How An Organ Works
A Quick Look at Organ History and Terminology
An organ produces sound by blowing wind into wood and metal pipes. The pipes are held by wooden racks on top of chests. A chest is an airtight box that has small leather valves inside which let wind to the pipes when the organist presses keys at the console. The wind comes from a small centrifugal blower driven by an electric motor. Wind passes from the blower into a bellows or reservoir that regulates the wind pressure. Windlines conduct the wind from the reservoir to the chests.
The small organ shown to the left has 5 rows (5 ranks) of pipes. There are as many pipes in each of those 5 ranks as there are keys in the keyboard, one pipe for each key, each pipe producing a similar tone quality but a different pitch. The first key opens the valve under the longest pipe, which produces the lowest note. Successive pipes are shorter and produce higher notes.
The simplest organ has one rank of pipes and can produce only one tone color. To produce a different color, a second rank of pipes of different shape is required. The organ then has two ranks of pipes, and the console must have two stop controls (drawknobs) that the organist can operate to choose between the two ranks. Adding more ranks of pipes and their corresponding stop controls increases the number of sounds available, as does adding more keyboards.
Manual keys are for the hands. Pedal keys are for the feet. The feet usually play the bass line, which usually means low notes. Low notes are produced by long pipes. However, the Pedal can also play higher-pitched melodies on ranks (stops) that have shorter pipes.
If the connection between the keys and the chests is by mechanical linkage, like the organ shown at the left, the organ has tracker action. If the connections are by low-voltage electric circuits connected to electromagnets, the organ has electric action. If the magnets operate small pneumatic motors that open the valves to the pipes, the organ has electro-pneumatic action.
From Human to Machine
Human beings recognize organs as friend and partner. Both humans and organs use moving air (wind) to produce sound: humans have lungs, organs have bellows. Both move the air past vibrating devices: vocal cords or mouth-blown whistles for humans, whistles and reeds for organs. Both require resonators to amplify the sound: head resonance and whistles for humans, cylindrical resonators called pipes for organs.
Human: human mouth blows whistle.
Machine: bellows blows pipes.
We do not know exactly when whistles (flue pipes) were first blown by a bellows instead of by mouth. Certainly the sort of organ drawn to the right was known in Greece several centuries B.C.E.
The organ as drawn has only three keys and a single row (rank) of three pipes. Each of the pipes in that one row, or rank, produces the same tone color. If more notes are needed, more keys and pipes must be added. If a different tone color is desired, it is necessary to have a second rank of pipes that differs from that first rank, perhaps larger in diameter, perhaps with a different shape, perhaps with a vibrating reed inside.
How Organs Grew
Some European churches in the Middle Ages used hand-held organs to play the notes during choir processions. There are paintings of such organs showing a neck strap, a bellows pumped by the left hand, and a keyboard controlling perhaps a dozen pipes – thus the Portatif, or portable choir organ.
As the number of pipes increased, the Portatif became too heavy to carry, gradually changing into the Positif – remaining in one position, not portable.
In European churches during the Middle Ages, the choir singers sat at the front, or east end, of the church building with the Choir organ, whether it was Portatif or Positif. Gradually, some churches, especially those with very long buildings, put a second organ in the west end of the building. Since more space was available at the west end, away from the choir and altar, those west end organs were able to grow quite large. First there was one keyboard and one rank of pipes. Then a second rank of pipes was added, then a third, etc. Compared to the Choir organs, they were Great organs.
Some of those Great organs grew to be quite large and loud. All the ranks sounded at the same time, their being no way to turn individual ranks off. To obtain contrast, loud vs. soft, two approaches were taken:
- Put the Positif organ near the Great organ. (Two organs = two sounds = two keyboards = Great and Positif) Sometimes the smaller organ was called the Choir organ if it had been used with the choir singers previously. In other cases it was called the Rueckpositiv organ if it sat behind the organist’s back. Still other times it was called the Chair organ, especially if it was placed near the chair or stool on which the organist sat, this being before the time of pedals and therefore before the time of organ benches.
- Add a device that could stop the wind going to one rank of pipes (thus the origin of our term “stop controls” or “stops”).
As time went on, individual stop controls were applied to all the ranks of pipes, making many different combinations of sound possible.
Keyboards for the hands are called manuals (Latin for hand is manus). Keyboards for the feet, called pedals (Latin for foot is pedis), were added in Germany between 1300 and 1500. The pedals in French organs developed later than those in Germany. They played only melody notes until the late 1700’s, when bass-sounding ranks of pipes were added. English organs did not get pedals until the middle 1800’s, more than a century after Bach and Handel.
By the late 1600’s there were organs in north European Hanseatic League cities that had perhaps 60 stops composed of perhaps 90 ranks of pipes controlled by pedals plus 4 sets of manual keys.
Producing a greater variety of sounds
In the 1800’s it became common to place the pipes played from the upper keyboard in a closed box that had shutters that could be opened and closed by the player to “swell” the sound. That keyboard was called the Swell in England and the Recit in France.
Thus the names of the manuals of an English organ in the late 1800’s:
Swell top manual keys
Great middle manual keys
Choir lowest manual keys
The corresponding organ in France in the late 1800’s:
Recit top manual (has swell shutters)
Positif middle manual
Grande(Grande = Great)
Another way to increase the variety of sounds is to employ pipes that have different shapes and different diameters.
Pipes sound like they look. A pipe of large diameter blown softly produces a round, full, complacent tone. That same pipe can be blown harder to produce a big, strong, dominant tone. Another pipe of the same length, and thus producing the same pitch, if it is smaller in diameter, will produce a soft, thin tone.
In organ lingo, the diameter of a pipe is often called its scale, not to be confused with the up-and-down of the musical scale. The large scale (diameter) of the first pipe shown above tells us to expect either a round, flutey sound if the pipe is blown gently or a very strong sound if it is blown harder. (The organ builder controls the amount of wind entering the pipe by adjusting the size of the hole in the toe of the pipe.) The second, third, and fourth pipes, being of moderate scale, will likely be voiced as Principal pipes. The two smallest pipes will be useful as string pipes.
All the pipes shown to the right are known as flue pipes. They have no moving parts. They produce tone in the same way that humans do when they blow across the top of a Coke bottle. The tone comes from the oscillations of air in the resonant column contained inside the pipe.
Incidentally, the metal of a pipe does not resonate, and the type of metal (or whether the pipe is made of wood or metal) is relatively unimportant.
Pipes are still made by melting tin and lead together in an iron pot. The metal is poured out to cool in a thin sheet on a table. The sheet is cut by hand into rectangles that are then formed into tubes. With the addition of the foot and the mouth, each tube becomes the whistle that we call an organ pipe.
By the 1600’s all the major types of pipes had been invented. Significant changes since then have not been in the pipes but in the mechanism, such as electric blowers replacing human-pumped bellows, and keys opening valves via electric or pneumatic assistance rather than directly.
Most of the pipes in an organ are flue pipes, but about one-fourth of the pipes are called reed pipes because they produce sound by blowing wind past a vibrating reed or tongue.
Examples of reeds: Trumpet, Oboe, Clarinet.
The tone of reed pipes is more distinctive than that of flue pipes.