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A Study of Effects of Boundary and Directional Sound Sources on Virtual Sound Barrier Systems

Author: RaoWei
Tutor: QiuXiaoJun
School: Nanjing University
Course: Acoustics
Keywords: Virtual Sound Barrier Rigid reflective surface Directional sound source Continuous sound source
CLC: O422.8
Type: Master's thesis
Year: 2011
Downloads: 29
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Abstract


Virtual sound barrier (VSB) system using active control method to generate local quiet area in a noisy environment , domestic and foreign research is mainly based on the virtual sound barrier in free space , secondary sound source to a point source . In this paper, rigid reflective surfaces and directional sound source VSB system performance ; explore new secondary sound source driving function , and for three - dimensional local spatial sound field reproduction . First studied rigid the reflector face of the VSB system performance , and found that when the VSB system near rigid reflective surface , the amount of noise reduction versus frequency curve fluctuations in the free-field noise reduction curve up and down , the amount of noise reduction with the distance of the reflecting surface was the cyclical changes in the case of normal incidence , the period is a half-wavelength . When the distance of the reflecting surface is respectively equal to a quarter wavelength of the even multiple of an odd multiple of , the amount of noise reduction were taken the minimum value and the maximum value , which is determined by the secondary sound field and the degree of matching of the primary sound field . Also proposed reflecting surface into a combination of the VSB system VSB and analyze its performance . Based on the concept of continuous sound source derivation the new VSB system secondary source driver formula discussed on this basis of the directivity of the sound source and changes the directivity of the sound source on the VSB system performance , while compared with the conventional least square method . Directional sound source in the least square method monopole sound source in noise reduction than the Noise Reduction large ; close to the VSB system at the center of continuous sound source noise reduction than minimum mean high and away from the VSB system at the center of a continuous sound source noise reduction method is slightly lower than the minimum average amount of noise reduction methods ; monopole secondary source compared to directional secondary source VSB system can reduce the impact of its external space . Finally, the continuous sound source method for sound field reproduction dimensional local spatial sound field reproduction method based on the concept of continuous sound source and simulation of the feasibility of the method . Driving function of a sound source are derived , it is decided that the reproduced sound field , a sound source position and the playback frequency . Spherical harmonic function expansion method compared to the method avoids matrix inversion as well as the possible cause of the error ; compared with the wave occasions became law , the small area containing the replay center to improve the reproduction accuracy ; under heavy discharge achieve a better balance between the accuracy and the reproducing area size .

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CLC: > Mathematical sciences and chemical > Physics > Acoustics > Sound propagation > Noise
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