Campanology - Shape and Tuning

Shape and Tuning

"A bell is divided into the body or barrel, the ear or cannon, and the clapper or tongue. The lip or sound bow is that part where the bell is struck by the clapper." The traditional profile (or shape), hollow cup with wide flaring lip, of a bell is determined by the acoustic properties sought. The tone of a bell is increased with the depth of the bowl. Bells are generally around 80% copper and 20% tin (bell metal), with the tone varying according to material. Tone and pitch is also affected by the method in which a bell is struck. It will be noticed that in Asian large bells are often bowl shaped but lack the lip and are often not free-swinging. Also note the special shape of Bianzhong bells, allowing two tones. The scaling or size of most bells to each other may be approximated by the equation for circular cylinders: f=Ch/D2, where h is thickness, D is diameter, and C is a constant determined by the material and the profile. Previously tuned through chipping, bells are now tuned after casting with vertical lathes by paring out the inside to flatten or edge to sharpen, with sharpening best being avoided.

"Good tone means that a bell must be in tune with itself." A bell is generally considered well-tuned if it corresponds to certain standards regarding its partials and thus proportions. These partials or elements of the sound of a bell are split up into hum (an octave below the named note, see subharmonic), strike tone (tap note, named note), tierce (minor third), quint (fifth), and nominal (octave). Further notes include the major third and perfect fifth in the second octave. "Whether a founder tunes the nominal or the strike note makes little difference, however, because the nominal is one of the main partials that determines the tuning of the strike note." A heavy clapper brings out lower partials (clappers often being about 3% of a bell's mass), while a higher clapper velocity strengthens higher partials (0.4 m/s being moderate).

On the theory that pieces in major keys may better be accommodated, after many unsatisfactory attempts, in the 1980s, using computer modeling for assistance in design by scientists at the Technical University in Eindhoven, bells with a major-third profile were created by the Eijsbouts Bellfoundry in the Netherlands, being described as resembling old Coke bottles in that they have a bulge around the middle; and in 1999 a design without the bulge was announced.