ISO/TS 16755-1:2025

Technical
Specification
ISO/TS 16755-1
First edition
Acoustics — Non-acoustic factors
2025-05
influencing the perception,
interpretation and response to
environmental sounds —
Part 1:
Definition and conceptual
framework
Acoustique — Facteurs non acoustiques influençant la
perception, l'interprétation et la réponse aux sons de
l'environnement —
Partie 1: Définition et cadre conceptuel
Reference number
© ISO 2025
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ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Conceptual framework of non-acoustic factors . 1
4.1 General .1
4.2 Categories of non-acoustic factors .2
Annex A (informative) Non-acoustic factors categories . 4
Bibliography . 5

iii
Foreword
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This document was prepared by Technical Committee ISO/TC 43, Acoustics, Subcommittee SC 1, Noise.
A list of all parts in the ISO/TS 16755 series can be found on the ISO website.
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iv
Introduction
Many countries already have regulations in place concerning the acceptability of environmental noise
exposure, while others are likely to do so in the future. Such regulations often take into account relationships
between noise exposure and noise-induced health outcomes, including long-term annoyance and sleep
disturbance.
International standards have been developed for the measurements of certain characteristics of
[1]
environmental sound. Two examples are ISO 1996-1 , which contains detailed specifications about basic
quantities and procedures, measurement of sound and guidance on the application of these data to set noise
[2]
limits, and ISO 20906 , which specifies criteria for unattended monitoring of aircraft sound in the vicinity
of airports.
Other standards focus on the effects of sound on humans. Long-term annoyance is an important health
effect attributable to environmental noise, both as a health outcome in its own right, and as a potential
[3] [4]
risk factor to other clinical health outcomes . ISO/TS 15666 provides a standardised specification for
the assessment of noise annoyance by social and socio-acoustic surveys. This specification has enabled a
more robust consolidation of the international evidence on noise annoyance, by ensuring consistency in the
[3]
definition and measurements of this specific health endpoint .
It is generally accepted that human reaction to environmental sound is determined partly by the acoustic
characteristics of the physical stimulus, and partly by factors that frame the sound exposure within a
[5]to[9]
broader context . Such factors are often referred to as non-acoustic factors in the noise and health
literature.
In recent years there has been a growing interest in the soundscape approach. Whilst the term “soundscape”
has seen widespread academic and popular adoption in various fields and applications (including urban,
[10]
underwater and ecological contexts) , the most relevant definition for the purposes of this document is
the ISO 12913-1 definition, refers to how sound in an environment is experienced by a person and/or people
in context. According to ISO 12913-1 assessing soundscape in context includes:
“the interrelationships between person and activity and place, in space and time. The context may influence
soundscape through (1) the auditory sensation, (2) the interpretation of the auditory sensation, and (3) the
[11]
responses to the acoustic environment” .
[11]to[13]
There is clear overlap between the concept of the “context” as discussed in the ISO 12913 series and
the term “non-acoustic factors” as used by the noise and health community. Therefore identifying, measuring
and assessing non-acoustic factors is an important process of measuring and assessing soundscape in
[5][7]
accordance with ISO 12913 series as well as assessing non-acoustic factors in noise and health research
[8][30][31]
.
Multivariate regression analyses of socio-acoustic surveys suggest that known non-acoustic factors can
[6][14]to[17]
account for up to one third of the variance observed in noise annoyance reactions . These results
have been further replicated in soundscape studies, with multi-level regression analysis indicating that non-
acoustic factors can explain 35 % of the variance in pleasantness perception (i.e. the opposite dimension to
[18]
annoyance) and 18 % of the variance in eventfulness perception .
There is clear evidence that non-acoustic factors offer significant opportunities in a) understanding the
drivers of annoyance and soundscape appraisal and b) opening up new possibilities for reducing the health
burden attributable to the sound environment. In fact, several projects have already explored how non-
[19]
acoustic factors can be used to reduce noise annoyance (see for example the ANIMA project for aviation
[20]
noise and FAMOS project for road traffic noise). Consideration of non-acoustic factors in policy and
[21]
practice could also lead to more equitable health outcomes . In business terminology, non-acoustic factors
have the potential to significantly increase the return on investment in noise effects investigation and
[22]
mitigation and soundscape design . The WHO Environmental Noise Guidelines for the European Region
2018 also acknowledge the important contribution of non-acoustic factors, and recommend that:

v
“Future intervention studies … should use measures of moderators and confounders, including repeated meas-
urements of situational and personal variables such as activity interference, potential confounders such as
[23]
noise sensitivity, coping strategies and a range of other attitudinal variables.”
Despite the key role that non-acoustic factors play in both the health protection (noise control) and health
promotion/improvement (good acoustic quality and soundscape design) approaches, to date, there is no
standardised specification for the assessment of non-acoustic factors in social surveys and soundscape
assessments. For example, the definition and standardisation of non-acoustic factors fall outside scope of
ISO/TS 15666. This means that the extent to which non-acoustic factors are investigated in a particular
study is limited by the specialist expertise within the study group, and different studies tend to develop
project-specific survey instruments.
The aim of ISO/TS 16755 series is to help define, measure and interpret specific attributes of the context
that helps to better understand the human interpretation of, and response to a sound environment. The
objective of this document is to harmonise the definition and conceptual framework for non-acoustic factors
related to noise and soundscape data collection activities, such as via social and socio-acoustic surveys,
soundwalks, questionnaires and guided interviews. This definition and conceptual framework form the
foundation for data collection, analysis and interpretation covered in subsequent parts of this document.
ISO/TS 16755 series applies to any sound in the acoustic environment (“acoustic environment” is defined in
ISO 12913-1:2014, 2.2).
When these specifications are met, it will be possible to identify, compare and po
...