## 1 Introduction  
During the last decade, thermal comfort research has seen a revival of natural ventilation (NV) as a passive design strategy to reduce cooling and ventilation energy demand [1; 2], while providing pleasant thermal environments [2; 3; 4; 5; 6] and reducing the possibility of sick building syndrome [7; 8]. NV uses temperature differences or wind pressure differentials to supply and remove air across ventilation openings to and from indoor spaces [9], without the adoption of mechanical systems to drive air movement (e.g., fans). The successful implementation of NV depends on several factors, such as the implemented ventilation strategy [10], the configuration of ventilation devices [11; 12], the building floor plan [13], the characteristics of the neighboring buildings [14], the local climate [4; 15], the outdoor air quality [1; 16; 17], and the external acoustic environment [18]. In addition, as a consequence of building users' needs and lifestyle changes (e.g., people spending more and more time out of home) the successful management and control of passive design solutions such as NV could depend on their effective integration into home automation systems, eventually controlled by sensor-driven building management systems. When such constraints make NV not suitable as the only ventilation strategy, NV could be combined with mechanical ventilation, thus referring to \"mixed-mode\" ventilation. Windows and other ventilation openings constitute the main interfaces between outdoor and indoor environments. The indoor-outdoor connection they provide has been, so far, a major limiting factor in the use of NV due to the conflict between ventilation needs and the intrusion of external noise, which impedes naturally ventilated buildings from meeting background noise limits set by acoustic standards, building design regulations and rating protocols. As a response, for a long time, research has been developing a number of solutions that try to guarantee ventilation without compromising facade noise insulation [19; 20; 21; 22; 23; 24]. Each of them presents advantages and disadvantages, but, up to the now, none has taken hold on large scale. Attempts to block out external sounds while allowing for ventilation and silent indoor environments reflect the traditional noise control engineering approach, where sound is considered to be a \"waste\", inherently unwanted (i.e., noise) and as such to be reduced, regardless of its meaning, and its temporal or spectral characteristics. Perceptual outcomes of noise have been mainly evaluated in terms of resulting annoyance, being among the most relevant health issues caused by noise exposure [25]. Exposure-response relationships between noise levels and the percentage of highly annoyed residents have been derived for road traffic, railway, aircraft, and wind turbines [26]. Several annoyance models have been developed to predict total annoyance due to multiple simultaneous sources (e.g., model of energy summation, independent effects, energy difference, and dominant source). Such models are psychophysical if they are based on sound pressure level metrics, or perceptual if they are built on partial annoyance models. Their predictive powers have been compared through several studies, both in laboratory conditions and from social survey data, and extensive description and discussion can be found in the literature [27; 28; 29; 30]. Annoyance models for single or combined sources have typically focused on different disturbing source types, such as: road traffic [28; 29; 31; 32; 33; 34; 35; 36], railways [37; 38], tramways [35; 39], industrial noise [27; 28; 29; 31; 40; 41], and aircraft noise [36; 42]. Consequently, little is said about \"wanted\" sounds or sounds of preference. Differently, soundscape research integrates noise control engineering approaches with physical, social, and psychological approaches to reach a holistic characterization of the acoustic environment, its perceived dimensions, and its health outcomes.