Sound Reflections from Concave Spherical Surfaces. Part II: Geometrical Acoustics and Engineering Approach
Focussing arising from concave surfaces has long been a well-known problem in room acoustics. The focussing can cause high sound pressure levels, colouration or an echo. Part I of this paper  provides a mathematical approximation based on wave extrapolation of the sound field in and around the focal point due to reflections by a spherical surface. This second part of the paper provides some practical methods for calculating the sound field. A geometrical approach is presented, the limitations of image source methods are described and an engineering method is presented. Computer models based on image source methods are not capable of describing the pressure in or out of the focal. The sound field outside the focal area can be calculated within reasonable accuracy with a geometrical approach. The results show that for a small wavelength the focussing effect is fairly strong. Generally the possible reduction of the focussing effect by absorbers or diffusers is not enough to eliminate the focussing effect by spherical surfaces.
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Document Type: Research Article
Publication date: 2010-01-01
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- Acta Acustica united with Acustica, published together with the European Acoustics Association (EAA), is an international, peer-reviewed journal on acoustics. It publishes original articles on all subjects in the field of acoustics, such as general linear acoustics, nonlinear acoustics, macrosonics, flow acoustics, atmospheric sound, underwater sound, ultrasonics, physical acoustics, structural acoustics, noise control, active control, environmental noise, building acoustics, room acoustics, acoustic materials, acoustic signal processing, computational and numerical acoustics, hearing, audiology and psychoacoustics, speech, musical acoustics, electroacoustics, auditory quality of systems. It reports on original scientific research in acoustics and on engineering applications. The journal considers scientific papers, technical and applied papers, book reviews, short communications, doctoral thesis abstracts, etc. In irregular intervals also special issues and review articles are published.
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