The 2025 IEEE International Ultrasonics Symposium

One hundred and twelve meters above the city of Utrecht, the Dom Tower houses one of the most significant and heaviest bell ensembles in Europe, in a total of 49 tons of bell bronze which uniquely represents the key milestones in the history of bell tuning.

Based on empirical knowledge acquired through trial and error, bell tuning gradually evolved with the understanding that certain vibrational modes—specifically the first five—must align with fixed frequency ratios to produce a harmonious tone. For carillons, this internal tuning must be further refined across multiple bells to ensure accurate musical scales. Another distinctive aspect of bell acoustics stems from their near-axial symmetry. Inevitably, small imperfections introduced during the casting process disturb the degeneracy of normal modes, resulting in audible beats in the radiated sound, an effect known as "warble". Additionally, the perceived pitch—or strike note—remains a complex psychoacoustic phenomenon, often arising from virtual pitch effects rather than a single vibrational mode. These intricacies made bell tuning a rare and closely guarded craft, mastered by only a few founders over the centuries.

This presentation will explore more than ten centuries of gradual transformation and development of bell design and tuning through the lens of the exceptional example of the Utrecht Dom Tower, emphasizing how collaborative work between scientists and bellfounders shaped the art of bell making since its early mystical and secretive origins to the most recent scientific advances, where physical modelling, optimization techniques, psychoacoustics, and other state-of-the art engineering strategies play a central role.