A Closer Look at the Pipes

Sound Characteristics of Stops

The beauty of the organ is contained in the wide variety of tonal colors available through all the different kinds of pipes. There are hundreds of stops available, limited only by the builder's imagination. The variety in tonal colors is made possible through scaling which is the proportion between the length and width of the pipe. Two metal pipes with the same length but different widths will have different tones. Stops can be grouped according to the two types of pipes: Flues and Reeds.

Flue Pipes

Flue pipes make up the majority of pipes on the organ. These pipes have a mouth which is a hole in the front of the pipe. The air flows up from the foot, the part resting on the wind chest, and out the mouth. As the air flows across the mouth, it hits the lip (labia), which is the edge of the hole. This causes the column of air inside the pipe to vibrate and sound is produced. (Ritchie and Stauffer, p.373).

Very large flue pipes can have trouble producing a stable tone because the mouth is so large. Builders often put tabs on either side of the pipe's mouth to direct the air as it flows out of the pipe. These tabs are ears. In this picture, you can see a full view of the mouth with ears circled in red. The parts circled in yellow are the ears themselves. Sometimes a metal rod will be attached to the ears so that it runs lengthwise in front of the mouth. This rod, called a beard, also helps to focus the sound on large flue pipes.

There are several families of pipes within the flue pipe group: Flutes, Principals, and Strings. These are not meant to imitate orchestral sounds but can sometimes suggest them.


Flutes are made of wood or metal. Flutes have a clear sound, much like the flute in an orchestra and few overtones. Their scalings are the widest of all pipes so they are fairly wide in proportion to their length. They can be open, stopped, or tapered.

Stopped flutes have a more hollow tone than the open flutes. The stopper in the top enables them to be half the length of an open flute pipe but still produce the same pitch. Tapered flutes produce an unusual sound because they are wider at the bottom and narrower at the top. Their length is somewhere between an open pipe and a stopped flute of the same pitch. Their sound is a crossover between a flute and string. Think of it as a flute with a nasal tone to it. Because their sound is neither true flute or true string, they are also known as hybrid stops. Some examples of the names of flutes are Rhorflote, Bourdon, and Spitzflote (Ibid., p.373-75).


Principals are the strongest sounding flue pipes on the organ. They are usually made of metal but some are occasionally made of wood. Wooden principals were more common in the past with names like Melodia or Open Diapason.

Principals are more narrowly scaled than the flutes which gives them a brighter sound. Some common principal names are Montre, Prestant, Octave, and, of course, Principal. The mutations and compound stops are also composed of principal pipes. Common mutation names are Tierce and Nazard. Sample names of compounds, or mixtures, are Fourniture, Plein Jeu, Cymbale, and Mixture. For more on mutations and compounds, see Pitch Levels of Stops.


Strings are even narrower than the principal and produce a thinner sound (Ibid., p.375). Although it does not resemble the stringed instruments such as violin, the string pipes can be used to produce a warm sound. In the Romantic Period (approx. 1800-1900), it was common to build organs with many string stops on every division. Viola, Viola da Gambe, Violone and Quintadon are some common names of string stops.

The celeste is a popular type of string stop. It is tuned slightly sharper than the other pipes so the sound wavers slightly when it is used with properly tuned pipes. The notes do not actually sound out of tune and the effect is a rich sound. The celeste is not meant to be used alone and the organ builder often designs a string stop tuned at normal pitch to be its partner. On some older organs, pulling out the celeste draw knob automatically pulls out the partner string stop. Some common names are Voix Celeste and Unda Maris. Sometimes an organ may have a flute celeste. Do not confuse these with string celestes. This is a flute stop tuned slightly sharp and its partner stop is another flute. The wavering sound is less pronounced than and not as warm as the string and string celeste.

Reed Pipes

Diagram of a Reed Pipe

Reed pipes do not produce sound in the same way as the flue pipes. It is imitative of single reed orchestral instruments like the clarinet. The reed pipe has a metal tongue (the reed) resting against a shallot. A small removable wedge holds the tongue against the shallot which is connected to a block. This whole segment of the pipe fits inside a boot, which is the part of the reed pipe visible from the outside and rests on top of the wind chest. A tuning wire goes through the block and fits tightly against the tongue. Above the boot is a flared pipe, the resonator, which amplifies the sound. The resonator can be open or partially closed, or fully closed.

When the wind enters the bottom of the pipe, it causes the tongue to vibrate against the shallot. The sound this produces is amplified by the resonator. Reeds have a very strong sound but do not sound like their orchestral counterparts. The trumpet family of reed pipes lacks the brassy sound of orchestral trumpets but is bolder and more penetrating. Some of the softer organ reeds in the trumpet family are somewhat similar to the double reed orchestral instruments. Common trumpet reed names are Posaune, Bombard, Trumpet, and Clarion. The softer reeds are Bassoon, Fagott, and Oboe. Some reed stops are meant to be used as solo stops and will imitate orchestral instruments. Some of these are the Clarinet, English Horn, and French Horn.

Baroque reed pipes included those in the trumpet family but they also used reeds with half-length resonators. These were not as full and buzzy as the trumpet family but were still bold. They were often soloistic. Some examples are Cromorne and Schalmei (Ibid., p.375).

Now that you know more about the names of the stops, you can visit the Pitch Levels page to learn about the number in a stop's name.

Glossary Resources

This site is part of the Pipe Organ Education Project. © Copyright 1996-2001 by Marya J. Fancey.