Theater Organ TechTalk -


A Series of Articles on Theater Organ technology - how things were (and are) done - and why.


Extension and Unification

The technology behind a Theater Organ.


Extension and unification came about as an effort to get the absolute most sound from a minimum number of pipes. In a classical instrument each rank (voice) of pipes consists of 61 pipes - and covers five octaves. Ranks are identified by the "pitch" at which they speak. Because various pipe technologies, etc. can create pipes of various length that speak at the same note - it was decided many years ago to standardize on a convention that identified each rank by it's "speaking" pitch - rather than physical pitch.

Explanation: An open column pipe of approximately 2 foot length has a natural resonance at C4 (middle C). A closed column pipe speaks at twice it's physical length - so a closed pipe that speaks at C4 (middle C) would in fact be approximately 1 foot in length. Other construction methods can also cause considerable difference between the actual pitch the at which the pipe speaks and it's phsyical length. Just for reference, note that a pipe twice as long as a similar pipe will speak at 1/2 the frequency - i.e. one octave lower. In the same manner - a pipe 1/2 the length of a similar pipe will speak at twice the frequency - i.e. one octave higher.

A similar issue exists between keys of the manuals (and pedals) and the ranks - on a piano - the 4th C always sounds the the same pitch - C4 (middle C). However - depending on the pitch of a rank of pipes, "middle C" on an organ's manual may sound anywhere from C2 to C6 (or more on very large organs).

It would be a huge problem, then - for an organist to figure out at what pitch a rank of pipes spoke if they are identified by physical length - so a better way of identifying the pitch of a rank had to be found; and some "standard" that related to the keys of a keyboard.

That "standard" was to consider the pitch of a rank of open pipes whose longest pipe is (approximately) 8 foot. When such an 8' rank is played from a standard 61 key manual - Middle C on the manual indeed sounds the 2' pipe - which sounds Middle C. By extension, then - any rank that "speaks" at 8' will play the same pitches (unison pitch) - regardless of their physical length or construction. A rank of 16' then when played on the same keys of a manual (or pedals) will speak an octave lower, a rank of 4' will speak an octave higher (than 8'). This, then is one part of unification - ranks that speak in unison - regardless of physical length, construction, etc. Note that unification can be used in Classical Organs as well as Theater Organs (particularly modern designed and built Classical Organs) - but as a general rule - unification is taken much further in Theater Organs than in Classical Organs.

8' rank attached to a manual 4' rank attache to a manual
In a Classical Organ - to play a "rank" - you draw the stop for a rank - in this case let's say the 8' FLUTE - and the 8' Flute rank is connected to the chosen manual. If you instead draw a 4' Flute - then a different 61 note rank is connected - only this rank consists of 61 pipes - each 1/2 as long as the same pipe in the 8' rank. For each "pitch" there is a complete set of pipes.
Both 8' and 4' attached to a manual.

If you draw both the 8' and the 4' stops - both full 61 pipe ranks play - giving two notes (an octave apart) for every key pressed. That means to play four "pitches" on a key (16' 8' 4' 2') one would have four ranks of 61 pipes - or a total of 244 pipes.

One of the design goals of a Theater Organ - is to provide the most sound and versatility with the fewest pipes to minimize both cost -and space needed. To accomplish this goal - Extension and Unification is used to accomplish the same (or nearly) sound with many less pipes. Here's how it's done: let's start with an 8' flute rank. A 4' rank plays one octave higher - so if we were to add 12 pipes to the "top" of our 8' Flute pipes, - we would now have the ability to play the same extra octave - but now using only a total of 73 pipes. Adding another 12 pipes to the top of this extended rank now allows gives us the ability to play those two extra octaves - but now using only 85 pipes instead of the 183 pipes a traditional organ would use. Adding a "fourth" octave - this time to the bottom of our extended rank- and we have the ability to produce notes from 16', 8' 4' and 2' ranks - but using only 97 pipes rather than the 244 pipes a traditional organ would take.

Here is an extended rank (97 pipes) with the keyboard attached at the 8' pitch.
Note that middle C on the keyboard plays C4 (middle C) pipe.

Here the keyboard is connected to the rank at the 4' pitch. Now the middle C key will sound the C an octave higher.
Here the keyboard is connected at the 16' pitch. Middle C key now sounds one octave lower. Here the keyboard is connected at the 2' pitch. Middle C key now sounds two octaves higher.

An example of Extension and Unification - and how it conserves resources:
A "typical" Robert Morton 2/6 Theater Organ might consist of six ranks of pipes: Tibia having 97 - ("extended" through 4 standard pitches (stops) 16', 8' 4' and 2'); then , Trumpet, Flute and Violin 73 pipes - so "extended through 3 standard pitches (16' 8' and 4'). Finally two 61 pipe ranks - Vox Humana andViolin Celeste - extended through 2 standard pitches (8' and 4'). Thats 18 "stops" using 438 pipes. Since there is one-wire to each pipe - that's 438 wires. A traditional organ with 61 pipes per stop - would use 1098 wires to do the same thing - well very nearly the same. As noted here and above - giving the Clasical Organ it's due - we have to note a "compromise" that extension and unification imposes. As noted before - in a traditional or classical organ - each rank is separate and complete. So - if we have 2 flute ranks drawn (at say 8' and 4'), then pressing down two keys an octave apart on a Classical Organ sounds 4 pipes (two per key). If we do the same thing on a theater organ - because of "Extension and Unification" - pressing down the same two keys only sounds 3 pipes - because the lower key's 4' pipe is the same pipe as the higher key's 8' pipe. In the case of the Classical Organ - that "part" of the sound would be twice as lound - since it is coming from two pipes - rather than one "shared" pipe in the Theater Organ's Extended (single) rank. This then would cause the Theater Organ to sound "different" all other things being the same. Of course - no two organs (even from the same manufacturer) sound the same - so that is a small compromise the Theater Organ gives up for the flexibility and fullness (with far fewer pipes) Extension and Unification provides.


Here is a bit more complex example- the keyboard is connected to both the 8' and 4' pitches. Middle C key now sounds both C4 (middle C) and C5 - an ocvate above.

These examples show both how the extension of a single rank replaces many pipes duplicated in the ranks of a Classical instrument - and a further bit of Unification. As noted - when multiple stops of a similar pipe are used on a Classical Organ - multiple pipes speak the same note - but - not quite- no matter how carefully tuned the pipes are - no two pipes are going to speak the same- they may be quite close - but there will always be subtle differences is pitch, tonal quality, etc. When two pipes "speak" the same pitch (considering only two similar pipes - say two pipes from Flute or two pipes from String ranks) the minor differences cause an interaction - a modulation if you will - that produces yet a third sound. This can vary from subtle shimmering - like violins in an orchestra playing one note - to much more pronounced chorus - much like a vocal section of a choir. Classical instruments produce the very lightest of this effect simple by the nature of it's multiple ranks. Theater Organs do not similarly produce this effect because of Unification. Since the same pipe is used to produce one note - even if called for by more than one key - there is no natural chorus effect. To produce this - Theater Organs often have "Celeste" ranks - which are in fact duplicate ranks such as in a Classical instrumemt. With the number of pipes a premium - very small organs seldom have a Celeste rank - but instruments having 6 or more ranks usually include at least one Celeste rank (usually string). When included - the Celeste rank is intentionally voiced to produce a strong but pleasing chorus - so that one is not aware two pipes are speaking each note (and as a consquence- Celeste ranks are - except in the largest of instruments - a single Unison rank (i.e. 8').

Two things quickly become apparent when Unification is used to practical limits: while the number of pipes and the complexity of the connecting pipework is greatly reduced, the complexity of "connecting" all of these pipes to the manuals (keys) in all of the possible combinations would appear to become a nightmare very fast. Even in our simple example of one 61 key keyboard and one 97 pipe rank - switching of all of the possible key to pipe combinations creates a matrix of several thousand connections - dozens to nearly a hundred needing to be connected and disconnected in a fraction of a second. In organs having three or four manuals (plus pedals) and 30, 40 or more ranks of pipes (again ranging from 61 to 97 pipes each) - a mechanism that can accomplish all of that - at first thought - might seem more magical than practical. However - that mechanism does exist - and is called simply - The relay. While called a "relay" - in reality - a relay for a Theater Organ is actually made of of dozens to hundreds of relays - depending on the size of the instrument.


In the next TechTalk - we'll explore the relay - and how one manufacturer made them, and employed then in several ways.


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