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Diffusion, in architectural acoustics, is the spreading of sound energy evenly in a given environment. A perfectly diffusive sound space is one in which the reverberation time is the same at any listening position. Most interior spaces are non-diffusive; the reverberation time is considerably different around the room. At low frequencies, they suffer from prominent resonances called room modes.
Acoustic diffusing discs (illuminated blue) hanging from the ceiling of the Royal Albert Hall.
Diffusors (or diffusers) are used to treat sound aberrations, such as echoes, in rooms. They are an excellent alternative or complement to sound absorption because they do not remove sound energy, but can be used to effectively reduce distinct echoes and reflections while still leaving a live sounding space. Compared to a reflective surface, which will cause most of the energy to be reflected off at an angle equal to the angle of incidence, a diffusor will cause the sound energy to be radiated in many directions, hence leading to a more diffusive acoustic space. It is also important that a diffusor spreads reflections in time as well as spatially. Diffusors can aid sound diffusion, but this is not why they are used in many cases; they are more often used to remove coloration and echoes.
Diffusors come in many shapes and materials. The birth of modern diffusors was marked by Manfred R. Schroeders' invention of number-theoretic diffusors in the 1970s. He got the idea during a 1977 Göttingen lecture by André Weil, Gauss sums and quadratic residues, celebrating the 200th anniversary of the birth of Gauss.[1]
Maximum length sequence diffusorsedit
MLS Diffusor
Maximum length sequence based diffusors are made of strips of material with two different depths. The placement of these strips follows an MLS. The width of the strips is smaller than or equal to quarter the wavelength of the frequency where the maximum scattering effect is desired. Ideally, small vertical walls are placed between lower strips, improving the scattering effect in the case of tangential sound incidence. The bandwidth of these devices is rather limited; at one octave above the design frequency, diffusor efficiency drops to that of a flat surface.
Quadratic-residue diffusorsedit
1000Hz Quadratic-Residue Diffusor
MLS based diffusors are superior to geometrical diffusors in many respects; they have limited bandwidth. The new goal was to find a new surface geometry that would combine the excellent diffusion characteristics of MLS designs with wider bandwidth. A new design was discovered, called a quadratic residue diffusor.[2] Today the quadratic residue diffusor or Schroeder diffusor is still widely used. Quadratic-Residue Diffusors can be designed to diffuse sound in either one or two directions.
Primitive-root diffusorsedit
Primitive-root diffusors are based on a number theoretic sequence based on primitive roots. Although they produce a notch in the scattering response, in reality the notch is over too narrow a bandwidth to be useful. In terms of performance, they are very similar to Quadratic-Residue Diffusors.[3][4]
Optimized diffusorsedit
By using numerical optimisation, it is possible to increase the number of theoretical designs, especially for diffusors with a small number of wells per period. But the big advantage of optimisation is that arbitrary shapes can be used which can blend better with architectural forms.
Two-dimensional ("hemispherical") diffusorsedit
Example of a 2D acoustic diffusor using QRD method
Designed, like most diffusors, to create "a big sound in a small room," unlike other diffusors, two-dimensional diffusors scatter sound in a hemispherical pattern. This is done by the creation of a grid, whose cavities have wells of varying depth, according to the matrix addition of two quadratic sequences equal or proportionate to those of a regular diffusor.[5] These diffusors are very helpful for controlling the direction of the diffusion, particularly in studios and control rooms.[6]
^Xiang, Ning; Sessler, Gerhard M., eds. (2015). "20: Bell Laboratories". Acoustics, Information, and Communication: Memorial Volume in Honor of Manfred R. Schroeder. Cham: Springer International Publishing. p. 396. doi:10.1007/978-3-319-05660-9. ISBN978-3-319-05659-3.
^M. R. Schroeder (April 1979). "Binaural dissimilarity and optimum ceilings for concert halls: More lateral sound diffusion". J. Acoust. Soc. Am. 65 (4): 958–963. Bibcode:1979ASAJ...65..958S. doi:10.1121/1.382601.
^Eliot Feldman (July 1995). "A reflection grating that nullifies the specular reflection: A cone of silence". The Journal of the Acoustical Society of America. 98 (1): 623–634. Bibcode:1995ASAJ...98..623F. doi:10.1121/1.413656.
^Walker, R. "The design and application of modular acoustic diffusing elements" (PDF). BBC Research Department. Retrieved 25 March 2019.
^Strube, Hans Werner (1981). "More on the diffraction theory of Schroeder diffusors". The Journal of the Acoustical Society of America. Acoustical Society of America (ASA). 70 (2): 633–635. doi:10.1121/1.386757. ISSN 0001-4966.
^"The effects of 2d diffusers on sound diffusion". PF. (in Dari)
Further readingedit
T. J. Cox and P. D'Antonio, Acoustic Absorbers and Diffusors - Theory, Design and Application Spon press.
M. R. Schroeder, Number Theory in Science and Communication, Springer-Verlag, 1984; see especially sections 15.8 and 26.6.
February 15, 2024
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For other uses see Diffusion disambiguation This article needs additional citations for verification Please help improve this article by adding citations to reliable sources Unsourced material may be challenged and removed Find sources Diffusion acoustics news newspapers books scholar JSTOR February 2010 Learn how and when to remove this template message You can help expand this article with text translated from the corresponding article in German December 2019 Click show for important translation instructions View a machine translated version of the German article Machine translation like DeepL or Google Translate is a useful starting point for translations but translators must revise errors as necessary and confirm that the translation is accurate rather than simply copy pasting machine translated text into the English Wikipedia Consider adding a topic to this template there are already 8 987 articles in the main category and specifying topic will aid in categorization Do not translate text that appears unreliable or low quality If possible verify the text with references provided in the foreign language article You must provide copyright attribution in the edit summary accompanying your translation by providing an interlanguage link to the source of your translation A model attribution edit summary is Content in this edit is translated from the existing German Wikipedia article at de Diffusor Akustik see its history for attribution You should also add the template Translated de Diffusor Akustik to the talk page For more guidance see Wikipedia Translation Diffusion in architectural acoustics is the spreading of sound energy evenly in a given environment A perfectly diffusive sound space is one in which the reverberation time is the same at any listening position Most interior spaces are non diffusive the reverberation time is considerably different around the room At low frequencies they suffer from prominent resonances called room modes Acoustic diffusing discs illuminated blue hanging from the ceiling of the Royal Albert Hall Contents 1 Diffusor 1 1 Maximum length sequence diffusors 1 2 Quadratic residue diffusors 1 3 Primitive root diffusors 1 4 Optimized diffusors 1 5 Two dimensional hemispherical diffusors 2 See also 3 References 4 Further readingDiffusor editDiffusors or diffusers are used to treat sound aberrations such as echoes in rooms They are an excellent alternative or complement to sound absorption because they do not remove sound energy but can be used to effectively reduce distinct echoes and reflections while still leaving a live sounding space Compared to a reflective surface which will cause most of the energy to be reflected off at an angle equal to the angle of incidence a diffusor will cause the sound energy to be radiated in many directions hence leading to a more diffusive acoustic space It is also important that a diffusor spreads reflections in time as well as spatially Diffusors can aid sound diffusion but this is not why they are used in many cases they are more often used to remove coloration and echoes Diffusors come in many shapes and materials The birth of modern diffusors was marked by Manfred R Schroeders invention of number theoretic diffusors in the 1970s He got the idea during a 1977 Gottingen lecture by Andre Weil Gauss sums and quadratic residues celebrating the 200th anniversary of the birth of Gauss 1 Maximum length sequence diffusors edit nbsp MLS DiffusorMaximum length sequence based diffusors are made of strips of material with two different depths The placement of these strips follows an MLS The width of the strips is smaller than or equal to quarter the wavelength of the frequency where the maximum scattering effect is desired Ideally small vertical walls are placed between lower strips improving the scattering effect in the case of tangential sound incidence The bandwidth of these devices is rather limited at one octave above the design frequency diffusor efficiency drops to that of a flat surface Quadratic residue diffusors edit nbsp 1000Hz Quadratic Residue DiffusorMLS based diffusors are superior to geometrical diffusors in many respects they have limited bandwidth The new goal was to find a new surface geometry that would combine the excellent diffusion characteristics of MLS designs with wider bandwidth A new design was discovered called a quadratic residue diffusor 2 Today the quadratic residue diffusor or Schroeder diffusor is still widely used Quadratic Residue Diffusors can be designed to diffuse sound in either one or two directions Primitive root diffusors edit Primitive root diffusors are based on a number theoretic sequence based on primitive roots Although they produce a notch in the scattering response in reality the notch is over too narrow a bandwidth to be useful In terms of performance they are very similar to Quadratic Residue Diffusors 3 4 Optimized diffusors edit By using numerical optimisation it is possible to increase the number of theoretical designs especially for diffusors with a small number of wells per period But the big advantage of optimisation is that arbitrary shapes can be used which can blend better with architectural forms Two dimensional hemispherical diffusors edit nbsp Example of a 2D acoustic diffusor using QRD methodDesigned like most diffusors to create a big sound in a small room unlike other diffusors two dimensional diffusors scatter sound in a hemispherical pattern This is done by the creation of a grid whose cavities have wells of varying depth according to the matrix addition of two quadratic sequences equal or proportionate to those of a regular diffusor 5 These diffusors are very helpful for controlling the direction of the diffusion particularly in studios and control rooms 6 See also editSound baffleReferences edit Xiang Ning Sessler Gerhard M eds 2015 20 Bell Laboratories Acoustics Information and Communication Memorial Volume in Honor of Manfred R Schroeder Cham Springer International Publishing p 396 doi 10 1007 978 3 319 05660 9 ISBN 978 3 319 05659 3 M R Schroeder April 1979 Binaural dissimilarity and optimum ceilings for concert halls More lateral sound diffusion J Acoust Soc Am 65 4 958 963 Bibcode 1979ASAJ 65 958S doi 10 1121 1 382601 Eliot Feldman July 1995 A reflection grating that nullifies the specular reflection A cone of silence The Journal of the Acoustical Society of America 98 1 623 634 Bibcode 1995ASAJ 98 623F doi 10 1121 1 413656 Walker R The design and application of modular acoustic diffusing elements PDF BBC Research Department Retrieved 25 March 2019 Strube Hans Werner 1981 More on the diffraction theory of Schroeder diffusors The Journal of the Acoustical Society of America Acoustical Society of America ASA 70 2 633 635 doi 10 1121 1 386757 ISSN 0001 4966 The effects of 2d diffusers on sound diffusion PF in Dari Further reading editT J Cox and P D Antonio Acoustic Absorbers and Diffusors Theory Design and Application Spon press M R Schroeder Number Theory in Science and Communication Springer Verlag 1984 see especially sections 15 8 and 26 6 Retrieved from https en wikipedia org w index php title Diffusion acoustics amp oldid 1186749568, wikipedia, wiki, book, books, library,
