Assessment of fresco detachments through a non-invasive acoustic method

In artistic frescoes, the partial detachment of plaster portions is a typical and serious problem. At present, the standard procedure of diagnosis consists of manual inspection, but produces only approximate information. This work describes in more detail an acoustic, non-invasive, experimental technique of diagnosis, which has been already proposed by the authors. It is based on the acoustic-structural interaction which occurs when an acoustic duct is excited by a loudspeaker and closed by the investigated fresco at the opposite end. The analysis of the acoustic pressure field and of its alterations allows the assessment of detachments, since the acoustic modal parameters are affected by the acoustic system boundary conditions, i.e. the portion of fresco closing the duct. Experiments carried out on fresco specimens show the potential of this acoustic method.