Acoustic Quality of the External Environment: Indications on Questionnaire Structure for Investigating Subjective Perception

The subjective judgment on the annoyance produced by noise is always an important tool to complete an investigation, and to find the best way for its reduction. Therefore, acoustic analyses for environmental improvement frequently combine objective measures with subjective surveys to gain a comprehensive understanding of the problem. The technical specification, concerning the “Assessment of noise annoyance by means of social and socio-acoustic surveys”, ISO/TS 15666 (revised in 2021), has represented a basis for these activities since 2003, when it aimed to obtain information about noise annoyance “at home”. The more recent ISO/TS 12913-2 (2018), aimed at soundscape studies, investigations and applications, provides guidelines for conducting social and socio-acoustic surveys to assess noise annoyance and, in particular, it gives detailed indications on data collection and reporting. The indications provided by the technical specifications represent a common guideline for addressing the implementation of a subjective survey in the acoustic field, and to make investigations as comparable as possible. However, they do not cover all the fields of acoustic subjective investigations. Therefore, to make the collection of information from questionnaires more effective, it is useful to have a broader review of the issues that need to be addressed. To support this type of activity, this paper collects and presents relevant observations for the design of subjective survey questionnaires focused on outdoor acoustic quality. Drawing on previous research studies and experiences, it provides a series of observations on the main aspects to be considered in order to structure multipurpose acoustic evaluation questionnaires, including discussion of the general considerations for questionnaire structure, administration methods, population sample characterization, question formulation, and classification. It also deals with specific indications related to acoustic evaluations, such as the characteristics of annoying noise, boundary conditions, subjective feelings, and source features.