Room modes are known to be problematic in small critical listening environments. They degrade the acoustic quality at low frequencies, producing peaks and nulls in the frequency domain and ringing in the time domain. The Finite Element Method (FEM) is currently the easiest way to predict such resonances for arbitrarily shaped rooms. This solves for mode frequencies and shapes, as well as Q-factors and decay rates. Such 'eigenfrequency' solvers are commonplace in FEM, but FEM has the disadvantage of needing to mesh the entire air volume in the room. The Boundary Element Method (BEM) avoids this and only requires a simple boundary mesh, but solution of its eigenfrequency problems is much more challenging and appears in only a few academic papers. Here we transfer those approaches to Room Acoustics. We implement the block Sakurai-Sugiura method, which uses a contour integral in the complex frequency plane to convert the BEM eigenfrequency problem, which is usually non-linear in wavenumber, into a standard linear eigenfrequency problem that is straightforward to solve. The method is demonstrated through application to a cuboid room and an irregularly shaped room, both with impedance boundary conditions. Results are validated against FEM and discussed.

It is rather common experience to observe that many contemporary churches, in contrast with the effort to achieve refined architectonic shapes and finishes, exhibit poor acoustic quality, such as high reverberation times and low speech intelligibility. The causes of such deficiencies are ordinarily generated by the smooth and hard surfaces of walls, floor and ceiling that focus most of sound energy in late reflections, diminishing the effectiveness of direct and early reflected sound. Recently, the authors have been involved for analyzing the acoustic behavior of a modern church situated in Ragusa, (Italy), with the aim to individuate suitable interventions for improving the acoustic quality of that church. Preliminarily, a measurement survey was conducted to evaluate the main acoustic indices proposed by ISO 3382 (T 30 , STI, EDT, C 80 , D 50) and portray the current acoustic climate. After that, the Authors developed a simulation on a 3D model of the church, in order to calibrate the model comparing measured and simulated acoustic parameters. The previously described activities are necessary for testing the reliability and accuracy of the prediction of the acoustic simulations. The subsequent step of the work consists in the choice of suitable interventions for the acoustic corrections; three different typologies of materials were evaluated. Globally, the acoustic corrections allow to obtain noteworthy improvements of the acoustic quality of the church, e.g. the T 30 decrease from 7.3 to 2.5 s and the STI increase from 33% to 40%, at 1000 Hz. Further, the influence of the variation of the audience presence was analyzed, finding out a strict correlation between occupancy percentage and the law of variation of T 30. Finally, after the realizations of one of the suggested interventions of acoustic corrections, the Authors conducted a second survey to evaluate the effects of the refurbishment interventions on the acoustic climate. Since the obtained results do not match very well with the design previsions, some hypotheses that can justify such discrepancy are illustrated.

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Noise pollution is one of the main environmental stressors in urban areas. In particular, strong noise pollution can be experienced at nighttime in downtown areas with intense anthropic activities: here, dwellers may suffer from disturbance to their rest, which induces stress and – in turn – adverse effects on health.Usually, local authorities implement actions to tackle noise pollution, e.g. limiting the time allowed for outdoor events. However, these measures are often inadequate because the noise annoyance comes directly by the shouting of people spending time outdoors till late night.In this framework, this study proposes a procedure to optimize the shape of customized lightweight transparent noise screens that can be applied to façades in order to reduce noise disturbance in urban canyons. The case study of the “movida” area in the downtown of Marina di Ragusa (Southern Italy) is discussed to test the applicability of the proposed procedure.The results of this analysis allow defining the shape and the size of the noise screens that minimize the noise annoyance perceived by residents. The proposed mitigation approach can be applied in cities affected by significant noise pollution.