Dictionary of Music - Birding America

288 organrequired, each with five or six stops, plus a pedalboardwith two to five stops. Three and four manualsare quite common.Since each of the keyboards is more or less acomplete organ—that is, it could be played withoutnecessarily making use of the other keyboards—they often are called organs or divisions. They arenamed (except for the pedal) in order of their importancein British and American organs: PEDALORGAN, GREAT ORGAN, SWELL ORGAN, POSITIVE (orCHOIR) ORGAN, SOLO ORGAN, and ECHO ORGAN. Anorgan with but two manuals will practically alwayshave a great organ and a swell organ, the swell manualbeing placed above the great manual. If a third isadded, it is usually the positive (or choir) organ,whose manual is placed below that of the greatorgan. The solo manual is usually placed above thatof the swell, and the echo manual above the solomanual. The positive (choir) organ originally was aseparate instrument that in time became part of themain case.Except for the pedal organ, whose range is lowerthan that of the other divisions and whose pipes arenearly always connected to the pedalboard, assignmentof pipes and stops to the different keyboards isfairly flexible. Usually the great organ has the loudeststops and the swell organ the softest. In otherrespects the assignment of pipes to the different divisions,although it depends in part on tradition, varieswidely, and very few organs are exactly alike. Adevice called a coupler makes available the stops ofone division on the keyboard of another. By drawinga certain coupler the organist can, for example, useon the pedals all the stops of the swell. Further, anoctave coupler will bring into play the note anoctave higher than the one played (plus the one ordinarilyproduced), and a suboctave coupler will similarlyprovide the note an octave lower.Organ pipes are open at the top and tapered atthe bottom, where the air is blown in. The upper endof the pipe is surrounded by an adjustable sleeve (inan open pipe) or is closed by an adjustable stopper(in a closed pipe); either device makes it possible tochange the length of the air column slightly for tuning.Organ pipes range from half an inch to thirtytwofeet in length. The shorter a pipe, the higher itspitch. An open pipe (open at one end) that is two feetlong will sound middle C; for an octave lower, itmust be four feet long; for an octave higher, it mustbe only one foot long. In shape the basic organ pipe,called a flue pipe, resembles a whistle. If its SCAL-ING (diameter) is fairly large in relation to its length(if it is fairly “fat”), the pipe’s tone is muffled anddull; if its scaling is small (if the pipe is slender), thetone is much brighter. An open flue pipe that isoverblown (has air forced into it under more pressurethan usual; see OVERBLOWING) sounds anoctave higher than its ordinary pitch; a stopped fluepipe (closed at one end) sounds an octave plus a fifth(a twelfth) higher when it is overblown. In the fifteenthcentury another kind of pipe, the reed pipe,was introduced. Unlike the flue pipe, in which airpasses across a slit-shaped opening and causes theair column inside to vibrate, the reed pipe has abeating reed, a small piece of brass attached at oneend that is made to vibrate by air and in turn passesits vibrations on to the air inside the pipe. Reedpipes are normally cone-shaped; when they arecylindrical (in straight tube shape) they sound anoctave lower.Flue and reed pipes are further divided into categories,some of which are named for the tone colorof the instrument they resemble (often only in avague way), and all of which are based on minutedifferences in size, shape, and material of the pipes,which alter the proportion of the harmonics (overtones)and therefore the tone color. The main kindsof flue pipe are: diapason, made in all sizes (allpitches) and together producing the characteristicsound of the organ; there are further subdivisions infig. 171 p/u from p. 299