Indoor Soundscape Intervention (ISI) Criteria for Architectural Practice: A Systematic Review with Grounded Theory Analysis

Abstract

Indoor soundscape is a relatively new and developing field compared to urban soundscape in practice. To address this gap, this study aims to identify the key influencing factors as a first step of the indoor soundscape intervention approach. The study employed a two-phase methodology. Phase one involved a Systematic Review (SR) of the literature, conducted through the PRISMA 2020 guidelines, to collate data on the influencing factors and intervention criteria of the indoor soundscape approach. Searching was conducted using two databases, Web of Science and Scopus. As a result of the search, a total of 29 studies were included in the review. The review included studies addressing the soundscape influencing factors and theoretical frameworks. Studies that did not address these criteria were excluded. Phase two comprised the application of the Grounded Theory (GT) coding process to organize, categorize, and merge the data collected in phase one. As a result of the coding process, three levels of categories were achieved; L1: key concept, L2: overarching category, L3: core category. Four core categories were identified as ‘Sound’, ‘People’, ‘Building’, and ‘Environment’ by proposing the Indoor Soundscape Intervention (ISI) criteria. The repeatable and updatable nature of the proposed method allows it to be adapted to further studies and different contexts/cases.

1. Introduction

The current and common intervention of acoustic environment enhancement in the field is highly based on noise management policies and the reduction in noise exposure. The regulations/legislation enforced by governments and supportive documents such as guidelines and standards have provided applicable interventions and manageable environments for noise exposure, with the contribution of surveillance policies. Reduction in noise and management policies are implemented to avoid the adverse health effects of noise exposure. Still, a positive approach to providing acoustic comfort in a holistic attitude has been lacking. The soundscape approach, which discusses the acoustic environment “as perceived or experienced and/or understood by a person or people, in context” [1], combines noise management and the perceptual dimensions of people on the acoustic environment in a holistic attitude [2] and contributes a positive perspective through considering sounds as a resource rather than a waste to be managed [3,4,5]. Accordingly, embodying the soundscape approach into practice is more likely to take enhancement of acoustic environments one step further by focusing more on user perception, experience, and preference in addition to noise management applications. Increasing attempts and actions have proceeded in the form of the “International Organization for Standardization” ISO standard, and two, mostly research-based, technical specifications [1,6,7] on urban soundscape have been published. In other words, the user-oriented or subjective attitude of the soundscape approach makes the applicability of this approach more complicated in professional practice. Meanwhile, Part 4 of the ISO 12913 series [8], which establishes a framework for the soundscape interventions and aims to act as a guideline for determining whether a soundscape needs preservation and/or improvement, is currently under development. In this context, the Catalogue of Soundscape Interventions (CSI) project is developed to propose a method for urban soundscape interventions. It emerged from the need for a practical guideline for soundscape design, which is the scope of the ISO/TS 12913 Part 4 [8]. The essential aim of the CSI project is the determination of successful soundscape designs all around the world that would be used as essential knowledge to produce strategies for future designs [9,10,11]. The term soundscape intervention is defined under the scope of the CSI project as “a site-specific design, aimed at preserving or improving an acoustic environment” [10]. Hence, a consensus and systematic review of soundscape design and interventions, as well as a summary of empirical evidence on the benefits of sound methods” [12] still missing for in the practice field, and with the data that will be gathered all around the world will lead to developing a “design toolkit” for the soundscape design in the future [12].

On the other hand, the development of indoor soundscaping stays lagging behind the urban soundscape applications. Therefore, it is necessary to investigate how to raise awareness on the indoor soundscape approach during the architectural design and application process, in addition to noise and architectural acoustics applications. The term “soundscape intervention” is described as an umbrella term [9,10,11], that can be used for the indoor soundscape approach as well. The initial step to develop an Indoor Soundscape Intervention (ISI) approach would be the identification of the framework and intervention criteria based on the literature to be used in practice. In this manner, it is essential to identify all the factors that affect the perception of the indoor sound environment as the criteria are to be changed or intervened in. In other words, to design enclosed spaces under the scope of the soundscape approach, identification of specific intervention criteria for the indoor concept is needed. Consequently, the objectives of this study are to (1) identify the factors that influence perception, and to (2) systematically categorize these factors4 and propose that these categories form the basis for future intervention-approach-related studies. This study tries to extract and gather the influencing factors from the literature with a systematic review (SR) and organize the data with the Grounded Theory (GT) coding process. As a result, it is aimed to propose holistic and scientifically based indoor soundscape intervention criteria to be used as a guide in determining the practice principles by answering the following research questions:

• What are the factors that influence the perception of indoor soundscapes in enclosed spaces?
• How can these influencing factors be systematically categorized to support future developments and studies for potential soundscape interventions?

As a result, this study aims to establish a foundational framework of indoor soundscape influencing factors, serving as intervention criteria, intended to act as a multidisciplinary and adaptable backbone for future architectural applications and research.

2. Materials and Methods

This study and its method are designed in two phases: (1) data collection by SR, and (2) analyzing and merging the collected data by Grounded Theory (GT).

2.1. Phase 1: Systematic Review

For the SR, the PRISMA (The Preferred Reporting Items for Systematic Reviews and Meta-Analyses) 2020 guidelines, which are used for reporting sources for SRs and meta-analyses, are used as guidance [13].

2.1.1. Literature Search

A literature search is performed with the two databases Web of Science and Scopus, with the last search conducted in April 2025. Articles, proceedings/conference papers, review papers, and book chapters are included as document types in both databases. All fields (title, abstract, and keywords) are selected during the search for all keywords. The keywords, which have the potential to express the idea of the soundscape elements and theoretical framework, are used by using the ‘OR’ Boolean choice between them. These keywords are ‘component, element, factor, dimension, descriptor, indicator, theoretical model, model, conceptual, contextual, framework’. At the end of these keywords, ‘soundscape’ is added with the ‘AND’ Boolean choice. Even though the scope of the study involves indoor environments, theoretical models of urban or ecologic soundscapes are also evaluated and included in the search. The theoretical basis of urban or ecologic soundscapes has great importance in building the structure of indoor soundscape principles. In addition, urban sounds, sound environments, and urban context influence indoor environments as a part of the indoor acoustic environment. In this context, existing models on urban, ecologic, and indoor soundscapes are evaluated in order to reveal a merged model proposal for indoor soundscape criteria. As a result, the query of Web of Science is formed as (((((((((((ALL = (component*)) OR ALL = (factor*)) OR ALL = (element*)) OR ALL = (dimension*)) OR ALL = (descriptor*)) OR ALL = (indicator*)) OR ALL = (model)) OR ALL = (indices)) OR ALL = (conceptual)) OR ALL = (contextual)) OR ALL = (framework)) AND ALL = (soundscape*), and the query of Scopus is formed as (TITLE-ABS-KEY (component*) OR TITLE-ABS-KEY (factor*) OR TITLE-ABS-KEY (element*) OR TITLE-ABS-KEY (dimension*) OR TITLE-ABS-KEY (descriptor*) OR TITLE-ABS-KEY (indicator*) OR TITLE-ABS-KEY (model) OR TITLE-ABS-KEY (indices) OR TITLE-ABS-KEY (conceptual) OR TITLE-ABS-KEY (contextual) OR TITLE-ABS-KEY (framework) AND TITLE-ABS-KEY (soundscape*)). Moreover, the area of subjects is also restricted to eliminate the irrelevant areas. The Web of Science categories that could be relevant to the subject are included as ‘acoustics, environmental sciences, environmental studies, urban studies, behavioral sciences, architecture, psychology, engineering environmental’, and the subject areas ‘environmental sciences, arts and humanities, social sciences, engineering, psychology’ are included in the Scopus search.

2.1.2. Screening and Eligibility Process

The PRISMA 2020 flow diagram [13] (Figure 1) was used to guide the SR process. During the identification phase, records were retrieved from selected databases using predefined search terms, as well as “identified via other methods” to include the citation search of the related studies. In the screening phase, duplicates were removed, and titles and abstracts were evaluated for relevance. The eligibility phase involved assessing full texts against inclusion and exclusion criteria. Finally, in the inclusion phase, studies meeting all criteria were included. Accordingly, as a result of the database search, a total of 1386 studies were retrieved from Web of Science, and 2106 studies were retrieved from Scopus. A total of 1365 records from the Web of Science results and 2091 records from the Scopus results were removed due to irrelevance of title, keywords, and abstract before detailed screening for eligibility. After duplicated records are removed, 27 studies were retained for full-text assessment. Following the full-text evaluation, 7 studies were excluded due to the absence of identification of the field, affecting elements, or the conceptual/theoretical framework of the soundscape field. In the meantime, 6 articles, 2 books, and 1 standard were derived from the citation search (Figure 1). As a result, a total of 29 studies were included for data extraction for soundscape intervention criteria.

2.2. Phase 2: Organizing and Merging the Data with GT

To analyze and merge the comprehensive qualitative data collected during the SR conducted in the first phase of the study, the inductive GT coding process is employed, which has been used for soundscape studies in the literature [11,14,15,16,17,18,19,20]. GT is commonly used for analyzing and organizing data collected from interviews. However, in this research, the data is obtained from the literature through the SR, which is also applied in the studies of Bowers and Creamer [21] and Wolfswinkel et al. [22]. These studies both adapt GT to analyze data collected from the SR. The main difference between traditional GT and the adapted version is the data collection method. In the adapted version for the SR, data are collected from the secondary sources (published materials) instead of the primary data (interview) [21,22]. GT principles can be maintained while adapting the method to analyze secondary data derived from SRs; however, due to inherent time and source limitations, the traditional theoretical saturation in GT may not always be feasible in the adapted version [21,22]. The traditional GT needs a theoretical saturation as a process that continues as a cycle until the new concepts, information, or data are not revealed [11,22,23,24,25]. However, in review studies, as the data were collected from a systematic literature review and not from sources such as interviews, it can be said that traditional theoretical saturation could not be applied. Even so, the structured search presented in ‘Phase 1: Systematic Review’ was repeated three times in different periods (June 2023, July 2024, April 2025—for reporting, the latest search data was presented in the PRISMA guidelines) during the study process with two databases to reach theoretical saturation as much as possible. Here, since theoretical saturation is a process where data collection ends when the researcher believes that the categories are complete and well-defined [21], it is considered to have been reached in this study as well. However, since the literature is constantly evolving, growing, and being updated, this type of theoretical saturation is naturally limited by the duration of the study and the final date of the literature review. Moreover, transparency and repeatability were ensured through predefined inclusion criteria and a structured search strategy. As a result, this approach reflects an adapted use of GT for literature-based research.

GT is based on three types of coding process: open, axial, and selective coding [11,14,22,24,26]. As summarized in Figure 2, open coding aims to decompose the textual data into smaller, consistent pieces, such as keywords, key phrases, or concepts, to compare them by assigning conceptual labels [11,14,22,24,26]. Afterwards, axial coding groups the conceptually similar data to create categories and subcategories [24]. Axial coding identifies the relationships between the categories based on their relations and similarities [14], such as “causal conditions” or “consequences” [11,26]. Additionally, the categories continue to develop [24]. Selective coding aims to group all the categories around a “core category” and to extend categories with descriptive details that are added to the categories that require more explanation [22,24,26]. Afterwards, the relationships between categories were visualized through schematics, which were used to visualize the relationship patterns between core categories to explain the theory [14].

3. Influencing Factors of Soundscape in the Literature

The 29 sources were assessed to present the existing theoretical models or framework proposals in the literature through the SR. In this context, the previous models on both urban and indoor soundscapes were evaluated to reveal a merged model for indoor soundscape components and are listed in Table 1 in chronological order. Studies using the same models or proposals are placed chronologically according to the year in which they were first used.

As Schafer categorizes sound sources to evaluate four aspects in different approaches, including acoustics, psychoacoustics, semiotics and semantics, and aesthetics, the first soundscape term and approach was revealed under the scope of the soundscape ecology [5]. Acoustical aspects refer to the physical characteristics of a sound, psychoacoustics are related to how sounds are perceived by a listener, semiotics and semantics are used for the function and meaning of a source, and aesthetics means emotional or affective qualities that listeners assign to a source or acoustic environment [5]. With the development of the field, enhancement and evaluation of urban open public spaces through the soundscape approach has been revealed as an alternative or supportive attitude to noise management. Other studies on soundscape ecology [27,28] discussed the concept in four main components, including “atmosphere, natural environment, human system, built environment, and soundscape”

Different studies have emerged to identify the framework within the scope of urban soundscape and the influencing factors of the acoustic environments’ components. Most of them relied on similar fundamentals, yet the perspective of handling the discussion differed. Kang (2006) [29] identified the framework of the urban soundscape as a system that consists of “sound”, referring to sonic characteristics, “space”, as an influencing factor for the sonic characteristics, “people”, referring to different personal characteristics, and the “environment”, referring to all other environmental factors, including thermal, visual, lighting, etc. [29,30,31,32]. Herranz Pascual et al. (2010, 2016) [33,34] studied the relations between “person”, “activity”, and “place” interactions, which would be included in the standard ISO 12913-1:2014 [1] as the definition of context of the soundscape. Similarly, Jennings and Cain (2013) [35] stated the main components of the urban soundscape as “demographics, activity, time, and space”. Özçevik and Yüksel Can (2012) [36] identified the soundscape components for urban acoustic environments as types, features, physical characteristics, and temporal conditions of “sound sources”, physical, seasonal, and topographical conditions of “physical environment”, and social, psychological, sensational, and cultural aspects of “human being”. Kang et al. (2019) [37] discriminate the soundscape components into two main headings as auditory and non-auditory factors. Auditory factors refer to the dominance and meaning of sound sources, and non-auditory factors include physical contextual factors, which have environmental and visual connotations, and social contextual factors, which are the people’s socio-economic characteristics, other cultural aspects, and activities in the place. Chen and Ma (2020) [38] evaluate the urban soundscape approach as “sound sources and acoustic environment, context, people’s demand, and criteria and standards of the healthy acoustic environment”. “Sound sources and acoustic environment” refer to the source identification and the perceived characteristics of the sound environment. “Context” includes site/space, behavior states, and time. “Demands” are directly related to the psychological, physiological, and behavioral needs of the people [38]. Tarlao et al. (2021) [39] discuss the field in four main components, including “user, activity, auditory environments, and contextual factors”, and Zhang et al. (2021) [40] indicate the soundscape components as “audience subjectivity, perceptible sound characteristics, perceptual time, perceptual place, and auditory imagination”, with similar descriptives (L2:D) in people-, sound-, and place-related components. Additionally, “perceptual time” as duration, timing, and frequency is included [40]. Variously, Abdul Hamid et al. (2022)’s study [41] includes “noise sensitivity, visual perception and quality”, Grinfeder et al. (2022) [42] focuses more on geographical and topographical aspects, and Hasegawa and Lau (2022) [43] indicate audio–visual indicators, and visual contextual indicators in different from the other studies.

Table 1. Influencing factors in the literature as a preliminary preparation for the coding process. The chronological list of the studies on theoretical soundscape models is derived from the SR. The categories/groupings listed in the table are directly taken from the studies based on either their original diagrams or textual descriptions and have not been changed or compiled at this stage.

Source and Field	Parameter/Variable/Example/Explanation	Sub-Category	Main Category
Schafer, 1994 [5] Soundscape Ecology		Physical characteristics	Acoustics
		How sounds are perceived	Psychoacoustics
		Function and meaning	Semiotics and Semantics
		Emotional or affective qualities	Aesthetics
Kang, 2006 [29] Zhang and Kang 2007 [32] Kang, 2010 [30] Kang, 2023 [31] Urban Soundscape		Sound pressure level	Sound (Each Source Type)
		Spectrum
		Temporal conditions
		Location
		Source movement
		Psychological/social characteristics
		Reverberation	Space (Effect of Space)
		Reflection of pattern and/or echogram
		General background sound
		Sounds around the space
		Social/demographic characteristics of the users	People (Users)
		Acoustic condition at users’ home and work, experience, etc.
		Temperature, humidity, lighting, etc.	Environment (Other Aspects)
		Visual, landscape, and architectural characteristics
Herranz Pascual et al., 2010 [33] Herranz Pascual et al., 2016 [34] Urban Soundscape	Age, Sex, Labor activity, Socio-economic status, etc.	Socio-demography	Person
	Coping, Well-being, Locus of control, Satisfaction with life, etc.	Health (perception)
		Lifestyle
	Social support, Social cohesion, Relationships, etc.	Social dimension
	Linguistic aspects, Beliefs, Attitudes, etc.	Cultural dimension
	Preferences, (acoustic) Sensibility, Adaption, etc.	Personal dimension
	Emotion (feelings), Cognition (thoughts), Knowledge (meanings)	Perception and valuation
			Activity
		Geography and topography	Place
	Temperature, Humidity, Wind, Seasonal variations	Climate, meteorology
	Planning, Buildings, Infrastructures, Cultural heritage, Land use pattern, Urban vs. rural	Urbanism
	Air, Noise, Vibrations, LFN	Environmental quality and pollution
		Safety
		Humanization
	Water, birds, etc. …	Natural elements
	Courtyards	Quite areas
	Traffic	Mechanical sounds
	Church bells, etc.	Cultural elements
		Humans
	Square, Park, Urban public space, etc.	Place type
	Residential, Cultural, Recreation, Relax, Social	Place function
Pijanowski et al., 2011 [27] Smith and Pijanowski, 2014 [28] Soundscape Ecology		Rain	Atmosphere
		Wind
		Temperature
		Climate regime
	Habitat, Biodiversity, Life history	Biological	Natural Environment
	Landform, Wind–water, photoperiod	Geophysical
	Policy formulation, Policy legitimation	Policies	Human System
		Values
		Cultural identity
		Health
	Economic and lifestyle decisions	Behavior
	Psychological; cognitive, emotional, and behavioral needs	Needs
	Roads, buildings	Structures	Built Environment
	Urban, agriculture, water	Land use
		Composition	Soundscape
		Temporal patterns
		Spatial variability
		Interactions
Özçevik and Yüksel Can, 2012 [36] Urban Soundscape		Type	Sound Source
		Features
		Sound level power of the source
		Duration of the sound
		Physical factors	Physical Environment
		Seasonal factors
		Topographical factors
		Sociological factors	Human Being
		Psychological factors
		Sensational factors
		Cultural factors
Jennings and Cain, 2013 [35] Urban Soundscape			Demographics
			Activity
			Time
			Space
Dökmeci, 2013 [44], Dökmeci Yörükoğlu and Kang, 2016 [45] Dökmeci Yörükoğlu and Kang, 2017 [46] Indoor Soundscape	Type, Time, Intensity	Physical	Sound Environment
	Temporal, Energetic, Spatial, Quantitative SI	Acoustical
	Psychoacoustical, Musical, Other methods	Psychoacoustical
	Individual, Socio-cultural	Demographical	Contextual
	Expectation, Perception, Reaction	Psychological
	Preference, Usage frequency, Time spent	Space usage
	Purpose, Services	Functional	Built Entity
	Formal organization, Spatial relationships, Circulation patterns, Shape and dimension	Spatial
	Air, Thermal, Lighting, and Acoustical quality, Crowd level	Indoor environmental
ISO, 2014 [1] Urban Soundscape			Sound Source/ Acoustic Environment
		Auditory sensation	Context
		Interpretation of auditory sensation
		Responses
Aburawis and Dökmeci Yörükoğlu, 2018 [47] Indoor Soundscape		Type	Sonic
		Level
		Frequency
		Characteristics	Spatial
		Type
		Services/activities
		Time spent	Temporal
		Usage frequency
		Preferred time
		Sensation	Psychological
		Attention
		Expectation
		Reaction	Behavioral
		Response
		Preference
		Individual	Personal
		Socio-cultural
Acun, 2018 [48] Indoor Soundscape		Sound sources	Sound Environment Context
		Physical aspects	Built Environment
		Perceptual aspect
		Consistency	Expectation and Preference
		Inconsistency
		Positive interpretation	Interpretation of Soundscape
		Neutral
		Negative interpretation
Erçakmak and Dökmeci Yörükoğlu, 2019 [49] Indoor Soundscape	SPL, Leq, Lw, RT, EDT, SII, STI	Objective	Acoustical
	Loudness, Sharpness, Roughness, Fluctuating strength	Psychoacoustic
	Time spent, Usage frequency, Preferred time	Temporal	Contextual
	Sensation, Attention, Mood, Expectation, Past experience	Psychological
	Reaction, Response, Preference, Activities	Behavioral
	Individual and Socio-cultural characteristics	Personal/demographical
	Public, Commercial, Industrial, Private, Civil	Function	Architectural
	Organization, Form and shape, Proportion, Materials and furniture, Openings, Circulation, Voids, Overall interior design	Architectural properties
	Air, Thermal, Lighting, Acoustic quality, and Crowd level	Physical environment
Torresin, Albatici, Aletta, Babich, and Kang, 2019 [50] Indoor Soundscape		Sound level, spectral content, roughness, loudness, fluctuation strength, number of sound events, source distance, sound dominance, duration of sound events, intermittency, frequency of annoyance, combination of multiple sources, sound type	Acoustic
		Presence of greenspace, sea view at home, access to a quiet side, source visibility, visual pleasantness, other visual aspects, building spacing and separation distance between buildings, satisfaction with the residential area, wish to change the residence	Urban Context
		Room location, building insulation, window opening position	House-Related
		Age, gender, noise sensitivity, physical and mental health status, personal audiovisual aptitude, perceived noise control, opinion towards the noise source, perception of risk associated with sound source, consideration of the importance of noise, attention paid to the soundscape, mood, thinking style, window closing habits, and noise-related remedies	Person-Related
		Level of education, income, family status, family unemployment, home ownership, economic benefit from noise source, type of housing, country	Socio-Economic
		Context in laboratory studies, survey context, location, activity or task, company of other people, period of day, length of residence	Situational
		Temperature, environmental pollution, odor annoyance	Environmental
Kang et al., 2019 [37] Urban Soundscape	Preference, Usage frequency, Time spent Purpose, Services Formal organization, Spatial relationships, Circulation patterns, Shape and dimension Air, Thermal, Lighting, and Acoustical quality, Crowd level	Space usage	Auditory Factors Social Built Entity
		Functional
		Spatial	Physical Contextual Factors
		Indoor environmental
		Socio-economic	Contextual Factors
		Demographic
		Cultural
		Activities
Chen and Ma, 2020 [38] Urban Soundscape		Sound sources	Sound Sources and Acoustic Environment
		Perceived characteristics
		Sites/spaces	Context
		Behavior states
		Time
		Physiological	People’s Demands
		Psychological
		Behavioral
		Physiological	Criteria and Standards of a Healthy Acoustic Environment
		Psychological
		Behavioral
		Standards
Tarlao et al., 2021 [39] Urban Soundscape		Demographics	User
		Needs
		Familiarity
		Expectations
		Purpose
			Activity
		Perceptual measurements	Auditory Environments
		Acoustic sensor measurements
		Environmental conditions	Contextual Factors
		Spatiotemporal aspects
		Amenities
Zhang et al., 2021 [40] Urban Soundscape		Personal state	Audience Subjectivity
		Preference
		Familiarity
		Loudness	Soundscape (Perceptible Sound Characteristics)
		Pitch
		Richness
		Rhythm
		Duration	Perceptual Time
		Timing
		Frequency
		Space	Perceptual Place
		Environmental condition
		Environmental compatibility
		Mental picture	Outcome (Auditory Imagination)
		Atmosphere construction
		Aesthetic perception
		Emotional expression
		Emotional resonance
Abdul Hamid et al., 2022 [41] Urban Soundscape		Appropriateness	Soundscape Perception
		Eventfulness
		Calmness
		Perceives noise	Noise Sensitivity
		Visual perception	Contextual Characteristics
		Visual quality of environment
		Perceived sound source	Sound Source
		Urban sound environment
Grinfeder et al., 2022 [42] Urban Soundscape		Temporal factors	Environmental Factor
	Geography, Topography, Surface	Spatial factors
	Climate, Weather	Abiotic factors
	Vegetation, Acoustic behavior, Population density, Territory distribution	Biotic factors
	Ground effects, Sound scattering, Meteorological effects	Acoustic factors
		Geophony	Sound Sources
		Biophony
		Ambient sounds
	Attenuation	Sound propagation	Acoustic Filters
	Distortion	Receiver
Hasegawa and Lau, 2022 [43] Urban Soundscape	Traffic noise, Human noise, Nature sound	Audio indicators	Audio–Visual Indicators
		Visual indicators
		Visual indicators Emotional state	Non-Auditory Contextual Indicators
	Gender, Age, Noise sensitivity, Time spent, Frequent look	Demographical characteristics	Person-Related Confounders
		Behavioral characteristics
	Nature type, Region type	Neighborhood characteristics	Environmental Moderators

Note: Table 1 is source-based and constructed from the meaning units extracted from each study. Some sources included more overarching or detailed information than others. Empty cells reflect cases where the original studies did not report the corresponding data.

Table 1. Influencing factors in the literature as a preliminary preparation for the coding process. The chronological list of the studies on theoretical soundscape models is derived from the SR. The categories/groupings listed in the table are directly taken from the studies based on either their original diagrams or textual descriptions and have not been changed or compiled at this stage.

Source and Field	Parameter/Variable/Example/Explanation	Sub-Category	Main Category
Schafer, 1994 [5] Soundscape Ecology		Physical characteristics	Acoustics
		How sounds are perceived	Psychoacoustics
		Function and meaning	Semiotics and Semantics
		Emotional or affective qualities	Aesthetics
Kang, 2006 [29] Zhang and Kang 2007 [32] Kang, 2010 [30] Kang, 2023 [31] Urban Soundscape		Sound pressure level	Sound (Each Source Type)
		Spectrum
		Temporal conditions
		Location
		Source movement
		Psychological/social characteristics
		Reverberation	Space (Effect of Space)
		Reflection of pattern and/or echogram
		General background sound
		Sounds around the space
		Social/demographic characteristics of the users	People (Users)
		Acoustic condition at users’ home and work, experience, etc.
		Temperature, humidity, lighting, etc.	Environment (Other Aspects)
		Visual, landscape, and architectural characteristics
Herranz Pascual et al., 2010 [33] Herranz Pascual et al., 2016 [34] Urban Soundscape	Age, Sex, Labor activity, Socio-economic status, etc.	Socio-demography	Person
	Coping, Well-being, Locus of control, Satisfaction with life, etc.	Health (perception)
		Lifestyle
	Social support, Social cohesion, Relationships, etc.	Social dimension
	Linguistic aspects, Beliefs, Attitudes, etc.	Cultural dimension
	Preferences, (acoustic) Sensibility, Adaption, etc.	Personal dimension
	Emotion (feelings), Cognition (thoughts), Knowledge (meanings)	Perception and valuation
			Activity
		Geography and topography	Place
	Temperature, Humidity, Wind, Seasonal variations	Climate, meteorology
	Planning, Buildings, Infrastructures, Cultural heritage, Land use pattern, Urban vs. rural	Urbanism
	Air, Noise, Vibrations, LFN	Environmental quality and pollution
		Safety
		Humanization
	Water, birds, etc. …	Natural elements
	Courtyards	Quite areas
	Traffic	Mechanical sounds
	Church bells, etc.	Cultural elements
		Humans
	Square, Park, Urban public space, etc.	Place type
	Residential, Cultural, Recreation, Relax, Social	Place function
Pijanowski et al., 2011 [27] Smith and Pijanowski, 2014 [28] Soundscape Ecology		Rain	Atmosphere
		Wind
		Temperature
		Climate regime
	Habitat, Biodiversity, Life history	Biological	Natural Environment
	Landform, Wind–water, photoperiod	Geophysical
	Policy formulation, Policy legitimation	Policies	Human System
		Values
		Cultural identity
		Health
	Economic and lifestyle decisions	Behavior
	Psychological; cognitive, emotional, and behavioral needs	Needs
	Roads, buildings	Structures	Built Environment
	Urban, agriculture, water	Land use
		Composition	Soundscape
		Temporal patterns
		Spatial variability
		Interactions
Özçevik and Yüksel Can, 2012 [36] Urban Soundscape		Type	Sound Source
		Features
		Sound level power of the source
		Duration of the sound
		Physical factors	Physical Environment
		Seasonal factors
		Topographical factors
		Sociological factors	Human Being
		Psychological factors
		Sensational factors
		Cultural factors
Jennings and Cain, 2013 [35] Urban Soundscape			Demographics
			Activity
			Time
			Space
Dökmeci, 2013 [44], Dökmeci Yörükoğlu and Kang, 2016 [45] Dökmeci Yörükoğlu and Kang, 2017 [46] Indoor Soundscape	Type, Time, Intensity	Physical	Sound Environment
	Temporal, Energetic, Spatial, Quantitative SI	Acoustical
	Psychoacoustical, Musical, Other methods	Psychoacoustical
	Individual, Socio-cultural	Demographical	Contextual
	Expectation, Perception, Reaction	Psychological
	Preference, Usage frequency, Time spent	Space usage
	Purpose, Services	Functional	Built Entity
	Formal organization, Spatial relationships, Circulation patterns, Shape and dimension	Spatial
	Air, Thermal, Lighting, and Acoustical quality, Crowd level	Indoor environmental
ISO, 2014 [1] Urban Soundscape			Sound Source/ Acoustic Environment
		Auditory sensation	Context
		Interpretation of auditory sensation
		Responses
Aburawis and Dökmeci Yörükoğlu, 2018 [47] Indoor Soundscape		Type	Sonic
		Level
		Frequency
		Characteristics	Spatial
		Type
		Services/activities
		Time spent	Temporal
		Usage frequency
		Preferred time
		Sensation	Psychological
		Attention
		Expectation
		Reaction	Behavioral
		Response
		Preference
		Individual	Personal
		Socio-cultural
Acun, 2018 [48] Indoor Soundscape		Sound sources	Sound Environment Context
		Physical aspects	Built Environment
		Perceptual aspect
		Consistency	Expectation and Preference
		Inconsistency
		Positive interpretation	Interpretation of Soundscape
		Neutral
		Negative interpretation
Erçakmak and Dökmeci Yörükoğlu, 2019 [49] Indoor Soundscape	SPL, Leq, Lw, RT, EDT, SII, STI	Objective	Acoustical
	Loudness, Sharpness, Roughness, Fluctuating strength	Psychoacoustic
	Time spent, Usage frequency, Preferred time	Temporal	Contextual
	Sensation, Attention, Mood, Expectation, Past experience	Psychological
	Reaction, Response, Preference, Activities	Behavioral
	Individual and Socio-cultural characteristics	Personal/demographical
	Public, Commercial, Industrial, Private, Civil	Function	Architectural
	Organization, Form and shape, Proportion, Materials and furniture, Openings, Circulation, Voids, Overall interior design	Architectural properties
	Air, Thermal, Lighting, Acoustic quality, and Crowd level	Physical environment
Torresin, Albatici, Aletta, Babich, and Kang, 2019 [50] Indoor Soundscape		Sound level, spectral content, roughness, loudness, fluctuation strength, number of sound events, source distance, sound dominance, duration of sound events, intermittency, frequency of annoyance, combination of multiple sources, sound type	Acoustic
		Presence of greenspace, sea view at home, access to a quiet side, source visibility, visual pleasantness, other visual aspects, building spacing and separation distance between buildings, satisfaction with the residential area, wish to change the residence	Urban Context
		Room location, building insulation, window opening position	House-Related
		Age, gender, noise sensitivity, physical and mental health status, personal audiovisual aptitude, perceived noise control, opinion towards the noise source, perception of risk associated with sound source, consideration of the importance of noise, attention paid to the soundscape, mood, thinking style, window closing habits, and noise-related remedies	Person-Related
		Level of education, income, family status, family unemployment, home ownership, economic benefit from noise source, type of housing, country	Socio-Economic
		Context in laboratory studies, survey context, location, activity or task, company of other people, period of day, length of residence	Situational
		Temperature, environmental pollution, odor annoyance	Environmental
Kang et al., 2019 [37] Urban Soundscape	Preference, Usage frequency, Time spent Purpose, Services Formal organization, Spatial relationships, Circulation patterns, Shape and dimension Air, Thermal, Lighting, and Acoustical quality, Crowd level	Space usage	Auditory Factors Social Built Entity
		Functional
		Spatial	Physical Contextual Factors
		Indoor environmental
		Socio-economic	Contextual Factors
		Demographic
		Cultural
		Activities
Chen and Ma, 2020 [38] Urban Soundscape		Sound sources	Sound Sources and Acoustic Environment
		Perceived characteristics
		Sites/spaces	Context
		Behavior states
		Time
		Physiological	People’s Demands
		Psychological
		Behavioral
		Physiological	Criteria and Standards of a Healthy Acoustic Environment
		Psychological
		Behavioral
		Standards
Tarlao et al., 2021 [39] Urban Soundscape		Demographics	User
		Needs
		Familiarity
		Expectations
		Purpose
			Activity
		Perceptual measurements	Auditory Environments
		Acoustic sensor measurements
		Environmental conditions	Contextual Factors
		Spatiotemporal aspects
		Amenities
Zhang et al., 2021 [40] Urban Soundscape		Personal state	Audience Subjectivity
		Preference
		Familiarity
		Loudness	Soundscape (Perceptible Sound Characteristics)
		Pitch
		Richness
		Rhythm
		Duration	Perceptual Time
		Timing
		Frequency
		Space	Perceptual Place
		Environmental condition
		Environmental compatibility
		Mental picture	Outcome (Auditory Imagination)
		Atmosphere construction
		Aesthetic perception
		Emotional expression
		Emotional resonance
Abdul Hamid et al., 2022 [41] Urban Soundscape		Appropriateness	Soundscape Perception
		Eventfulness
		Calmness
		Perceives noise	Noise Sensitivity
		Visual perception	Contextual Characteristics
		Visual quality of environment
		Perceived sound source	Sound Source
		Urban sound environment
Grinfeder et al., 2022 [42] Urban Soundscape		Temporal factors	Environmental Factor
	Geography, Topography, Surface	Spatial factors
	Climate, Weather	Abiotic factors
	Vegetation, Acoustic behavior, Population density, Territory distribution	Biotic factors
	Ground effects, Sound scattering, Meteorological effects	Acoustic factors
		Geophony	Sound Sources
		Biophony
		Ambient sounds
	Attenuation	Sound propagation	Acoustic Filters
	Distortion	Receiver
Hasegawa and Lau, 2022 [43] Urban Soundscape	Traffic noise, Human noise, Nature sound	Audio indicators	Audio–Visual Indicators
		Visual indicators
		Visual indicators Emotional state	Non-Auditory Contextual Indicators
	Gender, Age, Noise sensitivity, Time spent, Frequent look	Demographical characteristics	Person-Related Confounders
		Behavioral characteristics
	Nature type, Region type	Neighborhood characteristics	Environmental Moderators

Note: Table 1 is source-based and constructed from the meaning units extracted from each study. Some sources included more overarching or detailed information than others. Empty cells reflect cases where the original studies did not report the corresponding data.

As for the indoor soundscape approach, it has a different aspect from urban soundscape to consider for enclosed spaces. The indoor soundscape approach emerged in the study of Dökmeci in 2013 and emphasizes the “built entity” as architectural characteristics of a building that affect the sound formation and, relatively, the soundscape perception [44,46]. Correspondingly, different from the urban soundscape, which primarily includes the sound level and psychoacoustics measurements, the importance of building and room acoustics for indoor environments has been highlighted within the scope of indoor soundscaping [2,49,51]. Therefore, indoor soundscape components are identified in several studies [44,46,49] as “sound environment or acoustical factors”. On the other hand, “context” refers to people or human-related factors, and “built entity or architectural characteristics” refers to architectural aspects of buildings and indoor environmental factors such as lighting, thermal, and air quality. Aburawis and Dökmeci Yörükoğlu (2018) [47] rely more on space experience within the indoor soundscape approach and presented indoor soundscape perception factors such as “sonic”, “spatial”, “temporal”, “psychological”, “behavioral”, and “personal”. Acun et al. [48] indicate the conceptual framework of indoor soundscapes as “sound environment”, “built environment”, “context”, and “expectation and preference”. Another study, which is research on soundscape perception in residential areas, proposed factors influencing the indoor soundscape perception such as “acoustic”, “urban context”, “house-related”, “person-related”, “socio-economic”, “situational”, and “environmental” [52] alongside a wide variety of indicators (L3:I).

4. Indoor Soundscape Influencing Factors

The GT process of this study is designed to extract data related to the factors that influence soundscape perception as well as intervention criteria that can be used for soundscape design and/or application in practice. It is also important to consider the hierarchical organization of the soundscape elements extracted from the literature.

ISI criteria entities start with the meaning units of data (open coding) and follow the form in the axial coding process by merging the data by eliminating duplicated concepts. The levels (labels) are then checked and identified by categorizing them (starting with the meaning unit) according to their similarities and relationships in concept. Therefore, similar and related entities are brought together, and overarching categories are defined. This process is repeated several times, and three levels (L1, L2, L3) occur during the data organization. L1 is the meaning unit extracted from the literature. Similar or related entities generate L2 as the overarching category. Subsequently, similar L2 concepts form L3 core categories (or can be described as the main components of an indoor soundscape). ‘Sound’, ‘People’, ‘Building’, and ‘Environment’ are the main components of the indoor soundscape approach (Table 2).

In this manner, recompiled influencing factors are presented in Table 2 by referring to the studies in Table 1. In addition, additional books on architectural acoustics [53,54,55] and the Turkish regulation entitled “Regulation on the protection of buildings against noise” [56] are used to exemplify several data that were not obtained from the SR.

Table 2. Indoor soundscape influencing factors to be considered in evaluation, intervention, and practice. Compiled and proposed as presented in the GT merging process.

L1 Key Concept/Indicator/Parameter (Explanation)	L2 Overarching Category	L3 Core Category Main Component
Identity (name of the source)	Sound sources [1,36,38,48]	Sound
Relation with context social characteristics [29,30,31,32] (soundmark, signal, keynote [5])
Meaning [37] (semiotics and semantics [5])
Aesthetics [5] (affective quality/perceived affective quality [38])
Dominance [37,50]
Status of sound source (location [29,30,31,32], distance between source and receiver [50], movement [29,30,31,32], temporal condition [29,30,31,32,44,45,46,50], and type [36,44,45,46,47,50])
General background sound [29,30,31,32]
Loudness	Psychoacoustic characteristics [44,45,46,49,50]
Sharpness
Roughness
Fluctuation strength, etc.
Frequency [47]	Spectrum [29,30,31,32]/spectral content [50]
Tonality
Complexity
Harmonics etc.
Noise indicators (Leq [49], Lden, Ld, etc. *)	Noise [33,34]
Background noise [54,55,56]
LFN [33,34] (low-frequency noise)
Sound pressure level (SPL—Lp [29,30,31,32,49])	Sound level parameters [36,47,50]
Intensity level (I—Lı)
Sound power level (W—Lw [49])
Age [43,50]	Demographic [29,30,31,32,33,34,35,37,39,43,44,45,46,49]	People
Gender [43,50], etc.
Education [50]	Socio-economic [33,34,36,37,44,45,46,47]
Standard of living, income [50]
Labor force and employment [33,34], etc.
Cultural background	Socio-cultural [36,37,44,45,46,47,49]
Linguistic aspects [33,34]
Beliefs [33,34]
Activity [33,34,35,37,39]	Activity [33,34,35,37,39]
Time spent [43,44,45,46,47,49]	Temporal usage conditions [35,38,42]
Usage frequency [44,45,46,47,49]
Preferred time [44,45,46,47,49]
Psychological health [33,34,36,38,50]	Individual dimensions
Physiological health [33,34,38,50]
Noise sensitivity [41,43,50]
Expectation [39,47,48,49]
Preference [33,34,39,40,44,45,46,47,48,49]
Emotion [33,34] (feelings [33,34])
Cognition [33,34] (thoughts [33,34])
Knowledge [33,34] (meanings [33,34])
Mood [49,50]
Attention [47,49,50]
Past experience [49]	User experience [1,36]
Familiarity [39,40]
Behavior [38]
Reaction [47,49]
Type [33,34,47] (public, commercial, industrial, private, civil [44,45,46,49])	Function [33,34,44,45,46,49] and type [33,34,47]	Building
Function [33,34,44,45,46,49]/activities [47,50] (residential, cultural, recreation, relax [33,34,44,45,46], etc.)
Neighbor characteristics [33,34] (nearby buildings, transportation, etc.)	Urban context and location
Location [50] (location of the building, building spacing [50])
Overall interior design [49]	Visual integrity
Visual meaning [37]
Audio–visual appropriateness [41]
Building foundation	Constructive properties
External envelope and internal structure
Structural system
Internal vertical and horizontal partition elements
2D and 3D properties and organization [44,45,46] (form, shape, dimension, proportion, volume [44,45,46,49], etc.)	Spatial properties
Spatial relations and circulation pattern [44,45,46]
Voids, openings on façade, and internal partitions [49]
Building element’s sound transmission values (DnT,w *, Rw *, L’nT,w *, R, etc. *)	Building acoustics *
Vibration [33,34]
Absorption [54,55,56] * (α *, αw *, NRC *, etc.)	Room acoustics [54]
Reverberation/decay time [29,30,31,32,53,54,55,56] (RT—T60, T30, T20 [54], EDT—T10 [49,54])
Diffusion [53,54,55] (SDI [53])
Clarity [53,54,55] (C80 [53,54] etc.)
Warmth [53,54,55]
Intimacy [53,54,55]
Definition
Speech intelligibility [54] (SII [49,54], STI [49,54], AI [53,54,55])
Mechanical conveying system	Building services
HVAC systems
Automated indoor elements and technologies
Technical and mechanical spaces
Electrical installations and electronic technologies
Sanitary systems
Building insulation [50] (existing sound and/or thermal insulation)	Building insulation [50]
Surface finishing materials	Interior finishing and elements
Detailing
Furniture
Appliances and devices
Fittings and fixtures
VOC	Indoor air quality [44,45,46,49]	Environment
Humidity
CO2, etc.
Humidity	Indoor thermal quality [44,45,46,49]
Temperature
Natural	Lighting quality [44,45,46,49]
Artificial
Appropriateness with context
Illuminance
Color
Type, etc.
Crowd level [44,45,46,49]	Crowd level [44,45,46,49]
Vegetation circumstance	Indoor natural elements
Presence of water elements
Vegetation, greenery space circumstance/presence [50]	Outdoor natural elements
Presence of water elements [50]
Temperature [33,34,50]	Outdoor weather conditions
Climate, weather, season [33,34,36,42]
Humidity [33,34]

‘etc.’ is used to express certain/some examples, and they can be multiplied. * The units that are used and indicated in acoustics-related European and Turkish standards and Turkish noise regulation [56].

Table 2. Indoor soundscape influencing factors to be considered in evaluation, intervention, and practice. Compiled and proposed as presented in the GT merging process.

L1 Key Concept/Indicator/Parameter (Explanation)	L2 Overarching Category	L3 Core Category Main Component
Identity (name of the source)	Sound sources [1,36,38,48]	Sound
Relation with context social characteristics [29,30,31,32] (soundmark, signal, keynote [5])
Meaning [37] (semiotics and semantics [5])
Aesthetics [5] (affective quality/perceived affective quality [38])
Dominance [37,50]
Status of sound source (location [29,30,31,32], distance between source and receiver [50], movement [29,30,31,32], temporal condition [29,30,31,32,44,45,46,50], and type [36,44,45,46,47,50])
General background sound [29,30,31,32]
Loudness	Psychoacoustic characteristics [44,45,46,49,50]
Sharpness
Roughness
Fluctuation strength, etc.
Frequency [47]	Spectrum [29,30,31,32]/spectral content [50]
Tonality
Complexity
Harmonics etc.
Noise indicators (Leq [49], Lden, Ld, etc. *)	Noise [33,34]
Background noise [54,55,56]
LFN [33,34] (low-frequency noise)
Sound pressure level (SPL—Lp [29,30,31,32,49])	Sound level parameters [36,47,50]
Intensity level (I—Lı)
Sound power level (W—Lw [49])
Age [43,50]	Demographic [29,30,31,32,33,34,35,37,39,43,44,45,46,49]	People
Gender [43,50], etc.
Education [50]	Socio-economic [33,34,36,37,44,45,46,47]
Standard of living, income [50]
Labor force and employment [33,34], etc.
Cultural background	Socio-cultural [36,37,44,45,46,47,49]
Linguistic aspects [33,34]
Beliefs [33,34]
Activity [33,34,35,37,39]	Activity [33,34,35,37,39]
Time spent [43,44,45,46,47,49]	Temporal usage conditions [35,38,42]
Usage frequency [44,45,46,47,49]
Preferred time [44,45,46,47,49]
Psychological health [33,34,36,38,50]	Individual dimensions
Physiological health [33,34,38,50]
Noise sensitivity [41,43,50]
Expectation [39,47,48,49]
Preference [33,34,39,40,44,45,46,47,48,49]
Emotion [33,34] (feelings [33,34])
Cognition [33,34] (thoughts [33,34])
Knowledge [33,34] (meanings [33,34])
Mood [49,50]
Attention [47,49,50]
Past experience [49]	User experience [1,36]
Familiarity [39,40]
Behavior [38]
Reaction [47,49]
Type [33,34,47] (public, commercial, industrial, private, civil [44,45,46,49])	Function [33,34,44,45,46,49] and type [33,34,47]	Building
Function [33,34,44,45,46,49]/activities [47,50] (residential, cultural, recreation, relax [33,34,44,45,46], etc.)
Neighbor characteristics [33,34] (nearby buildings, transportation, etc.)	Urban context and location
Location [50] (location of the building, building spacing [50])
Overall interior design [49]	Visual integrity
Visual meaning [37]
Audio–visual appropriateness [41]
Building foundation	Constructive properties
External envelope and internal structure
Structural system
Internal vertical and horizontal partition elements
2D and 3D properties and organization [44,45,46] (form, shape, dimension, proportion, volume [44,45,46,49], etc.)	Spatial properties
Spatial relations and circulation pattern [44,45,46]
Voids, openings on façade, and internal partitions [49]
Building element’s sound transmission values (DnT,w *, Rw *, L’nT,w *, R, etc. *)	Building acoustics *
Vibration [33,34]
Absorption [54,55,56] * (α *, αw *, NRC *, etc.)	Room acoustics [54]
Reverberation/decay time [29,30,31,32,53,54,55,56] (RT—T60, T30, T20 [54], EDT—T10 [49,54])
Diffusion [53,54,55] (SDI [53])
Clarity [53,54,55] (C80 [53,54] etc.)
Warmth [53,54,55]
Intimacy [53,54,55]
Definition
Speech intelligibility [54] (SII [49,54], STI [49,54], AI [53,54,55])
Mechanical conveying system	Building services
HVAC systems
Automated indoor elements and technologies
Technical and mechanical spaces
Electrical installations and electronic technologies
Sanitary systems
Building insulation [50] (existing sound and/or thermal insulation)	Building insulation [50]
Surface finishing materials	Interior finishing and elements
Detailing
Furniture
Appliances and devices
Fittings and fixtures
VOC	Indoor air quality [44,45,46,49]	Environment
Humidity
CO2, etc.
Humidity	Indoor thermal quality [44,45,46,49]
Temperature
Natural	Lighting quality [44,45,46,49]
Artificial
Appropriateness with context
Illuminance
Color
Type, etc.
Crowd level [44,45,46,49]	Crowd level [44,45,46,49]
Vegetation circumstance	Indoor natural elements
Presence of water elements
Vegetation, greenery space circumstance/presence [50]	Outdoor natural elements
Presence of water elements [50]
Temperature [33,34,50]	Outdoor weather conditions
Climate, weather, season [33,34,36,42]
Humidity [33,34]

‘etc.’ is used to express certain/some examples, and they can be multiplied. * The units that are used and indicated in acoustics-related European and Turkish standards and Turkish noise regulation [56].

4.1. Sound

As a result of the review, sound sources [1,36,38,48], perceived affective quality [38], psychoacoustic characteristics [44,45,46,49,50], spectrum [29,30,31,32]/spectral content [50], noise [33,34], and sound level parameters [36,47,50] generate the ‘Sound’ component.

Sound sources include the indicators about the characteristics of the sources’ identity, relation with social or cultural context [29,30,31,32] such as soundmark, signal, keynote [5], semiotic, semantic and aesthetic meaning [5,37] of the source, dominancy [37,50], or being a general background sound [29,30,31,32] source in a sound environment. Status of sound sources such as location [29,30,31,32], distance between source and receiver [50], movement [29,30,31,32], temporal condition [29,30,31,32,44,45,46,50], and type [36,44,45,46,47,50] are also the sound source indicators. Psychoacoustic characteristics [44,45,46,49,50] (loudness, sharpness, roughness, fluctuation strength, etc.) is another overarching category of the sound component. Spectrum [29,30,31,32]/spectral content [50] (frequency [47], tonality, complexity, harmonics, etc.), and sound level parameters, [36,47,50] (sound pressure level [L_p] [29,30,31,32,49], intensity level [L_ı], sound power level [L_w [49]]) are stated for evaluation of the physical characteristics of sound. Noise is another descriptor for both indoor and outdoor generated sounds as background noise [54,55,56], low-frequency noise [33,34], and noise indicators exemplified with the equivalent continuous sound level (L_eq [49], L_Aeq,time, L_den, L_d [56], etc.).

4.2. People

The ‘People’ component is related to the different dimensions and conditions of users. L2:D of the people component is presented as demographic information [29,30,31,32,33,34,35,37,39,43,44,45,46,49], socio-economic conditions [33,34,36,37,44,45,46,47], socio-cultural backgrounds [36,37,44,45,46,47,49], activity [33,34,35,37,39], temporal usage conditions [35,38,42], individual dimensions, and user experience [1,36]. Demographic information refers to age [43,50] and gender [43,50]. Socio-economic conditions are extended with the education level, standard of living/income, and labor force/employment [33,34]. Socio-cultural backgrounds include cultural background, linguistic aspects, and beliefs [33,34]. Temporal usage conditions are related to the space usage behaviors such as how much time a user spends [43,44,45,46,47,49], frequency of the usage [44,45,46,47,49] of a space, and user’s preferred time [44,45,46,47,49] to use a particular space. People’s individual conditions, which are psychological [33,34,36,38,50] and physiological [33,34,38,50] health, noise sensitivity [41,43,50], expectation [39,47,48,49] from a space, preference [33,34,39,40,44,45,46,47,48,49] about the sound environment, emotion [33,34], cognition [33,34], knowledge [33,34], mood [49,50], and attention [47,49,50], are collected under the individual dimensions. Finally, user experiences are identified by past experience [49], familiarity [39,40], behavior [38], and reaction [47,49].

4.3. Building

The ‘Building’ component consists of function and type, urban context and location, visual integrity, constructive properties, spatial properties, building and room acoustics characteristics, building services, building insulation condition, interior finishing, and elements. Function [33,34,44,45,46,49] and/or activities [47,50] are exemplified as residential, cultural, recreation, relaxation [33,34,44,45,46], etc., buildings, and type [33,34,47] is identified as public, commercial, industrial, private, and civil [44,45,46,49]. Urban context and location identify the neighbor characteristics of the building [33,34], activities and functions of the nearby buildings, transportation opportunities, and location of the building with building spacing [50]. Visual integrity is related to the overall interior design [49], visual meaning [37] for the users, and audio–visual appropriateness [41] of an interior space. Constructive and spatial properties directly indicate the architectural characteristics of a building, which have a strong relation with the sound propagation in a space. Constructive properties can be clarified with the building foundation, external envelope and internal structure, structural system, and internal vertical and horizontal partition elements. In addition, spatial properties are the 2D and 3D properties and organization [44,45,46] (such as form, shape, dimension, proportion, and volume [44,45,46,49]), spatial relations, circulation pattern [44,45,46], voids, openings on the façade, and internal partitions [49]. Building and room acoustics characteristics of a building are part of the building component, as they are the intervention criteria for indoor sound transmission and sound quality for acoustic comfort. Transmission values of the building elements [56] and vibration [33,34] issues are included as the descriptives of building acoustics. Absorption [54,55,56], reverberation/decay time [29,30,31,32,53,54,55,56], diffusion, clarity, warmth, intimacy [53,54,55], definition, and speech intelligibility [54] (SII [49,54], STI [49,54], AI [53,54,55]) are identified as the indicators of room acoustics. The indicators of building services are the sound or noise sources themselves that should be controlled [56] and can be exemplified as mechanical conveying systems, HVAC systems, automated indoor elements and technologies, technical and mechanical spaces, electrical installations, electronic technologies, and sanitary systems. Finally, interior finishing and elements are the surface finishing materials, detailing, furniture, appliances, devices, fittings, and fixtures, which are also significant for the acoustic properties and material effects on the building acoustics and room acoustics phenomenon.

4.4. Environment

‘Environment’ is the last component of the indoor soundscape, which addresses the indoor and outdoor environmental factors such as indoor air quality [44,45,46,49], indoor thermal quality [44,45,46,49], lighting quality [44,45,46,49], crowd level [44,45,46,49], indoor vegetation, indoor natural elements, outdoor natural elements, and outdoor weather conditions. Indoor air quality includes the VOC, humidity, and CO₂ levels for comfortable and healthy air conditions. Indoor thermal quality is related to indoor temperature and humidity. Lighting quality involves natural and artificial lighting and related parameters such as illuminance, color, type, etc. In addition, the appropriateness with the context of the lighting quality can be considered as well, to support the activity and meaning. Another overarching category of the ‘Environment’ component pertains to the presence and/or usage of natural elements, including vegetation and water in both indoor and outdoor spaces. Lastly, outdoor weather conditions (temperature [33,34,50], climate, weather, season [33,34,36,42], humidity [33,34]) influence the indoor environment or usage of service equipment (for ventilation, air conditioning, etc.)

5. Results and Discussion on Indoor Soundscape Intervention (ISI) Criteria to Be Considered in Practice

As a result of the review and GT coding process, four core categories of sound, people, building, and environment were reached. The ‘Sound’ component includes sound-related data such as characteristic aspects of sound, objective (measurable) and subjective (perceptual) aspects. The ‘People’ component is formed by the data, including the whole user aspects, conditions, and outcome (behavioral and/or reactional). The ‘Building’ component includes functional, physical, structural, and organizational aspects of a building. Finally, the ‘Environment’ component is related to data on indoor and outdoor environmental conditions (Figure 3).

The core category of the classification aligns partially with previous distinctions found in the literature between physical and perceptual soundscape dimensions. However, the current study proposes a more holistic and unified framework with the overarching and key concepts for ISI criteria to be used in architectural practice (Figure 4).

These four main components consist of criteria that influence a soundscape and can be intervened in as a part of the architectural process. Correspondingly, criteria are schematized as presented in the theory development and schematic representation of the GT selective coding process (Figure 4), where the data were organized according to principles given in Figure 3. However, the evaluation of the factors under the concept of intervention criteria raises the question of whether all the factors can be intervened in in architectural practice. The projected criteria that may not always be possible to intervene in are indicated in green at the overarching category level in Figure 4, and detailed evaluations are needed in further studies. This distinction between available or not available criteria is one of the key contributions of this framework and guides the ongoing study by clarifying which elements should be addressed through intervention and which should be considered in architectural processes.

In this manner, the aforementioned discussion starts with the key concepts of the sound source category, since the identity, context relation, meaning, dominance, status of the source, and being background sound are self-characteristics of the source itself/themselves and may not be intervened in or changed in all cases but need to be considered in architectural design and application process. Similarly, aesthetics/affective quality of a source may not be intervened in but can be changed according to the perception of an individual. The criteria of the ‘people’ component may not be intervened in or changed except for the user activity, since the ‘demographic, socio-economic, socio-cultural, temporal usage conditions, individual dimensions, and user experience’ are the individual characteristics that should be considered as the focal point of the design. On the other hand, user ‘activity’ and ‘crowd level’ are function-dependent criteria that can only be changed by re-functioning projects. ‘Urban context and location’ and ‘outdoor weather condition’ are criteria that cannot be changed but should be considered in practice. The ‘outdoor natural element’ may be intervened in as it is included within the boundaries of a project. Finally, the features of a building (visual integrity, constructive properties, spatial properties, building acoustics, room acoustics, building services, building insulation, interior finishing, and elements) and indoor environmental conditions (indoor air quality, indoor thermal quality, lighting quality, indoor natural elements) are criteria that are available for intervention in practice.

Limitations of the Study

This review has certain limitations. One of them is the lack of analysis on regional and cultural differences in indoor soundscape influencing criteria, which may influence the applicability of the proposed criteria across diverse contexts. However, the ISI criteria have been categorized as comprehensively as possible, and the framework’s repeatable and updatable nature allows for adaptation to different contexts. Additionally, the search scope was limited to studies available in selected databases and published in the English language, and this may cause the potential exclusion of relevant studies published in other languages. These limitations highlight the need for further studies to investigate the cultural and contextual variability in indoor soundscape design and interventions.

Another limitation of the study is the theoretical saturation of the GT process, which is also explained in detail in Section 2.2. The study uses an adapted form of Grounded Theory without traditional theoretical saturation, since the data were derived from published studies rather than from interview-based data collection. This may limit the depth of theoretical saturation but provides a structured and repeatable framework for future updates.

6. Conclusions

Current noise management policies predominantly focus on reducing noise exposure rather than enhancing acoustic comfort in a holistic approach. Despite advances in urban soundscape research and emerging standards such as the ISO 12913 series [1,6,7,8] and the CSI [10,11] project, gaps remain in the practical application of indoor soundscape approaches. Consequently, there is a need for developing a systematic framework that identifies key influencing factors as intervention criteria as a first step to bridge the gap between theoretical research and the practical architectural process.

In order to investigate the applicability of the concept of indoor soundscape and the factors influencing user perception in the architectural process, it has become necessary to combine various theoretical models in the literature and propose a single model. In this research, the influencing factors of soundscape are reviewed with the SR by PRISMA, since the concept has been identified, and the found key concepts are compiled with the GT coding process under the indoor soundscape intervention approach. Furthermore, the categorizations of the factors were reconsidered, and the data were reorganized for the proposed criteria categorization. As a result, the indoor soundscape intervention (ISI) criteria to be considered in architectural practice were presented as a first step for indoor soundscape applicability. In other words, the criteria were proposed that can be intervened in, considered, and/or used for evaluation to improve indoor soundscapes in the architectural process.

The prospective aim of the ISI criteria proposal is to investigate the use of the fundamental research aim, which is the indoor soundscape intervention approach in real-world applications. This fundamental aim is currently being studied in ongoing research. Another noteworthy point is whether all the factors can be intervened in in architectural practice, which raises a new research question. Are all the influencing factors amenable to intervention during the architectural design and application process? Although the framework of this study draws attention to this point, it is not sufficient to answer this revealed research question, and this issue will be considered in ongoing and further studies.