Acoustic holography of musical instruments using radiation directivity method.

Abstract

Static and time-dependent acoustic holography is applied to the radiation of musical instruments using the acoustic camera developed at the Institute of Musicology consisting of 128 microphones simultaneously recording at a 48-kHz sample rate. Here a radiation directivity method was developed suiting the great amount of microphones as well as the high sampling frequency. It uses not only the radiation strength but also the radiation directivity pattern of 128 points on the geometry as a dependent variable. This does not only allow for a precise reconstruction of the vibration of the instruments but also results in a detailed description of the radiation directivity for the overall geometry or for each radiating point individually. Furthermore the time-dependent reconstruction avoids any temporal integration and reconstructs the vibration of the geometry with the samplerate precision. With this method the different role and strength instrument parts have in the overall body radiation, scattering effects caused by geometrical inhomogeneities, and time-dependent initial transients reconstructed as radiation patterns were investigated. The material as well as the air parts of the instrument are considered simultaneously, i.e., with guitars or violins, the enclosed air radiating through the sound holes is investigated in relation to the surrounding plates.