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• The concept of aperture angle map is introduced. • A cost function based on the symmetry of the aperture angle map is proposed. • The optimized microphone array is used with the generalized cross correlation. • The optimized array removes side lobes without increasing the main lobe surface. Many workers are exposed daily to excessive noise levels. In order to reduce the noise exposure at the workstation, the main noise sources have to be detected. This task can be done with a microphone array and a source localization technique. Previous studies have shown promising results with time domain beamforming based on the generalized cross-correlation technique. The objective of this work is to propose an optimal spherical microphone array geometry dedicated to this technique. A cost function based on the symmetry of the aperture angle maps is proposed and is maximized using a Nonlinear Optimization by Mesh Adaptive Direct Search. Numerical results show that the optimized geometry improves the noise source map by reducing the side lobe amplitude without increasing the main lobe surface. Experimental measurements are carried out in a semi-anechoic chamber with prototyped spherical microphone arrays confirming that the optimized microphone array improves the quality of the noise source map. [ABSTRACT FROM AUTHOR]

This paper addresses source localization technique in time domain for broadband acoustic sources. The objective is to accurately and quickly detect the position and amplitude of noise sources in workplaces in order to propose adequate noise control options and prevent workers hearing loss or safety risk. First, the generalized cross correlation associated with a spherical microphone array is used to generate an initial noise source map. Then a linear inverse problem is defined to improve this initial map. Commonly, the linear inverse problem is solved with an l 2 -regularization. In this study, two sparsity constraints are used to solve the inverse problem, the orthogonal matching pursuit and the truncated Newton interior-point method. Synthetic data are used to highlight the performances of the technique. High resolution imaging is achieved for various acoustic sources configurations. Moreover, the amplitudes of the acoustic sources are correctly estimated. A comparison of computation times shows that the technique is compatible with quasi real-time generation of noise source maps. Finally, the technique is tested with real data. [ABSTRACT FROM AUTHOR]

Structure borne noise induced by vibrating systems is considered as a major contribution to the noise generated inside vehicles and can be assessed using Transfer Path Analysis (TPA) methods. Their theoretical formulation requires the mobility of either the vibrating system, the receiving structure or the assembly of the two components according to all Degrees of Freedom (DoFs). However, rotational and in-plane DoFs cannot be measured easily and their determination may result in a more complex experimental set-up or an increase in measurement uncertainties. The need for assessing the full mobility matrices thus deserves to be investigated. In this work, the robustness of multiple TPA methods dedicated to the design and validation phases of aircraft light equipment is investigated numerically according to the mobility matrices completeness and by considering several configurations of assemblies (i.e., different active source properties, different numbers of contact points). Numerical models have been developed to simulate a source with controlled vibratory behavior and the spatial averaged mean-square velocity on the receiving structure is used as an objective indicator of the method's robustness. For proper predictions accuracy, it is shown that the required completeness should account for the terms of highest amplitude and thus depends on the (i) TPA method, (ii) active behavior of the source and (iii) coupling configuration. A completeness involving all the DoFs is generally required for TPA methods based entirely on the mobility of the decoupled components. Otherwise, the omission of rotational or in-plan DoFs could be suitable for TPA methods based on the mobility of the assembly. • All Degrees of Freedom (Dofs) are not required for accurate predictions provided by the Transfer Path Analysis (TPA) methods. • The required Dofs depend on the TPA method considered and on the active and passive dynamic behavior of the structures. • Component-Based TPA (CB-TPA) without Dynamic Substructuring (DS) methods only requires the consideration of the translational Dofs. • Aeronautical structures may be characterized considering only a quarter of the Dofs for accurate predictions provided by the CB-TPA methods with DS. [ABSTRACT FROM AUTHOR]

Millions of workers are exposed to excessive noise levels each day. Acoustic solutions have to be developed to protect workers from hearing loss. The first step of an acoustic diagnosis is the source localization which can be performed with a microphone array. Spherical microphone arrays can be used to detect the acoustic source positions in a workplace. In this study, a spherical microphone array, with polyhedral discretization, is proposed and compared with a spherical array with a slightly different geometry. The generalized cross-correlation technique is used to detect the source positions. Moreover, two criteria are introduced to improve the noise source map. The first is based on the geometric properties of the microphone array and the scan zone whereas the second is based on the energy of the spatial likelihood function. Numerical data are used to provide a systematic comparison of both geometries and criteria. Finally, experiments in a reverberant room reveal that the polyhedral microphone array associated with both criteria provides the best noise source map. [ABSTRACT FROM AUTHOR]

In this paper, an alternative formulation of the time-domain beamforming is proposed using the generalized cross-correlation of measured signals. This formulation uses spatial weighting functions adapted to microphone positions and imaging points. The proposed approach is demonstrated for acoustic source localization using a microphone array, both theoretically and experimentally. An increase in accuracy of acoustic imaging results is shown for both narrow and broadband sources, while a factor of reduction up to 20 in the computation time can be achieved, allowing real-time or volumetric source localization over very large grids. [ABSTRACT FROM AUTHOR]

Microphone arrays have become a standard technique to localize and quantify source in aeroacoustics. The simplest approach is the beamforming that provides noise source maps with large main lobe and strong side lobes at low frequency. Since a decade, the focus is set on deconvolution techniques such as DAMAS or Clean-SC. While the source map is clearly improved, these methods require a large computation time. In this paper, we propose a sound source localization technique based on an inverse problem with beamforming regularization matrix called Hybrid Method. With synthetic data, we show that the side lobes are removed and the main lobe is narrower. Moreover, if the sound noise source map provided by this method is used as input in the DAMAS process, the number of DAMAS iterations is highly reduced. The Hybrid Method is applied to experimental data obtained in a closed wind-tunnel. In both cases of acoustic or aeroacoustic data, the source is correctly detected. The proposed Hybrid Method is found simple to implement and the computation time is low if the number of scan points is reasonable. [ABSTRACT FROM AUTHOR]