Modelization of mechanical vibrations in organ pipes by independent component analysis

Abstract

Several experiments have been carried out to investigate the mechanical vibrations generated by an organ pipe. Measurements were made by using Laser Doppler Vibrometry. It is a not-invasive optical measurement technique which allows to detect pipe-wall vibrations. The mechanical vibration field is compared with the acoustic field. Namely, we study the behaviour of these fields when they are excited by different levels of pressure. Strong analogies have been evidenced by using techniques in time e frequency domain supporting the assumption that the pipe is not a passive resonator. The challenge is to understand the complex mechanism of coupling between modes of air and eigen-modes of pipe that produces the sound. Here, we present, in first approximation, a low dimensional dynamical system which describes the main characteristics of pipe-wall vibrations. What is interesting is that the same low dimensional dynamical system is able to reproduce also the recorded acoustic field, implying that wall vibrations and acoustic pressure field are strictly related one to each other.