THE ORGAN

The organ Specification

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The Grant, Degens and Bradbeer organ in New College chapel

An article written by Maurice Forsyth-Grant for the instrument’s inauguration in 1969

The organ in New College chapel is a radical departure from British organ building as generally practised in the last hundred years—and as still continuing in most organs today. What are the differences?

1. It is a mechanical action instrument, and by that we mean that it is the player’s fingers or feet which directly operate all the pipe valves in the organ. By this true extension of the human muscles, a very intimate control of touch is possible. The more usual (in Britain) use of pneumatic or electric action makes a personal or individual keyboard touch quite impossible.
2. A rigid discipline has to be maintained in the general layout of the organ. From each key and pedal there are thin rods of wood or metal called 'trackers' which run from the console up to the various windchests inside the instrument. There are 198 of these; the design must be such that they are tidily arranged, but are as short and direct as possible.
3. The frame of the organ is entirely of steel. The reason for this is quite simple: all the trackers which run from the console to the windchests must be kept at just the right tension. If for some reason or other they were to tighten up, there would be the chance of an undesired sounding of a note, or in organ builders’ terminology, a ‘cypher’. On the other hand, should the trackers become loose, the keys would have a false motion in them making the action noisy, and possibly resulting in insufficient opening of the pipe valves. With seasonal variations of temperature and humidity, frames of wood (seasoned or unseasoned) alter in dimensions quite considerably, and this upsets the delicate adjustments of the trackers. Of course, steel also changes its dimensions with change of temperature, but not with humidity changes. Further, the difference between the dimensional stability of wood and steel is absolutely known, and whatever movement may arise from its use, it can be ‘designed out’ in the overall planning of the instrument. Automatic self-adjusting tensioners are used on all the trackers in this instrument; and, in conjunction with the steel frame, the keyboard and pedal action is always kept in correct adjustment.
4. Although the type of windchest used throughout this organ has been known and made for over 400 years, this ‘slider chest’ went out of use almost entirely about 100 years ago largely because it was not suitable for the high wind pressures for the pipes in vogue at that time, but also for the reason that its construction in natural timbers gave great trouble in dimensional stability (as mentioned above). The situation became even worse when heating was introduced into most buildings, and the slider chest was discarded in favour of other designs of windchest, none of which gave such good musical quality to the sound of the pipes. The last 50 years or so have seen the development of all kinds of man-made timber substitutes, most of these being so designed that they have no ‘grain’ as in natural timber. They are thus relatively stable dimensionally, with predictable characteristics. The hearts of the windchests in this organ are made entirely of this material, and even the moving pipe valves or ‘pallets’ are made of special aluminium section.
5. The layout or positioning of these slider chests is most important. Bearing in mind that there is one chest for each division, i.e., Great, Positiv and Swell, the one for the Pedal being divided in two halves, all these must be on the front elevation of the organ. Further, the pipes on each divisional windchest must have their sound
   
   
   (photo: John Miller)
   projected in one direction. By looking at the front prospect of any correctly designed organ, the separate divisions of the instrument are immediately apparent. In this particular instrument the Positiv division—or more correctly the ‘Ruck Positiv’—projects just below the gallery. Just above it, the Swell division with its glass expression shutters can be seen with the Great Organ mounted on top of it. The Pedal Organ is positioned in two halves on either side of the instrument. Each division is enclosed in a correctly proportioned ‘tonal box’ which is open only at the front, thus projecting all the sound in a forward direction.
6. Any observer, when looking inside this organ, will probably say “Where are the bellows?” There are none in the accepted sense. Instead, mounted in the bottom of each windchest, there is a small moving diaphragm. This does all that is necessary to control the wind pressure. This development of wind regulation, almost universal amongst organ builders in North Europe sine 1950, is perhaps one of the most significant improvements to the Organ for many years. The wind pressure is now controlled accurately and precisely just where it is used, that is, at the pipes. Further, it enables pipes to speak more quickly and precisely, a characteristic that can never be achieved by enormous bellows occupying the whole floor of an organ as is more customary in the old style. An interesting attachment to these new wind regulators is the modern form of tremulant. Listen to the musical quality it imparts to any stop used in conjunction with it.
7. The voicing of the pipes should be mentioned, and perhaps this very important matter should take precedence over all others. For the benefit of the layman, it should be pointed out that the strength of sound emitted by an organ pipe may be altered in one of two ways—by opening or closing the hole at the foot, or by widening or reducing the wind slot at the mouth of the pipe. The former method has been almost universal in Britain, and still is, whereas the latter method was used by the great classic organ builders of Northern Europe in the 17th and 18th centuries, and is today almost universal on the continent. This organ is voiced entirely on this ‘open foot’ method, and this (together with the use of low wind pressures) makes the organ sound quite different from the usual organs in this country. The more musical sound, the definition and clarity, the greater blending capability, bring a completely new interest to the organ music of all periods. No longer need complex, contrapuntal music sound dead, dull and lifeless. Inner parts of fugues are all heard as they must have been in the great days of Bach and Buxtehude.
8. Apart from the voicing of the pipes, the material of which they are made is also an important point in setting their tone quality. The majority of pipes in this instrument are 50% tin, but those in the front are between 75% and 90% tin—the latter figure applying particularly to the large pipes in the pedal towers on either side. Variation of tone, particularly in the colourful reed stops, is achieved by using various metals, singularly or in combination, and thus there is a Trompette on the Pedal made of copper, a Rohrschalmei of brass and 50% tin, a Regal in the Great Organ of brass, another similar stop in the Positiv of mahogany, and the projecting Spanish Trumpet of copper throughout.
9. The ‘scaling’ or dimensioning of the pipes in this organ is worth noting. Before any of this work was undertaken, the chapel was ‘sounded’ by using special electro-acoustical appparatus, so that the reverberation time in seconds could be ascertained at various frequencies throughout the musical spectrum. With these figures to hand, and knowing the desired tone quality of tone required from individual stops, a great deal of calculation had to be done to finalise the dimensions of all the pipes. Fortunately, an electronic digital computer was available, and its use greatly assisted what would otherwise have been an enormous task of perseverance and drudgery. There are only three stops in the whole organ with scales of conventional ‘trade practice’.

Having dealt so far with some of the constructional aspects of the instrument, we should now turn to more musical considerations which govern the choice and place of the various stops throughout the organ. The instrument has three keyboards each of 56 notes, and pedals of 30 notes. DIstributed over these are 48 stops (or tone colours). There are certain conventios dictated by the organ literature as to where many of these stops should be positioned, but the selection and positioning becomes increasingly more difficult if one requires an organ to deeal with the literature of all countries and of all schools. This organ is primarily based on the North European School which demands a chorus of principal tone on each division, supported by flutes and reeds in various proportions. Such an arangement will make possible the authentic performance of most of the great classic literature. However, in the last 20 years there has been a great reawakening interest in hthe French classic organ music of the 17th and 18th centuries, and whilst this school generally also requires a similar arrangement as the North Europe one, there are a few additional and very characteristic tonalities which are essential for the true performance of this music. One must mention particularly the French Cornet, composé and separé, both of which are readily available in this instrument.

Any organ which contains all the stops necessary for the authentic performance of North European and French classic literature will be capable of doing justice to music of any period, but it must be admitted that there are a few particularly characteristic tone colours which are desirable (but perhaps not essential) for certain occasions. For instance, the Trompetta Real for Spanish music, the mild string Céleste for liturgical use, and the modern Aliquot and Oberton harmonics providing a mid-20th-century new sound, and necessary in modern German organ music. All these are provided as far as possible within the confines of a total of 48 stops. Moreover, the need to accompany both choir and congregation in a great variety of styles and moods has been carefully considered in designing the instrument. In fact, the rôle of the organ as an accompanying instrument is no less (and perhaps more) important than its rôle as a solo instrument. I do not believe that the two functions are in any way incompatible, as is sometimes suggested. Indeed, the proper voicing and winding of pipes improves the balance and blend with voices, since the method of tone production is much closer to that of the human voice, relaxed and unforced.

Maurice Forsyth-Grant