scholarly journals Effects of a near-field rigid sphere scatterer on the performance of linear microphone array beamformers

2016 ◽  
Vol 140 (2) ◽  
pp. 924-935
Author(s):  
Yuxiang Hu ◽  
Haoran Zhou ◽  
Jing Lu ◽  
Xiaojun Qiu
Keyword(s):  
Microphone Array ◽  
Near Field ◽  
Rigid Sphere

scholarly journals Instability wave models for the near-field fluctuations of turbulent jets

2011 ◽  
Vol 689 ◽  
pp. 97-128 ◽  
Author(s):  
K. Gudmundsson ◽  
Tim Colonius
Keyword(s):  
Flow Field ◽  
Large Scale ◽  
Microphone Array ◽  
Near Field ◽  
Turbulent Jets ◽  
Instability Wave ◽  
Mean Flow ◽  
Velocity Fluctuations ◽  
The Mean ◽  
Scale Structures

AbstractPrevious work has shown that aspects of the evolution of large-scale structures, particularly in forced and transitional mixing layers and jets, can be described by linear and nonlinear stability theories. However, questions persist as to the choice of the basic (steady) flow field to perturb, and the extent to which disturbances in natural (unforced), initially turbulent jets may be modelled with the theory. For unforced jets, identification is made difficult by the lack of a phase reference that would permit a portion of the signal associated with the instability wave to be isolated from other, uncorrelated fluctuations. In this paper, we investigate the extent to which pressure and velocity fluctuations in subsonic, turbulent round jets can be described aslinearperturbations to the mean flow field. The disturbances are expanded about the experimentally measured jet mean flow field, and evolved using linear parabolized stability equations (PSE) that account, in an approximate way, for the weakly non-parallel jet mean flow field. We utilize data from an extensive microphone array that measures pressure fluctuations just outside the jet shear layer to show that, up to an unknown initial disturbance spectrum, the phase, wavelength, and amplitude envelope of convecting wavepackets agree well with PSE solutions at frequencies and azimuthal wavenumbers that can be accurately measured with the array. We next apply the proper orthogonal decomposition to near-field velocity fluctuations measured with particle image velocimetry, and show that the structure of the most energetic modes is also similar to eigenfunctions from the linear theory. Importantly, the amplitudes of the modes inferred from the velocity fluctuations are in reasonable agreement with those identified from the microphone array. The results therefore suggest that, to predict, with reasonable accuracy, the evolution of the largest-scale structures that comprise the most energetic portion of the turbulent spectrum of natural jets, nonlinear effects need only be indirectly accounted for by considering perturbations to the mean turbulent flow field, while neglecting any non-zero frequency disturbance interactions.

A beamforming paradox: Using far‐field techniques to design a near‐field microphone array

1997 ◽  
Vol 102 (5) ◽  
pp. 3208-3208
Author(s):  
Darren B. Ward ◽  
Rodney A. Kennedy ◽  
Thushara Abhayapala
Keyword(s):  
Microphone Array ◽  
Near Field ◽  
Far Field ◽  
Field Techniques

Near field acoustic holography with microphones on a rigid sphere (L)

2011 ◽  
Vol 129 (6) ◽  
pp. 3461-3464 ◽  
Author(s):  
Finn Jacobsen ◽  
Guillermo Moreno-Pescador ◽  
Efren Fernandez-Grande ◽  
Jørgen Hald
Keyword(s):  
Near Field ◽  
Rigid Sphere ◽  
Acoustic Holography

scholarly journals Robust Multichannel Microphone Beamforming

2021 ◽  
Author(s):  
◽  
Craig Anderson
Keyword(s):  
Blind Source Separation ◽  
Correlation Functions ◽  
Microphone Array ◽  
Near Field ◽  
Source Separation ◽  
Source Location ◽  
Mobile Platforms ◽  
Signal Path ◽  
Von Mises ◽  
2D And 3D

<p>In this thesis, a method for the design and implementation of a spatially robust multichannel microphone beamforming system is presented.  A set of spatial correlation functions are derived for 2D and 3D far-field/near-field scenarios based on von Mises(-Fisher), Gaussian, and uniform source location distributions. These correlation functions are used to design spatially robust beamformers and blocking beamformers (nullformers) designed to enhance or suppress a known source, where the target source location is not perfectly known due to either an incorrect location estimate or movement of the target while the beamformers are active.  The spatially robust beam/null-formers form signal and interferer plus noise references which can be further processed via a blind source separation algorithm to remove mutual components - removing the interference and sensor noise from the signal path and vice versa. The noise reduction performance of the combined beamforming and blind source separation system approaches that of a perfect information MVDR beamformer under reverberant conditions.  It is demonstrated that the proposed algorithm can be implemented on low-power hardware with good performance on hardware similar to current mobile platforms using a four-element microphone array.</p>

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