Hard vibroacoustic metrology for intangible cultural heritage: The case of church bells tuning

This work presents a vibroacoustic metrology approach to investigate the tuning systems of historical church bells as expressions of intangible cultural heritage. Focusing on eight bells from Salerno Cathedral, dated between the 13th and 19th centuries, we performed spectral analysis to identify partial frequencies and compared them against reference scales derived from five historical temperaments. Results indicate, prior to the 19th century, when the well-tempered system gradually became the standard tuning reference in Western music, a clear and repeated alignment with the 1/4 comma meantone system. This result suggests that bell founders relied on stable and culturally informed tuning references, transmitted through craft practice rather than written documentation. Thus, the act of tuning emerges not only as a physical adjustment, but as an immaterial expression of shared acoustic knowledge. In other words, the experiential knowledge developed by bellmakers, despite its uncodified nature, allowed to refine the construction techniques to obtain a repeatable result in terms of functionality with desired characteristics. By revealing this connection through a non-invasive analysis, the study contributes to the understanding, documentation, and safeguarding of the intangible sonic dimension of this cultural heritage object.