Prior to every concert, the carillonneur adjusts the distance between the clapper and its strikepoint at the side of each bell. This adjustment, made while the performer is sitting at the keyboard, necessitates playing the same bell a number of times so as to regulate wire length. Because this repetitive action is naturally heard by listeners below, it is sometimes assumed that the carillon is "being tuned." Although understandable, this assumption is incorrect. As a matter of fact, the tuning of a carillon is a highly sophisticated and complex process. Unlike the familiar tuning of a violin or piano before a concert, the tuning of a carillon is done while the instrument is manufactured at the bellfoundry and generally is not re-tuned for years.
Bell tuning requires a delicate balance of knowledge of harmonics and technical skills. A brief description of the process might illustrate the degree of expertise involved. Once the size and pitch of a particular carillon have been determined, the actual work of scaling each bell begins on the drawing board of the foundry's draftsman. Because by nature each bell has five distinct pitches, it first must be put in tune with itself and then in tune with all of the other bells which comprise the instrument. Obviously, this distinction makes the carillon one of the most difficult instruments to tune. Every modern bellfounder uses a range of precision instruments to aid in the tuning process, including tone generators and electronic tuners enhanced with computers.
Significantly, the single most important determinant to the correct pitch of a bell is its profile, or exterior shape. This profile is part of a formula which has remained largely unchanged for over three hundred years. `When a bell is cast with the correct proportion of copper and tin (usually about 80 and 20 percent respectively), and is poured into a mold reflecting the correct profile, its pitch already has been determined, to a great extent, because of its size and shape.
Carillon bells differ from most other bells for two reasons. First, carillon bells are made of bronze, while other bells can be comprised of silver, gold, wood glass or clay. Second, carillon bells have many of their harmonics tuned. Even though the human ear can only discern five harmonics, or partials, in a bell, there are actually many more in the upper frequencies. The major difference between carillon bells and the more familiar handbells is that the former are tuned only from the inside. After the bells have been cast and allowed to cool, the bellfounder begins the arduous task of removing metal from the inside of each bell, while maintaining the correct proportion between the harmonics. This process involves inverting each bell and placing it on a slowly rotating table and attaching electronic sensors at numerous locations on the outside of the bell. While the bell rotates slowly, small amounts of metal are removed until the correct tone, singular to that bell, has been achieved. At all times, the five essential partials must be in tune with each other. These partials are the strike tone, hum tone, minor third, fifth, and octave. It is indicative of the complexity of tuning carillon bells that the process of removing metal from one location alters not only that partial, but other partials at the same time.
On larger bells, it is easy to see where the tuning process has taken place by discerning the grooves or rings scored all along the inside of the bell. Generally speaking, the larger the bell, the easier it is to tune because the additional surface area allows for a greater margin of error-there is more room to grind down as needed to achieve the desired sound. Conversely, the removal of slightly too much metal on smaller bells quickly becomes a problem not readily correctable.
One tremendous advance in the last three hundred years of carillon tuning is that the range of the instrument has been extended in both directions. Nowadays, bellfounders routinely tune very small bells (some as small as twenty pounds) and have cast and tuned some very large bells (up to twenty tons). Until the beginning of the twentieth century, most carillons were instruments of between twenty-five and thirty-six bells. The average size of modern carillons is about fifty bells, with a number having sixty and even seventy bells. The single most important reason for the increased size in carillons has been the advances made in tuning bells.
