Wave field synthesis is a reproduction technique developed at TU Delft, that enables the generation of high-quality three-dimensional spatial sound fields. The benefit of the method is that spatial impressions are highly independent of the position of the listeners within a large listening area. In short, the method uses a limited number of audio channels that are reproduced by generating plane and spherical wave fields with arrays of loudspeakers that surround the listening place. Applications include spatial sound reproduction in the home and in cinemas, sound reinforcement in theaters, teleconferencing with large video screens, and variable acoustics.
The concept of wave field synthesis (WFS) was introduced by Berkhout in 1988 [1]. It enables the generation of sound fields with natural temporal and spatial properties within a volume or area bounded by arrays of loudspeakers. Applications are found in real time performances as well as in reproduction of multitrack recordings. A logic next step was the formulation of a new wave field analysis (WFA) concept by Berkhout in 1997 [2], where sound fields in enclosures are recorded with arrays of microphones and analyzed with postprocessing techniques commonly used in acoustical imaging. This way, both the temporal and spatial properties of the sound field can be investigated and understood. WFS and WFA meet in auralization applications: sound fields measured (or modeled) along arrays of microphone positions can be generated by arrays of loudspeakers for perceptual evaluation.
A new method is proposed to acquire impulse responses in concert halls with large signal-to-noise ratios and with a high resolution. In our proposal an omnidirectional loudspeaker is used which is driven by an amplified sweep: a signal containing all frequencies of interest smeared out in time. By using a deconvolution technique, an almost perfect pulse is obtained with a high peak pressure and a short effective duration. Measurements were made in two different concert halls to illustrate the practical implications of the new technique.PACS numbers: 43.55.Br, 43.55.Gx
In this paper, a new ray-tracing algorithm is presented that can handle arbitrary temperature and wind profiles in horizontal and vertical directions. This is accomplished by following a ray tube instead of a ray path. The algorithm is a direct finite difference implementation of the ray-tracing equations for arbitrary temperature and wind profiles. A computer model has been made, based on this algorithm. Special attention is given to the shortcomings of ray theory in the case of caustics, which are compensated for by appropriate phase and amplitude corrections of the computed ray tubes. The method is well suited to study the effect of locally heated areas on the sound propagation, as occurring on for instance petrochemical plants. Numerical experiments show that the proposed ray-tracing method and the relatively expensive, but accurate, wave field extrapolation method agree very well in many cases.
POGGIAGLIOLMI, E., BERKHOUT, A.J. and BOONE, M.M., 1982, Phase Unwrapping, Possibilities and Limitations, Geophysical Prospecting 30, 281-291. An unwrapped phase curve from the principal values of the phase can be computed in a simple way. The validity of the unwrapping procedure is tested by exploiting the phase information in the signal's first moment. The significance of the unwrapped answer around notches in the amplitude spectrum is seriously degraded by noise.The proposed method and the validity test are illustrated with examples.
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