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최정우(Choi, Joung-Woo),김양한(Kim, Yang-Hann),박영진(Park, Young-Jin) 한국소음진동공학회 2005 한국소음진동공학회 논문집 Vol.15 No.12
Spatial control of sound is essential to deliver better sound to the listener's position in space. As it can be experienced in many listening environments. the quality of sound can not be manifested over every Position in a hall. This motivates us to control sound in a region we select. The primary focus of the developed method has to do with the brightness and contrast of acoustic image in space. In particular, the acoustic brightness control seeks a way to increase loudness of sound over a chosen area, and the contrast control aims to enhance loudness difference between two neighboring regions. This enables us to make two different kinds of zone - the zone of quiet and the zone of loud sound - at the same time. The other perspective of this study is on the direction of sound. It is shown that we can control the direction of perceived sound source by focusing acoustic energy in wavenumber domain. To begin with, the proposed approaches are formulated for pure-tone case. Then the control methods are extended to a more general case, where the excitation signal has broadband spectrum. In order to control the broadband signal in time domain, an inverse filter design problem is defined and solved in frequency domain. Numerical and experimental results obtained in various conditions certainly validate that the acoustic brightness, acoustic contrast, direction of wave front can be manipulated for some finite region in space and time.
최정우(Choi, Joung-Woo) 한국소음진동공학회 2008 한국소음진동공학회 논문집 Vol.18 No.2
A hybrid technique that combines the advantages of binaural reproduction and sound field reproduction technique is proposed. The concept of HRTF-field, which is defined as the set of HRTFs corresponding to the various head dislocations, enables us to realize virtual source imaging over a wide area. Conventional binaural($2{\times}2$) reproduction system is redefined as a MIMO system composed of multiple control sources and multiple head locations, and HRTF variations corresponding to various head movement are quantified. Through the direct control of HRTF-field, reproduction error induced by head dislocation can be minimized in least-square-error sense, and consequential disturbances on the virtual source image can be reduced within a selected area. Simple lateralization examples are investigated, and the reproduction error of the proposed technique is compared to that of higher-order Ambisonics.
김양한(Yang-Hann Kim),최정우(Joung-Woo Choi) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.11
In this paper, we aim to control the sound field spatially, so that a desired or target acoustic variable is enhanced within a zone where the listener is located. This is somewhat analogous to have manipulators that can draw sound picture in any place we want. In order to manipulate sound field over a finite area in space, it is essential to control multiple sound sources. With all these regards, we propose a unified approach that can manipulate selected acoustic variables using multiple sources. However, the shape or color of the sound picture fully depends on the acoustic variable we want to enhance. Among the many possible choices, we focus on three acoustic variables that have to do with the magnitude and direction of sound: acoustic potential energy, sound intensity, and direction of wavefront. Various numerical and experimental results of the proposed methods certainly validate that we can draw our own sound picture in space and time.