Fourier Acoustics: Sound Radiation and Nearfield Acoustical Holography

One approach to the reproduction of a sound field is to ensure the reproduction of the acoustic pressure on the surface bounding the volume within which reproduction is sought.However, this approach suffers from technical limitations when the loudspeakers used for the reproduction of the surface acoustic pressures are unevenly spaced. It is shown in this paper that sound field reproduction with a spatially non-uniform loudspeaker arrangement can be considerably improved by changing the physical quantity to be controlled on the bounding surface from pressure to particle velocity. One of the main advantages of the velocity control method is the simplicity with which the inverse problem can be regularized, irrespective of the direction of arrival of the sound to be reproduced. In addition, the velocity controlled sound field shows better reproduction of the time averaged intensity flow in the reproduction region which in turn appears to be closely linked with better human perception of sound localization. Furthermore, the proposed method results in smoother "panning functions" that describe the variation of the source outputs as a function of the angle of incidence of the sound to be reproduced. The performance of the velocity matching method has been evaluated by comparison to the conventional pressure matching method and through simulations with several non-uniform loudspeaker layouts. The simulated results were also verified with experiments and subjective tests.

Section: B Proposed Velocity Matching Methodsmentioning

confidence: 99%

“…where ( The particle velocity of the reproduced field is given by applying the Euler's relation [17] to Eq. (1), thus obtaining Neumann non-homogeneous boundary conditions, depending on whether the target pressure or normal velocity is given, respectively.…”

Section: Theorymentioning

confidence: 99%

Velocity controlled sound field reproduction by non-uniformly spaced loudspeakers

Shin

Nelson

Fazi

et al. 2016

“…Due to the analogy with classical optics it is commonly assumed that the spatial resolution of most sound localization methods is limited by the wavelength of radiation [8]. However, in acoustic near-fields, it is possible to overcome the spatial resolution limit via the inclusion of evanescent waves [28,29,5].…”

Section: Direct Sound Mapping Resolution Limitsmentioning

confidence: 99%

“…Near-field acoustic holography [5], acoustic beamforming [6] and various inverse methods [7] offer different approaches to localize, and ultimately quantify, the sources of noise. However, pressure-based techniques often encounter difficulties adapting from controlled experiments to industrial applications [8].…”

Section: Introductionmentioning

confidence: 99%

Spatial resolution limits for the localization of noise sources using direct sound mapping

Comesaña

Holland

Fernández-Grande

2016

One of the main challenges arising from noise and vibration problems is how to identify the areas of a device, machine or structure that produce significant acoustic excitation, i.e. the localization of main noise sources. The direct visualization of sound, in particular sound intensity, has extensively been used for many years to locate sound sources. However, it is not yet well defined when two sources should be regarded as resolved by means of direct sound mapping. This paper derives the limits of the direct representation of sound pressure, particle velocity and sound intensity by exploring the relationship between spatial resolution, noise level and geometry. The proposed expressions are validated via simulations and experiments. It is shown that particle velocity mapping yields better results for identifying closely spaced sound sources than sound pressure or sound intensity, especially in the acoustic near-field.

“…Among the most common techniques for which commercial systems currently exists, one finds: beamforming [1,2], nearfield acoustical holography (NAH) [3] and inverse methods [4,5,6,7,8,9]. One advantage of the inverse approach and conformal NAH for arbitrary geometries [3] is the possible use of non-uniform or source-conformal microphone arrays. Our attention is focused on 1) practical inverse problems which involve a finite number of sensors and 2) numerical inversion of matrix-form problems subject to measurement noise and random errors [6].…”

Section: Introductionmentioning

confidence: 99%

Acoustical inverse problems regularization: Direct definition of filter factors using Signal-to-Noise Ratio

Gauthier

Gérard

Camier

et al. 2014

1377Acoustic imaging aims at localization and characterization of sound sources using microphone arrays. In this paper a new regularization method for acoustic imaging by inverse approach is proposed. The method first relies on the singular value decomposition of the plant matrix and on the projection of the measured data on the corresponding singular vectors. In place of regularization using classical methods such as truncated singular value decomposition and Tikhonov regularization, the proposed method involves the direct definition of the filter factors on the basis of a thresholding operation, defined from the estimated measurement noise. The thresholding operation is achieved using modified filter functions. It has the advantage of simplifying the selection of the best regularization amount. Theoretical results show that this method is promising, in terms of ease of implementation and accuracy of results, in comparison with Tikhonov regularization and truncated singular value decomposition.