Pipe Length, Scale, and Stop Footage Explained

A footage figure names the speaking length of the lowest pipe of the rank it labels, not the length of every pipe in it. Each pipe up the rank is shorter than the one below, because higher pitches come from shorter speaking lengths, so the label records only where the rank begins. Builders’ glossaries put it the same way: the number in a stop name designates its pitch according to the length of its largest pipe.

On this page, stop means the rank or ranks that one stop control brings into play, and stop control means the knob or tablet itself.

Eight foot is unison because an open flue pipe sounding the lowest C of a manual keyboard is approximately eight feet long, so an 8-foot rank sounds at the pitch of the key played. The other figures follow from octave relationships: a 16-foot rank sounds an octave below the key, a 4-foot rank an octave above, and a 2-foot rank two octaves above. Stop names in several traditions encode the same steps, which is why the Italian Ottava names the rank an octave above the foundation and the English Fifteenth names the 2-foot rank two octaves above it.

The figure is a convention shared by builders, teachers and component suppliers, and it is a pitch label rather than a measurement that holds for every rank. Stopped and harmonic construction both depart from the nominal length, which is the subject of the next section.

A stopped flue pipe sounds approximately an octave lower than an open pipe of the same physical length, so an 8-foot stopped rank is built from pipes roughly four feet long. The label still reads 8 foot because the rank sounds at unison; the number records pitch, not the height of the pipework. This is the standard surprise for anyone who measures a pipe and compares it with the stoplist, and it is also why a stoplist cannot be used to infer how tall a chamber must be. The relationship is approximate rather than an exact halving.

A harmonic flue pipe, pierced with a small hole near the middle of its body, sounds approximately an octave above the pitch a plain open pipe of that length would give, so a harmonic rank is built roughly double the nominal length for its stated footage. A 4-foot harmonic rank therefore stands about as tall as an 8-foot open one.

Stopped construction shortens the body below the label and harmonic construction lengthens it beyond the label, and in neither case does the figure change. It names what the rank sounds, and the body is whatever the construction needs in order to sound it.

Reed ranks carry footage figures too; how a reed pipe’s resonator relates to the pitch its label names is explained on the page about how reed pipes produce sound.

A fraction such as 2 2/3 marks a mutation: a rank that sounds a pitch other than the note played or an octave of it. The fractional footage identifies the interval sounded. Because 8 foot is unison and 4 foot the octave, 2 2/3 foot falls between them at the twelfth above the key, which is why English usage has long called that rank the Twelfth. Other common fractions are 1 3/5, 1 1/3 and 10 2/3. The glossaries of the American Guild of Organists, the Organ Historical Society and the Wicks Organ Company define the term consistently. What the fraction does not identify is the tonal family of the pipes, which may be principal-scaled or flute-scaled; the interval is all the number encodes.

In the Italian tradition stop names are given relative to the lowest Principal of the instrument rather than as fixed footages. Ottava may therefore denote an 8-foot rank on a 16-foot organ, a 4-foot rank on an 8-foot organ, or a 2-foot rank on a 4-foot organ, and a named pitch in an Italian specification cannot be converted to a footage without knowing the instrument’s foundation pitch. The convention is summarized in an Association of Lutheran Church Musicians registration handout, which also records the English side of the problem.

English names carry their own trap. In English usage Principal denotes the 4-foot octave rank, while the German Prinzipal commonly denotes the 8-foot foundation, a classic false friend. Restoration-period English nomenclature ran Diapason, whether open or stopped, then Principal, Twelfth at 2 2/3 foot, Fifteenth at 2 foot, Sesquialtera, Cornet in the treble, Mixture or Furniture, Trumpet and Clarion, a scheme that maps onto continental names without translating directly into them.

Organ stop nomenclature is complicated by the instrument’s long history across many countries, each with its own naming tradition, and every organ is different. When a specification prints both a name and a footage figure, read the pitch from the figure; the name tells you which tradition the builder was working in.

Scale is the ratio of a pipe’s length to its diameter, and it is a principal determinant of tone. Wider pipes sound louder, and narrower-scaled pipes generate more overtones relative to the fundamental and therefore sound brighter. Put the other way around, the larger the diameter of a pipe at a given pitch, the fuller and more fundamental its sound becomes.

Footage and scale are independent quantities. The footage names the pitch, the scale names the proportion, and a shared stop name fixes neither. Scale is not recorded in an ordinary stoplist, so two stops sharing a name may be scaled quite differently and sound quite differently.

A stated scale applies only to the first pipe of a rank, because diameters are reduced progressively up the rank to keep the perceived timbre consistent from bass to treble. The usual description is that the diameter halves around the seventeenth or eighteenth note. The halving point is a design variable rather than a physical constant: Organ Supply Industries, a component supplier, published seventeenth halving as its standard basis in a catalog dated 2006, describing it as Normalmensur with a ratio of one to the fourth root of eight.

Normalmensur is a reference scale established by Toepfer, defined with an internal diameter of 155.5 millimeters, about 6.12 inches, at 8-foot C. It is a definition within one normalizing system, not a measurement of any particular organ, and other suppliers and builders use other scaling systems and other starting scales.

Considerably. John Bishop, writing in The Diapason, gives middle C of an 8-foot Principal as anywhere from one and three-quarter inches to two and a quarter inches in diameter depending on the tonal character desired. That is an illustrative range from one practitioner rather than a survey, but it shows that the same stop name admits materially different pipes. Two organs whose stoplists both read Principal 8 can be built to noticeably different proportions, and nothing in either stoplist will reveal it.

The number does not say whether the rank is open, stopped or harmonic, and the construction changes the tone as well as the body length. Stopped pipes emphasize the odd-numbered partials of the harmonic series, which limits how well they lock into an octave-based chorus compared with open pipes. An 8-foot stopped flute and an 8-foot open principal share a number and little else.

Material and wind pressure are two further variables the number leaves out. Bishop attributes part of the tonal difference between organs to pipe material, writing that hard metal such as tin produces a bright tone and soft metal such as lead a darker one, and that softwoods such as spruce or fir give darker tones than hardwoods such as oak or maple. How much the material itself contributes is debated among acousticians, so this is one practitioner’s account rather than a settled finding.

He also links wind pressure to tonal style: bright, transparent choruses in classic-style organs require low pressures, while the broad, rich voices of a romantic or symphonic organ are produced by high pressures. Neither the metal nor the pressure appears in a stoplist.

Voicing, the adjustments made to each pipe after it is built, actually determines the timbre the pipe produces. That is the decisive reason a stop name cannot fix a tone: two ranks of identical footage, scale and material can be voiced to different ends, and the footage figure has no say in the matter.

The variables a voicer works with belong to the page on how flue pipes produce sound, and no page in this section gives a voicing procedure.

A footage figure printed on a coupler means an octave relationship, not a length: a coupler marked 4 means an octave higher, and one marked 16 means an octave lower. The same numerals appear on speaking stops with a different meaning, which makes coupler lines a frequent source of misreading in stoplists; Brigham Young University’s OrganTutor makes the point explicitly for that reason.

What each coupler does to the keys and divisions it connects is explained on the page about how pipe-organ couplers work.

A specification that reads Principal 8 has told the pipe maker almost nothing yet. Organ Supply Industries’ 2006 catalog required a customer ordering pipework to supply the starting scale, the material, the operating wind pressure, the pitch, whether the toes are open or closed, the windchest type, the dimensions of the room, and voicing instructions before a rank could be made. That list is one supplier’s requirement at that date, and current practice may differ, but it shows concretely which variables are decisions rather than consequences of the label. A stop of a given name is built to order against entries that no stoplist carries, which is why two identically named stops need not be the same stop.

A stoplist states pitch and name and leaves out the rest. From the footage figures you can read the pitch of each rank against the key played and, from the fractions, which ranks are mutations. You cannot read scale, construction, material, wind pressure or voicing, and you cannot infer the height of the pipework or of the chamber, because stopped and harmonic ranks depart from the nominal length.

One more caution applies before counting anything. Authoritative glossaries place the word stop differently. The American Guild of Organists glossary puts it on the knob or tablet that brings a rank into play, while the Organ Historical Society and Wicks glossaries put it on the rank or ranks the control activates. A stop count is therefore not comparable between documents unless the sense in use is stated. This page states at the outset which sense it uses and does not adjudicate between the glossaries; the page on stops, ranks, voices and divisions explains both senses and what they do to the counts.

For the same reasons, work that begins with a stoplist does not end with one. Establishing what a rank actually is means examining and documenting the pipework itself: its construction, its scale, its material, the wind it stands on and the voicing it carries. Those findings, rather than the printed figures, are what a project plan can be built on.