Sound Reflections from Concave Spherical Surfaces. Part I: Wave Field Approximation
Focussing arising from reflections at concave surfaces is a well-known problem in room acoustics. Focussing can cause high sound pressure levels, colouration or an echo. Although the problem is known, the amplification in the focal point and the sound field around the focal point are not. This paper provides some mathematical formulations for sound reflections from concave spherical surfaces. The formulation is based on a wave extrapolation method. The approximations given can be used to calculate the sound field in and around the focal point. The calculation method is verified with an experiment. In the focal point the pressure depends on the wavelength. The width of the peak pressure is also related to the wavelength. For small wavelengths the amplification is high but the area is small, while for lower frequencies the amplification is less, but the area is larger. In a second part of this paper  geometrical and engineering methods will be discussed for describing the focussing effect.
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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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