# Sound Environments in Large Public Buildings for Crowd Transit: A Systematic Review
## 4 Discussion
### Perceptual Attributes  
The used subjective measures for perceptual attributes were found to be abundant. Most studies collected individual responses through surveys, which assessed six aspects, including the overall acoustic evaluation, sound noticeability, sound preference, soundscape descriptors, sound descriptors, and control, covering topics in both room acoustics and soundscape. The subjective items characterizing the acoustics of spaces could be classified into four categories as below:  
* Annoyance: \"annoying\" or \"comfortable\", etc., demonstrating the positive/negative effects of the sound environments
* Affective Quality: \"cool\" or \"warm\", etc., which is associated with the emotional fluctuations of individuals caused by the sound or acoustic activities
* Room-Acoustic Quality: \"loudness\" or \"reverberation\", etc., which neutrally (i.e., no valence-related scales) describes the auditory perceptions of the space
* Acoustic Spatiality: \"directionality\", \"large\", etc., which is a subjective impression rather than a measure related to the spatial localization or recognition of sound source or sound environment.  
The former two categories, that is, annoyance and affective quality, were focusing on the individual-related changes, and the latter two, that is, room-acoustic quality and acoustic spatiality, were treated objectively. As it can be seen, perceptual attributes as annoying, comfortable, and loudness could be the basic descriptors which have been most frequently surveyed at present and used to measure the levels subjectively in the spaces. The selections of other measures and their results were highly project-specific, and it is reasonable to believe that the comparisons across building types could be unsuitable at this stage.  
In terms of special considerations on users' dynamics of subjective perception, some attributes appeared to be concerned with a number of users, such as \"crowded-uncrowded\", \"crowded-empty\", and \"unsteady-steady\". Meanwhile, some attributes were applied with the source noticeability, such as \"directionality\", \"far away-nearby\", and \"know the position-don't\". However, detailed results of these descriptors were limited, comparing to the reports of loudness and comfort.  
Regarding the spatial features of sound environment of such large public, some attributes looking at the space scale, such as \"large-small\", \"tight-loose\", \"spacious-narrow\", were also found to be of interests to be known in one or two surveys, especially for the visually impaired people, besides the \"reverberation\" or \"intelligibility\".  
Most studies have confirmed certain associations between objective and subjective measures, although they were discussing sound levels and annoyance, or loudness. Some studies [29; 46] started to consider user-related factors together, such as acoustic sequence in sound levels and users' directions. Some studies [26] pointed out that the effects of sound source content were more dominant than those of sound levels in perceptions of such spaces. Overall, the present deficiencies were somehow similar to those of objective measures, that is, overlooking the effects of space scale and type, as well as sound source. Given the current application of these subjective measures are not standardized with building types, four basic perceptual assessments belonging to each category are recommended: (1) \"annoying-not annoying\"; (2) \"crowded-uncrowded\"; (3) \"long-short\" (reverberation), and (4) \"far away-nearby\". In addition, other attributes related to building type affecting the crowd are suggested, such as \"concentrating\" for museums/exhibition spaces, \"exciting\" for shopping malls, and \"clear\" for transportation hubs/stations. These main four perceptual constructs should be the core around which developing assessment scales, rather than proposing long lists of items for users to assess.