Modelling and Order of Acoustic Transfer Functions Due to Reflections from Augmented Objects
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Research Article Modelling and Order of Acoustic Transfer Functions Due to Reflections from Augmented Objects Martin Kuster1, 2 and Diemer de Vries1 1 Laboratory
of Acoustical Imaging and Sound Control, Department of Imaging Science and Technology, Faculty of Applied Sciences, Delft University of Technology , 2600 Delft, GA, The Netherlands 2 Sonic Arts Research Centre, Faculty of Engineering and Physical Sciences, Queen’s University Belfast, Belfast, BT7 1NN, UK Received 30 April 2006; Revised 29 September 2006; Accepted 14 October 2006 Recommended by Aki H¨arm¨a It is commonly accepted that the sound reflections from real physical objects are much more complicated than what usually is and can be modelled by room acoustics modelling software. The main reason for this limitation is the level of detail inherent in the physical object in terms of its geometrical and acoustic properties. In the present paper, the complexity of the sound reflections from a corridor wall is investigated by modelling the corresponding acoustic transfer functions at several receiver positions in front of the wall. The complexity for different wall configurations has been examined and the changes have been achieved by altering its acoustic image. The results show that for a homogenous flat wall, the complexity is significant and for a wall including various smaller objects, the complexity is highly dependent on the position of the receiver with respect to the objects. Copyright © 2007 M. Kuster and D. de Vries. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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INTRODUCTION
For the simulation and prediction of the acoustics in enclosed spaces, the geometry and acoustic properties of the enclosing boundaries are the primary parameters. The acoustic properties are represented by the acoustic impedance of the boundary. For a simple shoebox room with perfectly rigid walls (i.e., infinite acoustic impedance), the method of mirror image sources leads to a solution that satisfies the wave equation exactly [1]. In practice, rooms are neither of simple shoebox shape nor are the walls perfectly rigid. Instead, the modelling of all geometric details down to the order of the shortest acoustic wavelength would be required and the acoustic impedances of practical materials are generally complex, frequency-dependent, and nonlocally reacting [2]. One of the primary aims in room acoustics research over the past two to three decades has been the realistic and reliable prediction of room acoustics from a subset of the detailed geometric and acoustic information required theoretically [3–5]. In particular, the scattering of sound from nonsmooth finite-size surfaces, leading to diffuse reflections [6–9] and diffraction [10–12], has been recognised as one, if not the, key contributing factor.
The research presented in the current paper aims to shed some light on the complexity of measured reflec
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