Different Times Bring a Demand for a Different Bonshou Tone
After a Bonshou bell has been cast and polished, it is not simply shipped off for delivery. First, it is left outside for at least two months and for as long as a year to experience the wind, rain and other elements. Copper and tin, two metals with different properties, are mixed together during the casting and pouring process, and it takes at least two months for the metal alloy that they form to stabilize. Even after the elements of an alloy have been mixed together, changes continue to take place at the molecular level, and the alloy gradually reaches a state of equilibrium as it expands and contracts with outdoor temperature changes – a lesson learned from the university professor with whom the Iwasawa Bell Company carried out its joint research project.
The process of exposing a bell to the outdoor elements is referred to as yōjō, or “becoming healthy” and it has been noted that bells exposed to the climate conditions of Kyoto will develop a particularly pleasant tone. To know whether this process will take two months or a full year, it is necessary to listen to the bell. However, since striking the bell is an act that causes it to vibrate, it is not abruptly hit with full force, but is instead rung lightly at first, and then with increasing strength. A Bonshou bell is more delicate than it might appear.
Transforming the sound of a Bonshou bell into data can be accomplished by converting the waveforms of the bell's vibrations into data, or by recording and documenting the sounds that are produced, but the most important test involves considering how the sound of the bell will register on the human ear. In order to do this, the Iwasawa Bell Company hangs Bonshou bells at the sites where they will eventually be installed permanently, and makes sound recordings from a certain distance away which are later converted into data. A bell located in a mountain temple that is open on one side and surrounded on the other three by woods will naturally produce a sound different from that of a bell at a concrete wall-enclosed temple in the middle of Tokyo, and these sounds will be perceived differently by the human ear. For a Bonshou bell, an earthen floor and plaster walls are said to constitute the ideal environment.
Recently, there are some who seem to consider the sound of Bonshou bells as “noise.” The sounds that people prefer today are not the same as they once were, and there is a tendency to prefer soothing sounds over those that echo far and wide. These “soothing” sounds seem to be in the 100-110Hz range, which is where the tones of gagaku court music fall. These are the frequencies of a grandmother singing a lullaby, or a baby sleeping peacefully, or other sounds that we all find calming. We now know enough to understand that our changing times have brought a demand for a different Bonshou tone, but as we consider how to evaluate and utilize our findings on the sounds that reach our ears, we are left with many questions to ponder.
[Allowing the Bonshou bell tone to mature]
After a Bonshou bell is completed, it is exposed to wind, rain and other outdoor elements for at least two months and up to as long as a year. The copper-tin alloy from which a bell is cast requires time to achieve equilibrium, and outdoor exposure is an important element in the maturing of the Bonshou tone.