Organ stops: the planning of an organ

An organ stops' list contains the palette of colours of an organ and thus lists the abundance of different sound and playing possibilities that the organ builder offers in his instrument. However, even if identical on paper, no two organs sound exactly the same. The spread and fusion of the sounds depends largely on the conditions of the room in which the organ stands. An organ plan nevertheless largely reveals the intentions of the organ builder. Some registers and construction methods are almost omnipresent, others are typical of a single organ builder (or an organ building school), an organ landscape or a certain time period. A stop "subbass" resembles any other of the same name, while a "vox humana" can look and sound completely different from one organ builder to another, even if the underlying intention - the imitation of the sound of the human voice - is the same.

The stop list contains information about the number of keys, the enumeration of the stops and of the secondary elements like couplings or sound effects. To the latter belong gadgets like tuned bells, nightingale/ bird song, cuckoo or timpani (mostly two extremely deep off-tune pipes sounding together, whose beats imitated a drum roll, but sometimes also real timpani, which could be attached to the case or the gallery, beaten by the organist by pedalling!)

The sequence of stops

 The arrangement of the stops is not completely standardised: in organ designs, the stops are often listed according to their position within the organ, from the front diapason to the stops at the rear. As informative as this can occasionally be (regionally typical, for example, in South German organs the registers cymbal and mixture were directly behind the principal, which favoured their sound emission and fusion) this does not assist the overview of the stops as a whole. Therefore, the stops are usually sorted for a listing according to the following criteria:

Flue pipes at first, reeds afterwards, followed by individual effects if they are operated from a certain keyboard (such as bells).

Deeper stops before higher, according to size

Within individual foot ranges: first the principal/open diapason, then wide-scaled flutes, narrow „strings“ and stopped ranks, and if necessary multiple ranks if their lowest rank (relative to C) is not specified.

planning and construction of an organ

Open diapasons usually give the framework of such a list. Since they are placed in the façade as far as possible they determine the height of an organ case: 1 foot at about 30 cm, the deepest pipe (the tone C) of a rank of 8' (the sounding length of this deepest pipe) gives about 2.40 m (plus the pipe foot). Furthermore, adding the substructure of wind machinery, keyboard action etc. this corresponds to a total height of the organ of at least three and a half to about four and a half meters, a frequent size of an organ. An open diapason 16' (pipe length without foot 4.80 m) results in an organ height of at least 6 to 7 m, not to mention the furthermore reinforced substructure, which must bear such a weight. Of course, there might be hardly sufficient space for any further decorative work above it ...

Small organs for a civil interior, or those that should still be easy to transport (for example, processional organs), with dimensions the size of a cabinet, usually offer only about two to two and a half meters of space in height- here an organ builder could at best supply a diapason 4' (1.20 m without foot).

The ranks which do not belong to the diapason group form the other ingredients to the basic sound structure: Some are to supplement the diapasons, others form special alternatives to them, or are pronounced solo ranks of individual shape. Stopped pipes with their reduced pipe lengths allow to add a fundament as well as an alternative in the basic sound registers, as in the following example:

Alternatives to diapasons at higher altitudes, on the other hand, are usually wide-dimensioned open flue stops; they each color the sound mixture of the three starting stops a little softer/sweeter/more reserved, or - in the language of the 18th century – more „delicate."

 
Solo stops (many of which bear the names of orchestral instruments of the time) such as gamba, hautbois (oboe) or flute traversiere (flute) have distinctly independent sound qualities and usually do not require brightening by higher ranks. In addition to the purely soloistic use of such registers (for example, to emphasize a melody), syntheses with another register of the same range, but different construction, were loved to create new timbres.

A special phenomenon are the reed imitators Sesquialtera/Tertian and Cornett. These are composite ranks, which often mimic reed stop sounds very deceptively by their specific addition of certain overtones, as they also appear prominently in the sound spectra of many reed stops.

If such ranks add a quality of sweetness, the Baroque also appreciates "gravity", the sublime effect of an organ that fills the space with strength and acoustic omnipresence. For this purpose, the aliquot ranks (for reinforcement of certain overtones) and the reeds of the trombone/trumpet group are used in addition to the diapasons.

A (fictional) organ, which contains the indicated registrations and thus sound possibilities, could therefore have the following disposition:

I+P

Manual:

Open Diapason 8'

Gemshorn 8'

Flute travers 8'

Gamba 8'

Chimney flute 8'

Stopped diapason 8'

Octave 4'

Block flute 4'

Fifth 2²/₃'

Superoctave 2'

Wood flute 2'

Mixture (2' 4f.)

Cymbal (1' 2f.)

Trumpet 8'

Hautbois 8'

P:

Subbass 16'

Diapason 8'

Octave 4'

Mixture (2²/₃' 5f.)

Trombone 16'

This organ, with its 20 stops, would have been considered a small to medium-sized organ (depending on where and for what purposes), for a richer village church or a smaller municipal parish church; well suited to fill a room of about 400 seats sufficiently and effectively with multiple sound qualities.

If a poorer community might have been able to afford only 14 registers, one could have avoided one or two 8' registers in the manual (only flute travers or gamba, stopped or chimney flute). Moreover, if a parish had not had a permanent organist to re-tune the organ regularly, three reed stops would have been considered somewhat problematic, so that an organ builder eventually switched the Trumpet 8' and Hautbois 8' with a reed imitator Sesquialtera 2f.. Even the independent Octave 4' in the pedal might have appeared dispensable; its main purpose is the option to play a higher melody with the pedal keyboard. Finally, it might have been decided to install only one 2' stop, and the reduced disposition now looks like this:

 I+P

Manual:
Diapason 8’
Gemshorn 8’
Gamba 8’
Stopped 8’
Octave 4’
Block flute 4’
Sesquialtera 2²/₃’+1³/₅’
Wood flute 2’
Mixture (2’ 4f.)
Cymbal (1’ 2f.)

P:
Subbass 16’
Octave 8’
Mixture (4’ 5f.)
Trombone 16’

This organ - naturally with some minor limitations – still offers a large part of the sound variations and effects described above. The pedal, however, is only a pure bass keyboard as a solid foundation but hardly any properties for melody play.

Depending on the musical requirements, however, a second manual keyboard may be needed, for example for "trio playing" (2 different manuals and pedal) or to be able to highlight a melodic voice (eg typical for the Protestant organ chorale) with a distinct sound quality! So the first step of further planning would be to consider where this second manual work should be set up. Generally it is tried to position its pipes it as far away from the main organ as possible. The classical solution offers a back positive or parapet positive, which is installed separately from the main organ case in the back of the organist in the gallery parapet. Other solutions are the „chest“ (Brustwerk), below the main and directly above the keyboards, a „top“ above the main organ or a Hinterwerk behind it (rarely). Depending on the installation location, there are other technical and acoustic requirements: Although the rear positive is in an acoustically very favorable position, the action must be guided there with greater technical effort, and it reduces the available space on the gallery.

As an alternative to the parapet positive, the second manual ranks could be placed inside the main organ case, but separately from the main organ, for example as a chest or upper positive (below or above the main). But for this, it is important to consider the available space in the organ case - in an upper positive, even more in a chest positive, there is often only insufficient space for lower pipes. After all, a rear positive in the rear can only be heard through the main and a part of its sound volume is lost again. The external design of a second manual work also depends to a large extent on its placement and assignation to the main organ. Parapet positives usually represent a reduced image of the main organ case. This is, however, hardly possible with the chest, upper or rear positives more or less integrated into the main organ case.

Assuming the traditional decision for a parapet positive, a fictitious draft for it, derived from the design above, could now look like this:

The Open Diapasons get their direct correspondents one octave higher, in addition some colour registers from the main work are assigned to the parapet positive and can now no longer serve as alternatives, but may be used in contrast to the stops in the main organ. The contrast between gravity and delicacy characterizes the two manuals. An organ builder of the 18th century have enhanced that further, for example with a stopped 16' stop for the main and a reed stop with short resonators for the positive. The extended design would then look like this:

In a last step the pedal should be supplemented with one or two lovely" sounds, in order to be able to be played only to the back positive, for example a quieter 16' register (eg Bordun) and an 8' flute and then look like this:

P:

Subbass 16'

Bordun 16'

Octave 8'

Flute 8'

Octave 4'

Mixture (22/3' 5f.)

Trombone 16'

The addition of further manuals denotes large-scale projects. As a rule, the contrasting sound characteristics between the different manuals were emphasized further and supplemented with new sound components: the main organ for gravity,  the smallest of the partial positives, eg a chest positive für delicacy, the parapet-positive "penetrating" (in 18th century usage without any negative association the term may evoke today). Another option was to design one of the manuals as a pure solo piano like the French „Reçit," or an English Echo, with few, but very individual and viable colors like the Cornet 8' 5f. (8'+4'+2²/₃'+2'+1³/₅').

The design possibilities that organ builders have developed over the centuries are too diverse to be presented in detail here. The surviving dispositions of such instruments of the 17th and 18th centuries reveal manifold choices in different regions and traditions.