Pipe Organ Specifications
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Pipe Organ Specifications

18:07 16 June in Pipe Organ Resources

Understanding Organ Specifications

To an organist or committee person involved with an organ project, or even for the concert listener, the written specification for an instrument can prove to be a valuable asset. A visiting organist may ask for a copy of the specification to become familiar with an organ in preparing a concert. An organ committee person will find the specification valuable as they analyze a proposal for a new or renovated organ. Organ specifications, as we provide them, are clear and concise about the stops provided on an organ and the tone source of each stop. This distinction becomes crucial for a committee reviewing proposals as there are different ways to achieve a speaking stop for the organ, and some builders are using electronic voices to augment or build an organ. (See Section II for organ definitions).

The following definitions are offered for ease of understanding:

Specification – The list of speaking stops in an organ, as arranged by divisions or departments. A proper specification should indicate how many pipes are assigned to a given stop. If there is not a rank(s) of pipes for a given stop, it should indicate that the tone source for a stop is unified or duplexed from another set of pipes, or that it is provided as a digital/electronic stop. The specification will also give the basic information regarding the number of manuals or keyboards, the number of speaking stops and the complement of couplers and capture action provided.

Division – The organ stops will be grouped together in divisions – or, in British specifications, departments. Each division is assigned to a given manual or to the pedals on the organ console. Likewise, the pipes for that division will be grouped together in a given chamber or section of the organ case.

Rank (or pipe rank) – A set of pipes that develops a particular tone for the pipe organ, ranging from lowest note to highest note on the keyboard or pedalboard. Pedal ranks can have from 27 to 32 pipes, while manual ranks may range from 37 pipes for a short compass rank to 97 pipes for a unit rank. The average straight manual rank is 61 pipes.

Stop (or speaking stop) – A stop is a control for a particular sound and pitch for a given manual division or pedal division.

Pitch notations – In the specification you will see a list of stop names in each division. Each name will include numbers such as 16′, 8′, 4′ and so on. Based on a concert pitch of middle A=440Hz, these numbers indicate the pitch of a given stop. Unison pitch is based on an 8′ pitch, meaning that for an open flue pipe or full-length reed stop, low C will be approximately 8′ tall (not counting the toe of the pipe). The number 16′ indicates that low C will be approximately 16’ tall, so this stop will play one octave below unison pitch. Conversely, 4′ pitch will be one octave above unison pitch. If a stop name includes a Roman numeral, this numeral indicates the number of ranks in a stop rather than the length of the low C. Stops with Roman numerals often indicate mixtures, which add brightness to the ensemble by playing several higher-pitched ranks at the same time. Most manual mixture stops are no more than 2′ long at low C. This is an important item to understand, because single rank stops of 16′ and 8′ designations take far more space in the organ chamber or case than would a IV-rank mixture. This will also have bearing on the “price per rank” used to estimate cost, because mixture ranks take far less metal and labor to build, and they produce less foundation tone.

Straight ranks – A straight manual or pedal stop will have one independent set of pipes dedicated for use for that one stop only. Straight stops are one rank of pipes unless designated by a Roman numeral on the stop knob or stop tab. For example, IV Mixture would have 4 independent ranks of pipes for the one Mixture stop.

Unit ranks – A unit rank is a single rank of pipes has been extended to play at multiple pitches in a given division. For example, an 8′ Gedeckt (flute) will require 61 pipes. However, if we add 12 pipes to the treble, we can use a unit chest and relay to play the rank as a 4′ Flute: 61 notes in total, with the first 49 pipes drawn from the upper end of the 8′ flute and the last 12 notes played from the 12-pipe extension. In some cases a builder may number their stops in the specification, and the higher or lower pitch stop may say “from no. xx” indicating the rank that was extended to create the extended stop. Note: With unit ranks, you will have multiple stops drawn from a single rank of pipes.

Duplex stops – A duplex stop is a single rank of pipes that has been wired to play as two or more independent stops. An excellent example is the “duplexing” of solo stops, commonly a Trompette (En Chamade, Festival, or Fanfare) or a Tuba. Only one rank of pipes exists, but for reasons of literature, the stop may be required to play in different divisions without the use of couplers. The stop may be duplexed as an independent stop in multiple divisions by means of a relay and stop control. In addition, manual 16′ stops may also be duplexed to a pedal division.

Capture System (sometimes referred to as a combination system) – The capture system allows the organist to set predetermined registrations or selected stops and “capture” them to a piston or toe stud memory. Older organs only employed one level or channel of memory for each piston, as the mechanisms were mechanical or electro-mechanical by design. Later, organbuilders began to employ the use of solid-state electronics for capture memory, thus allowing additional memory levels or channels. The description of the capture system should indicate the number of available memory levels or channels for memory. Note: Capture systems used with mechanical (tracker) action pipe organs will require the use of electric stop action to make the organ accessible for a capture system.

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Organ action – Pipe organs use one of two primary conveyances between the key and the valve under the pipes.

A – Mechanical or tracker action systems use a physical mechanical link between the key and pipe valve. This link is built using rods or conveyances (called trackers) and various squares or corner connections. The rods and squares may be constructed of wood or metal. A well-designed tracker precisely transmits the action of the organist’s finger to the pipe valve and is extremely advantageous for practicing performance technique. One of the keys to good design is the arrangement and the length of the tracker runs. Therefore, large instruments — or instruments that require considerable distance between the key and the pipe valve — may present limitations or challenges that might better warrant electric actions.

B – Electric action systems use electro-magnetic solenoids either to directly open pipe valves or, the preferred option with our company, to trigger a pneumatic action to open the pipe valves. Pneumatic designs may be referred to as electro-pneumatic actions and will be offered in unit, pitman, or slider chest configurations. (See Section V for chest action details.) In any configuration, the signal is sent from the console key as an electric signal rather than a mechanical link. Thus, electric consoles offer almost infinite options for placement.

Console – The part of the pipe organ which contains the keyboards, pedalboard, stop controls, swell shoes and capture action is called the console. This is often mistakenly called the “organ.” In the realm of a pipe organ, the console serves as the control center for playing the pipes. Most electric action pipe organs will have a stand-alone console. For tracker organs, this will be called a “detached” console. If the organ is built as a free-standing case instrument, the organ console may be attached directly to the case of the instrument. Attached consoles are most common with tracker organs.

Derived or Synthetic stops – In some pipe organs, certain stops may be derived from a combination of stops when space and/or budget will not permit the installation of a real set of pipes for the stop. One of the most common situations is the inclusion of a 32’ pitch stop. A 32’ stop usually requires the space for pipes that are 32 feet long. Since many churches cannot house such stops, the ear is lead to believe they exist by playing higher pitches in the harmonic series of a 32’ tone. For example, a 32’ Resultant plays a unison and quint (or fifth) tone from the 16’ octave to create overtones for a 32’. A 32’ cornet uses pitches to play the octave, quint, tierce, seventh, and ninth harmonics for a reedy overtone pitch. In our company, such stops are denoted in the specification as derived.

Digital stops – These stops are created not with pipes but with computer tone generation sources. Our policy is to limit these stops to 32′ pedal stops and percussion stops such as Chimes and Harp. Other builders may use digital stops for a wide variety of stops in the instrument. In any case, each digital stop should be duly noted in the specification. There are different manufacturers of digital stops, much as there are different builders of pipe organs.

Winding systems – Like actions and windchests, there are different ways to build winding systems. Except for historic restorations or historical replicas, all current modern pipe organs use electric blowers to provide wind to the organ. The blowers are designed to provide high-volume, low-pressure wind for the organ pipes. The wind pressure and volume are regulated by devices called reservoirs or Schwimmers. (See Section VI for more on reservoirs.)

AGO specifications – The American Guild of Organists (AGO) is a professional guild for concert and church organists. The AGO has established a set of physical configuration and measurement standards for the construction of pipe organ consoles. These standards have been refined over the decades to provide ergonomically efficient and comfortable designs for organ consoles. Our firm uses these standards in our own console design to promote a comfortable and user-friendly instrument.

Cases – Cases are used for architectural presentation on two levels. Cases may provide a front for an existing organ chamber designed as part of the building, or they may be designed as complete, free-standing enclosures for the pipe organ. The case offers benefits for focusing sound and providing tonal egress for the pipe organ. The cases also provide the visual personality of the instrument.

F/L or L/2 – These are designations sometimes found when addressing reed ranks. When building reed pipes, the speaking length of an actual vibrating reed can affect the pitch of the pipe in spite of the actual length of the reed pipe resonator. Thus a reed pitch may speak a pitch lower or higher than the actual length of the pipe might dictate. Commonly in organ building, pipe organ builders may build reed stops that speak one octave lower than the actual length of the pipes. For example, a pipe organ may include a Trombone or Contra Bombard that speaks at 32’ pitch, even though the lowest pipe is only 16′ long. The pipe organ builder will designate this by indicating the stop as follows:

32′ Contra Bombard L/2 12 pipes
(F/L @ C2)

“L/2” is length divided by 2 or half-length. “F/L” indicates full-length.

Since the church may not have space for the 32′ pipes, the organ builder opts to build the pipes half-length (L/2) in the bottom octave, reverting to full-length (F/L) at C2 or note #13 (the second octave) and remaining full length for the balance of the rank of pipes.

Enclosed or expressive – The term “enclosed” will usually appear just under the Division name. This indicates that the following pipes are enclosed in a chamber or in part of the organ case that has swell shades over the tone opening. These shades are controlled by a shoe on the console, which opens and closes the shades to express or control volume of the pipes. These shades control volume in much the same way that window blinds can be adjusted to let in or block out light.

Unenclosed or non-expressive – These terms indicate that this division does not have swell shades to control tonal egress of the division.


Tools for the Church Organ Committee.

For a compilation of in-depth information ranging from industry standards and descriptions to the format of purchasing a pipe organ, please download our Tools for the Church Organ Committee.

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