A Carillon is a musical instrument consisting of at least two octaves of carillon bells arranged in chromatic series and played from a keyboard permitting control of expression through variation of touch. A carillon bell is a cast bronze cup-shaped bell whose partial tones are in such harmonious relationship to each other as to permit many such bells to be sounded together in varied chords with harmonious and concordant effect.
from the Articles of Incorporation of The Guild of Carillonneurs in North America
The first properly tuned carillon was installed in Zutphen, the Netherlands, in 1652. It was the result of the combined efforts of Pieter and Francois Hemony, itinerant Alsatian bell-founders, and Jacob van Eyck, a blind carillonist and recorder player. The tuning of bells had eluded discovery until van Eyck began a series of experiments and his contact with the Hemony brothers was an happy historical coincidence. The Hemonys went on to produce about 50 carillons. Although the transmissions have been replaced, two Hemony carillons (Middelstum, and the Zuidertoren in Amsterdam) have all their original bells four centuries after their founding. After the death of the Hemonys, the only other bell-founder who had success in tuning was Andreas Joseph Van den Gheyn in the mid-eighteenth century. His bells form the basis for the carillons at Nijkerk and Veere, The Netherlands. After the death of these men, the principles of tuning bells were generally lost until the end of the nineteenth century when Arthur Simpson, a rural English cleric became puzzled over precisely what pitch the bell in his church was sounding. He began a series of experiments which resulted in the publication of two articles in the Pall Mall Magazine in 1895 and 1896. The articles were entitled "Why Bells Sound Out Of Tune," and "How To Cure Them." The publication of these papers prompted English bellfounders to cast bells according to the principles Simpson promulgated and the resulting successes paved the way for the amazing increase of carillon installations beginning in the early twentieth century.
The basic problem is this: unlike other western instruments, where a column of air or a string can be divided evenly at various points and the resulting sound predicted, a carillon bell is a wildly vibrating object. That is to say, carillon bells vibrate in all directions simultaneously. Van Eyck discovered (and Simpson rediscovered) the location of nodes on the bell profile that sounded discrete notes of the harmonic series. As a result of their experiments, a single carillon bell actually has five pitches that are tuned in relation to form the one sound.
The most interesting of these pitches is the minor tierce. This harmonic, high in the natural harmonic series, is brought low and into prominence in the tuning of a carillon bell. The result is the somewhat plaintive sound of the carillon, and the sensation that carillons sound 'out of tune.' In fact, they simply use a different tuning system than other western instruments.
While an instrument of two octaves is technically a carillon, a four octave instrument is now generally considered the minimum for a concert instrument. The carillon at Berkeley is a fully-chromatic, five octave carillon.
The carillon is played from a large keyboard containing both manual and pedal keys, similar in design to an organ but much larger. A carillon is very sensitive to the touch of the player, and has the largest dynamic range of any acoustical instrument. The keyboard is linked to the clapper of the bell by a manual transmission mechanism that allows the player great expressive range.