Piezoelectric electret films as vibration sensors for musical instruments

We present a measuring technique for radial oscillations of tube walls that are excited by variations of the internal air pressure. As an example the oscillations of organ-pipes walls were investigated by means of piezoelectric polymer films that were slightly tensioned around the pipe bodies. With patterned and uniform sensors, respectively, the well-known elliptical oscillations of the cross section as well as an additional monopole breathing of the organ-pipe body were detected. For the monopole breathing, a close relationship between the pressure distribution of the air-column resonances inside the pipe and the amplitude of the circumference oscillations along the pipe was observed.