have four separate ranks of Flutes at 16, 8, 4 and 2ft. pitches, each with sixty-one pipes and a total of 244 pipes, one extended rank of ninety-seven pipes could provide exactly the same range, if mechanisms were introduced whereby the sixty-one pipes appropriate to the stop used could connect them to the organ keyboards. To enable this, each set of pipes has to be dealt with as a separate unit, with an individual action for each pipe (strictly speaking, each pipe and its associated action form a separate unit), and thus was born “unification” and the “unit organ”.
In practice, the saving of pipes would be greater than is suggested above, as the unit would be available throughout the organ, whereas each department of the “straight” organ might contain ranks in identical pitches. The following imaginary specification may help to clarify this point, as although the “straight” example contains twenty-four ranks of pipes, it provides only four distinct tone colours, namely Diapason, Flute, String and Trumpet. In the “unit” example, the identical specification results from only four sets of pipes. It will be seen that the 8ft. pitch is used as the basis for sixty-one pipes, the upwards or downwards extension by twelve pipes being shown against the pitch concerned.