Sound field synthesis for line source array applications in large-scale sound reinforcement

The thesis deals with optimized large-scale sound reinforcement using line source arrays. This is treated as a sound field synthesis problem. The synthesis of a virtual source via the line source array allows for audience adapted wavefront shaping. For practical array designs and setups this is affected by the deployed loudspeakers and their arrangement, its electronic control and spatial aliasing occurrence. The influence of these parameters is discussed with array signal processing revisiting the Wavefront Sculpture Technology and proposing Wave Field Synthesis as a suitable control method.Die Arbeit beschäftigt sich mit optimaler Beschallung großer Auditorien mit Line Source Arrays. Das Problem wird mit Schallfeldsynthese beschrieben. Die Synthese einer virtuellen Quelle mit einem Line Source Array ermöglicht eine für das Auditorium angepasste Wellenfront. In der Praxis wird dies beeinflusst von den verwendeten Lautsprechern, ihrer Anordnung, ihrer Ansteuerung und räumlichem Aliasing. Der Einfluss der Parameter wird mit Array-Signalverarbeitung diskutiert, wofür Wavefront Sculpture Technology aufgegriffen und Wellenfeldsynthese als Ansteuerungsmethode vorgeschlagen wird

Beamforming Techniques for Environmental Noise

Projecte final de carrera realitzat en col.laboració amb la Technical University of Denmark i Brüel & KjaerA problem of practical interest when dealing with outdoor acoustic measurements is to estimate the noise contributions from di erent directions around the measurement point. This estimation can be done by means of microphone arrays. More speci - cally, circular arrays are suitable for this purpose as, in combination with proper signal processing techniques, they are capable of mapping the sound eld in a plane over 360 . Two processing techniques meant to be used with circular arrays are implemented: the `classical' Delay-and-Sum beamforming and a novel technique called Circular Harmonics beamforming. The latter is based on the decomposition of the sound eld in series of circular harmonics. The performance of these beamforming techniques is analyzed by means of simulations and evaluated by two parameters, the resolution and the maximum side lobe level. Making use of the results of the simulations, a circular array has been designed for the localization of environmental noise sources around a measurement point. Finally, a prototype implemented in accordance with the design has been tested in anechoic conditions. The results, which agree very well with the simulations, reveal that the array is suitable for the purpose of concern

Recent progress in research on virtual sound barriers

A virtual sound barrier is an active noise control system that uses arrays of loudspeakers and microphones to create a practical size of quiet zone in a noise environment just like an acoustic barrier but without blocking air and light. This technology can be used to reduce sound radiation from noise sources or to reduce noise level around one or few person heads in noisy environments in many industrial and domestic situations. This paper introduces the history, principle and design methods of the virtual sound barriers first, and then describes recent progress in research on the systems, especially the application on power transformer noise radiation control from an enclosure. The paper is concluded by the limitations and future direction discussions of the virtual sound barriers

A finite volume-based high-order, Cartesian cut-cell method for wave propagation

Computational aeroacoustics requires numerical techniques capable of yielding low artificial dispersion and dissipation to preserve the amplitude and the frequency characteristics of the physical processes. Furthermore, for engineering applications, the techniques need to handle irregular geometries associated with realistic configurations. We address these issues by developing an optimized prefactored compact finite volume (OPC-fv) scheme along with a Cartesian cut-cell technique. The OPC-fv scheme seeks to minimize numerical dispersion and dissipation while satisfying the conservation laws. The cut-cell approach treats irregularly shaped boundaries using divide-and-merge procedures for the Cartesian cells while maintaining a desirable level of accuracy. We assess these techniques using several canonical test problems, involving different levels of physical and geometric complexities. Richardson extrapolation is an effective tool for evaluating solutions of no high gradients or discontinuities, and is used to evaluate the performance of the solution technique. It is demonstrated that while the cut-cell method has a modest effect on the order of accuracy, it is a robust method. The combined OPC-fv scheme and the Cartesian cut-cell technique offer good accuracy as well as geometric flexibility. Copyright © 2008 John Wiley & Sons, Ltd.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/58070/1/1517_ftp.pd

Two-Dimensional Spatial Control using Multiple Circular Loudspeaker Arrays and Elliptical Loudspeaker Array

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2.5D multizone reproduction using weighted mode matching: Performance analysis and experimental validation

Mode-matching based multizone reproduction has been mainly focused on a purely two-dimensional (2D) theory, where infinite-long 2D secondary sources are assumed for 2D multizone reproduction. Its extension to the three-dimensional (3D) case requires more secondary sources and a higher computational complexity. This work investigates a more practical setup to use 3D sound sources as secondary sources for multizone reproduction in a 2D horizontal plane, i.e., 2.5D multizone reproduction. A weighted mode-matching approach is proposed to solve the dimensionality mismatch between the 2D desired sound field and 3D reproduced sound field. The weighting is based on an integral of Bessel-spherical harmonic modes over the entire control region. A detailed analysis of the weighting function is provided to show that the proposed method controls all the reproduction modes present on the 2D plane to minimize the reproduction error. The method is validated in both simulation-based and hardware-based experiments. The results demonstrate that in comparison with the conventional sectorial mode-matching method, the proposed approach can achieve more accurate reproduction over a wide frequency range and a large control region. 2020 Acoustical Society of America.This work was supported by the National Natural Science Foundation of China (NSFC) funding scheme under Project No. 61671380

Secondary source and error sensing strategies for the active control of sound transmission through a small opening

© 2019 Elsevier Ltd The openings of an enclosure allow natural ventilation and light ingress but also act as a point of entry for noise of the whole structure. In this paper, the active control of the sound transmitted through a small opening in a wall formed by two infinitely-large baffles is investigated up to 4 kHz. Based on an analytical model developed with the modal expansion method, the effects of different secondary source and error sensor strategies are compared numerically for different types of primary sound fields. The upper frequency limit of effective control is found to be determined by the eigen-frequency of the acoustic modes of the opening. Experimental results with an opening of 6 cm by 6 cm on a 31.8 cm thick wall agree well with the numerical results. The upper frequency limit of effective control is found to be 2750 Hz for a single-channel system and 3900 Hz for a 4-channel system with more than 10 dB noise reduction. It is concluded that implementing active control in small openings with an appropriate secondary source and error sensing strategy can extend the frequency range of control significantly, so that the active control systems can be applied to more noise control scenarios which have both noise reduction and ventilation requirements in the middle to high frequency range