Localization and tracing of early acoustic reflections in enclosures

Aalto University, P.O. Box 11000, FI-00076 Aalto www.aalto.fi Author Sakari Tervo Name of the doctoral dissertation Localization and tracing of early acoustic reflections in enclosures Publisher School of Science Unit Department of Media Technology Series Aalto University publication series DOCTORAL DISSERTATIONS 143/2011 Field of research Acoustics Manuscript submitted 23 August 2011 Manuscript revised 9 November 2011 Date of the defence 13 January 2012 Language English Monograph Article dissertation (summary + original articles) Abstract Objective room acoustic studies are conducted by measuring room impulse responses. The standard techniques include the use of an omni-directional source and, in most cases, one omni-directional microphone. This approach is well defined when measuring the standard room acoustic parameters.Objective room acoustic studies are conducted by measuring room impulse responses. The standard techniques include the use of an omni-directional source and, in most cases, one omni-directional microphone. This approach is well defined when measuring the standard room acoustic parameters. Recently, early reflections, the first arriving sound waves in the room impulse response after the direct sound, have gained attention in research. The spatial location of the early reflections, i.e., the location of the image-source, can be used in room acoustic studies, auralization, room geometry inference, and in-situ measurement of acoustic properties of surfaces from room impulse responses. The location, however, cannot be obtained from the standard room impulse response measurement. Therefore, special microphone array techniques have been used for spatial analysis of room impulse responses. This thesis studies the localization of early reflections. Firstly, a measurement technique of room impulse responses with directional loudspeakers is proposed. This allows better spatial and temporal separability between the reflections than the standard omni-directional loudspeaker. Secondly, the use of microphone array techniques on the localization of early reflections is studied. Several techniques used in other localization tasks are transformed and applied for the localization of early reflections. In detail, the combination of time of arrival and time difference of arrival is researched. Moreover, interpolation of the time difference of arrival estimation function is proposed. The use of sound intensity vector based localization is also considered. Finally, novel ad-hoc localization techniques for early reflections are proposed. Results for theoretical, simulation, and real data experiments are presented.