A brief guide to the Pipe Organ


~ by Geoffrey Redman


Photo of lots of pipes


On this page:~


So how does an organ work?

        In order for it to work, an organ requires wind~ and lots of it!  Nowadays, the wind in the bellows is supplied by electric blowers but in days of old, bellows had to be pumped by hand.  The wind from the bellows is controlled by the action, that determines which pipes are allowed to speak, and which pipes are to remain silent.  Since it is the length of a pipe that determines the pitch of the sound it makes, there must be at least one pipe for every note on the keyboard.  To get the different colours of sound and varying degrees of loudness, there needs to be a lot of pipes.
        There are many, many different types of organ pipe and each type has its own timbre and name.  For example Stopped Diapason, Lieblich Flute, Dulciana and Principal.  Such a vast number of varying designs has come about through experimentation and a desire to emulate other musical instruments like the Trumpet or Oboe, Flute or Violin.  The result is that the organ is both the loudest and the quietest of all instruments.  However, all organ pipes belong to one of two families~ the Flue pipes and the Reed pipes.  An example of the sound produced by a reed pipe is the Trumpet.  An example of the sound produced by a flue pipe is the Flute.
        There are many other variables that control the sound other than the design of pipe.  For example the wind pressure; the materials used in construction and even the fabric of the building in which the organ is installed.


How do the pipes work?

        As mentioned above, there are two main families of organ pipes~ Flue pipes and Reed pipes.  Here, we look at a simple Flue pipe.
        Wind enters the pipe at the Tip (a) and fills the Foot of the pipe (b).  Since it is under pressure, the wind is forced through the narrow gap called the Flue or Wind-way (d) between the Languid (e) and the Lower Lip (c).  The thin sheet Diagram of a Flue pipe of air which leaves the Flue, rushes across the Mouth of the pipe (f) and flows past the front of the Upper Lip (g) into the room.  This flow of air across the Mouth pulls air from inside the Body of the pipe (h) along with it, out into the room and so the column of air inside the Body of the pipe, which until now has been at rest, begins to travel downwards.  At this point, there is a large amount of air leaving the Mouth of the pipe.  There is the air coming from the Foot (b) together with the air from the Body (h).
        The air does not continue behaving in this fashion for very long because as the air column moves downwards, it creates a depletion of air molecules at the top of the pipe.  When the force of the depletion becomes greater than the force of the air flow from the Flue, the column of air inside the Body stops moving downwards and begins ascending.  As the air column moves back up the pipe, a depletion of air molecules now develops at the Mouth and so the air coming from the Flue, which until now has been flowing across the Mouth and into the room, is sucked back into the Body of the pipe to maintain an even air pressure.  At this point, there is no air leaving the Mouth of the pipe, in fact some air from the room may even be drawn in through the Mouth.  And so we return to the beginning of the cycle.  It is the movement (oscillation) of air molecules up and down the Body of the pipe that produces the sound waves.


Length of pipes

        The pitch of the sound produced is determined by the length of the body of the pipe~ just as the pitch of a note made by a stringed instrument is determined by the length of the string hit or plucked.  A short string will create a higher pitch than a long string~ a short pipe will create a higher pitch than a long pipe.  So the longer the pipe, the lower the note; the shorter the pipe, the higher the note.
Photo of some Reed pipes         Pitch can be expressed in terms of the frequency of the vibrating column of air in the pipe.  Middle C on a piano has a frequency of about 256 Hertz (cycles per second) and to produce the same pitch on an organ, a 2 foot organ pipe would be required.  As it happens, if the length of a pipe is doubled, the frequency is halved and the pitch goes down an octave.  So the pitch of a 4 foot pipe will be Tenor C and an 8 foot pipe will produce a Bass C.  Going the other way, a 1 foot pipe will produce a Treble C and a ½ foot pipe will produce a Top C and the octave above that is a 3 inch pipe.
        The longest pipe in an organ is usually in the pedal department and on most organs is 16 foot in length.  Cathedral organs usually have one or two 32 foot ranks, the 32 foot pipes having a frequency of just 16 Hertz!  The longest pipes in existence are 64 foot long, but these enormous pipes are few and far between.  As far as I know, there are only two organs in the world having pipes that are actually 64 feet in length.  The famous Hill organ in Sydney Town Hall which has a 64 foot Contra Trombone and the colossal Midmer-Losh organ in Atlantic City which has a 64 foot Diaphone-Dulzian.
        Just to confuse things a little, some pipes are stopped which means that the top is blocked off by a stopper. This has an harmonic effect and the sound heard from a stopped pipe is an octave lower than its open counterpart.  For example, when it says Stopped Diapason 8' on the Stop Knob, the longest pipe is actually only 4 foot long.


Close-up photo of some very small pipes


What are Stops?

        The Stops are used to stop the air from flowing through the pipes.  The Stops are part of the action that controls which pipes are allowed to speak and which are to remain silent.  The Stop action links the Stop Knobs in the Console to the Sliders in the Soundboard.  The actual Slider is a piece of wood with holes drilled in it to line up with the feet of the pipes.  The Slider can move either in or out~ when it is in, the holes don't line up with the pipes and the air is stopped from getting through.  When it is pulled out, the holes do line up and air is allowed to pass through to the pipes.  There has to be one Stop for each rank of pipes.
        Without organ Stops, whenever a key is pressed on the keyboard, every pipe above that note on the Soundboard would speak!  Before organ Stops were invented, that is exactly what happened.  This chorus of pipes for every note on the keyboard is called "Blockwerk".
        Organ Stops are identified at the Console by the names of the pipes that they control.  So the Stop that controls the Open Diapason rank has "Open Diapason" inscribed on the Stop Knob.  Also inscribed is a number that corresponds to the length in feet of the longest pipe within that rank, so that the organist has some idea of the pitch.  If the pipes are stopped, the longest pipe won't actually be as long as it says!  It will be half the length, because a stopped pipe sounds an octave lower than its open counterpart.  However, the length inscribed on the Stop Knob is always the equivalent open length.
        Many people use the term "Stops" to identify the different sounds produced by an organ or to describe a particular set of pipes.  For example, "The trumpet Stop is out of tune again!", or "That's a nice Stop, what's it called?"  This is not strictly correct because it is the pipes that make the sound, the Stops merely control which pipes are allowed to speak.


What are Ranks?

        The pipes in an organ are grouped together in rows or ranks according to the particular sound that the pipes make.  Each rank has enough pipes for every note on the keyboard and so there are usually 61 pipes in a rank.
Photo of some Nazard pipes         Ranks are identified by the length of the longest pipe in the rank.  For example, a rank of Open Diapasons (8 foot) will hold pipes varying in length from a couple of inches to 8 feet.  In this example, the lowest note is produced by the 8 foot pipe and so this rank is referred to as the 8 foot Open Diapason rank.  As already mentioned, it is this name that appears on the Stop Knob in the Console.  A Stop Knob with "Principal 4" inscribed, controls the 4 foot Principal rank.
        Sometimes pipes are named according to the interval between them and the 8 foot pitch.  For example, a 2 foot Flageolet produces a note that is fifteen notes higher up the scale than an 8 foot pipe (a interval of a fifteenth).  This means that when a middle C on the keyboard is pressed, with only the Flageolet Stop out, the note that is heard is actually a top C (two octaves higher).  So it is called a Fifteenth.
        The Nazard pipes sound a twelfth higher than the note that is being played and the inscription on the Stop Knob will read "Nazard" or "Twelfth".  If a length is inscribed, it would be "2 2/3" because that's the length of the longest pipe in the rank (2 foot 8 inches).  If a Nazard middle C is pressed on the keyboard, a treble G is what we would actually hear!  The Nazard is referred to as a Mutation Stop which means that it sounds odd when played on its own.  However, when played together with another rank, it can enhance the colour of sound.


Different types of action

        The action is the system that is used to allow the organist to control the instrument.  There are two parts of an organ that are controlled by the action.  The first is the Stops and the second is the Pallets.  In some organs the type of action used is the same for everything and in other organs there might be one type of action for the Stops and another type of action for the Pallets.

Tracker action

        Tracker action, or mechanical action as it is often called, is the oldest type of action.  It does not require any electrical apparatus for it to operate because the link between the organist and the Pallets is completely mechanical.  A series of levers and connecting rods transfers the movement from the keys to the Pallets. 

Electropneumatic action

        This type of action uses electric current between the manuals and the Soundboard and then pneumatic motors to actually open the Pallets.  Pressing a key on the keyboard completes an electrical circuit and the corresponding solenoid is energised.  The solenoid releases air from a pneumatic motor which opens the Pallet for that note.


Bibliography

BICKNELL, Stephen. The history of the English organ. Cambridge : Cambridge University Press, 1996.

BONAVIA-HUNT, Noel. The church organ. London : William Reeves, 1920.

BONAVIA-HUNT, Noel. Modern organ stops: a practical guide to their nomenclature, construction, voicing and artistic use with a glossary of technical terms relating to the science of tone-production from organ pipes. London : Musical Opinion, 1923.

CLUTTON, C. and NILAND, A. The British organ. London : Batsford, 1963.

DICKSON, W. E. Practical organ-building. Portsmouth : Bardon Enterprises, 1997.

NORMAN, Herbert and NORMAN, John. The organ today. London : Barry and Rockliff, 1966.

SUMNER, William. The organ. 3rd Ed. - London : Macdonald, 1962.

THISTLETHWAITE, Nicholas and WEBBER, Geoffrey. The Cambridge companion to the organ. Cambridge : Cambridge University Press, 1998.

WHITWORTH, Reginald. Organ stops and their use. London : Pitman, 1951.




 

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