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Periodic surfaces involve strong dependence of incidence angle and frequency on scattering directivity, which can be harmful to auditory tonal impressions in room acoustics, while non-periodic surfaces have potential in yielding uniform directivity and moderate frequency characteristics. This paper aims to develop a new type of aperiodic diffuser based on the Penrose tiling of the plane, and furthermore incorporating a fractal expansion for broadening the effective frequency range. In numerical calculation and scale model experiment, the effects of shape, height and arrangement of Penrose tiles on random- and normal-incidence scattering coefficients are examined. In addition, the uniformity of scattering directivity is evaluated in the calculation of directional diffusion coefficients. [ABSTRACT FROM AUTHOR]

In room acoustics design, one-dimensional periodic surfaces, such as ribbed or corrugated walls, are ordinary used to scatter reflected sound and to increase sound field diffuseness. There exists some measured data of random-incidence scattering coefficient for periodic surfaces, however a substantial database is not yet provided. Instead of the measurement, numerical analysis in a free field is useful to calculate directional scattering coefficients. This paper numerically investigates the characteristics of random- and normal-incidence scattering coefficients of one-dimensional periodic surfaces, focusing on the effects of shape, height and width of surface profile. Additionally, 1/4-scale model measurements are conducted for typical profiles in order to verify the numerical results. Finally, optimal height-to-period ratios, maximizing random- or normal-incidence scattering coefficient, are found for sinusoidal, triangular and rectangular profiles, respectively. [ABSTRACT FROM AUTHOR]

Abstract: This paper investigates the material characteristics of diffusers for acoustical renovation of existing small performing spaces. Consideration is given to acoustical effects on sound fields through the practical cases of two performing halls: the Chamber Hall (450 seats) and the M-Theater (630 seats) in the Sejong Performing Arts Center, Seoul. The Chamber Hall was completely refurbished into a recital hall from its previous shape of a rectangular conference space. The saw-tooth shaped wall diffuser profile in the Chamber Hall was designed using glass-fiber reinforced concrete for mid-frequency sound diffusion. The M-Theater was renovated as a live and intimate space for dramatic performances with a design that included more seats on the upper floors and additional spaces above ceiling reflectors. The vertically-patterned diffuser profile with protruded cubic surfaces in the M-Theater was designed using glass-fiber reinforced gypsum for sound diffusion in the major speech frequency range. Designed diffuser profiles were evaluated for both halls by measurements of scattering and diffusion coefficients of the 1:10 scale model diffusers. The effects of diffusers in both halls were also investigated by covering the lateral walls close to the stages with reflective materials to control diffusive surfaces. As a result, spatial uniformity increased with diffusive wall profiles in both halls. [Copyright &y& Elsevier]

Abstract: A turntable apparatus and measurement procedure, based on ISO 17497-1, were developed for measuring the random-incidence absorption and scattering of surfaces, without specialized facilities. While not highly accurate, they proved adequate for determining the general characteristics of surfaces. Two original profiled wooden architectural surfaces, and a hard, flat reference surface, were characterized, and found to have low absorption and scattering. They were then modified for increased absorption by creating Helmholtz-resonator configurations, obtaining good performance at low- and mid-frequencies. They were also modified for increased scattering, in one case by creating a Schroeder diffuser. In the other case, the surface was integrated into a novel frame-array configuration, which scattered sound very well above 500Hz. [Copyright &y& Elsevier]

Abstract: This paper presents the effects of height and coverage density of diffusive surfaces through the measurements of scattering and diffusion coefficients using scale models. Measurements were conducted using a 1:10 scale model. Scattering coefficients of 1D, 2D, and 3D diffuser profiles as well as diffusion coefficients of the 3D diffuser profile (hemisphere) were measured. It was found that the structural height of the diffuser is closely related to the frequency characteristics of the scattering coefficients, while the coverage density of the diffuser is closely related to the values of the scattering coefficients. Diffusion coefficients were less sensitive to structural height and coverage density than were the scattering coefficients. Using the measurement results, scattering and diffusion coefficients were estimated. In addition, the relationship between scattering and absorption coefficients was discussed. [Copyright &y& Elsevier]

Abstract: An experimental investigation is performed to determine the random-incident scattering coefficients of wooden diffuser structures characterized by different materials, geometrical designs, groove depths and baffle features. In general, it is found that the reliability of the measurement results obtained using the ISO 17497-1 standard can be improved by inserting the test sample into the rotating turntable in order to reduce the edge effect. The experimental results show that a higher scattering coefficient is obtained when the diffuser is fitted with flutters, has a double-triangular upper-surface profile, and has a greater groove depth. The results and discussions presented in this study provide architectural acousticians with a useful framework for evaluating the sound-scattering performance of various wooden diffuser structures in indoor environments. [Copyright &y& Elsevier]

Abstract: Currently there is limited information on what scattering coefficients (SCs) to assign materials in geometrical room acoustic computer models. As a result, room modelers rely on general guidelines and intuition when assigning SCs. How sensitive is the predicted sound field to the user’s choice of scattering coefficients? The sound field’s sensitivity depends on its diffusivity (without SCs); the more diffuse the room’s sound field is, the less sensitive the virtual room is to the selection of SCs. In rooms with no fittings to diffuse sound energy, the sound field diffusivity is influenced by (1) room shape, (2) volume, (3) amount and (4) location of absorption, and (5) the choice of SCs. This investigation focuses only on the latter three factors. A rectangular room is modeled in ODEON v6.5 with 10 absorption schemes. These schemes vary in terms of the area of mirrored reflective surfaces, average absorption coefficient, and standard deviation of absorption. The amount of diffuse reflections at each room boundary as dictated by the SC is increased uniformly in each room. Changes in the room sound field, in particular in the reverberation time (T30), are examined at each step. Sound field diffusivity, and consequently a virtual room model’s sensitivity to SCs, is found to depend most on the area of mirrored reflective surfaces. Also, a proposed quantity called the Scattering Sensitivity Index appears to predict sound field diffusivity. [Copyright &y& Elsevier]

Abstract: To predict acoustics of rooms using computer programs based on geometrical assumptions, it is important that scattering is included in the calculations. Therefore scattering is usually included in terms of scattering coefficients which are assigned to each surface telling the software the ratio between the part of the reflected energy which is not being reflected specularily and the total reflected energy. However the effective scattering coefficient of a surface depends not only on the roughness of the surface material indeed diffraction caused by limited dimensions of the surface as well as edge diffraction also causes scattering. For complex rooms it can be difficult to give a reasonable estimate to the magnitudes of scattering coefficients if these should also include diffraction and even if these frequency dependent coefficients could be obtained in the design phase, the processes of obtaining the data becomes quite time consuming thus increasing the cost of design. In this paper, practical methods to define scattering coefficients, which is based on an approach of modeling surface scattering and scattering caused by limited size of surface as well as edge diffraction are presented. The predicted and measured acoustic parameters in real rooms have been compared in order to verify the practical approaches recommended in the paper. [Copyright &y& Elsevier]

The degree of diffusion, characterized by the “scattering coefficient” of surface materials, has been known to be one of the most important factors in determining the acoustical qualities of concert halls. Based on the suggested ISO method, which measures the random-incidence scattering coefficient of surfaces in a diffuse field, the scattering coefficients of different sizes and densities of wooden hemispheres and cubes were measured in model-scale reverberation rooms. The results show that hemispheres with a height of more than 15 cm have the highest average (500 Hz to 4 kHz) scattering coefficient. It was also found that the scattering coefficient becomes higher when the diffuser density reaches about 50% for hemispheres and 30% for cubes. [Copyright &y& Elsevier]

Since the invention of Schroeder diffusers, extensive studies have been carried out on the prediction and measurement of diffusion coefficients and correlation scattering coefficients in the far field, providing valuable referring data for public. However, as another important evaluation index, the random-incidence scattering coefficients of Schroeder diffusers, which are popularly used in geometric room acoustic models for accurate predictions, have not yet been systematically studied in the diffusing field. This paper presents an experimental study on the scattering coefficients of two well-known Schroeder diffusers (maximum length sequence (MLS) diffusers and quadratic residue diffusers (QRDs)) in one 1:10 scaled-down reverberation room. The scattering coefficients of these Schroeder diffusers were compared to discover their variation laws as a function of well depth, well width, sequence length and the ratio of the maximum well depth to the wave length. To validate the accuracy and reliability of the scaled-down measurements, the scattering coefficients of six MLS diffusers, as well as their standard deviations, were also measured in a full-size reverberation room. The results measured in this study provide engineers and acousticians with some useful reference data in room acoustics design. [ABSTRACT FROM AUTHOR]