# A Psychoacoustic Investigation on the Effect of External Shading Devices on Building Facades
## 1 Introduction and Objectives  
Traffic noise is a major sound pollutant in densely populated cities. It has been largely demonstrated that long-term and short-term exposure to noise has a strong impact on human health and behaviour [1]. There are many possibilities to mitigate traffic noise inside dwellings in crowded cities, using noise barriers between traffic lanes and buildings, or enhancing the facade sound insulation. The efficacy of the noise barriers, of various types and shapes, has also been studied [2; 3; 4; 5; 6]. Recent research funded by the European Union's Seventh Framework Programme (FP7/2007-2013--HOSANANA [7]) studied the optimisation of green areas and surfaces, in order to reduce noise propagation in urban areas. Noise barriers often present installation problems due to lack of space between the noise source and the buildings to be protected. If the noise barrier installation is not possible or not effective, the design of the building facade becomes very important. It is quite easy to obtain good performances in sound insulation of the opaque components of a building facade. Furthermore, its shape design represents a good opportunity to protect dwellings from external noise [8; 9; 10; 11; 12; 13]. Since the windows represent the weak element in facade sound insulation, they have been widely studied: they represent the visual and the ventilating interface between the internal and the external space of a building. [PERSON] [14] presented a laboratory study on the possibility to enhance the noise attenuation of windows, introducing transparent micro-perforated sound absorbing panels, in order to maintain natural ventilation and daylighting comfort. The results of similar experiments, both on a scale model and using a full-scale model, are respectively shown in [15; 16]. Different issues arise in buildings with large glazed surfaces on the facade, such as curtain wall systems. For example, they force designers to use shading systems in order to avoid excessive solar irradiation, which can increase the energy consumption to cool the building, while reducing the discomfort due to thermal and glare effects perceived by the users. The efficiency of the external shading devices in terms of the reduction of energy consumption and visual comfort enhancement has been largely demonstrated [17; 18; 19; 20], but their acoustic effects on the building facade have not yet been well studied. Some recent works have focused their attention on the acoustic effects of the shading devices on the buildings in terms of sound pressure level (SPL) differences over the building facade (insertion loss (IL), in dB), behind the louvres [21; 22; 23]. It has been demonstrated that the external louvres tend to increase the sound pressure level over the facades, since they receive not only the direct sound waves, but also the sound reflections that are generated by the louvres. In [23], a laboratory study was presented to acoustically optimise the louvres, applying to them a layer of sound absorptive material, in order to reduce the sound pressure level over the building facade: The insertion loss provided by the sound absorbing louvres is much higher if compared with the effect of the traditional shading system. The use of the insertion loss in dB is a commonly used procedure in the evaluation of the acoustic effects of a barrier or other building components. However, it has been demonstrated [24; 25; 26] that objective values in dB are not necessarily correlated to human perception in terms of the disturbing characteristics of noise. In [27], the airborne sound insulation was studied using a loudness model instead of making a traditional evaluation [28]. The study was conducted in order to introduce a procedure to find a subjective estimation for airborne sound insulation. This paper presents analyses related to the effect over the building facade of a shading device in terms of variation of some psychoacoustic parameters, namely loudness, roughness and sharpness [29].