Abstract:
The acoustical characteristics of a room are traditionally determined using omnidirectional impulse response measurements, yielding information about sound reflections in terms of magnitude and time, but not direction. However, the direction of reflections (early or late) is of great interest in this application, and thus the need for practical measurement systems to determine this. A number of directional impulse response measurement systems have been reported in the literature, but most incorporate proprietary, expensive or impractical hardware, and frequently, specific c details of their capabilities and limitations have not been made available. This has effectively limited their use to the researchers who developed them. This thesis presents an investigation into the determination and display of 3D room impulse responses using relatively inexpensive, commercially available and practical hardware, notably the Core Sound TetraMic A-format microphone array. Further, straightforward processing routines are adopted. The performance of this system in a highly controlled environment (i.e., an anechoic chamber) is presented. It is shown that if the impulse response measurements are low pass ltered prior to subsequent processing, the accuracy of directional estimation is generally within ±5° . Further, the accuracy of time estimation in the early reflection region is limited only by the sample rate of the recordings. The situation where early reflections are overlapped in time is presented and it is shown that similar levels of directional accuracy are achievable provided correlation techniques are employed to identify these reflections. The accuracy of magnitude estimation is not a focus of this work and requires further investigation. The measurement system presented in this work is highly accessible to practitioners, and the findings presented should permit them to use such a system in real world environments, and to interpret the results with a high degree of confidence. By way of example, the use of the system presented in this thesis in a real world environment, namely the Music Theatre at The University of Auckland, is presented. It is shown that there is close correspondence between the acoustic reflections estimated by the measurement system, and the room's architectural features.