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Unit & Extension Pipework

As An Adjunct to the Straight organ

By Mr.
Extract from the Journal of the Incorporated Society of Organ Builders
Published 1949

The subject I have chosen to consider this evening is really that of trying to answer the question:- How far can, and how far is it economical and artistic, to combine unit and extension pipework with a straight organ scheme?
I expect most organ builders have faced this question in one form or another, either verbally, or in digesting schemes submitted to them by organists, some of such schemes being quite intelligent, but others often very weird and impracticable for various reasons.
In attempting to cover this subject logically, some of my remarks may sound rather obvious or elementary, and some aspects admittedly are very much a matter of opinion, or depend upon the care and skill in which any idea is carried out. Its controversial nature, however, makes the subject of interest and also because it involves many artistic points, as well as such questions as estimating problems, space requirements and avoidance of complication of mechanism, which point often has a distinct bearing on relative costs and the question of easy maintenance.
All of us present have probably been brought up, like I was, in the straight organ school of thought, but I hope that none are of the opinion that all unit and extension work has as its main objective the production of a cheaper instrument. In fact, in my opinion, it is often a means of getting something additional and artistically useful added to an organ scheme, beyond the expenditure originally contemplated.
I have heard it said that: ":all true craftsmanship, like true art, must accept some limitations of medium":. Whoever originated that statement may have intended it to apply to the actual nature of the materials in which the craftsman works, but I think it can also be expanded a little further to include other aspects and even the idea of "best value for expenditure", at which no craftsman need sneer, provided always that this limitation is not too irksome. The organ builder does in fact have to face the limitations of available expenditure and space restrictions; happily, not always, but often so. In the case of these two limitations it is, obviously, up to the customer to make these factors as less irksome as possible to the organ builder, and I think the members of our craft can do much by constantly reminding clients of this fact.
Other limitations also face us of a nature depending upon inventions and design and which obviously have altered in the course of time. The almost universal use nowadays of sliderless soundboards has introduced several factors of an advantageous kind, although not really helping as a space saver. In the obvious example of that of actions, the various limitations associated with tracker mechanism have long since been swept away by pneumatic types, and more so still by electro -pneumatic and electric mechanisms as in use to-day.
Nearly every organ builder has taken advantage of some of these facilities, e.g., detached consoles and the space saving factor, but whereas electric mechanism really made the extension organ a feasible proposition, opinion still varies greatly amongst organ builders and organists as to how far the facility of unification, and its corollary of extension, should be carried.
The wholly extension organ is beyond the scope of my subject, but it should be realised that by suitable choice of registers, many extension organs can be played in a straight way and that many such organs have some features that are really straight. However, I have no wish to revive the rather useless controversy of "straight versus extension', and am really reviewing this subject of unification and extension in the light of its possible help to organ design in general, which, before the advent of electric mechanism, was really compelled to be on traditional straight lines by force of circumstances then existing.
I often feel that we as organ builders will have to help to guide the organist of to-day and to-morrow as to what should, or should not, be done either artistically or mechanically, and I would say that it is an undoubted fact that many intelligent and musically gifted organists of to-day are becoming more and more inclined to think in terms of "straight plus extension", or even "extension plus straight", and that they consider that the vista opened up by the removal of the limitations imposed by old types of action and slider chests should, to say the least, be explored.
In discussing this subject, many words in current use rather overlap each other, such as :-borrowing, derivation, augmentation, duplexing, unification, extension, etc. I prefer the use of the word "unification" in a general sense wherever possible, and not necessarily implying "extension" as well. By the use of the word "unit" I mean to denote a group of pipes in which every pipe is equipped with an entirely separate action and its own electric magnet, so that they are capable of being played from two, or more, different points. It is important to note that unification may also include the introduction of extension, but not necessarily.
I am not going into the past history of unification, but it will be appreciated that with pneumatic mechanisms, and even with tracker actions, a measure of unification was always possible, although limited by cost and constructional considerations rather than artistic reasons, and these practices have already led to a very general adoption of a certain amount of unification for duplexing and to the use of extension on the pedal organ. Such practices are indeed accepted by organists and organ builders who would normally consider themselves advocates of the straight organ. Admittedly there can be objection to extensions on the manuals, or I should rather say unsuitable extensions on the manuals, but once having admitted that octave couplers may at times have artistic merit, it is difficult to see why the more flexible method of individual transferences of pitch should not also have some consideration, if it helps to provide an instrument on which an organist can express his feelings more adequately.
To come to practical considerations, the following four points give my personal opinion on the use of unification:-

1. Mere unification of stops above 16 ft. pitch for the sake of duplexing only is not very economical, but is worthy of consideration for definite purposes, e.g., where a use from two points does in fact give more variety.
2. If desirable to unify a stop, then it is well worth while also considering whether it can usefully be extended for use in several pitches and possibly from several points.
3. From the action aspect, unification with extension is most adaptable for the Pedal Organ and Great Organ departments, but, artistically, especially on the Great, it is desirable to keep it within limits. As regards other manual departments it is more suitable for the Solo, Choir and Swell, and in that order.
4. It is advisable to avoid mixing a lot of extended units with a few straight stops as liable to become costly and complicated, especially if in a department affected by octave couplers, and one needed to be coupled to other departments. As an example in the opposite direction, a group of straight stops with one extended unit is comparatively simple, and even more so if the latter is not on the octave couplers. In general, therefore it can be said that, rather than have too much of a mix up in any one department, it is usually better to keep it mainly straight plus one or two units only, or else have it wholly unified and extended.

  The following Diagrams show examples of straight and unit pipework combined in various organ schemes, and with brief notes thereon. The specifications are in abbreviated form, set out to show the composition and in which departments and in which pitches the ranks are used, and are not intended to be in the usual stop list order. The vertical lines on the left denote ranks on straight chests. In some cases where only a portion of a stop is unified, it is reckoned as a straight rank.
Diagram 1. Small a manual. Seven straight ranks and 2 Units.

  Built new in 1936. Situated in. a West End gallery of a Convent Chapel, seating about 90 persons. Building is of lofty proportions and good acoustically.
Pipes Gt. Sw. Ped.
16 Bour. 42 16.8
8 Open 61 8
8 Wald Fl 61 8
Dul 61 8
4 Har Fl 61 4
Sw Box
8 L Ged. 61 8
V. Da Gam. 61 8
4 Prin 61 4
Oct. Sub.
16 Oboe 85 16.8.4 16.8.4 16.8.4
554 7 6 5
Sw to Gt Trem Gt to Ped
Sw to Ped


(1) This should be regarded as a one manual scheme, with a few stops put into a box and given octave couplers. There can be differences of opinion about the choice of the 7 straight stops, and naturally the scheme could be improved by additions.
(2) The 85 pipe reed rank is a specially bright Oboe so as to give reed chorus effect, as well as for solo use. It is not on the octave couplers.
(3) Some uses of this Oboe unit:-
(a) A second 16 ft. on Pedal.
(b) Reed chorus on Pedal against Great coupled to Swell flues with octave couplers.
(c) Oboe 8 ft. can be combined with other 8 fts.
(d) Oboe solo on either Great, or Swell, with variety of accompaniment.
(e) Swell flues as a solo against Oboe as accompaniment.
(f) Variety of Swell effects, e.g., flues with octave coupler and 16 ft. Oboe, or with 8 ft. and 4 ft.

Diagram 2. Large a manual. 15 Straight rank and 6 Units.

A rebuild of 1937 in a West End gallery of a church. Detached console and choristers also in the gallery. Space for organ rather restricted. An old tracker actioned organ was given to the church. Slider soundboards good and too valuable to scrap. Additions made by new unit chests. All old pipework incorporated with the new.
Pipes Gt Sw Ped
16 Bour 54 (32) 16.8.4
16 Open 1 Met 73 8 16
16 Dul 73 16.8 16.8
16 Tromba 73 8 8 16
8 Clarinet 61 8 8
8 Open 2 61 8
Wald Fl 61 8
4 Prin 61 4
Har F1 61 4
22/3 12th 61 22/3
2 15th 61 2
Sw Box
8 Open 61 8
L. Ged 61 8
V. da Gam 61 8
V. Cel. T.C. 49 (8)
4 Gems. 61 4
3 R. Mix 183 (15-19-22)
8 Trumpet 61 8
16 Fag. & Oboe 73 16.8 16
1310 11 11 9
Sw. to Gt. Oc. Sub. Gt. To Ped
Sw. Oct. to Gt. Trem. Sw. to Ped.
Sw. Sub. To Gt.

Notes :-

(1) No room for an Open Wood, so Great No. 1 Open carried down to 16 ft. as the main pedal stop.
(2) Choice of five 16 fts. on Pedal.
(3) 16 ft. Dulciana unit on Great and Pedal.
(4) Clarinet on unit chest over the Great, unenclosed and also playable on Swell. No room to put in swell box, which would be preferable.
(5) Swell all straight, except unit of Contra Fagotto two octaves) running into an Oboe. Everything on octave couplers.
(6) Great Tromba (unenclosed) also playable from swell. It can be used as a solo against the Great, and also useful for a climax, e.g., full Great with Tromba, coupled to full swell (without Tromba) and Swell octave and sub. to Great, followed by putting on the Tromba on the Swell, thus adding 16 ft. and 4 ft.

Diagram 3. Treatment of a small straight Swell with one extended Unit.

There is a considerable variety of arrangements possible with one extended reed unit and a group of straight stops, for making up a Swell department.
Below are two arrangements, A and B, of a typical small Swell of 6 to 8 straight stops, plus one unit. Fifteenth (for a more gradual build up) and 4ft. flute can be included, if feasible. Composition of Mixture would depend upon whether a separate Fifteenth.
8 Open. 61
As for A up to Mix
Gedeckt. 61
Sal. 61
4 Prin. 61
(Flute 61
2 (15th 61
3 R. Mix 183
8 Trumpet 61 8 Oboe 61
16 Con. Fag.  73 and Oct. Sub
8 Oboe  on Ped. 16 16 Dou. Truim. 85 and
Oct. Sub. 8 Trumpet on Ped
4 Oct. Trum 16.8.4
Here is another alternative, C, but I have no experience of the use of a 16 ft. Clarinet in this way. This arrangement is the suggestion of an organist and has some points of interest, although I think raising doubts (see Note C 1).
C 61
8 Open 61
Gedeckt 61
Sal. 61
4 Prin. 61
2 15th 61
1 1/3 19th 61
8 Trumpet 61
Oct. Sub
16 Dou. Clnt. 73 and on Great 8
8 Clarinet and on Pedal 16


(1) Trumpet is straight, with the softer 16 ft. reed unified.
(2) In this case everything is usually on the octave couplers.
(3) Reed chorus provided by Trumpet and Contra Fagotto with octave coupler (plus Mixture and other stops, if desired).


(1) Oboe is straight and the Trumpet extended I6.8.4. A very satisfactory arrangement combined with straight Mixtures, and good for a large building.
(2) In this case the Trumpet rank is usually not on the octave couplers.
(3) Need not be on the Tremulant, if heavy wind available.
(4) The reed chorus from Swell has its uses on the Pedal.

C. This idea of an organist is based on these opinions:-

(1) That a 16 ft. Clarinet should make a good swell double reed.
(2) That for the second reed in an organ, a Clarinet 8 ft. is more generally useful than an Oboe.
(3) That the Clarinet should be in the Swell box and playable on the Great, as a solo against the Swell stops.
(4) That after a Swell 15th, the most useful mutation rank is the 19th to give the Mixture effect. If necessary, could be combined as a Mixture 2 ranks (15-19).

  Diagram 4.Three Manual. 16 straight ranks and 8 Units.
  A concert hail organ, built in 1934- Space much restricted.
Pipes Gt. Sw. Ch. Ped
16 Op. Wd 44 16.8
Bour. 56 (32) 16.8.4
Trom. 85 8 (16) 8.4 16.8
Dou. Op 61 (32off) 16 16
8 Op. 1 61 8
Op. 2 61 8
4 Prin 61 4
2 2/3 12th 61 2 2/3
2 15th 61 2
Sw. Box
8 Gei. 61 8
Rohr. Fl 61 8
Viol. 61 8
V. Cel. T.C. 49 (8)
4 Oct. Gei 61 4
3 R. Mix 183 (15-19-22)
16 Con. Fag. 61 (32 off) 16 16
8 Trum. 61 8
Ch. Box Trem
8 Har. Fl 85 8.4. 8.4.2
16 L. Ged 92 8 8.4.22/3 16
8 Dul. 85 8 (16) 8.4.2
Clarinet 61 8 (16) 8
Orch. Oboe 61 8 8
1533 11 10 16 11
Sw. to Gt. Oct. Sub. Trem Ch. To Ped
Ch. To Gt. Uni. Off Sw. to Ch. Gt. To Ped
Sw. to Ped

(2) Very bold and resourceful organ for its size.
(3) Choice of six 16 fts. on Pedal.
(3) Straight Diapason chorus up to 12th and 15th.
(4) Extended Tromba on Great, Choir and Pedal.
(5) Swell all straight. No usual Oboe.
(6) Extension and Unit Choir, also providing flutes on Great. No octave couplers. 16 ft. Dul. bass from L. Ged.
(7) Choir solo reeds also on Swell.

Diagram 5. Large Three Manual (with a part Extension Great).

A new organ completed in 1948. Commenced in 1940 as an average sized Two Manual. More money available after the war, so completed as a Three Manual by adding an extension choir, and various unit chests consistent with space available; 19 straight ranks and 10 Units.
Summary of scheme
16 Open 3. 85 16.8.4 and on pedal 16.8
8 Open 2. 73 8.4
Open I. 61 8
Wald. Fl 61 8
4 Stpd. Fl 61 4
22/3 12th 61 22/3
2 15th 61 2
4 R. Mix. 244 (17-19-b21-22)
16 Trom. 85 8 | and on choir 8.4
12 | and Pedal 16.8.4

The above is associated with a Swell of 10 straight ranks and one Unit; an extension Choir of 4 Units (including a 16 ft. Gedeckt and a 16 ft. Dolce), and a Pedal of Open Wood, Bourdon and extensions, etc. Total of 1,887 pipes, 53 stops, 10 couplers.
(1) Choice of seven 16fts. on Pedal.
(2) Complete Diapason chorus up to 4 rank Mixture including 17th and flat 21st.
(3) Open 1. can be used with a 4ft. from No. 2: Open 2. with a 4 ft. from No. 3: Open 3. with 4ft. Stopped Flute.
(4) 4ft. Stopped Flute probably more useful than the usual Harmonic Flute, as it combines with the small Open as well as with the Wald Flute.
(5) Swell reed chorus consists of straight Trumpet and Clarion and a unit of Contra Fagotto and Oboe.
(6) Organ is voiced boldly in a very large and resonant Church.

Diagram 6. Use of Unification for a Divided Organ.

Example of a rebuild, carried out in 1934, in a large church, where for various reasons the Great, Swell and Pedals are accommodated on a West End gallery, the Choir Organ (with its own blower), and the console, being at the East End. The Choir Organ, in a side arch of Chancel, is usable by itself for choir practices and for weekday services in a chapel at side of Chancel. When the choir Organ is thus employed it can be used as a two-manual, as two choir stops are playable on the Great and two soft Pedal stops available. There is included in the specification one extended rank in the choir and two in the Swell (a reed and a Viola da Gamba), which permit of a small accompaniment section on the Great. This is also useful to enable a solo and accompaniment to be played at either end of the building, e.g. Choir Clarinet against Choir Lieblich Gedeckt or Swell Oboe against Swell Viola da Gamba. Brief details are:-
Choir or (Chancel) Organ.
8 Vio. Diap 61 8
Echo Viol 61 8
V Cel. T. C. 49 (8)
4 Sal 61 4
8 Clarinet 61 8
16 L, Ged 97
and on Ped 16.8
Great Acc. Section
8 V. da Gam (S.w.)
L. Ged (Ch.)
4 L. Flute (Ch.)

Total Organ comprises: Great 10, plus 3; Swell 11; Choir 10, plus 1; Pedal 12; Couplers 10. 23 Straight ranks and 6 units. 1,827 pipes.

Diagram 7. Unit additions to a Pedal Organ. (To provide upper-work and Mixture)

Several arrangements possible at varying cost.
Here is the suggestion of an organist, with some alternatives showing my suggested improvement:-
Rank (a) Prin 8 86 8 4 2
Rank (b) 12th 51/3 44 51/3 22/3
Rank (c) 17th 31/5 32 31/5
This Gives Prin 8(a)
15th 4(a)
Mix 4 rks. 12(b) - 17(c) - 19(b) - 22(a)
Better would be:-
Rank (a) 8 Prin 44 8 4
Rank (b) 51/3 12th 44 51/3 22/3
Rank (c) 415th 44 4 2
Rank (d) 31/5 17th 32 31/5
Giving :- Prin 8 (a)
15th 4 (c)
Mix 5 rks 12(b) - 15(a) - 17(d) - 19(b) - 22(c)
Prin 8 (a)
12th 51/3 (b)
15th 4 (c)
17th 31/5 (c)
Mix Mix. 3 rks. 15(a) - I9(b) - 22 (c)
Note:-In this last arrangement it will be seen that 8. 51/3. 4 and 31/5 are, in effect, separate straight stops, and mix. 3 rks. extension.
Diagram 8. Economy by use of Extension for expenditure on other straight features.
An example of this aspect is provided by a rebuild now in hand. Specially desired are a Positive division to the Great and very adequate provision of straight Mixtures. The organ is based on the following lines:-
16 Dou. Ged 61 (32 off for pedal)
8 Open 1 61
4 Prin 61
22/3 12th 61
2 15th 61
4 R. Fourn 244 (19-22-26-29)
8 Dul (From Ch.)
16 Tromba unit 85 for Great, Choir and Pedal
Positive Division
8 Open 2 61
Wald F1 61
4 Spitz F1 61
3 R. Cornet 183 (12-15-17)
Pos. on Ch. Pos on Sw
Swell Straight, up to two 4 rank Mixtures (one for reed) and 16 Trumpet unit 85, not on octave couplers.
Choir Mainly extension and of a solo character.
Pedal straight and extension, up to a straight 4 rank Mixture.


(1) Positive division is floating. Choir Dulciana on Great for convenience.
(2) More Mixtures than usual.
(3) Economy on the unit reeds and extension choir, etc.

Advantages of Unification and Extension combined with straight pipework
  1. Permits generally a more useful Pedal Organ with variety of 16ft. tone. Also can be helpful to provide more upperwork and mixture arrangements.
  2. Tends to be able to provide more usable variety in an organ, partly by variety of combinations possible, and partly in the facility of choice of solo and accompanying registers.
  3. Where space if restricted, or of an awkward shape, it often helps in the provision of an adequate organ and a good lay-out.
  4. Provides a useful method of making addition to an old organ in a rebuild, where old soundboards are good and too valuable to scrap.
  5. Helps to overcome some of the drawbacks associated with a divided organ.
  6. By its economy in certain directions, it allows of a more complete tonal scheme in other directions.