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Attenuation of Sound Reflections due to Diffraction
... The model assumes that the attenuation between two orchestra members is mostly caused by players sitting in line of sight: by idealising these as simple 1D knife-edge obstacles, the insertion loss between players can be parameterized by using a combination of analytical formulations for diffraction shadow zones [32,31] and reflections [33]. These were combined with additional model parameters identified by fitting the model predictions to the measured data using the Nelder-Mead method [34]. ...
... and 1 is a one-dimensional reflection coefficient given by Eqs. 9-12 in [33]: * = 2 ...
... Parameters S and R correspond to 1 and 2 , and 2 = 1∕(4.11 ) in [33]. The latter is a distance-dependent opening factor identified via Nelder-Mead method [34]. ...
One of the main challenges in predicting the room acoustic conditions on a stage is taking into account the presence of the ensemble and its effect on sound propagation. In a scenario where diffraction effects are dominant and the shape and arrangement of obstacles are not only highly complex but also time-varying, geometric acoustic methods do not yet provide sufficient accuracy for calculating room acoustic parameters or for auralisation. To address this limitation, anechoic measurements from a group of seated subjects were combined with Boundary Element Method simulations at lower frequencies to obtain broadband insertion loss values for a total of 104 paths within a typical orchestra setup. These transfer functions have been converted into a Diffraction-Induced Attenuation by Seated Persons FIR Database, which includes linear phase approximations of the direct sound as well as floor reflections, and reproduces the attenuation that occurs between players in an orchestra. Based on these filters, a parametric model was developed to predict insertion loss within different groups of seated people. This can be used in geometric acoustic simulations and auralisations to account for insertion loss within different groups of seated people, as they occur in many acoustically relevant everyday situations.
... Fig. 8 shows a typical situation for the diffraction from the edge. Rindel [7] has developed an approximation of Fresnel/Kirchhoff. (See App. ...
... Q' is the mirror source. Rindel [7] states that attenuation due to diffraction is of minor importance above a limiting frequency: ...
... App.D.1: Diffraction from a finite surface (from[7]) ...
... This proved to be a complicated process and one that was very expensive in terms of computer time. In references [4] and [5], the author found that increasing the speed of the Genetic Algorithm (GA), and thus increasing the number of optimising generations, was more important than the accuracy of calculations within each generation. For this reason, in the simplified geometric method described here, the perturbation of the control points is only performed along the V axes of each plane. ...
... This allows for a simple and systematic evaluation of diffraction effects using the methods developed by Rindel 6 . An advantage that has been put to use in ref. [5], studying the diffraction effects on flat surface stage reflector arrays. ...
... This was done up to about 1 kHz, where most diffraction effects are expected for audible frequencies. Fig. A.11. Reflector frequency responses (11 m x 12 m): 'Analytical 2D' refers to a continuous canopy modelled with 2D assumption in two directions with analytic approximation ( [38]). 'BEM 3D Continuous' refers to this continuous canopy modelled with BEM, while 'BEM 3D Split' refers to the same canopy but patched in a grid with gaps modelled with BEM, see Fig. 2. ...
Early reflections are an important factor for the acoustic conditions on stage. To better understand their effect on the perception of musical performers, an experimental study was conducted to investigate how the time and direction of arrival, the diffusivity and the strength of early reflections affect the perceived acoustic quality on stage. Architectural variations of a typical stage structure were created in computer models. Combinations of different stage widths, canopy heights, and surface scattering were modelled using geometric acoustics and Boundary Element Method (BEM) simulations. Listening experiments carried out with musicians of different instrumental groups playing with real-time auralisations of these virtual concert hall stages revealed that both the time and direction of arrival of early reflections have a significant effect on the stage acoustic conditions perceived by solo musicians. In a larger battery of stage acoustic parameters determined for each architectural variation, the ‘Top to Sides’ and ‘Top to Horizontal’ ratios (TS, TH) proved to be the best predictors of the acoustic quality of the stage configurations presented, although the interrelation within the musicians seems to be less uniform than for room acoustic parameters from the audience perspective.
... First, each surface must be assigned a scattering coefficient (user defined scattering coefficient). Second, the software selects a simplified method to automatically account for the scattering caused by diffraction (reflection based scattering coefficient) [31,32]. The final scattering is calculated from the two scattering coefficients. ...
Residential perimeter blocks can shield traffic noise, but the acoustical quality may be sub-optimal in the inner courtyards. This study investigated how effective sound-absorbing facade surfaces and balcony soffits as well as an absorbing floor (lawn) influence the acoustical quality in inner courtyards. Room acoustical simulations were carried out for eight generic and two real-world models with very large numbers of transmission paths. Facades (reflecting, fully absorbing, partially absorbing), balcony soffits (reflecting, absorbing) and courtyard floor (reflecting, absorbing) were varied. A range of room acoustical parameters were evaluated, namely, reverberation time T20, early decay time EDT, strength G, speech transmission index STI, and Dietsch’s echo criterion EK. The simulations revealed that fully absorbing facades are an effective measure to improve the acoustical quality in inner courtyards, while partially absorbing facades result in smaller improvements. In fact, each additional storey of absorbing facades further improves the situation. In the case of non-absorbing facades, absorbing balcony soffits or an absorbing floor in the inner courtyard are not very effective as individual measures and may even increase disturbances due to echoes. The same holds true for situations with absorbing facades. Their feasibility should therefore be clarified for the individual situation in question.
... D'Orazio). out the space is closely related to their physical and acoustic features, such as their height, sound-absorbing, and sound-transmitting properties [15,16]. Table 1 offers a non-exhaustive list of references concerning screens in open-plan offices. ...
Sound-absorbing barriers and screens are commonly employed to mitigate one of the most annoying noises in workplaces: intelligible speech. However, isolating their acoustic contribution from all the other elements (ceilings, wall treatment, or carpets) is challenging. This study uses a wave-based room acoustic modeling
approach to explore the acoustic function of desk screens in a virtually reconstructed open-plan office. Analytical models, finite-element simulations, and experimental data from 3D-printed samples allowed defining a multi-resonator unit cell, attenuating the voice signal’s main formants. The sound-absorbing panels composed of the unit modules iteration are assessed in the full-scale digital model, starting from the calibrated version on in-field measurements. The wave-based engine employed in this study grants the crucial aspect of computing the
acoustic performance of the potential multi-resonator screens, including the edge diffraction due to their desk installation. In the virtual workplace, the acoustic role of such screens in increasing the speech level decay is outlined in comparison with the calibrated scenario and the traditional screens’ option.
... If a receiver lies within this contour, a reflection path exists between the source and the receiver via the corresponding surface, as shown in figure 10. The algorithm will then provide a ∆L curv (in dB) corresponding to the change of reflection strength due to the curvature of the surface [17], and a ∆L diffr (in dB) corresponding to the attenuation of the reflection due to diffraction and the finite size of the surface [21]. Figure 9: The canopy is shaped after a disk and convexly curved in two directions, with varying radii of curvature in both short and long sections. ...
A new music centre is currently under construction in Turku, Finland, containing a 1300-seat concert hall dedicated to symphonic concerts and a 300-seat multipurpose hall primarily designed for chamber music concerts and orchestra rehearsals. The centre will become the new home of the Turku Philharmonic Orchestra. Design work started in early 2021 and opening is planned for spring 2026. The architectural design is led by PES-Architects, with the acoustic design by Kahle Acoustics and Akukon Ltd.
This paper describes the acoustic intentions for the main symphony hall and the specific design process developed for the project. The typology developed for the hall aims above all at acoustical excellence, while also seeking to transform the traditional frontal shoebox shape into a new, more intimate paradigm. The design is entirely based on curved surfaces, requiring precise analysis of the acoustical behaviour of 3D curved shapes and an appreciation of their potential to convey early reflections with optimum delay, strength and direction of arrival. Excellent clarity and strong acoustic impact are expected from this concert hall, since the design optimisation – with architects and acousticians working within the same 3D parametric environment – has achieved multiple early reflections to all audience seats.
Particular consideration was also given to the spatial distribution of the acoustic volume, aiming at maximizing the audience’s sensation of being immersed in and enveloped by the music.
Inspired by successful precedents and displaying very promising acoustic simulation results, anticipation for the forthcoming Turku Fuuga music centre is growing.
... The offset distance can be approximated by applying Rindel's equation for sizing reflectors, which factors in reflection angle and characteristic distance between source, reflection point and receiver. 23 The materiality of a surface is determined by the originating image source's attenuation. If its attenuation is due to distance alone, a rigid, massive and smooth material will be required. ...
... The offset distance can be approximated by applying Rindel's equation for sizing reflectors, which factors in reflection angle and characteristic distance between source, reflection point and receiver. 23 The materiality of a surface is determined by the originating image source's attenuation. If its attenuation is due to distance alone, a rigid, massive and smooth material will be required. ...
Geometrical acoustics (GA) offers a high computational efficiency, as required for real-time renderings of complex acoustic environments with applications in, e.g., hearing research, architectural planning, and entertainment. However, the assumed ray-like sound propagation does not account for perceptually relevant effects of diffraction. In indoor environments, diffraction at finite objects and apertures such as tables, music stands, and doors is of interest for computationally efficient rendering. Outdoors, buildings and barriers are relevant. Here, we extend the recent physically-based universal diffraction filter approximation (UDFA) for GA to approximate spectral effects of higher-order diffraction and apply it to a flat finite object and a double edge. At low frequencies, such effects predominantly occur when sound is diffracted repeatedly at the edges of a finite object, and at high frequencies when sound is propagating around subsequent edges of, e.g., buildings or sound barriers. In contrast to existing methods, the suggested filter approaches and topology offer spatially smooth infinite impulse response implementation for modelling higher-order diffraction at flat objects for arbitrary geometrical arrangements. For double diffraction at a three-sided barrier, errors are considerably decreased in comparison to a state-of-the-art sequential approach. Both suggested methods are computationally highly efficient and scalable depending on the desired accuracy.
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