• Journal of KSNVE
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• v.9 no.1
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• pp.131-140
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• 1999

A method to reconstruct the sound field around a Korean bell is developed. The sound radiation problem is formulated based on the boundary element method by using the algorithm of the acoustical holography. Sound pressures at the hologram surface are measured and used as input data for the analysis program that was developed in this study. An error minimization scheme is presented to overcome difficulties that arise in the backward reconstruction of the BEM-based acoustical holography In the model fictitious source surfaces were also introduced to reduce the complexity stemmed from the source shape. The sound field associated with the (4.0) vibrational mode of the Korean bell was visualized and verified experimentally.

• The Journal of the Acoustical Society of Korea
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• v.28 no.8
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• pp.723-731
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• 2009

In this paper, we propose a novel sound field reconstruction algorithm using a three dimensional loudspeaker array for providing realistic sound field to multiple listeners. The proposed algorithm is based on minimization of the squared error between the original sound field and the reconstructed sound field by the loudspeaker array over a predefined three dimensional region of the space using a loudspeaker array surrounding the listening area. For evaluating the proposed algorithm, we constructed the three dimensional array composed of 40 loudspeakers and discuss the relevant experiment results.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.7
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• pp.924-929
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• 2000

This paper addresses a new technique of measuring the mean flow velocity over the cross sectional area of the pipe using sound field reconstruction. When fluid flows in the pipe and two plane waves propagate oppositely through the medium, the flow velocity causes the change of wave number of the plane waves. The wave number of the positive going plane wave decreases and that of negative going one increases in comparison to static medium in the pipe. Theoretical backgrounds of this method are introduced in detail and the measurement of mean flow velocity using the sound field reconstruction is not affected by velocity profile upstream of microphones.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.06a
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• pp.1747-1751
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• 2000

It is well known that acoustic signals, even measured in an anechoic chamber, can be contaminated due to the wall interference. Therefore, it is necessary to reconstruct the original signal from the measured data, which is very critical for the case of measurement of source signal in a water tunnel. In this thesis, new methods for the reconstruction of sound sources are proposed and validated by using Boundary Element Method from measured data in a closed space. The inverse Helmholtz integral equation and its normal derivative are used for the reconstruction of sound sources in a closed space. An arbitrary Kirchhoff surface over the sources is proposed to solve the surface information instead of direct solution for the source. Although sound sources are not directly known by the inverse Helmholtz equation, the original sound source of pressure-field outside of the wall can be indirectly obtained by using this new method.

• 한국정보디스플레이학회:학술대회논문집
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• 2003.07a
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• pp.451-462
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• 2003

At the paper the method of 3D holographic moving image reconstruction is discused. The main idea of this method is based on the substitution of optically created static hologram by equal diffraction array created by acoustical (AO) field which formed by bulk sound waves. Such sound field can be considered as dynamic optical hologram, which is electrically controlled. At the certain moment of time when the whole hologram already formed, the reference optical beam illuminates it, and due to acoustooptical interaction the original optical image is reconstructed. As the acoustically created dynamic optical hologram is electronically controlled, it can be used for moving 3-dimentional scene reconstruction in real time. The architecture of holographic display for moving scene reconstruction is presented at this paper. The calculated variant of such display laboratory model is. given and discussed. The mathematical simulation of step by step images recording and reconstruction is given. The pictures of calculated reconstructed images are presented. The prospects, application areas, shortcomings and main problems are discussed.

• Journal of Information Display
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• v.4 no.3
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• pp.29-34
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• 2003

At the paper the method of 3D holographic moving image reconstruction is discused. The main idea of this method is based on the substitution of optically created static hologram by equal diffraction array created by acoustical (AO) field which formed by bulk sound waves. Such sound field can be considered as dynamic optical hologram, which is electrically controlled. At the certain moment of time when the whole hologram already formed, the reference optical beam illuminates it, and due to acoustooptical interaction the original optical image is reconstructed. As the acoustically created dynamic optical hologram is electronically controlled, it can be used for moving 3-dimentional scene reconstruction in real time. The architecture of holographic display for moving scene reconstruction is presented at this paper. The calculated variant of such display laboratory model is given and discussed. The mathematical simulation of step by step images recording and reconstruction is given. The pictures of calculated reconstructed images are presented. The prospects, application areas, shortcomings and main problems are discussed.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2011.10a
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• pp.643-648
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• 2011

This paper deals with the ESM(equivalent source method) with the continuation of acoustic near-field for NAH(near-field acoustic holography) to overcome the finite measurement aperture effect and reconstruct the normal velocity on an arbitrarily shaped structure surface. The continuation method is an extension of the measured sound field into a region outside and is based on the Green's function relating acoustic quantities on the two conformal surfaces. This algorithm is not limited to planar surfaces and can be applied to arbitrarily shaped surfaces. The ESM is an alternative approach of BEM-based NAH for the reconstruction on a general structure. In ESM the acoustic field is represented by a set of point sources located over a surface that is close to the structure surface. The simulation results of this study shows that the reconstruction error of particle velocity on the source surface is 11% and 16% for planar and cylindrical sources separately.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.11a
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• pp.1101-1106
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• 2004

This study presents the reconstruction of sound field radiated from an automotive engine using equivalent sources. Basic concept of the method presented is to replace the engine noise source with elementary sources of multipoles, e.g., monopoles and dipoles. The so-called Helmholtz equation least-squares (HELS) method can reconstruct the sound radiation fields from spherical geometries in a series expansion of spherical Hankel functions and spherical harmonics. In this paper, multi-Point, multipole equivalent sources are employed to reconstruct the sound field radiated from an automotive engine with a fixed rotation speed. To ensure and improve the accuracy of reconstruction, the spatial filters of multipole coefficients and wave-vectors are adopted for suppressing the adverse effect of high-order multipoles. Optimal filter shapes are designed with regularization parameters minimizing the generalized cross validation (GCV) function between actual and reproduced model. After regeneration of field pressures using the proposed method as many as necessary, the vibro-acoustic field of an engine could be reconstructed by using the BEM-based near-field acoustic holography (NAH) technique in a cost-effective manner.

• Journal of KSNVE
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• v.8 no.3
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• pp.435-440
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• 1998

The main objective of this study is to estimate location and strength of sound sources distributed on the surface of an enclosure. Acoustic holography method has been used to identify the sources in an interior sound field. However, it can not completely distinguish between the direct sound field from sources and the reflections from surfaces. The method just reconstructs the entire sound field based on the sound pressure at the finite number of measurement points. In this stduy, a method which estimates only the active sources by using measurements of field pressure and surface admittance is proposed. An in-situ technique to estimate the general boundary condition is also proposed by using acoustic holography, assuming the surfaces are locally reacting.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2012.10a
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• pp.630-635
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• 2012

Nearfield acoustic holography method predicts an unmeasured sound field, therefore it depends on its prediction methods. In particular, if one has radiators or scatters, which cannot be expressed by simple geometry, then inverse boundary element method (BEM) is normally employed to reconstruct the sound field induced by sound sources with irregular profiles. The characteristics of boundary element, including the element shape, characteristic length, order of shape function and others, affect the reconstruction error. Investigating the errors by means of changing these factors will provide a guide line for selecting appropriate factors, associated with the elements of BEM. These factors are investigated by numerical simulations, and the accuracies with respect to the variant factors are compared. Novel suggestions for selecting appropriate boundary element factors are described based on the simulation results.