The Organ Cavaillé-Coll Never Built!
"Aristide Cavaillé-Coll, the organ world's chief engineer - and a chief inspiration"
Andrew Mellor, The Gramophone 
Posted: 27 November 2013
Revised: 31 July 2015
Copyright © C E Pykett 2015
Abstract. Cavaillé-Coll built organs of all sizes, and I have already simulated one of his small Model 9 instruments which was installed at Bellahouston Parish Church in Glasgow (now lost). However it was a baby organ with no independent pedal stops, so I have now extended it to a substantial two manual instrument with 30 speaking stops. Loosely based on that formerly at Paisley Abbey (also lost), it includes the batteries of powerful reeds and mixtures which characterised his larger instruments together with his beautiful colour reeds such as the Voix Humaine, Basson-Hautbois and Clarinette. This article describes the instrument in detail.
(click on the headings below to access the desired sections)
You've heard of the house that Jack built? Well, this article is about an organ that Cavaillé-Coll never built. Let me explain ...
Some while ago I simulated a Cavaillé-Coll organ digitally using my Prog Organ virtual pipe organ system. It was one of of his small Model 9 instruments, installed in Bellahouston Parish Church, Glasgow, in 1874. This pipe organ no longer exists but it is described elsewhere on this website  and some examples of how the simulation sounds can also be auditioned there. Although the simulation was pretty satisfactory as far as I was concerned, the organ itself is small and therefore somewhat limited in scope. For instance, it has no independent pedal stops. Consequently I wanted to extend it so that more of the French romantic repertoire could be rendered. At the same time the disposition had to remain sufficiently constrained such that it could be played from my existing two manual Prog Organ console with its 46 stop keys - I had little enthusiasm for a huge three or four manual console as I already have two organs in the house anyway. This meant that the essentials of a typical large Cavaillé-Coll behemoth had to be identified and distilled down to fit. This was an interesting exercise in itself which this article addresses. It also describes how the extended stop list was derived, based around the nucleus of the original Bellahouston simulation. The resulting simulation is called Bellahouston-X (for Xtended).
Aristide Cavaillé-Coll was first and foremost a superb engineer who was also exceptionally gifted in mathematics and science, especially that relating to the acoustics of his day. This is not to decry in any way his artistic ability to create wonderfully holistic organs in a musical sense, instruments which were all of a piece and whose sounds blended and coalesced so successfully that it can be argued that no subsequent builder has possessed these talents. His skills prompted a non-organist journalist to name him recently as "the organ world's chief engineer", and it is worth reading this piece . Whatever one might think about the limited scope and aspirations of French organ music in the latter half of the nineteenth century, limitations which were partly imposed by the instruments themselves, surely few will fail to fall under the spell of a Cavaillé-Coll organ in full cry in one of those amazing Gothic cathedrals. Speaking personally, the experience always makes my hair stand on end. So that is what I wanted to achieve, or at least approach, with this new simulation - if possible.
To my mind there are five important aspects of a Cavaillé-Coll organ, which will now be considered in turn. All of them have to be captured in a simulation if it is to stand a chance of being successful, measured in the subjective terms of whether it actually sounds right.
There should be at least three foundation stops at 8 foot pitch - Montre, Flûte Harmonique and Bourdon. Additional string stops are also desirable, such as a Viole de Gambe (keen, dessicated and hungry), Gambe (usually less so) or Salicional (more reticent still). Any and all of the first three must be useable together, with the addition of a string if available and desired, to produce that range of exquisite mezzo-forte effects known as the Jeux de Fonds. This implies that there should not be large differences in subjective loudness between these stops, and moreover their regulation (the way the loudness of each varies across the compass) is of pivotal importance. One of my preoccupations with both pipe and electronic organs for many years has been to get their regulation right, because in my view regulation is just as important as the timbres or tone qualities of the individual stops. The late Ralph Downes was one of the few professionals who has emphasised this, to the extent that he elevated it almost to the status of a science . Following his thinking, I have suggested elsewhere how modern digital techniques might be used to improve the regulation of an existing pipe organ, or to assist in designing a new one .
As many organists know, one comes up against these problems of regulation forcefully when trying to register French romantic music on a typical British organ. Usually there is too much disparity between the loudnesses of the diapasons, flutes and strings, which are the Anglo-Saxon analogues of the Jeux de Fonds, and the variation of loudness across the keyboard of a typical Open Diapason means that it will often swamp everything else in the tenor octave and below (and frequently elsewhere as well). I have shown in another article how the variation in sound pressure level of such a diapason over its compass compares with that of a Cavaillé-Coll Montre (and a Silbermann Principal for that matter) . These properties of the British organ commonly result in its inability to achieve the essential blending properties between the unison flue stops which is realised in a Cavaillé-Coll instrument, and hence its inability to replicate the Jeux de Fonds.
Cavaillé-Coll's organs have a number of characteristic quiet reeds, and the way they are distributed across the various manual divisions is as important as the tonal characteristics of the stops themselves.
It is de rigeur to have a quiet and refined reed such as an Hautbois or Basson-Hautbois, or even an exceptionally delicate Trompette, on the Récit so that one can use it for solo work. If there is to be a Voix Humaine this, too, should be on the Récit so that it can be under expression and tremulated. A Clarinette, on the other hand, should desirably be on a separate division to enable it to be used in duet fashion with the Hautbois - Guilmant was one composer who exploited this beautifully in the Pastorale movement of his first Sonate.
The pedal organs of Cavaillé-Coll's larger instruments contain both flue and reed stops at 16 foot and often at 32 foot as well. The 32 foot flues, of both flute and string tone, are pervasive in the sense that they underpin and can be heard as part of full organ, yet they are also quiet enough to be used with the gentlest manual stops such as the Voix Humaine inside a swell box. Indeed, Franck (e.g. in his Chorals) and Guilmant (e.g. in his Sonates) were just two composers who called explicitly for this combination.
The pedal reeds are quite another matter. The mind-blowing pedal Bombardes at St Sernin, Toulouse crackle and roar like a car engine sans silencer, and if you have yet to experience them you have something to look forward to. You do not need to travel to the church - try David Briggs's splendid recording of Vierne and Widor Organ Symphonies on an excellent CD made and issued by the BBC . Gettting Cavaillé-Coll's pedal reeds right in a digital simulation is not easy, and it helps if one analyses and understands the nature of French reed stops with their so-called open shallots and other characteristics peculiar to the French organ. Two articles on this site explore the technical issues of reed pipe construction and harmonic structure in detail , .
For the purposes of this article this simply means Full Organ - we shall not go into the derivation of the term nor the minutiae of how it relates to the rather different chorus work of the earlier French Classical organ before the Revolution.
One can usefully regard the Grand Choeur as comprising two independent components - flues and reeds. This is because Cavaillé-Coll's organs had separate soundboards for these stops, and they were controlled by means of a ventil system. The performer can set up the desired reedwork at an unaltered Cavaillé-Coll console before commencing to play initially on the flues only, and then add the chosen reeds to the flue stops simply by pressing a ventil pedal at the appropriate point. When opened, the ventil valve activates the pipes on the reed soundboard, whereupon the stops previously drawn on it will be brought into play. At such a console it is therefore more difficult to move fluidly among the myriad combinations of flue and reed stops which our system of thumb pistons and motorised stop controls allows. Rather, variations in the tone colour and loudness of Cavaillé-Coll's ensembles is more 'blocky' or 'terraced' than most Anglo-American organists are accustomed to nowadays. The system also meant that the dispositions of the flue and reed choruses on a Cavaillé-Coll organ had some distinctive features which organists could exploit when registering.
One example concerns the structure of his mixture work. Cutting to the chase for the sake of brevity, not many Cavaillé-Coll organs have mixtures which continue to shriek upwards almost beyond the range of audibility as one ascends the keyboard. On the contrary, they often break back in such a manner that one is playing on (what we might think are) unusual mixture compositions in the top octave or so. Sub-quint ranks at 10 2/3 foot are sometimes found for example , and this means that they will generate resultant beats (though not, repeat not, actual acoustic energy ) at 32 foot pitch if a 16 foot flue is drawn as well. One reason for this was - presumably - to maintain the necessary aural depth when music is being played towards the top of the compass, a topic explored later on in the context of couplers.
Another feature of Cavaillé-Coll's fluework is the limited opportunities for synthetic tone building, even in his largest organs. In particular, seventeenth-sounding ranks such as Tierces are rarely found as separate stops. They only occur within compound Cornet stops. This differs from the earlier Classical French organ which did have such ranks. In Cavaillé-Coll's case, my conjecture is that he was more interested in using the Tierces (within a Cornet) to generate a shimmer of ersatz reed-like sounds in full choruses consisting only of flue stops, before the reeds proper were added, than in using them to generate synthetic solo voices.
As for the reeds themselves, more often than not their fiery tones are characterised by a vast retinue of harmonics extending across a large part of the entire audio spectrum. This differs from the smoother reeds produced by contemporary builders such as Willis, in which the harmonics tend to drop off more rapidly in amplitude after the 10th or so. Cavaillé-Coll's chorus reeds are generally rather loud, a feature encouraged by his use of divided reed soundboards delivering a higher pressure to the treble pipes, and these pipes are also often harmonic (double length) in construction. Moreover, the distribution of their acoustic energy across a wide frequency range (many harmonics) contributes still further to their subjective loudness. All these factors are discussed in more detail in references  and .
Quite a lot of loud French organ music lies high in the keyboard, and endowing it with sufficient gravitas can be problematical if the music is not to tinkle inanely away, at the same time leaving a large gap between the sounds of the manuals and pedals. The answer is to improve the balance by introducing not only 16 foot but 32 foot manual tone as well, especially if there are loud 32 foot pedal stops.
One way to achieve this, or at least to produce an aural hint of it, is to generate 32 foot beat frequencies using a real 16 foot stop with a 10 2/3 quint rank either on its own or as part of a mixture. This was mentioned above, but it is only relevant to flue-only choruses. When the loud reeds are added the effect is not pronounced enough. In that case one can then turn to suboctave couplers (Octaves Graves). Cavaillé-Coll's stop lists show that he regarded suboctaves as important. For example, even in the tiny Bellahouston organ , the Récit division could be coupled to the Grand Orgue at 16 as well as at 8 foot. It is noteworthy that there was no superoctave coupler on this instrument. By way of contrast, a small two manual British organ from the Victorian era would have done things in entirely the opposite fashion, typically having a swell superoctave but no vestige of a suboctave anywhere.
This bifurcated approach to coupling on the two sides of La Manche becomes understandable when one tries to use suboctave couplers in full combinations on an archetypal British organ. Frequently the effect is thick, heavy and generally awful on account of the regulation of the unison stops (loud and bass-heavy) and their timbres (relatively fewer harmonics with most of the acoustic power arising from the fundamentals and low-order harmonics). In Cavaillé-Coll's organs, as we have seen, the reverse is true. The different approach he adopted to regulating their unison flue stops has already been discussed in the context of the Jeux de Fonds, and in the case of the reeds their apparent power is partly achieved through their extended harmonic retinues which distribute the acoustic power more evenly across the audio spectrum. Together, these factors mean that suboctave couplers can be applied more successfully than on a British organ - they result in less fog and clog and more éclat and élan.
My personal list of five essentials - the quintessence if you will - of a Cavaillé-Coll organ has been outlined above and they were used to derive a stop list for the new simulated instrument. Recall that it will only have two manuals. With this in mind, the relatively large two manual organ which Cavaillé-Coll installed in Paisley Abbey in 1872 was first used as a starting point . (Like that at Bellahouston, this organ no longer exists). Omitting a lot of the intermediate detail, this trail finally resulted in the disposition of 30 speaking stops listed in Table 1 below:
Table 1. Stop list of the extended Bellahouston organ ('Bellahouston-X')
The abbreviation 'Orig' denotes stops on the original Bellahouston organ and 'New' indicates the additional ones.
Briefly, the five essences are present in this disposition as follows:
1. All four ingredients of the Jeux de Fonds are now available on the Grand Orgue, with the added benefit of two alternative string stops to be had via coupling from the Récit.
2. Three quiet imitative reeds are distributed over both manual divisions.
3. The pedal organ is now dominated by new flue and reed basses at 16 and 32 foot pitches, and it is this division which is furthest removed from what one might find on a pipe organ of comparable size - three 32 foot stops on a two manual organ? Of course, it is only because this is a digital simulation which makes it feasible. The option of having 16 and 32 foot tone as flute or string gives unusual flexibility on an organ of this size, especially as they can also be used together. The 16 and 32 foot Bombardes are adjusted to stand out over full organ (including the suboctave couplers), but without swamping it completely even when double pedalling is used.
4. The Grand Choeur can be built up in various ways from the plentiful flue and reed stops on both divisions.
5. There is a complete coupler complement, including two of the important suboctaves.
This extended instrument now allows the majority of the French romantic repertoire to be played. The few exceptions are mainly those where the physical limit of two manuals prevents works being performed where the continual use of three is required, such as Saint-Saëns's Fantaisie in E flat.
I suppose I would say this, but the resulting simulation is decidedly agreeable. Trying to be more objective, it is simply a fact that it is the only one of the many simulations I have attempted which evokes excitement to the extent of making my hair stand on end! Apart from the loud stuff, it is also pleasing to have such a wide range of the quieter sounds characteristic of Cavaillé-Coll's organs available in my home. A tolerably authentic version of the Jeux de Fonds is there, together with a variety of other delicate effects.
A number of recordings are already available on this site of the original Bellahouston organ which forms the nucleus of this simulation, and for convenience these are repeated below because all of them can still be played on the new simulation:
Some additional numbers which make use of the wider resources of the augmented instrument are:
A piece which illustrates Franck's enormous hands (he could easily span a tenth with other notes inbetween) as well as his "weakness for sharps" as Harvey Grace put it  :
A dialogue between the Basson-Hautbois and the Clarinette, with the Voix Humaine plus 32 foot pedal flue later on:
(You will need a very good audio system or headphones if you are to hear the fundamental of the 32 foot stop).
And the daddy of them all:
As with the original Bellahouston simulation, there is some simulated action noise, which can sometimes be detected here as the rhythmic thump-thump of the Barker machines as they respond to the ceaseless beat of this wonderful piece.
(For those into VPOs, you must have a system with no detectable latency when playing this in real time, otherwise you collapse in a heap after a couple of bars. Also you need a lot of polyphony to cope with the number of stops used here, including the suboctave couplers, because the music is very demanding in this respect - lots of heavy chords).
1. The former Cavaillé-Coll organ at Bellahouston is described in the article re-creating_vanished_organs.htm#Bellahouston.
2. "Why we should champion Aristide Cavaillé-Coll", Andrew Mellor, The Gramophone Blog, 2 June 2011
Available at http://www.gramophone.co.uk/blog/the-gramophone-blog/why-we-should-champion-aristide-cavaillé-coll (accessed on 21 November 2013)
3. "Baroque Tricks", Ralph Downes, Oxford, 1983. ISBN 0 906894 08 5
4. "Digital Techniques to Aid Pipe Organ Voicing and Regulation", C E Pykett, 2007. An article on this website (read).
5. "Gottfried Silbermann's Fluework", C E Pykett, 2008. An article on this website (read).
6. BBC MM291, cover CD issued with the BBC Music Magazine volume 16 number 8.
7. "How the Reed Pipe Speaks", C E Pykett, 2009. An article on this website (read).
8. "The Tonal Structure of Organ Reed Stops", C E Pykett, 2011. An article on this website (read).
9. "Étude de la tuyauterie d'Aristide Cavaillé Coll", Laurent Plet, 1993.
Available on Laurent Plet's website at http://lplet.org (accessed on 26 November 2013)
10. "Resultant Bass, Beats and Difference Tones - the facts", C E Pykett, 2011. An article on this website (read).
11. The former Cavaillé-Coll organ at Paisley Abbey is described under index number E01155 of the National Pipe Organ Register (NPOR).
12. "The Organ Works of César Franck", Harvey Grace, Novello & Co, 1948.