Directional room impulse response measurement

Klein, Johannes Christian; Vorländer, Michael (Thesis advisor); Rafaely, Boaz (Thesis advisor)

Berlin : Logos Verlag (2020)
Book, Dissertation / PhD Thesis

In: Aachener Beiträge zur Akustik 34
Page(s)/Article-Nr.: 1 Online-Ressource (XI, 222 Seiten) : Illustrationen, Diagramme

Dissertation, RWTH Aachen University, 2019

Abstract

Measured room impulse responses are inextricably linked with the distinct directivity patterns of the applied measurement sources and receivers. For the measurement of standardized room acoustic parameters these patterns are required to be omni-directional to ensure the comparability between measurements. This approach waives an abundance of information about single reflection paths, as well as the possibility to analyze and auralize the acoustic scene in relation to specific real-world sources and receivers. The impact of directivity patterns on the human perception of a signal is easily understood. The most intuitive example is the change in the perceived tone during a walk around a musician playing a highly directive instrument such as at rumpet. The effect can be described as a direction-dependent filter. It is straightforward to imagine the influence of the source and receiver directivity on reflection paths and a room acoustic analysis. Directivity patterns of any sort can be represented as spherical wave spectra by decomposing their angular functions into orthogonal spherical harmonics. In this domain, the complexity of such patterns can be regulated and uniquely specified. The sensitivity of room impulse responses, room acoustic parameters and subsequently of human listeners to a changing level of detail of a directivity is evaluated in this thesis. The measurement of directional room impulse responses as a set of measurements with unique directivity patterns can retain the directional information of an acoustic scene. Ideally, such a measurement consists of one session and allows for the flexibility of choosing the desired directivity patterns in post-processing by combining different impulse response sub-sets. Such a procedure requires specialized measurement arrays. The results can be used to analyze the room in relation to specific source and receiver directivity patterns or single reflection paths. Physical constraints and measurement artifacts hinder and feedback into the development of the instruments and methods. This thesis explores these limits, focusing primarily on the design of suitable sources allowing for directional room impulse response measurement procedures with variable directivity.