Acoustic imaging in enclosed spaces: Analysis of room geometry modifications on the impulse response

Abstract

Sound propagation in enclosed spaces is characterized by reflections at the boundaries of the enclosure. Reflections can be wanted in the case when they support the direct sound or give a feeling of envelopment or they can be unwanted when they lead to echoes and colouration. When measuring multiple impulse responses in an enclosed space along an array the reflections can be mapped to the reflecting objects. Similar to seismic exploration, medical diagnostics, and underwater acoustics, an image of the reflecting objects is obtained in terms of reflected energy. The imaging process is based on inverse wave field extrapolation with the Kirchhoff–Helmholtz and Rayleigh integrals. The inverse of the imaging process recreates the measured impulse responses from the image and it allows one to remove or alter reflecting objects in the image and investigate their influence on the wave field in the enclosed space in a physically correct way. This can be verified by reimaging the altered wave field. Preliminary results from listening tests for the perceptual evaluation are presented. They indicate that the influence of a reflecting object can only be perceived in its close proximity.