# Sound Environments in Large Public Buildings for Crowd Transit: A Systematic Review
###### Abstract  
Sound environments in large public buildings are likely to be different from those of performance spaces, as well as those not specifically designed for acoustic \"performance\", but where sounds still play an important role because of the function they can promote (or disrupt). The aim of this study was identifying common strategies and empirical approaches researchers have been implementing for these acoustically complex enclosures and to provide some methodological indications for future studies on the topic. Studies conducted in three building types for crowd transit, such as museums/exhibition spaces, shopping malls, and transportation hubs/stations, which were collecting data about either physical outcomes or individual responses for such sound environments, were selected. The Scopus databases were searched for peer-reviewed journal papers published in English without time limitations. An additional manual search was performed on the reference lists of the retrieved items. The general consideration on inclusion was to meet the requirement that the case belonged to the three building types, and then the specific inclusion criteria were: (1) including at least an objective acoustic measure of the space; or (2) including at least a subjective measure of the space. The search returned 1060 results; after removing duplicates, two authors screened titles and abstracts and selected 117 papers for further analysis. Twenty-six studies were eventually included. Due to the limited number of items and differences in measures across studies, a quantitative meta-analysis could not be performed, and a qualitative approach was adopted instead. The most commonly used objective measures were SPL, and more specifically often considered as \(L_{\text{Aeqy}}\) and \(T\). The intervals across studies were currently of inconsistency, and the selection is recommended to take space scale factor into account. The used subjective measures can be classified into four categories as annoyance, affective quality, room-acoustic quality, and acoustic spatiality. Four basic perceptual assessments concerning dynamic contents are accordingly suggested as \"an annoying-not annoying\", \"crowded-uncrowded\", \"long-short (reverberation\"), and \"far away-nearby\". The other descriptors can be project-specific. The methodologies involve measurement, questionnaire/interview, listening test, and software simulation. It is necessary for the former two to consider temporal and spatial features of such spaces, and the adoption of the latter two will lead to better understanding of users' exposure in such spaces, e.g., acoustic sequences and user amount. The outputs of investigations inform that background noise level, e.g., 90 dB in museum/exhibition spaces, and sound reverberation, e.g., 4.0 to 5.0 s in shopping malls and transportation hubs/station, are of fundamental importance to the design of such spaces. Sufficient acoustic comfort can be achieved with integrated design of indoor soundscape. room acoustics; soundscape; museum; shopping mall; transportation station +
Footnote †: journal: Medical  
for listening or performing) it is indeed crucial that clear criteria related to measurable parameters are in place to assess their acoustic quality and performance [3]. For this reason, international standards have been developed over time to harmonize measurement protocols and reporting requirements [4]. This gradually extended to spaces that are not specifically designed for acoustic \"performance\", but where sounds still play an important role because of the function they can promote (or disrupt), like libraries, open-plan offices, for which specific guidance has been produced [5; 6], and restaurants, canteens [7; 8; 9; 10] as well. In parallel, researchers have approached the acoustic characterization of large indoor spaces also from a perceptual perspective, that is, investigating how users actually experience themurally [11; 12; 13]. This applies to both spaces for acoustic performance and not, alike.