Acoustic absorbers and diffusers: theory, design and application

Acoustic conditions of a room, semi-enclosed spaces and the outdoor environment. Their correct use is important for delivering high quality acoustics. Thisunique and authoritative text describes how to effectively measure, model, design, optimise and apply diffusers and absorbers. Surface diffusion is a relatively young subject area, and diffuser design, application and characterisation are new to practitioners and researchers, who may not have been exposed to this new information in their formal training. This book is a resource for new and experienced acousticians seeking an understanding of the evolution and current state of the art in diffuser research and practice. Absorption is a more established technology, and so the book blends traditional design with modern developments. By collecting the key aspects of absorbers in one text, the bookoffers new and experienced professionals an opportunity to understand this subject in more depth. This detailed book serves to cover the practical and theoretical aspects of absorbers and diffusers and is well illustrated, with examples of installations and case studies. INDICE: Introduction: Absorption verses diffuse reflection. 1. Applications and basic principles of absorbers. 1.1 reverberation control. 1.1.1 A statistical model of reverberation. 1.2 Noise control in factories and large rooms with diffuse fields. 1.3 Modal control in critical listening spaces. 1.4 Echo control in auditoria and lecture theatres - basic sound propagation models. 1.4.1 Sound propagation - a wave approach. 1.4.2 Impedance, admittance, reflection factor and absorption. 1.5 Absorption in sound insulation. 1.5.1 Transfer matrix modelling. 1.6 Absorption for pipes and ducts - porous absorber characteristics. 1.6.1 Characterizing porous absorbers. 1.7 Summary. 1.8 References. 2.Applications and basic principles of diffusers. 2.1 Echo control in auditoria. 2.1.1 Example applications. 2.1.2 Wavefronts and diffuse reflections. 2.1.3 Coherence and terminology. 2.2 Reducing coloration in small rooms. 2.2.1 Soundreproduction. 2.2.2 Music practice rooms. 2.3 Controlling modes in reverberation chambers. 2.4 Improving speech intelligibility in underground or subway stations. 2.5 Promoting spaciousness in auditoria. 2.6 Reducing effects of earlyarriving reflections in large spaces. 2.7 Diffusers for uniform coverage withoverhead stage canopies. 2.8 Diffusers for rear and side of stage enclosures.2.9 Diffusers to reduce focusing effects of concave surfaces. 2.10 Diffusion and road side barriers. 2.11 Diffusion and street canyons. 2.12 Conclusions. 2.13 References. 3. Measurement of absorber properties. 3.1 Impedance or standing wave tube measurement. 3.1.1 Standing wave method. 3.1.2 Transfer function method. 3.2 Two microphone free field measurement. 3.3 Multi-microphone techniques for non-isotropic, non-planar surfaces. 3.3.1 Multi-microphone free fieldmeasurement for periodic surfaces. 3.4 Reverberation chamber method. 3.4.1 Measurement of seating absorption. 3.5 In situ measurement of absorptive properties. 3.6 Internal properties of absorbents. 3.6.1 Measurement of flow resistivity. 3.6.2 Measurement of flow impedance. 3.6.3 Direct measurement of wavenumber (or propagation constant). 3.6.4 Indirect measurement of wavenumber and characteristic impedance. 3.6.5 Measurement of porosity. 3.7 Conclusions. 3.8 References. 4. Measurement of diffusion. 4.1 Measurement of reflections in polar responses. 4.1.1 Near and far fields. 4.1.2 Sample considerations. 4.1.3 The total field and comb filtering. 4.2 Diffusion and scattering coefficients - general discussion. 4.3 The need for coefficients. 4.3.1 Diffuser manufacturer and application. 4.3.2 Geometric room acoustic models. 4.4 Diffusion coefficient. 4.4.1 Principle. 4.4.2 Obtaining polar responses. 4.4.3 Discussion. 4.5 Scattering coefficient. 4.5.1 Principle. 4.5.2 Rationale and procedure. 4.5.3 Sample considerations. 4.5.4 anisotropic surfaces. 4.5.5 Predicting the scatteringcoefficient. 4.6 From polar responses to scattering coefficients: the correlation scattering coefficient. 4.7 Contrasting diffusion and scattering coefficient: a summary. 4.8 Other methods for characterising diffuse reflections. 4.8.1 Measuring diffusion coefficients by solving the inverse problem. 4.8.2 Room diffuseness. 4.9 Conclusions. 4.10 References. 5. Porous absorption. 5.1 Absorption mechanisms and characteristics. 5.2 Covers. 5.3 Material types. 5.3.1 Mineral wool and foam. 5.3.2 Recycled materials. 5.3.3 Curtains (drapes). 5.3.4 Carpets. 5.3.5 Absorbent plaster. 5.3.6 Coustone or quietstone. 5.4 Basic material properties. 5.4.1 Flow resistivity. 5.5 Modelling propagation within porous absorbents. 5.5.1 Macroscopic empirical models such as delany and bazley. 5.5.2 Further material properties. 5.5.3 Theoretical models. 5.6 Predicting theimpedance and absorption of porous absorbers. 5.6.1 Single layer porous absorber with rigid backing. 5.7 Local and extended reaction. 5.8 Oblique incidence. 5.9 Biot theory for elastic framed material. 5.10 Summary. 5.11 References. 6. Resonant absorbers. 6.1 Mechanisms. 6.2 Example constructions. 6.2.1 Bass trap membrane absorber. 6.2.2 Helmholtz absorption. 6.2.3 Absorption and diffusion. 6.2.4 Clear absorption. 6.2.5 Masonry devices. 6.3 Design equations: resonant frequency. 6.3.1 Helmholtz resonator. 6.3.2 Losses. 6.4 Example calculations. 6.4.1 Slotted helmholtz absorber. 6.4.2 Porous absorbent filling the cavity. 6.5 More complicated constructions. 6.5.1 Double resonators. 6.5.2 Microperforation. 6.5.3 Lateral orifices. 6.6 Summary. 6.7 References. 7. Miscellaneous absorbers. 7.1 Seating and audience. 7.2 Absorbers from schroeder diffusers. 7.2.1 Energy flow mechanism. 7.2.2 Boundary layer absorption. 7.2.3 Absorption or diffusion. 7.2.4 Depth sequence. 7.2.5 Use of mass elements. 7.2.6 Number of wells. 7.2.7 Theoretical model. 7.3 Summary. 7.4 References. 8. Prediction of scattering. 8.1 Boundary element methods. 8.1.1 The helmholtz-kirchhoff...etc.

• ISBN: 978-0-415-47174-9
• Editorial: Routledge
• Encuadernacion: Cartoné
• Páginas: 496
• Fecha Publicación: 01/01/2009
• Nº Volúmenes: 1
• Idioma: Inglés