ISO/TS 9241-620:2023
(Main)Ergonomics of human-system interaction — Part 620: The role of sound for users of interactive systems
Ergonomics of human-system interaction — Part 620: The role of sound for users of interactive systems
This document provides users with a summary of the existing knowledge about ergonomics considerations for the influence of sound in use environments on humans. It describes how unwanted effects of sound (noise) can be controlled. The main goals for controlling the acoustic use environment are reducing the rating level of sound in general, optimizing signal-to-noise ratio and sound reduction within the workspace. This document also provides users with organizational measures that can be taken if and when technical measures do not help sufficiently. Also included are measures on a personal level. This document deals with sound events that can cause extra-aural effects. Noise-induced hearing loss prevention and the ways to eliminate or reduce hazardous noise exposure are not covered by this document. The intended users of this document include: — developers of systems, products and services; — public and corporate purchasers; — occupational health and safety professionals; — architects and interior designers; — human resource professionals; — usability, ergonomics or human factors professionals; — users of interactive systems.
Ergonomie de l'interaction homme-système — Partie 620: Rôle du son pour les utilisateurs de systèmes interactifs
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TECHNICAL ISO/TS
SPECIFICATION 9241-620
First edition
2023-07
Ergonomics of human-system
interaction —
Part 620:
The role of sound for users of
interactive systems
Ergonomie de l'interaction homme-système —
Partie 620: Rôle du son pour les utilisateurs de systèmes interactifs
Reference number
ISO/TS 9241-620:2023(E)
© ISO 2023
---------------------- Page: 1 ----------------------
ISO/TS 9241-620:2023(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2023
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
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ISO/TS 9241-620:2023(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Sound and noise . 3
4.1 How sound and noise impact users . 3
4.2 Types of sound events . 4
4.3 Interference with the task . 5
4.4 Lombard effect . 8
4.5 Irrelevant speech effect (ISE) . 9
4.6 The importance of the concept of T-O-P. 9
5 Measures to control the impact of sound events .10
5.1 Overview . 10
5.2 Controlling sound and noise . 10
5.2.1 General . 10
5.2.2 Reducing the rating level . 11
5.2.3 Reverberation time . 15
5.3 Optimizing signal-to-noise ratio . 15
5.3.1 General .15
5.3.2 Transmission paths for the voice in use environments . 17
5.3.3 How the communication is affected by unwanted sound . 18
5.3.4 How to improve the intelligibility of speech . 20
5.4 Sound reduction within use environments or immediate environments of
workstations. 22
5.5 User involvement . 23
Annex A (informative) Example of a user survey questionnaire .24
Bibliography .25
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ISO/TS 9241-620:2023(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to
the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see
www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 159, Ergonomics, Subcommittee SC 4,
Ergonomics of human-system interaction.
A list of all parts in the ISO 9241 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
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ISO/TS 9241-620:2023(E)
Introduction
In physics, sound is a vibration that propagates as an acoustic wave, through a transmission medium
such as a gas, liquid or solid. In human physiology and psychology, sound is the reception of such waves
and their perception by the brain. Unwanted sound is referred to as noise and is often perceived as the
most serious disturbance factor at office workstations. In many industrial environments, sound can be
a serious threat to health in general, not limited to auditory effects alone.
While sound is a measurable physical reality, acoustic noise is a psychoacoustical concept. The main
goal of this document is minimizing the impact of noise while operating interactive systems, for example
on the behaviour of users, their well-being and/or performance. This can be accomplished by technical
measures, organizational means, interventions at the personal level and any combinations thereof.
The overall concept T-O-P (technical – organizational – personal) indicates the reasonable order
of measures that can be taken to control the impact of the acoustic environment on human work. In
this context, technical solutions have priority over organizational measures and personal protective
equipment (PPE).
Psychoacoustics is the branch of psychophysics involving the scientific study of sound perception and
audiology – how humans perceive various sounds. More specifically, it is the branch of science studying
the psychological responses associated with sound (including noise, speech and music). This document
deals with the undesired effects of sound, which can be classified as follows:
— impaired hearing;
— undesired responses of the central and autonomic nervous system;
— hindrance of verbal and other communication;
— reduced performance and cognitive functioning;
— annoyance.
Acoustic satisfaction of a space cannot be guaranteed without consideration of each of the three
principle parameters of architectural acoustic design, formalized and established in the early 1900s
[28]
by Sabine. The three principle parameters are known as the ‘ABCs’ of architectural acoustics: A for
absorption – Sufficient absorption in the built environment; B for blocking – Sufficient isolation of the
built environment; and C for control – Control of sound levels in the built environment. For a given
space, various measures in combinations can be taken to control the acoustic environment to achieve
satisfaction. In ISO 9241-6 such measures are briefly listed and partly explained. Experience now
suggests that a more thorough consideration of the acoustic environment is required because of the
changes to work organization and tasks.
Controlling the acoustic environment is considered part of the T-O-P concept. It can comprise, for
example:
— reducing the rating level
— insulation in structural components;
— reducing noise emission from equipment;
— increasing sound absorption;
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ISO/TS 9241-620:2023(E)
— reducing the ambient noise level;
— optimizing the signal-to-noise ratio
— reducing the sound level in speech frequencies;
— sound reduction within use environments
— sound-absorbing ceilings;
— partitions;
— adequate distances between workstations;
— reducing reverberation.
While all these measures are of a technical nature (T of the T-O-P principle, Figure 1), the impact of
sound events on persons and work can require organizational measures, such as holding small meetings
dedicated to certain tasks outside the workspace. The final argument comprises measures at a personal
level, including training to cope with adverse environments.
Figure 1 — T-O-P principle for controlling the impact of the acoustic environment on human
work
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TECHNICAL SPECIFICATION ISO/TS 9241-620:2023(E)
Ergonomics of human-system interaction —
Part 620:
The role of sound for users of interactive systems
1 Scope
This document provides users with a summary of the existing knowledge about ergonomics
considerations for the influence of sound in use environments on humans. It describes how unwanted
effects of sound (noise) can be controlled. The main goals for controlling the acoustic use environment
are reducing the rating level of sound in general, optimizing signal-to-noise ratio and sound reduction
within the workspace.
This document also provides users with organizational measures that can be taken if and when
technical measures do not help sufficiently. Also included are measures on a personal level.
This document deals with sound events that can cause extra-aural effects. Noise-induced hearing loss
prevention and the ways to eliminate or reduce hazardous noise exposure are not covered by this
document.
The intended users of this document include:
— developers of systems, products and services;
— public and corporate purchasers;
— occupational health and safety professionals;
— architects and interior designers;
— human resource professionals;
— usability, ergonomics or human factors professionals;
— users of interactive systems.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
irrelevant speech effect
ISE
negative effect of verbal sound level
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ISO/TS 9241-620:2023(E)
3.2
rating level
L
AR
equivalent continuous A-weighted sound pressure level during a specified time interval plus adjustment
for tonal character and impulsiveness
Note 1 to entry: ΔLT = 0 dB or 5 dB according to subjective assessments
where
Δ is difference;
L is level;
T is tonal.
Note 2 to entry: Impulsiveness is specified only if the difference of the measured sound level with and without
impulses exceeds 2 dB.
[SOURCE: ISO 9241-6:1999, 3.19, modified — Notes to entry replaced.]
3.3
background noise level
L
p,B
A-weighted sound pressure level present at the workstation during working hours with people absent
Note 1 to entry: The A-weighted background noise level L is expressed in dB.
p,B
3.4
total noise sound pressure level
L
NA
sound pressure level that contains all noise components affecting the listener during use, such as noise
generated by building systems, operating equipment or the audience, and which is determined at ear
height for the area in which people are normally located
Note 1 to entry: The A-weighted total noise sound pressure level L is expressed in decibels.
NA
Note 2 to entry: If not otherwise specified, noise is determined according to DIN 45641 as the A-weighted
equivalent continuous sound pressure level averaged over the time that is representative for the disturbance.
3.5
impulsive sound
sound with a rapid rise and decay of sound pressure level, lasting less than one second and causing an
increase in the sound level of at least 6 dB(A)
3.6
reverberation time
T
time required for the sound pressure level in a room to decay by 60 dB once sound excitation has
stopped
Note 1 to entry: The reverberation time is expressed in seconds.
3.7
speech transmission index
STI
metric ranging between 0 and 1 representing the transmission quality of speech with respect to
intelligibility by a speech transmission channel
[SOURCE: IEC 60268-16:2020, 3.3]
Note 1 to entry: Speech transmission channel can also be the use environment.
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ISO/TS 9241-620:2023(E)
3.8
sound pressure level
SPL
logarithmic measure of the effective pressure of a sound relative to a reference value
4 Sound and noise
4.1 How sound and noise impact users
Hearing (audition, auditory sense) is one of the five basic senses used by humans to perceive the physical
environment, alongside sight (vision, visual sense), taste (gustation, gustatory sense), smell (olfaction,
olfactory sense) and touch (somatosensation, somatosensory sense). Even if its sensor, the ear, seems to
function independently from those of the other senses, they all function in concert. Sight and hearing,
or those sensory aptitudes that can collect information from a distance (relatively speaking), are called
far senses. Hearing is the only sense that can detect objects or events beyond the (optical) horizon.
Evolution has programmed human beings to be aware of sounds as possible sources of danger. The
hearing as the far sense gives notice of things that cannot be seen but that could be important. It plays
an alerting function. Even if this function is not needed in most use environments, it cannot be switched
off or ignored. While the sense of sight is relatively inactive during sleep, hearing remains on. The alert
function requires that hearing is almost non-directional compared with sight. It is possible to look
away or even close the eyelids, watch certain objects while ignoring others, but there is no mechanism
to ignore acoustic events.
The directionality of the human auditory system is limited to sound localization. The brain utilizes
subtle differences in intensity, spectral and timing cues to allow sound sources to be localized. Thus,
even if someone tries to ignore a certain acoustic event there will be a response. Although people tend
to get used to noise exposure, the degree of habituation differs for individuals and is rarely complete.
Adverse effects of sound events can be of a different nature. The simplest effect is characterized as
annoyance without further consideration of the genesis and aftermaths. Other effects can be of a
physiological and/or psychological nature (see Table 1).
[15]
Table 1 — Classification of factors that affect individual annoyance with noise
Factors that affect individual annoyance with noise
Sound level
Primary acoustic factors Frequency
Duration
Spectral complexity
Fluctuations in sound level
Fluctuations in frequency
Secondary acoustic factors
Rise-time of the noise
Localization of noise source
Physiology
Adaptation and past experience
How the listener’s activity affects annoyance
Non-acoustic factors Predictability of when a noise will occur
Is the noise necessary?
Individual differences and personality
SOURCE: Canadian Centre for Occupational Health and Safety (CCOHS). Noise – Non-Auditory Effects. Available
from: https:// www .ccohs .ca/ oshanswers/ phys _agents/ non _auditory .html. Reproduced with the permission of
CCOHS.
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ISO/TS 9241-620:2023(E)
Recent research supports earlier results regarding the association of ambient sound and heart rate with
longitudinal data that demonstrate that the real-world ambient signal-to-noise ratios are associated
with lowered heart rates, suggesting that sound conditions which reduce the auditory perceptual load
[16],[27]
and listening effort de-stress the human cardiovascular system.
If many people work together in close proximity, as is the case in multi-person offices, disturbances to
activities and annoyance reactions from staff due to various environmental factors become particularly
evident, in particular since working practices often require switching between communicative
exchange and focused work.
The resulting annoyance reactions can occur in the following forms:
— disturbance component “annoyance”;
— impairments of well-being, irritation, tension, exhaustion;
— changed communication behaviour (withdrawal, avoiding interactions).
The most disturbing characteristics of speech-specific noise are the information content and the
uncontrollability, whereas uncontrollability and unpredictability of the noise play a big role in the
case of noises from office environments. Only approximately 30 % to 40 % of the annoyance effects
resulting from noise can be explained by technical-acoustic factors. The predominant part originates
from moderators of annoyance (see VDI 2569).
4.2 Types of sound events
The type of sound has a bearing on how it is to be measured, what type of sound-level meter setting
should be used and what descriptors and other data should be presented.
Sound events are generally classified into the following categories (Figure 2):
a) steady sound levels (e.g. air conditioning);
b) steady but intermittent sound levels (e.g. printers that print in bursts);
c) time-varying sound (e.g. traffic sound over a specific time period);
d) impulsive sound signals that can include one or more impulses (e.g. ringing telephones, high-impact
printers).
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ISO/TS 9241-620:2023(E)
a) Steady sound b) Intermittent sound
c) Time-varying sound d) Impulsive sound
Key
X time
Y sound pressure level, dB(A)
Figure 2 — Types of sound events
Sound level descriptors or metrics differ according to the type of sound events. Most metrics, for
example A-weighted sound pressure level, have been developed for non-impulsive sound events. For
characterizing impulsive sound levels, different methods are used.
4.3 Interference with the task
The impact of sound from sources other than speech is normally considered by its sound pressure level
(L ) or the equivalent continuous A-weighted sound pressure level (L ). If the sound includes impulse
pA Aeq
noise, a certain margin is added to the level [e.g. +2 dB(A)].
Speech sounds and speech-like sounds lead to losses of performance of the working memory. This effect
does not necessitate the understanding of speech; an unknown foreign language or a musical piece can
also have adverse effects. In this context, it is essential that the sounds are not mandatorily perceived
as noise and that, despite focusing the attention on the material to be memorized, the irrelevant speech
effect (ISE) can occur. This disturbing effect can already occur at A-weighted speech levels from 35 dB
[30]
if they are clear speech signals. The disturbing effect is due to the spectro-temporal structure of
the speech or music sound, which results in this sound gaining access to the cognitive system (see
VDI 2569)
The interference of speech with the user performance can be a result of the disturbing effect on
the “inner speech”. Ambient noise can affect both reading and typing, because most users “speak to
themselves” during these tasks. As for the mechanism for such effects, some research indicates that
[28]
masking the relevant information with ambient sound is responsible. The role of inner speech in
human communication has been investigated (see Reference [20]). Inner speech, also called self-talk
or internal monologue, is a person’s inner voice that provides a running verbal monologue of thoughts
[18],[31]
while they are conscious. Inner speech plays several crucial roles in reading. Reading is a complex
process that involves the interaction of two levels of processing: decoding individual units and using
text as a whole to establish broader meaning. Both can be affected by ambient sound, but the effect
seems to be much stronger if the ambient sound is speech or speech-like.
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ISO/TS 9241-620:2023(E)
The characteristics of sound events are very different for environments with “normal” noise sources,
such as street noise or machine noise, than for those environments dominated by speech sound. While
for the first the concept of a sound “level” can hold true (Figure 3), in the latter each sound event is
separated from the others (Figure 4). In these studies, the base level without any work activity was
33 dB(A); single events were up to 65 dB(A) in the recorded session. The highest recorded level was
75 dB(A) with a speaker at a distance of 11 m. Whereas in acoustics, mostly a level of 65 dB(A) for
normal speech in one meter from the speaker’s mouth is assumed.
In real work environments, speakers can emit sound levels between 45 dB(A) and 75 dB(A) while
telephoning, depending on the task and the quality of the sound transmission from the opposite side. In
contrast to earlier landline phones, mobile networks do not guarantee a certain transmission quality.
In addition, users do not speak in rooms with controlled acoustic conditions.
A “silent” train compartment in modern trains has noise levels beyond any recommended environments
for acceptable telephone communication. However, those levels are still lower than those in cars or
aeroplanes. While communicating with people in such environments, the speaker adjusts her or his
speech level to a certain degree to the level of that noisy environment.
Key
X time
Y sound pressure level, dB(A)
NOTE The red line approximates the sound “level”.
Figure 3 — Typical sound event with slow changes in the level
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ISO/TS 9241-620:2023(E)
Key
Y sound pressure level, dB(A)
a
Base level = 33 dB(A).
NOTE The base level is the sound pressure level (SPL) with all users if they are inactive.
Figure 4 — Sound events in an office room within 90 seconds
In a given room with good acoustic conditions, the sound level can be 15 dB(A) higher if many people
use a telephone (Figure 5).
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ISO/TS 9241-620:2023(E)
Key
Y sound pressure level, dB(A)
1 regular office work with computers
2 office work with intensive telephone conversations
a
Base level = 37 dB(A).
NOTE The base level is the SPL with all users if they are inactive. The events do not include ringing
telephones.
Figure 5 — Acoustic events in a multi-person room according to type of work
Uncontrolled phoning can heavily interfere with the work of others. One of the mechanisms leading to
this level of interference is the Lombard effect.
4.4 Lombard effect
The Lombard effect or Lombard reflex is the involuntary tendency of speakers to increase their vocal
effort when speaking in loud noise (total noise sound pressure level) to enhance the audibility of their
[24]
voice. This change includes not only loudness but also other acoustic features such as pitch and rate
and duration of sound syllables. This compensation effect results in an increase in the auditory signal-
[33]
to-noise ratio of the speaker’s spoken words.
[24]
It is suggested that the magnitude of the speakers’ response to noise is likely to be governed by the
desire to achieve intelligible communication, as in noisy conditions speakers would not change their
voice level if talking to themselves.
Speech is often considered the primary communicative signal, but it is heavily integrated with signals
from the face and body. Visual signals, including hand gestures, are integral to human communication
[19]
and can play a particularly important role in noisy situations when verbal communication fails.
In noisy environments, noise is not only associated with increased speech intensity but also with
enhanced gesture kinematics. Acoustic modulation of the speech signal only occurs when gestures
are not present, while gesture kinematic modulation occurs regardless of co-occurring speech.
Thus, in face-to-face encounters, the Lombard effect is not constrained to speech but is a multimodal
[32]
phenomenon where gestures carry most of the meaning . This means that noise modifies the entire
behaviour of the users.
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ISO/TS 9241-620:2023(E)
4.5 Irrelevant speech effect (ISE)
In work environments such as open-plan offices, users communicate and interact with co-workers
verbally, and an open-plan office layout is commonly assumed to facilitate communication and
interaction between co-workers, promoting workplace satisfaction and teamwork effectiveness. The
assumption reflects the main purpose for selecting such layouts. On the other hand, open-plan layouts
are also widely acknowledged to be more disruptive due to uncontrollable noise. As an overall result,
the benefits need to overweigh the negative effects.
While most sources of noise can be controlled effectively, human speech is not that easy to control
because it is part of communication, although irrelevant to most users by definition.
The irrelevant speech effect (ISE) is the finding that serial recall performance is impaired under
[17]
complex auditory backgrounds, such as speech, as compared to white noise or silence. The effect
refers to the degradation of serial recall when speech sounds are presented, even if the list items are
presented visually. The sounds need not be a la
...
FINAL
TECHNICAL ISO/DTS
DRAFT
SPECIFICATION 9241-620
ISO/TC 159/SC 4
Ergonomic requirements for office
Secretariat: BSI
work with visual display terminals
Voting begins on:
2023-04-03 (VDTs) —
Voting terminates on:
Part 620:
2023-05-29
The role of sound for users of
interactive systems
RECIPIENTS OF THIS DRAFT ARE INVITED TO
SUBMIT, WITH THEIR COMMENTS, NOTIFICATION
OF ANY RELEVANT PATENT RIGHTS OF WHICH
THEY ARE AWARE AND TO PROVIDE SUPPOR TING
DOCUMENTATION.
IN ADDITION TO THEIR EVALUATION AS
Reference number
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO-
ISO/DTS 9241-620:2023(E)
LOGICAL, COMMERCIAL AND USER PURPOSES,
DRAFT INTERNATIONAL STANDARDS MAY ON
OCCASION HAVE TO BE CONSIDERED IN THE
LIGHT OF THEIR POTENTIAL TO BECOME STAN-
DARDS TO WHICH REFERENCE MAY BE MADE IN
NATIONAL REGULATIONS. © ISO 2023
---------------------- Page: 1 ----------------------
FINAL
TECHNICAL ISO/DTS
DRAFT
SPECIFICATION 9241-620
ISO/TC 159/SC 4
Ergonomic requirements for office
Secretariat: BSI
work with visual display terminals
Voting begins on:
(VDTs) —
Voting terminates on:
Part 620:
The role of sound for users of
interactive systems
COPYRIGHT PROTECTED DOCUMENT
© ISO 2023
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
RECIPIENTS OF THIS DRAFT ARE INVITED TO
ISO copyright office
SUBMIT, WITH THEIR COMMENTS, NOTIFICATION
OF ANY RELEVANT PATENT RIGHTS OF WHICH
CP 401 • Ch. de Blandonnet 8
THEY ARE AWARE AND TO PROVIDE SUPPOR TING
CH-1214 Vernier, Geneva
DOCUMENTATION.
Phone: +41 22 749 01 11
IN ADDITION TO THEIR EVALUATION AS
Reference number
Email: copyright@iso.org
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO-
ISO/DTS 9241-620:2023(E)
Website: www.iso.org
LOGICAL, COMMERCIAL AND USER PURPOSES,
DRAFT INTERNATIONAL STANDARDS MAY ON
Published in Switzerland
OCCASION HAVE TO BE CONSIDERED IN THE
LIGHT OF THEIR POTENTIAL TO BECOME STAN-
DARDS TO WHICH REFERENCE MAY BE MADE IN
ii
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NATIONAL REGULATIONS. © ISO 2023
---------------------- Page: 2 ----------------------
ISO/DTS 9241-620:2023(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Sound and noise . 3
4.1 How sound and noise impact users . 3
4.2 Types of sound events . 4
4.3 Interference with the task . 5
4.4 Lombard effect . 8
4.5 Irrelevant speech effect (ISE) . 9
4.6 The importance of the concept of T-O-P. 9
5 Measures to control the impact of sound events .10
5.1 Overview . 10
5.2 Controlling sound and noise . 10
5.2.1 General . 10
5.2.2 Reducing the rating level . 11
5.2.3 Reverberation time . 15
5.3 Optimizing signal-to-noise ratio . 15
5.3.1 General .15
5.3.2 Transmission paths for the voice in use environments . 17
5.3.3 How the communication is affected by unwanted sound . 18
5.3.4 How to improve the intelligibility of speech . 20
5.4 Sound reduction within use environments or immediate environments of
workstations. 22
5.5 User involvement . 23
Annex A (informative) Example of a user survey questionnaire .24
Bibliography .25
iii
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ISO/DTS 9241-620:2023(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to
the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see
www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 159, Ergonomics, Subcommittee SC 4,
Ergonomics of human-system interaction.
A list of all parts in the ISO 9241 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
iv
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ISO/DTS 9241-620:2023(E)
Introduction
In physics, sound is a vibration that propagates as an acoustic wave, through a transmission medium
such as a gas, liquid or solid. In human physiology and psychology, sound is the reception of such waves
and their perception by the brain. Unwanted sound is referred to as noise and is often perceived as the
most serious disturbance factor at office workstations. In many industrial environments, sound can be
a serious threat to health in general, not limited to auditory effects alone.
While sound is a measurable physical reality, acoustic noise is a psychoacoustical concept. The main
goal of this document is minimizing the impact of noise while operating interactive systems, for example
on the behaviour of users, their well-being and/or performance. This can be accomplished by technical
measures, organizational means, interventions at the personal level and any combinations thereof.
The overall concept T-O-P (technical – organizational – personal) indicates the reasonable order
of measures that can be taken to control the impact of the acoustic environment on human work. In
this context, technical solutions have priority over organizational measures and personal protective
equipment (PPE).
Psychoacoustics is the branch of psychophysics involving the scientific study of sound perception and
audiology – how humans perceive various sounds. More specifically, it is the branch of science studying
the psychological responses associated with sound (including noise, speech and music). This document
deals with the undesired effects of sound, which can be classified as follows:
— impaired hearing;
— undesired responses of the central and autonomic nervous system;
— hindrance of verbal and other communication;
— reduced performance and cognitive functioning;
— annoyance.
Acoustic satisfaction of a space cannot be guaranteed without consideration of each of the three
principle parameters of architectural acoustic design, formalized and established in the early 1900s
[28]
by Sabine. The three principle parameters are known as the ‘ABCs’ of architectural acoustics: A for
absorption – Sufficient absorption in the built environment; B for blocking – Sufficient isolation of the
built environment; and C for control – Control of sound levels in the built environment. For a given
space, various measures in combinations can be taken to control the acoustic environment to achieve
satisfaction. In ISO 9241-6 such measures are briefly listed and partly explained. Experience now
suggests that a more thorough consideration of the acoustic environment is required because of the
changes to work organization and tasks.
Controlling the acoustic environment is considered part of the T-O-P concept. It can comprise, for
example:
— reducing the rating level
— insulation in structural components;
— reducing noise emission from equipment;
— increasing sound absorption;
v
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ISO/DTS 9241-620:2023(E)
— reducing the ambient noise level;
— optimizing the signal-to-noise ratio
— reducing the sound level in speech frequencies;
— sound reduction within use environments
— sound-absorbing ceilings;
— partitions;
— adequate distances between workstations;
— reducing reverberation.
While all these measures are of a technical nature (T of the T-O-P principle, Figure 1), the impact of
sound events on persons and work can require organizational measures, such as holding small meetings
dedicated to certain tasks outside the workspace. The final argument comprises measures at a personal
level, including training to cope with adverse environments.
Figure 1 — T-O-P principle for controlling the impact of the acoustic environment on human
work
vi
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TECHNICAL SPECIFICATION ISO/DTS 9241-620:2023(E)
Ergonomic requirements for office work with visual
display terminals (VDTs) —
Part 620:
The role of sound for users of interactive systems
1 Scope
This document provides users with a summary of the existing knowledge about ergonomics
considerations for the influence of sound in use environments on humans. It describes how unwanted
effects of sound (noise) can be controlled. The main goals for controlling the acoustic use environment
are reducing the rating level of sound in general, optimizing signal-to-noise ratio and sound reduction
within the workspace.
This document also provides users with organizational measures that can be taken if and when
technical measures do not help sufficiently. Also included are measures on a personal level.
This document deals with sound events that can cause extra-aural effects. Noise-induced hearing loss
prevention and the ways to eliminate or reduce hazardous noise exposure are not covered by this
document.
The intended users of this document include:
— developers of systems, products and services;
— public and corporate purchasers;
— occupational health and safety professionals;
— architects and interior designers;
— human resource professionals;
— usability, ergonomics or human factors professionals;
— users of interactive systems.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
1
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ISO/DTS 9241-620:2023(E)
3.1
irrelevant speech effect
ISE
negative effect of verbal sound level
3.2
rating level
L
AR
equivalent continuous A-weighted sound pressure level during a specified time interval plus adjustment
for tonal character and impulsiveness
Note 1 to entry: ΔLT = 0 dB or 5 dB according to subjective assessments
where
Δ is difference;
L is level;
T is tonal.
Note 2 to entry: Impulsiveness is specified only if the difference of the measured sound level with and without
impulses exceeds 2 dB.
[SOURCE: ISO 9241-6:1999, 3.19, modified — Notes to entry replaced.]
3.3
background noise level
L
p,B
A-weighted sound pressure level present at the workstation during working hours with people absent
Note 1 to entry: The A-weighted background noise level L is expressed in dB.
p,B
3.4
total noise sound pressure level
L
NA
sound pressure level that contains all noise components affecting the listener during use, such as noise
generated by building systems, operating equipment or the audience, and which is determined at ear
height for the area in which people are normally located
Note 1 to entry: The A-weighted total noise sound pressure level L is expressed in decibels.
NA
Note 2 to entry: If not otherwise specified, noise is determined according to DIN 45641 as the A-weighted
equivalent continuous sound pressure level averaged over the time that is representative for the disturbance.
3.5
impulsive sound
sound with a rapid rise and decay of sound pressure level, lasting less than one second and causing an
increase in the sound level of at least 6 dB(A)
3.6
reverberation time
T
time required for the sound pressure level in a room to decay by 60 dB once sound excitation has
stopped
Note 1 to entry: The reverberation time is expressed in seconds.
2
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ISO/DTS 9241-620:2023(E)
3.7
speech transmission index
STI
metric ranging between 0 and 1 representing the transmission quality of speech with respect to
intelligibility by a speech transmission channel
[SOURCE: IEC 60268-16:2020, 3.3]
Note 1 to entry: Speech transmission channel can also be the use environment.
3.8
sound pressure level
SPL
logarithmic measure of the effective pressure of a sound relative to a reference value
4 Sound and noise
4.1 How sound and noise impact users
Hearing (audition, auditory sense) is one of the five basic senses used by humans to perceive the physical
environment, alongside sight (vision, visual sense), taste (gustation, gustatory sense), smell (olfaction,
olfactory sense) and touch (somatosensation, somatosensory sense). Even if its sensor, the ear, seems to
function independently from those of the other senses, they all function in concert. Sight and hearing,
or those sensory aptitudes that can collect information from a distance (relatively speaking), are called
far senses. Hearing is the only sense that can detect objects or events beyond the (optical) horizon.
Evolution has programmed human beings to be aware of sounds as possible sources of danger. The
hearing as the far sense gives notice of things that cannot be seen but that could be important. It plays
an alerting function. Even if this function is not needed in most use environments, it cannot be switched
off or ignored. While the sense of sight is relatively inactive during sleep, hearing remains on. The alert
function requires that hearing is almost non-directional compared with sight. It is possible to look
away or even close the eyelids, watch certain objects while ignoring others, but there is no mechanism
to ignore acoustic events.
The directionality of the human auditory system is limited to sound localization. The brain utilizes
subtle differences in intensity, spectral and timing cues to allow sound sources to be localized. Thus,
even if someone tries to ignore a certain acoustic event there will be a response. Although people tend
to get used to noise exposure, the degree of habituation differs for individuals and is rarely complete.
Adverse effects of sound events can be of a different nature. The simplest effect is characterized as
annoyance without further consideration of the genesis and aftermaths. Other effects can be of a
physiological and/or psychological nature (see Table 1).
[15]
Table 1 — Classification of factors that affect individual annoyance with noise
Factors that affect individual annoyance with noise
Sound level
Primary acoustic factors Frequency
Duration
Spectral complexity
Fluctuations in sound level
Fluctuations in frequency
Secondary acoustic factors
Rise-time of the noise
Localization of noise source
Physiology
3
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ISO/DTS 9241-620:2023(E)
TTabablele 1 1 ((ccoonnttiinnueuedd))
Factors that affect individual annoyance with noise
Adaptation and past experience
How the listener’s activity affects annoyance
Non-acoustic factors Predictability of when a noise will occur
Is the noise necessary?
Individual differences and personality
SOURCE: Canadian Centre for Occupational Health and Safety (CCOHS). Noise – Non-Auditory Effects. Available
from: https:// www .ccohs .ca/ oshanswers/ phys _agents/ non _auditory .html. Reproduced with the permission of
CCOHS.
Recent research supports earlier results regarding the association of ambient sound and heart rate with
longitudinal data that demonstrate that the real-world ambient signal-to-noise ratios are associated
with lowered heart rates, suggesting that sound conditions which reduce the auditory perceptual load
[16],[27]
and listening effort de-stress the human cardiovascular system.
If many people work together in close proximity, as is the case in multi-person offices, disturbances to
activities and annoyance reactions from staff due to various environmental factors become particularly
evident, in particular since working practices often require switching between communicative
exchange and focused work.
The resulting annoyance reactions can occur in the following forms:
— disturbance component “annoyance”;
— impairments of well-being, irritation, tension, exhaustion;
— changed communication behaviour (withdrawal, avoiding interactions).
The most disturbing characteristics of speech-specific noise are the information content and the
uncontrollability, whereas uncontrollability and unpredictability of the noise play a big role in the
case of noises from office environments. Only approximately 30 % to 40 % of the annoyance effects
resulting from noise can be explained by technical-acoustic factors. The predominant part originates
from moderators of annoyance (see VDI 2569).
4.2 Types of sound events
The type of sound has a bearing on how it is to be measured, what type of sound-level meter setting
should be used and what descriptors and other data should be presented.
Sound events are generally classified into the following categories (Figure 2):
a) steady sound levels (e.g. air conditioning);
b) steady but intermittent sound levels (e.g. printers that print in bursts);
c) time-varying sound (e.g. traffic sound over a specific time period);
d) impulsive sound signals that can include one or more impulses (e.g. ringing telephones, high-impact
printers).
4
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ISO/DTS 9241-620:2023(E)
a) Steady sound b) Intermittent sound
c) Time-varying sound d) Impulsive sound
Key
X time
Y sound pressure level, dB(A)
Figure 2 — Types of sound events
Sound level descriptors or metrics differ according to the type of sound events. Most metrics, for
example A-weighted sound pressure level, have been developed for non-impulsive sound events. For
characterizing impulsive sound levels, different methods are used.
4.3 Interference with the task
The impact of sound from sources other than speech is normally considered by its sound pressure level
(L ) or the equivalent continuous A-weighted sound pressure level (L ). If the sound includes impulse
pA Aeq
noise, a certain margin is added to the level (e.g. +2 dB(A)).
Speech sounds and speech-like sounds lead to losses of performance of the working memory. This effect
does not necessitate the understanding of speech; an unknown foreign language or a musical piece can
also have adverse effects. In this context, it is essential that the sounds are not mandatorily perceived
as noise and that, despite focusing the attention on the material to be memorized, the irrelevant speech
effect (ISE) can occur. This disturbing effect can already occur at A-weighted speech levels from 35 dB
[30]
if they are clear speech signals. The disturbing effect is due to the spectro-temporal structure of
the speech or music sound, which results in this sound gaining access to the cognitive system (see
VDI 2569)
The interference of speech with the user performance can be a result of the disturbing effect on
the “inner speech”. Ambient noise can affect both reading and typing, because most users “speak to
themselves” during these tasks. As for the mechanism for such effects, some research indicates that
[28]
masking the relevant information with ambient sound is responsible. The role of inner speech in
human communication has been investigated (see Reference [20]). Inner speech, also called self-talk
or internal monologue, is a person’s inner voice that provides a running verbal monologue of thoughts
[18],[31]
while they are conscious. Inner speech plays several crucial roles in reading. Reading is a complex
process that involves the interaction of two levels of processing: decoding individual units and using
text as a whole to establish broader meaning. Both can be affected by ambient sound, but the effect
seems to be much stronger if the ambient sound is speech or speech-like.
5
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ISO/DTS 9241-620:2023(E)
The characteristics of sound events are very different for environments with “normal” noise sources,
such as street noise or machine noise, than for those environments dominated by speech sound. While
for the first the concept of a sound “level” can hold true (Figure 3), in the latter each sound event is
separated from the others (Figure 4). In these studies, the base level without any work activity was
33 dB(A); single events were up to 65 dB(A) in the recorded session. The highest recorded level was
75 dB(A) with a speaker at a distance of 11 m. Whereas in acoustics, mostly a level of 65 dB(A) for
normal speech in one meter from the speaker’s mouth is assumed.
In real work environments, speakers can emit sound levels between 45 dB(A) and 75 dB(A) while
telephoning, depending on the task and the quality of the sound transmission from the opposite side. In
contrast to earlier landline phones, mobile networks do not guarantee a certain transmission quality.
In addition, users do not speak in rooms with controlled acoustic conditions.
A “silent” train compartment in modern trains has noise levels beyond any recommended environments
for acceptable telephone communication. However, those levels are still lower than those in cars or
aeroplanes. While communicating with people in such environments, the speaker adjusts her or his
speech level to a certain degree to the level of that noisy environment.
Key
X time
Y sound pressure level, dB(A)
NOTE The red line approximates the sound “level”.
Figure 3 — Typical sound event with slow changes in the level
6
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ISO/DTS 9241-620:2023(E)
Key
Y sound pressure level, dB(A)
a
Base level = 33 dB(A).
NOTE The base level is the sound pressure level (SPL) with all users if they are inactive.
Figure 4 — Sound events in an office room within 90 seconds
In a given room with good acoustic conditions, the sound level can be 15 dB(A) higher if many people
use a telephone (Figure 5).
7
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ISO/DTS 9241-620:2023(E)
Key
Y sound pressure level, dB(A)
1 regular office work with computers
2 office work with intensive telephone conversations
a
Base level = 37 dB(A).
NOTE The base level is the SPL with all users if they are inactive. The events do not include ringing
telephones.
Figure 5 — Acoustic events in a multi-person room according to type of work
Uncontrolled phoning can heavily interfere with the work of others. One of the mechanisms leading to
this level of interference is the Lombard effect.
4.4 Lombard effect
The Lombard effect or Lombard reflex is the involuntary tendency of speakers to increase their vocal
effort when speaking in loud noise (total noise sound pressure level) to enhance the audibility of their
[24]
voice. This change includes not only loudness but also other acoustic features such as pitch and rate
and duration of sound syllables. This compensation effect results in an increase in the auditory signal-
[33]
to-noise ratio of the speaker’s spoken words.
[24]
It is suggested that the magnitude of the speakers’ response to noise is likely to be governed by the
desire to achieve intelligible communication, as in noisy conditions speakers would not change their
voice level if talking to themselves.
Speech is often considered the primary communicative signal, but it is heavily integrated with signals
from the face and body. Visual signals, including hand gestures, are integral to human communication
[19]
and can play a particularly important role in noisy situations when verbal communication fails.
In noisy environments, noise is not only associated with increased speech intensity but also with
enhanced gesture kinematics. Acoustic modulation of the speech signal only occurs when gestures
are not present, while gesture kinematic modulation occurs regardless of co-occurring speech.
Thus, in face-to-face encounters, the Lombard effec
...
ISO/WD TS DTS 9241-620:2022(E)
ISO/TC 159/SC 4/WG 3
Secretariat: BSI
Date: 2022-10-012023-03-20
Ergonomic requirements for office work with visual display
terminals (VDTs) —
Part 620:
The role of sound for users of interactive systems
WDFDIS stage
Warning for WDs and CDs
This document is not an ISO International Standard. It is distributed for review and comment. It is subject to
change without notice and may not be referred to as an International Standard.
Recipients of this draft are invited to submit, with their comments, notification of any relevant patent rights of
which they are aware and to provide supporting documentation.
A model manuscript of a draft International Standard (known as “The Rice Model”) is available at
© ISO 2022 – All rights reserved
---------------------- Page: 1 ----------------------
ISO #####-#:####(X)
2 © ISO #### – All rights reserved
---------------------- Page: 2 ----------------------
© ISO 2022
© ISO 2023 – All rights reserved
---------------------- Page: 3 ----------------------
ISO/DTS 9241-620:(E)
© ISO 2023
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this
publication may be reproduced or utilized otherwise in any form or by any means, electronic or mechanical,
including photocopying, or posting on the internet or an intranet, without prior written permission. Permission can
be requested from either ISO at the address below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH--1214 Vernier, Geneva
Phone: + 41 22 749 01 11
EmailE-mail: copyright@iso.org
Website: www.iso.orgwww.iso.org
Published in Switzerland
iv © ISO 2023 – All rights reserved
---------------------- Page: 4 ----------------------
ISO/DTS 9241-620:(E)
Contents
Foreword . vi
Introduction .vi i
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Sound and noise . 3
4.1 How sound and noise impact users . 3
4.2 Types of sound events . 4
4.3 Interference with the task . 5
4.4 Lombard effect . 9
4.5 Irrelevant speech effect (ISE) . 10
4.6 The importance of the concept of T-O-P . 10
5 Measures to control the impact of sound events . 11
5.1 Overview . 11
5.2 Controlling sound and noise . 12
5.2.1 General . 12
5.2.2 Reducing the rating level . 12
5.2.3 Reverberation time . 17
5.3 Optimizing signal-to-noise ratio . 17
5.3.1 General . 17
5.3.2 Transmission paths for the voice in use environments . 20
5.3.3 How the communication is affected by unwanted sound . 22
5.3.4 How to improve the intelligibility of speech . 24
5.4 Sound reduction within use environments or immediate environments of workstations . 27
5.5 User involvement . 27
Annex A (informative) Example of a user survey questionnaire . 29
Bibliography . 31
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ISO/DTS 9241-620:(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. ISO
collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of any
patent rights identified during the development of the document will be in the Introduction and/or on
the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO’sISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see
www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 159, Ergonomics, Subcommittee SC 4,
Ergonomics of human-system interaction.
A list of all parts in the ISO 9241 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
vi © ISO 2023 – All rights reserved
---------------------- Page: 6 ----------------------
ISO/DTS 9241-620:(E)
Introduction
In physics, sound is a vibration that propagates as an acoustic wave, through a transmission medium such
as a gas, liquid or solid. In human physiology and psychology, sound is the reception of such waves and
their perception by the brain. Unwanted sound is referred to as noise and is often perceived as the most
serious disturbance factor at office workstations. In many industrial environments, sound can be a
serious threat to health in general, not limited to auditory effects alone.
While sound is a measurable physical reality, acoustic noise is a psychoacoustical concept. The main goal
of this document is minimizing the impact of noise while operating interactive systems, e.g.for example
on the behaviour of users, their well-being and/or performance. This can be accomplished by technical
measures, organizational means, interventions at the personal level and any combinations thereof. The
overall concept T-O-P (Technical – Organizational – Personal) indicates the reasonable order in which
efficient measures can be taken.
The overall concept T-O-P (technical – organizational – personal) indicates the reasonable order of
measures that can be taken to control the impact of the acoustic environment on human work. In this
context, technical solutions have priority over organizational measures and personal protective
equipment (PPE).
Psychoacoustics is the branch of psychophysics involving the scientific study of sound perception and
audiology – how humans perceive various sounds. More specifically, it is the branch of science studying
the psychological responses associated with sound (including noise, speech, and music). This document
deals with the undesired effects of sound. Undesired effects of sound, which can be classified as follows:
— Impairedimpaired hearing;
— Undesiredundesired responses of the central and autonomic nervous system;
— Hindrancehindrance of verbal and other communication;
— Reducedreduced performance and cognitive functioning;
— Annoyance
— Acousticalannoyance.
Acoustic satisfaction of a space cannot be guaranteed without consideration of each of the three principle
parameters of architectural acousticalacoustic design, formalized and established in the early 1900s by
[28 ]
Sabine. Sabin (Reference [15]). The three principle parameters are known as the ‘ABCs’ of architectural
acoustics: – A for Absorptionabsorption – Sufficient absorption in the built environment. – ; B for
Blockingblocking – Sufficient isolation of the built environment. – ; and C for Controlcontrol – Control of
sound levels in the built environment. For a given space, various measures in combinations can be taken
to control the acoustic environment to achieve satisfaction. In ISO 9241--6:1999 such measures wereare
briefly listed and partly explained. The experience since than isExperience now suggests that a more
thorough consideration of the acoustic environment is required because of the changes in theto work
organization and the tasks.
Controlling the acoustic environment is considered part of the T--O--P concept. It can comprise e.g., for
example:
— reducing the rating level
— insulation in structural components;
— reducing noise emission from equipment;
— increasing sound absorption;
© ISO 2023 – All rights reserved vii
---------------------- Page: 7 ----------------------
ISO/DTS 9241-620:(E)
— reducing the ambient noise level;
— optimizing the signal-to-noise ratio
— reducing the sound level in speech frequencies;
— sound reduction within use environments
— sound-absorbing ceilings;
— partitions;
— adequate distances between workstations;
— reducing reverberation.
While all these measures are of a technical nature (T of the T--O--P principle, Figure 1),), the impact of
sound events on persons and work can require organisationalorganizational measures like, such as
holding small meetings outside the workspace dedicated to certain tasks. outside the workspace. The
ultimo ratio, the measure of last resort,final argument comprises measures inat a personal level, including
training to cope with adverse environments.
viii © ISO 2023 – All rights reserved
---------------------- Page: 8 ----------------------
ISO/DTS 9241-620:(E)
Figure 1 — T--O--P Principleprinciple for the control ofcontrolling the impact of the acoustic
environment on human work
The acronym T-O-P (Technical – Organisational – Personal) stands for the reasonable order of measures
that can be taken to control the impact of the acoustic environment on human work. In this context,
technical solutions have priority over organisational measures and PPE (Personal Protective Equipment).
© ISO 2023 – All rights reserved ix
---------------------- Page: 9 ----------------------
ISO/DTS 9241-620:(E)
Ergonomic requirements for office work with visual display
terminals (VDTs) —
Part 620:
The role of sound for users of interactive systems
1 Scope
This Technical Specificationdocument provides users with a summary of the existing knowledge about
ergonomics considerations for the influence of sound in use environments on humans. It describes how
unwanted effects of sound (noise) can be controlled. The main goals for controlling the acoustic use
environment are reducing the rating level of sound in general, optimizing signal-to-noise ratio and sound
reduction within the workspace.
This document also provides users with organizational measures that can be taken if and whenwhere
technical measures do not help sufficiently. Also included are measures inon a personal level.
This document deals with sound events that can cause extra-aural effects. Noise-induced hearing loss
prevention and the ways to eliminate or reduce hazardous noise exposure are not covered by this
document.
The intended users of this document include:
— developers of systems, products and services;
— public and corporate purchasers;
— occupational health and safety professionals;
— architects and interior designers;
— human resource professionals;
— usability/, ergonomics/ or human factors professionals;
— users of interactive systems.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https://www.iso.org/obp
— IEC Electropedia: available at https://www.electropedia.org/
3.1
ISE irrelevant speech effect
ISE
negative effect of verbal sound level
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ISO/DTS 9241-620:(E)
3.2
rating level
L
AR
equivalent continuous A--weighted sound pressure level during a specified time interval plus adjustment
for tonal character and impulsiveness
[SOURCE: ISO 9241-6:1999]
Note 1 to entry: ΔLT = 0 dB or 5 dB according to subjective assessments.
where
Δ is difference;
L is level;
T is tonal.
Note 2 to entry: Impulsiveness is specified only if ΔLI = L − L > the difference of the measured sound level
AIeq Aeq
with and without impulses exceeds 2 dB according.
[SOURCE: ISO 9241-6:1999, 3.19, modified — Notes to ISO 11690-1.entry replaced.]
3.3
background noise level
L
p,B
A--weighted sound pressure level present at the workstation during working hours with people absent
Note 1 to entry: The A--weighted background noise level Lp,B is expressed in dB.
3.4
total noise sound pressure level
L
NA
sound pressure level that contains all noise components affecting the listener during use, such as noise
generated by building systems, operating equipment or the audience, and which is determined at ear
height for the area in which people are normally located
Note 1 to entry: The A--weighted total noise sound pressure level L is expressed in decibels.
NA
Note 2 to entry: If not otherwise specified, noise is determined according to DIN 45641 as the A--weighted
equivalent continuous sound pressure level averaged over the time that is representative for the disturbance.
3.5
impulsive sound
any sound with a rapid rise and decay of sound pressure level, lasting less than one second and causing
an increase in the sound level of at least 6 dB(A)
3.6
reverberation time
T
time required for the sound pressure level in a room to decay by 60 dB once sound excitation has stopped
Note 1 to entry: The reverberation time is expressed in seconds.
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ISO/DTS 9241-620:(E)
3.7
speech transmission index
STI
metric ranging between 0 and 1 representing the transmission quality of speech with respect to
intelligibility by a speech transmission channel
[SOURCE: IEC 60268--16:2020, 3.3]
Note 1 to entry: Speech transmission channel can also be the use environment.
3.8
sound pressure level
SPL
a logarithmic measure of the effective pressure of a sound relative to a reference value
4 Sound and noise
4.1 How sound and noise impact users
Hearing (audition, auditory sense) is one of the five basic senses ofused by humans to perceive the
physical environment. Even if its sensor, the ear, seems to function independently from those of the other
senses, , alongside sight (vision, visual sense), hearing (audition, auditory sense), taste (gustation,
gustatory sense), smell (olfaction, olfactory sense),) and touch (somatosensation, somatosensory sense),
they). Even if its sensor, the ear, seems to function independently from those of the other senses, they all
function in concert. Sight and hearing, or those sensory aptitudes that maycan collect information from a
distance (relatively speaking), are called far senses. Hearing is the only sense that can detect objects or
events beyond the (optical) horizon.
Evolution has programmed human beings to be aware of sounds as possible sources of danger. The
hearing as the far sense notifies usgives notice of things wethat cannot seebe seen but that maycould be
important. It plays an alerting function. Even if this function is not needed in most use environments, it
cannot be switched off or ignored. While the sense of sight is relatively inactive during sleep, hearing
remains “on”. The alert function requires that hearing is almost non-directional compared towith sight.
We canIt is possible to look away or even close the eyelids, watch certain objects while ignoring others,
but there is no mechanism to ignore acousticalacoustic events.
The directionality of the human auditory system is limited to sound localization. The brain utilizes subtle
differences in intensity, spectral, and timing cues to allow us to localize sound sources. to be localized.
Thus, even if onesomeone tries to ignore a certain acousticalacoustic event there will be a response. And
althoughAlthough people tend to habituateget used to noise exposure, the degree of habituation differs
for individuals and is rarely complete.
Adverse effects of sound events can be of a different nature. The simplest effect is characterized as
annoyance without further consideration of the genesis and aftermaths. Other effects maycan be of a
physiological and/or psychological nature (see Table 1.).
— A classificationTable 1 — Classification of the annoyance by noise in the order of their
importance for thefactors that affect individual annoyance towith noise[15 (Reference [2])]
Factors that affect Individual Annoyance to Noiseaffect individual annoyance with noise
Sound level
Primary acoustic factors Frequency
Duration
Spectral complexity
Secondary acoustic factors
Fluctuations in sound level
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ISO/DTS 9241-620:(E)
Factors that affect Individual Annoyance to Noiseaffect individual annoyance with noise
Fluctuations in frequency
Rise-time of the noise
Localization of noise source
Physiology
Adaptation and past experience
How the listener’s activity affectsaffects annoyance
NonacousticNon-acoustic factors Predictability of when a noise will occur
Is the noise necessary?
Individual differencesdifferences and personality
SOURCE: Canadian Centre for Occupational Health and Safety (CCOHS). Noise – Non-Auditory Effects. Available
from: https://www.ccohs.ca/oshanswers/phys_agents/non_auditory.html. Reproduced with the permission of
CCOHS.
Recent research supports earlier results regarding the association of ambient sound and heart rate with
longitudinal data that demonstrate that the real-world ambient signal-to-noise ratios are associated with
lowered heart rates, suggesting that sound conditions which reduce the auditory perceptual load and
[16],[27 ]
listening effort de-stress the human cardiovascular system. . [3], [13]
If many people work together withinin close proximity like it, as is the case especially in multi-person
offices, disturbances of theto activities and annoyance reactions on the workstations byfrom staff due to
various environmental factors become particularly evident, in particular since today’s workflowsworking
practices often require continuous changesswitching between communicative exchange and focused
work.
The resulting annoyance reactions can occur in the following forms:
— disturbance component “annoyance””;
— impairments of well-being, irritation, tension, exhaustion;
— changed communication behaviour (withdrawal, avoiding interactions)).
The most disturbing characteristics of speech-specific noise are the information content and the
uncontrollability, whereas uncontrollability and unpredictability of the noise play a big role in the case of
noises from office environments. Only approximately 30 % to 40 % of the annoying effectannoyance
effects resulting from noise can be explained by technical-acoustic factors. The predominant part
originates from moderators of annoyance (see VDI 2569).
4.2 Types of sound events
The type of sound has a bearing on how it is to be measured, what type of sound-level meter setting
should be used, and what descriptors and other data should be presented.
Sound events are generally classified into the following categories (Figure 2(Figure 2):):
a) steady sound levels (such ase.g. air conditioning);
b) steady, but intermittent sound levels (such ase.g. printers that print in bursts);
c) time-varying sound (such ase.g. traffic sound over a specific time period); and
d) impulsive sound signals that maycan include one or more impulses (such ase.g. ringing telephones,
high-impact printers etc.).).
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ISO/DTS 9241-620:(E)
—
a) Steady Soundsound b) Intermittent Soundsound
c) Time Varying Sound-varying sound d) Impulsive Soundsound
Key
X Timetime
Y
Sound Pressure Levelsound pressure level, dB(A)
Figure 2 — Types of sound events
Sound level descriptors or metrics differ according to the type of sound events. Most metrics, e.g.for
example A--weighted sound pressure level, have been developed for non-impulsive sound events. For
characterizing impulsive sound levels, different methods are used.
4.3 Interference with the task
The impact of sound from other sources other than speech is normally considered by its sound pressure
level (L ) or the equivalent continuous A--weighted sound pressure level (L ). If the sound includes
pA Aeq
impulse noise, the level is added a certain margin is added to the level (e.g. +2 dB(A)).
Speech sounds and speech-like sounds lead to losses of performance of the working memory. This effect
does not necessitate the understanding of speech; an unknown foreign language or a musical piece can
also have adverse effects. In this context, it is essential that the sounds are not mandatorily perceived as
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ISO/DTS 9241-620:(E)
noise and that, despite focusing the attention on the material to be memorized, the irrelevant speech
effect (ISE (Irrelevant Speech Effect) can occur. This disturbing effect can already occur at A--weighted
[30 ]
speech levels from 35 dB if they are clear speech signals. . [16] The disturbing effect is due to the
spectro-temporal structure of the speech or music sound, which results in this sound gaining access to
the cognitive system (see VDI 2569)
The interference of speech with the user performance can be a result of the disturbing effect on the “inner
speech”. Ambient noise can affect both reading and typing, because most users “speak to themselves”
during these tasks. As for the mechanism for such effects, some research indicates that masking the
[28 ]
relevant information bywith ambient sound is responsible. . [14] The role of inner speech in human
communication has been investigated e.g. by Johnson (see Reference [20 [7]).]). Inner speech, also called
self-talk or internal monologue, is a person’s inner voice that provides a running verbal monologue of
[18],[31 ]
thoughts while they are conscious. Inner speech plays several crucial roles in reading. . [5] [17]
Reading is a complex process that involves the interaction of two levels of processing: decoding individual
units and using text as a whole to establish broader meaning. Both can be affected by ambient sound, but
the effect seems to be much stronger if the ambient sound is speech or speech-like.
The characteristics of sound events are muchvery different for environments with “normal” noise sources
like, such as street noise, or machine noise et al from, than for those environments dominated by speech
sound. While for the first the concept of a sound “level” can hold true (Figure 3(Figure 3),), in the latter
environments each sound event is separated from the others (Figure 4(Figure 4). The). In these studies,
the base -level without any work activity was 33 dB(A),); single events were up to 65 dB(A) in the
recorded session. The highest recorded level was 75 dB(A) with a speaker at a distance of 11 m. Whereas
in acoustics, mostly a level of 65 dB(A) for normal speech in one meter from the speaker’s mouth is
assumed.
In real work environments, speakers can emit sound levels between 45 dB(A) and 75 dB(A) while
telephoning, depending on the task and the quality of the sound transmission from the opposite side. In
differencecontrast to earlier landline phones, mobile networks do not guarantee a certain transmission
quality. And, inIn addition, the users do not speak in rooms with controlled acoustic conditions.
A “silent” train compartment in modern trains has noise levels beyond any recommended environments
for acceptable telephone communication. ButHowever, those levels are still lower than others likethose
in cars or aeroplanes. While communicating with people in such environments, the speaker adjusts her/
or his speech level to a certain degree to the level inof that noisy environment.
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ISO/DTS 9241-620:(E)
Key
X Timetime
Y
Sound Pressure Levelsound pressure level, dB(A)
— UsualNOTE The red line approximates the sound “level”.
Figure 3 — Typical sound event with slow changes in the level (red line approximates the sound
“level”)
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ISO/DTS 9241-620:(E)
Key
Y Sound Pressure Levelsound pressure level, dB(A)
a
Base level = = 33 dB(A)).
— Sound events in an office room within 90 seconds (BaseNOTE The base level is the sound pressure level (SPL)
with all users if they are inactive).
Figure 4 — Sound events in an office room within 90 seconds
In a given room with good acoustic conditions, the sound level can be 15 dB(A) higher if many
personspeople use a telephone (Figure 5(Figure 5).).
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ISO/DTS 9241-620:(E)
Key
1Y Regular Worksound pressure level, dB(A)
21 Phone conversationregular office work with computers
Y2 Sound Pressure Level dB(A)office work with intensive telephone conversations
a
Base level = = 37 dB(A)).
— Acoustics events in a multi-person room in dependence of the task (BaseNOTE The base level is the SPL with
all users if they are inactive. The events do not include ringing telephones.).
Figure 5 — Acoustic events in a multi-person room according to type of work
Uncontrolled phoning can heavily interfere with the taskwork of others. One of the mechanisms leading
to this level of interference is the Lombard effect.
4.4 Lombard effect
The Lombard effect or Lombard reflex is the involuntary tendency of speakers to increase their vocal
effort when
...
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