AE-4.1

A DIRECT METHOD TO COMPUTATIONAL ACOUSTICS
Rudolf Rabenstein, Ahmed Zayati (University of Erlangen-Nuremberg, Telecommunications Laboratory)

The exact knowledge of the sound field within an enclosure is essential for a number of applications in electro-acoustics. Conventional methods for the assessment of room acoustics model the sound propagation in analogy to the propagation of light. More advanced computational methods rely on the numerical solution of the wave equation. A recently presented method is based on multidimensional wave digital principles. It allows a physically exact numerical modelling of the relevant acoustical effects and yields robust algorithms. This contribution presents a new foundation of the multidimensional wave digital principle as applied to room acoustics. It starts from the first principles of physics. From there, the derivation of the algorithm only involves basic knowledge of numerical mathematics, linear algebra, and multidimensional system theory. An example for the simulation of dynamic three-dimensional sound propagation demonstrates the capability of the method.

AE-4.2

Spatial Frequency Response Surfaces: An Alternative Visualization Tool for Head-Related Transfer Functions (HRTF's)
Corey I Cheng, Gregory H Wakefield (University of Michigan Dept. of EECS, Systems Division)

This paper presents an alternative visualization tool for head-related transfer functions (HRTF�s) which represents HRTF data sets as magnitude spatial frequency response surfaces. Qualitative analysis of HRTF data is easier in the spatial domain than in the magnitude frequency domain and allows quick comparisons between different subjects� HRTF sets. In addition, these surfaces exhibit many well-known HRTF-related psychophysical phenomena due to head, torso, and pinna filtering. Finally, these surfaces suggest an interpolation algorithm by which Directional Transfer Functions (DTF�s) corresponding to arbitrary spatial locations can be computed from existing DTF measurements at known locations.

AE-4.3

An Adaptable Ellipsoidal Head Model for the Interaural Time Difference
Richard O Duda (Department of Electrical Engineering, San Jose State University, San Jose, CA 95192), Carlos Avendano, V. R Algazi (CIPIC, University of California at Davis, Davis, CA 95616)

Experimentally measured head-related transfer functions reveal that the interaural time delay varies from person to person. Furthermore, it is not constant around a cone of confusion, but can vary by as much as 18% of the maximum interaural delay. The major sources for this variation are shown to be the shape of the head and the displacement of the ears from the center of the head. A simple ellipsoidal head model is presented that can accurately account for this ITD variation and can be adapted to individual listeners.

AE-4.4

Visualizing the Performance of Large-Aperture Microphone Arrays
Harvey F Silverman, William R Patterson III (Laboratory for Engineering Man/Machine Systems, Division of Engineering, Brown University, Providence, RI 02912)

The use of arrays of microphones having a large number of elements (hundreds) is now in place in research laboratories, and will soon be practical for real applications. In rooms of auditoruium or conference size, a large number of microphones will virtually always imply that the aperture will be large compared to the focal distance. This requires understanding the volume selectivity of irregular, widely-distributed sets of microphones. In this paper, several pictures of the beamforming performance of large-aperture distributions of microphones are presented. The purpose is to illustrate some of the pitfalls in large-aperture microphone-array design.

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Last Update: February 4, 1999 Ingo Höntsch